Category Archives: Moon Colonization

At a celebration commemorating the 48th anniversary of the Apollo 11 moon landing, Blue Origin CEO Jeff Bezos argued for permanent settlements on the Moon and advocated colonization of the solar system as a means of making room for up to one trillion people.

Unlike other advocates for colonizing solar system worlds, Bezos does not base his position on the notion that humans need a new planet because Earth will someday be destroyed.

Instead, he sees it as a next step important to life on Earth.

We can harvest resources from asteroids, from Near-Earth Objects, and harvest solar energy from a much broader surface areaand continue to do amazing things. I want my grandchildrens grandchildren to be in a world of pioneering, exploration, and expansion throughout the solar system, he said.

Colonizing the solar system will free humanity from population concerns and open up resources capable of meeting up to one trillion peoples needs, Bezos emphasized.

Reusable rockets are the key to bringing down the expense of space travel and are a goal toward which Blue Origin is working, he noted.

An important step toward the larger goal of solar system colonization is returning to the Moon and establishing settlements on its poles to obtain water and gain access to solar power.

Its time for America to go back to the Moon, this time to stay. We know things about the Moon we didnt know back in the 1960s and 1970s, and with reusable rockets, we can do it affordably. We can get that done today, Bezos stated.

He also said he wants Blue Origin to operate a cargo service named Blue Moon, which would transport the supplies necessary for robots to build a human habitat on the Moon.

Blue Origin plans to take tourists to suborbital space with its New Shepard rocket but is also developing rockets capable of reaching orbit.

Bezos, who spoke on a stage at Cape Canaveral in front of the huge Saturn V rocket that launched the Apollo 11 mission to the Moon, was awarded the first annual Buzz Aldrin Innovation Award by Aldrins ShareSpace Foundation, a non-profit dedicated to inspiring and educating people about science, technology, engineering, arts, and math.

Laurel Kornfeld is a freelance writer and amateur astronomer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science in astronomy from Swinburne Universitys Astronomy Online program.

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Jeff Bezos outlines vision of colonizing the solar system - The Space Reporter

1. Damien Turchi is a graduate of Drexel University in Mechanical and Aerospace Engineering, founder and former president of the Icarus Interstellar Drexel University Student Chapter and lead coordinator of the first Interstellar Hackathon at Starship Congress 2015 at Drexel University, PA. He is currently a director of Icarus Interstellar.

On the Development of a Permanent Lunar Settlement: A Micro-Literature Review and Suggested Action

Since the 1960s, humanity seriously discusses the idea of a permanent lunar settlement. In both academic and professional literature, many designs for an initial settlement are proposed to varying fidelity. NASA published a comprehensive review of the most promising designs in the 1990s. Recent literature is not as detailed in its scope.

This study analyzes the designs NASA considered to be of significance in the 90s and discusses the benefits and cons of each. In addition, several recent works are assessed. From this review, the author concludes that an initial lunar settlement is possible through further development of existing design work, but that a superior option is neither immediate nor obvious.

Selecting a single framework (or a specific hybrid of several) is critical to best funnel capital into the most promising technologies. An action path is proposed that leverages consideration of permanence and significance as feedback to clearly characterize the best design choice for initial funding. Permanence seeks to answer, How can we ensure that the construction of the first lunar base is able to expand into the foreseeable future in both population and space?, while significance seeks to answer, How can we ensure that the consequences of operating the settlement are economically beneficial to society? There is not much literature to answer these questions, despite the importance of the answers.

The solutions will no doubt be a culturally diverse response, considering the needs of society as a whole to serve as a safeguard for the temporal success of a permanent lunar settlement.

2. Haym Benaroya is a Professor of Mechanical and Aerospace Engineering at Rutgers University. His research interests are focused on the conceptualization and analysis of structures placed in challenging environments. These include offshore drilling structures and lunar surface structures for manned habitation. Often, the characterization of the environment is the primary challenge, as with problems of flow-induced vibration.

The Moon as the Site for Humanitys Expansion into the Solar System and Beyond

The Moon offers numerous advantages, providing a foothold for humanity as it struggles to escape Earths gravity well to become a spacefaring civilization. While the battle for most has been between the Moon and Mars, the vision of the Starship Congress is beyond those, even beyond the Solar System. Here, our goal is the next star system, with a sophisticated exploration of the technologies that are needed to send a precursor robotic ship many light years from Earth.

Even with such a long-‐term mission, the Moon remains the ideal spot to develop technologies, understand the low and microgravity space environment, assess the effects of radiation on our machines and structures, and learn how to build these so that they can self-‐repair and be reliable in this way for decades.

We will provide a background to current thinking and the engineering and other issues regarding the Moon as a viable place for humans to begin the long journey into space.

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Starship Congress presentations make the case for permanent moon colonization - Next Big Future

Titan, Saturn's largest Moon, has the potential to be an ideal location forhuman colonization and explorationwithin our Solar System, along withMars (though Mars' prospects have gotten less rosy lately). Some even arguethat,besidesEarth, it is theonly place suitable for human colonization in our celestial neighborhood. While it is unbelievably cold, distant, and strange, it is also home tolarge bodies of surface liquid, solid ground, a thick atmosphere, and more. And, to add to that list,scientists recently discoveredcalm hydrocarbon lakesthat could make landing future probes a piece of cake.

The highest that waves reach on the lakes of Titan is about one centimeter.These alien lakesare more tranquil than we might be able to picture, sitting remarkably still. And so, if and when we are able to send probes to that Moon, scientists think that these lakes would make a good landing point. According to lead author Cyril Grima, a research associate at the University of Texas Institute for Geophysics (UTIG): "There's a lot of interest in one day sending probes to the lakes, and when that's done, you want to have a safe landing, and you don't want a lot of wind...Our study shows that because the waves aren't very high, the winds are likely low."

Image Credit: NASA

So what does this mean? It might not sound that exciting at first glance, but it is a huge step forward in our never-ending cosmic exploration. Especially with the recent news that Mars' soilcould be toxic to any potential bacterial life, it is important to remember that the Red Planet isn't the only possible destination for future astronauts and probes. Titan could be the future location of a permanent human colony and the ability of a probe to successfully and smoothly land is crucial to missions going well. So, while we still have a long way to go (literally and more figuratively), this is one huge step in the right direction.

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Titan's Alien Lakes Might Be Perfect Landing Spots for Colonization ... - Outer Places

Whether its the proliferation of science-fiction movies that show man exploring the stars, or bold claims from the likes of Elon Musk and Stephen Hawking about imminent space colonization, theres a collective interest in space right now that doesnt look like itll die down anytime soon or at least not until weve set up camp on Mars.

But how much do you really know about the universe? Unless youre a serious astrophile, the chances are you do little else than look at cool photography, follow Nasa on Instagram (if you dont, you seriously should) and retweet nuggets of Elon Musks wisdom about taking us all to space.

A company called AstroReality wants to change all that, and deliver education about space thats more accessible, interactive and tech-enabled than ever before and there isnt a dull textbook in sight.

AstroReality has big, bold plans about space education. But the companys first creation is an extremely detailed version of the moon called the AstroReality Lunar. Although the model itself is extremely cool, and would look damn fine on your desk, theres a lot more to it than looks.

The company claims its not only the most precise model of the moon on this planet, its the only AR-enabled one thats this detailed. The team at AstroReality have mapped the most famous moon spots on the model, which you can explore with AR tech and a dedicated smartphone app.

It created the model using data from Nasa, state-of-the-art design tools and sophisticated 3D printing tech. Look closely and youll see the craters Copernicus and Petavius and 2001: A Space Odyssey fans will be happy to spot Clavius too (just be sure to put some ear muffs on before you head down into the crater).

We tested out the prototype for ourselves. All you have to do is let the app track the surface in front of you with a QR code and labels about sites around the moon pop up in front of you, with the features set to get more advanced over time.

There are three different versions of the AstroReality Lunar: the Mini at 3cm, the Regular at 8cm and the Pro, which comes with more feature, at 12cm.

Its a great way for people to, quite literally, get to grips with space, and its not hard to imagine who might benefit from an interactive, AR-enabled model like this, from those who are just interested in space to kids in an education setting.

But although the Lunar model is fascinating, its only the start for AstroReality. We spoke to James Li, founder of AstroReality, about what the future holds for his moon models, AR and learning about space.

The process of creating the Lunar was a painstaking one. We used [digital modeling tool] Zbrush to design the Lunar model integrating Nasas Lunar Reconnaissance Orbiters data early on in our process, Li explains.

Data is downloaded from NASA LROC the Lunar Reconnaissance Orbiter Camera, or LROC, is a system of three cameras mounted on the Lunar Reconnaissance Orbiter (LRO) that capture high-resolution black and white images and moderate-resolution multi-spectral images of the lunar surface. We leveraged the high-resolution Elevation Map and Global Map.

This promotional video shows the process

After creating a version of the moon thats modelled to 0.006 millimeters per pixel precision, it was time to pack it full of AR smarts. We created three tiers of AR experiences, Li told us. We used [game engine] Unity and [AR platform] Vuforia AR SDK for front-end and [cloud platform] Microsoft Azure for back-end data, specific for the three sizes we offer for Lunar in.

Right now if you get the Lunar model and the app you can see labels of the key craters and sites. But theres going to be much more to the AstroReality Lunar over the coming months.

The second stage will be to see and learn about landmarks that we know about but we have never visited before the dark side of the moon revealed, Li tells us. The third part is to simulate a mission to the moon, with the ability to land on all the Apollo landing stations 11 through to 17, and to travel through the moon listening, learning, watching and reading about the historic landmarks visited by the astronauts on the Apollo missions. This is where we tell the story and you can personalise your journey.

AstroReality founder James Li. When I painted Lunar, Copernicus is the one that I spent the most time on.

From there therell be more locations added, a game-like element introduced and way more interaction. And its not just the moon that AstroReality wants to help us understand better the company already has a mini solar system set, and plans to roll out an entire solar system of larger, more interactive models in the future.

Lunar will add another dimension to learning in the classroom, as its interactive using rich media and advanced AR technology, all of which have been proven to keep children engaged with their learning, Li says.

But its not just a toy the data and scale are so precise that its an excellent tool for professional scientists in laboratories and research centres to visualize the moon.

And Li and the team at AstroReality want this knowledge will come in handy much quicker than we all expert.

At the Breakthrough Starshot conference last month, Stephen Hawking set a deadline of 100 years for humans to start colonizing another planet for us to survive climate change, deadly diseases and other fatalities, Li explains.

AstroReality's moons are modeled to a precision of 0.006 millimeters per pixel

AstroReality models will educate everybody to help themunderstand space, be more familiar with it and make this statement less of a daunting one. As humans our imaginations have always run wild with space and astronomy; now AR allows us to experience it as closely as possible without being there.

Were not sure that AR tech will answer the big, logistical questions about how we get everyone up in space or colonise other planets. But were all for the idea of more and more people learning about space and the possibilities it might hold for the future.

Finally, we wanted to hear what Li thought about the future of AR and VR when it comes to learning. Its already happening, but I expect to see a surge of augmented reality and virtual reality combined in mixed reality experiences in education,he says.

This will be the case in classrooms to add more interactivity into education and at Astronaut training camps for those on their way to space. This is the closest people will get to going to the moon without actually getting on a rocket; it will fulfil so many lifelong dreams and prepare those on a space mission for the real thing.

But ultimately, AR VR and MR is the future of so many industries, astronomy and science included.

And after spending so much time researching, designing and engaging with the moon, we asked Li what his favourite bit of lunar geography is. Copernicus, he says. I can see Copernicus with my bare eyes from Earth every time I look at the moon its almost right in the middle. Its pattern is complex and goes in various directions. When I painted Lunar, Copernicus is the one that I spent the most time on.

AstroReality is currently seeking crowdfunding for Lunar on Indiegogo, with discounts on its models for backers.

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We took an AR trip to the moon | TechRadar - TechRadar

Titan, Saturn's largest Moon, has the potential to be an ideal location forhuman colonization and explorationwithin our Solar System, along withMars (though Mars' prospects have gotten less rosy lately). Some even arguethat,besidesEarth, it is theonly place suitable for human colonization in our celestial neighborhood. While it is unbelievably cold, distant, and strange, it is also home tolarge bodies of surface liquid, solid ground, a thick atmosphere, and more. And, to add to that list,scientists recently discoveredcalm hydrocarbon lakesthat could make landing future probes a piece of cake.

The highest that waves reach on the lakes of Titan is about one centimeter.These alien lakesare more tranquil than we might be able to picture, sitting remarkably still. And so, if and when we are able to send probes to that Moon, scientists think that these lakes would make a good landing point. According to lead author Cyril Grima, a research associate at the University of Texas Institute for Geophysics (UTIG): "There's a lot of interest in one day sending probes to the lakes, and when that's done, you want to have a safe landing, and you don't want a lot of wind...Our study shows that because the waves aren't very high, the winds are likely low."

Image Credit: NASA

So what does this mean? It might not sound that exciting at first glance, but it is a huge step forward in our never-ending cosmic exploration. Especially with the recent news that Mars' soilcould be toxic to any potential bacterial life, it is important to remember that the Red Planet isn't the only possible destination for future astronauts and probes. Titan could be the future location of a permanent human colony and the ability of a probe to successfully and smoothly land is crucial to missions going well. So, while we still have a long way to go (literally and more figuratively), this is one huge step in the right direction.

The rest is here:
Titan's Alien Lakes Might Be Perfect Landing Spots for Colonization Probes - Outer Places

The Moon is Earths 8th continent; a new frontier for humanity with precious resources that can bring enormous benefits to life on Earth and our future in space. Expanding Earths economic and social sphere to the Moon is our first step in securing our future. Not long from now, a new generation will look up and see lights on the Moon, and know that they are part of a multi-world species.

Moon Express is working closely with the U.S. government to assure our freedom of enterprise in space with deference to international treaties.

The Space Resource and Utilization Act of 2015 was the first step in the process, recognizing U.S. private sector rights to seek, obtain and utilize space resources.

On July 20, 2016, Moon Express became the first company to receive U.S. government approval to send a robotic spacecraft beyond traditional Earth orbit and to the Moon. This was the first time in history that any government signatory to the Outer Space Treaty exercised its rights and obligations to formally authorize and supervise a commercial entity to fly a mission beyond Earth orbit. This historic ruling is a breakthrough U.S. policy decision supporting our commercial lunar exploration and discovery and heralding a new era of expanding space enterprise.

Our maiden Mission Approval establishes an important precedent for the private sector to engage in peaceful space exploration, bringing with it monumental implications for the advancement of technology, science, research, and development, as well as commercial ventures that expand Earths economic sphere.

On October 1, 2015, we announced a multi-mission launch contract with Rocket Lab USA for up to five launches starting in 2017. Moon Express is the first company in history to contract multiple launches for space exploration missions.

Our MX family of robotic explorers are configurable to a wide variety of available and emerging launch systems, all designed to collapse the cost of deep space access beyond Earth orbit.

MX-1E robotic explorer aboard the Rocket Lab USA Electron rocket

Moon Express occupies Launch Complexes 17 & 18 at Cape Canaveral, adjacent to the Kennedy Space Center on Floridas Space Coast, where many of the robots that explored new worlds and unlocked the secrets of our solar system began their journeys. We are now honored to be able to re-purpose these historic sites into a vibrant new commercial spaceport, ~70 acres of facilities and range, supporting Moon Express spacecraft development and test, and incubating fresh new dreams of extraordinary adventures into the space frontier.

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Moon Express

Two Apollo EVA spacesuits, covered in dark gray lunar dust. The short times spent on the Moon by the Apollo astronauts meant that the long-term issues associated with dust could be ignored during those missions.

A recent study has shown that the red dust on the surface of Mars, in combination with surface conditions of intense solar ultraviolet and cosmic radiation, is probably one of the most sterilizing environments imaginable. These new results cast some very cold water on the fervent hopes of some planetary scientists for indigenous martian life. Some have extended the list of potential worries for future explorers to problems these conditions might pose for martian agriculture. But none seem to be particularly concerned about the toxic effect Mars red dust might pose for the occasional visitor, let alone settlers.

The martian dust contains significant amounts of perchloratea chemical compound made up of one chlorine and four oxygen atoms. Perchlorate is found naturally in various salts; on Mars, it is probably joined with magnesium and sodium. This substance is highly reactivealuminum perchlorate is one of the compounds in solid rocket propellant. The high reactivity of perchlorate means that interactions with other chemical substances are almost certain, which in turn means that perchlorate in martian soil is a chemical hazard to living organismsnot only for microbial life and plants, but to humans as well.

Experience gained during the Apollo program taught us that dust can be a problem for the unprepared. Lunar dust is the smallest grain size fraction of the lunar regolithparticles smaller than 40 microns, finer than talcum powder but with much greater hardness. Extremely abrasive, this dust can make most moving equipment parts immobile. During the short duration of the Apollo missions (the longest stay on the surface was three days), the crew simply put up with the inconvenience of coping with fine, abrasive dust, but longer stays will require that steps be taken to mitigate its negative effects.

Although lunar dust is physically abrasive, it is largely inert chemically. Testing done on the first lunar samples at the Lunar Receiving Laboratory exposed seeds and germinating plants to lunar regolith. As expected from the chemical composition of the regolith, the plants continued to thrive despite repeated and prolonged exposure to lunar dust. While actual growth experiments were not conducted (largely because lunar material was allocated in extremely small amounts, to maintain sample integrity), we have no reason to suppose that the fine lunar regolith cannot support vigorous plant growth, provided that some key nutrients like phosphorous and nitrogen (naturally present in extremely low quantity on the Moon) are added to the soil.

The situation on Mars, however, appears to be different. The soil of Mars is composed predominantly of clay mineralsweathering products of igneous rocks created in the presence of liquid water, resulting in dust grains that are fine and relatively soft. Thus, martian soil is probably not physically abrasive like the lunar regolith (although care will still need to be taken to keep moving parts as clean as possible). The problem lies with the highly reactive (and probably toxic) chemistry of the smallest particles in martian soil.

One aspect of the lunar experience relevant to the issue of future Mars surface exploration is the ubiquity of dust and how it coats, covers and invades all pieces of equipment, up to and including the human body. On the Moon, these phenomena did not result in any long-term ill effects. A broken fender on the lunar rover during the Apollo 17 mission sprayed lunar dust over the crew and their suits, stressing the heat rejection properties of the suits and equipment on the lunar rover. Fine dust coated the fittings of air hoses in the suit, impairing the crews ability to get good seals to prevent leaks. Although the astronauts inhaled minute amounts of lunar dust when they re-pressurized the LM cabin (they said that it smelled like gunpowder), there were no ill effects to crew breathing and health. Although silicosis (similar to black lung disease) might result from long-term exposure to the fine lunar dust, in terrestrial settings such effects (without mitigating efforts) would require years of exposure to develop.

This may not be the case on Mars. The highly reactive chemistry of perchlorates in the soil could make martian dust not simply an annoyance, but a dangerous hazard. Corrosive chemicals within dust grains suspended in air can be inhaled and could seriously and permanently damage lung and esophageal tissue. It may be possible to mitigate contamination through dust management and clever engineering. For example, weve found that most of the Moons dust grains are magnetica result of the deposition of vapor-phase metallic iron coatings, which allows for the removal of virtually all of the dust using strong magnetic cleaning. This technique will probably not be possible for the martian dust, which formed from chemical weathering on Mars and does not possess the vapor-deposited iron of the lunar dust grains.

The new results about martian soil strongly suggest that the Red Planet may not be the welcoming second Eden for humanity that is commonly portrayed. Even if we are able to somehow mitigate the toxic effects of the soil (for example, through chemical treatment), such an approach may not be easy enough to warrant the effort. Certainly, the scenario in the book and film The Martian, in which one simply plants pieces of seed potato, adds excrement and water, then harvests a locally grown food source, just isnt plausible. The toxic effects of martian soil might be dealt with for short visits by exploring crews, but long-term human habitation and colonization of Mars is an entirely different proposition.

To successfully journey beyond Low Earth Orbit, we must provision ourselves using the vast resources of spaceextracting resources beyond Earth will present many challenges as we master the skills necessary to work in new environments. This journey begins on the Moonthe staging ground, supply station and classroom for our coming voyage into the universe.

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Nothing to Sneeze At - Air & Space Magazine

Have you ever wondered what it would be like to live in space or on another world? One day it may be possible to do so, but whenever and wherever we colonize, we take with us our microbiota. Would they affect our ability to live beyond Earth? New research published today indicates that the health of space travelers could be negatively impacted by fungi in our microbiota.

Srimathy Sriskantharajah 11 Jul 2017

pixabay - public domain image

Long before the first living creature was sent into space, humans have looked up at the night sky and wondered what it would like to live in space. Space agencies and commercial companies are researching longer term habitation in space and on other worlds. We all assume that, one day, we will establish colonies on other planets and celestial bodies (e.g moons), but not many people have considered whether there are other Earthlings better adapted to space colonization than us microorganisms. The microorganisms that make up our microbiota will also come with us if and when we colonize another world. How they adapt could also influence our own ability to colonize other planets.

In 2015, AleksandraChecinska and colleagues published a study of the International Space Station that showed microbes from the human skin form a substantial part of the ISS microbiota. The results indicate better cleaning regimes are required on the ISS and that these microorganisms could affect the health of astronauts.

A recently published article by the same group looked at the mycobiome (fungal microbiota) of a prototype lunar modules during a 30-day occupation period by a group of humans. Fungi can live in extreme environments on Earth, so should be relatively amenable to living in space and on extra-terrestrial bodies. The study showed human presence influenced fungal presence and diversity within the lunar module, and consequently could affect human health in space. Furthermore, the presence of fungi in the module could affect its structural integrity, impacting the safety of the occupants.

These two studies show how our microbiota can cause health or safety issues in space when they leave our bodies and enter the surrounding environment, but what about the impact of space travel on our microbiota when it is still inside us? NASA recently investigated these effects on two ISS missions between 2013 and 2016, collecting swab samples (saliva, blood, sweat and fecal) from astronauts over the course of their missions. The results have yet to be published, but the fact that the investigation occurred indicates a belief that the impact of space travel on our microbiota is a serious concern.

Considering how closely our microbiota affect our lives here on Earth, it is not surprising that they could impact our ability to colonize the moon or any other celestial body. Even the journey to these new homes could be hampered or helped by our microbiota. Could certain microorganisms within our microbiota enable us to adapt better to space travel? Would our microbiota colonize other worlds successfully before we do? Or would deep space travel send our microbiota into meltdown? It would be interesting to see whether our microbiota, rather than technology, were to be the limiting factor in space exploration.

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Space invadersthe dangers of fungi in space - BMC Blogs Network (blog)

Titan is the largest moon of Saturn. It is the only moon known to have a dense atmosphere, and the only object in space other than Earth where clear evidence of stable bodies of surface liquid has been found.

Titan is the sixth ellipsoidal moon from Saturn. Frequently described as a planet-like moon, Titan is 50% larger than Earth's Moon, and it is 80% more massive. It is the second-largest moon in the Solar System, after Jupiter's moon Ganymede, and is larger than the smallest planet, Mercury, but only 40% as massive. Discovered in 1655 by the Dutch astronomer Christiaan Huygens, Titan was the first known moon of Saturn, and the sixth known planetary satellite (after Earth's Moon and the four Galilean moons of Jupiter). Titan orbits Saturn at 20 Saturn radii. From Titan's surface, Saturn subtends an arc of 5.09 degrees and would appear 11.4 times larger in the sky than the Moon from Earth.

Titan is primarily composed of water ice and rocky material. Much as with Venus before the Space Age, the dense opaque atmosphere prevented understanding of Titan's surface until new information from the CassiniHuygens mission in 2004, including the discovery of liquid hydrocarbon lakes in Titan's polar regions. The geologically young surface is generally smooth, with few impact craters, although mountains and several possible cryovolcanoes have been found.

The atmosphere of Titan is largely nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog. The climateincluding wind and raincreates surface features similar to those of Earth, such as dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle is analogous to Earth's water cycle, at the much lower temperature of about 94K (179.2C).

Titan was discovered on March 25, 1655 by the Dutch astronomer Christiaan Huygens.[10][11] Huygens was inspired by Galileo's discovery of Jupiter's four largest moons in 1610 and his improvements in telescope technology. Christiaan, with the help of his brother Constantijn Huygens, Jr., began building telescopes around 1650 and discovered the first observed moon orbiting Saturn with one of the telescopes they built.[12] It was the sixth moon to be discovered.[13]

He named it Saturni Luna (or Luna Saturni, Latin for "Saturn's moon"), publishing in the 1655 tract De Saturni Luna Observatio Nova (A New Observation of Saturn's Moon). After Giovanni Domenico Cassini published his discoveries of four more moons of Saturn between 1673 and 1686, astronomers fell into the habit of referring to these and Titan as Saturn I through V (with Titan then in fourth position). Other early epithets for Titan include "Saturn's ordinary satellite".[14] Titan is officially numbered Saturn VI because after the 1789 discoveries the numbering scheme was frozen to avoid causing any more confusion (Titan having borne the numbers II and IV as well as VI). Numerous small moons have been discovered closer to Saturn since then.

The name Titan, and the names of all seven satellites of Saturn then known, came from John Herschel (son of William Herschel, discoverer of Mimas and Enceladus) in his 1847 publication Results of Astronomical Observations Made during the Years 1834, 5, 6, 7, 8, at the Cape of Good Hope.[15][16] He suggested the names of the mythological Titans (AncientGreek: ), brothers and sisters of Cronus, the Greek Saturn. In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age.

Titan orbits Saturn once every 15 days and 22 hours. Like the Moon and many of the satellites of the giant planets, its rotational period (its day) is identical to its orbital period; Titan is tidally locked in synchronous rotation with Saturn, and permanently shows one face to the planet, so Titan's "day" is equal to its orbit period. Because of this, there is a sub-Saturnian point on its surface, from which the planet would always appear to hang directly overhead. Longitudes on Titan are measured westward, starting from the meridian passing through this point.[17] Its orbital eccentricity is 0.0288, and the orbital plane is inclined 0.348 degrees relative to the Saturnian equator.[2] Viewed from Earth, Titan reaches an angular distance of about 20 Saturn radii (just over 1,200,000 kilometers (750,000mi)) from Saturn and subtends a disk 0.8 arcseconds in diameter.

The small, irregularly shaped satellite Hyperion is locked in a 3:4 orbital resonance with Titan. A "slow and smooth" evolution of the resonancein which Hyperion migrated from a chaotic orbitis considered unlikely, based on models. Hyperion probably formed in a stable orbital island, whereas the massive Titan absorbed or ejected bodies that made close approaches.[18]

Size comparison: Titan (lower left) with the Moon and Earth (top and right)

A model of Titan's internal structure

Titan is 5,151 kilometers (3,201mi) in diameter,[3] 1.06 times that of the planet Mercury, 1.48 that of the Moon, and 0.40 that of Earth. Before the arrival of Voyager 1 in 1980, Titan was thought to be slightly larger than Ganymede (diameter 5,262 kilometers (3,270mi)) and thus the largest moon in the Solar System; this was an overestimation caused by Titan's dense, opaque atmosphere, which extends many kilometres above its surface and increases its apparent diameter.[19] Titan's diameter and mass (and thus its density) are similar to those of the Jovian moons Ganymede and Callisto.[20] Based on its bulk density of 1.88g/cm3, Titan's composition is half water ice and half rocky material. Though similar in composition to Dione and Enceladus, it is denser due to gravitational compression. It has a mass 1/4226 that of Saturn, making it the largest moon of the gas giants relative to the mass of its primary, with Titan being 1/22.609 of Saturn's diameter, Triton is larger in diameter relative to Neptune at 1/18.092.

Titan is likely differentiated into several layers with a 3,400-kilometer (2,100mi) rocky center surrounded by several layers composed of different crystalline forms of ice.[21] Its interior may still be hot enough for a liquid layer consisting of a "magma" composed of water and ammonia between the ice Ih crust and deeper ice layers made of high-pressure forms of ice. The presence of ammonia allows water to remain liquid even at a temperature as low as 176K (97C) (for eutectic mixture with water).[22] The Cassini probe discovered the evidence for the layered structure in the form of natural extremely-low-frequency radio waves in Titan's atmosphere. Titan's surface is thought to be a poor reflector of extremely-low-frequency radio waves, so they may instead be reflecting off the liquidice boundary of a subsurface ocean.[23] Surface features were observed by the Cassini spacecraft to systematically shift by up to 30 kilometers (19mi) between October 2005 and May 2007, which suggests that the crust is decoupled from the interior, and provides additional evidence for an interior liquid layer.[24] Further supporting evidence for a liquid layer and ice shell decoupled from the solid core comes from the way the gravity field varies as Titan orbits Saturn.[25] Comparison of the gravity field with the RADAR-based topography observations[26] also suggests that the ice shell may be substantially rigid.[27][28]

The moons of Jupiter and Saturn are thought to have formed through co-accretion, a similar process to that believed to have formed the planets in the Solar System. As the young gas giants formed, they were surrounded by discs of material that gradually coalesced into moons. Whereas Jupiter possesses four large satellites in highly regular, planet-like orbits, Titan overwhelmingly dominates Saturn's system and possesses a high orbital eccentricity not immediately explained by co-accretion alone. A proposed model for the formation of Titan is that Saturn's system began with a group of moons similar to Jupiter's Galilean satellites, but that they were disrupted by a series of giant impacts, which would go on to form Titan. Saturn's mid-sized moons, such as Iapetus and Rhea, were formed from the debris of these collisions. Such a violent beginning would also explain Titan's orbital eccentricity.[29]

In 2014, analysis of Titan's atmospheric nitrogen suggested that it has possibly been sourced from material similar to that found in the Oort cloud and not from sources present during co-accretion of materials around Saturn.[30]

Titan is the only known moon with a significant atmosphere,[31] and its atmosphere is the only nitrogen-rich dense atmosphere in the Solar System aside from Earth's. Observations of it made in 2004 by Cassini suggest that Titan is a "super rotator", like Venus, with an atmosphere that rotates much faster than its surface.[32] Observations from the Voyager space probes have shown that Titan's atmosphere is denser than Earth's, with a surface pressure about 1.45 atm. It is also about 1.19 times as massive as Earth's overall,[33] or about 7.3 times more massive on a per surface area basis. Opaque haze layers block most visible light from the Sun and other sources and obscures Titan's surface features.[34] Titan's lower gravity means that its atmosphere is far more extended than Earth's.[35] The atmosphere of Titan is opaque at many wavelengths and as a result, a complete reflectance spectrum of the surface is impossible to acquire from orbit.[36] It was not until the arrival of the CassiniHuygens spacecraft in 2004 that the first direct images of Titan's surface were obtained.[37]

Titan's atmospheric composition in the stratosphere is 98.4% nitrogen with the remaining 1.6% composed mostly of methane (1.4%) and hydrogen (0.10.2%).[9] There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene and propane, and of other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, argon and helium.[8] The hydrocarbons are thought to form in Titan's upper atmosphere in reactions resulting from the breakup of methane by the Sun's ultraviolet light, producing a thick orange smog.[38] Titan spends 95% of its time within Saturn's magnetosphere, which may help shield it from the solar wind.[39]

Energy from the Sun should have converted all traces of methane in Titan's atmosphere into more complex hydrocarbons within 50 million yearsa short time compared to the age of the Solar System. This suggests that methane must be replenished by a reservoir on or within Titan itself.[40] The ultimate origin of the methane in its atmosphere may be its interior, released via eruptions from cryovolcanoes.[41][42][43][44][45]

On April 3, 2013, NASA reported that complex organic chemicals could arise on Titan, based on studies simulating the atmosphere of Titan.[46]

On June 6, 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan.[47]

On September 30, 2013, propene was detected in the atmosphere of Titan by NASA's Cassini spacecraft, using its composite infrared spectrometer (CIRS).[48] This is the first time propene has been found on any moon or planet other than Earth and is the first chemical found by the CIRS. The detection of propene fills a mysterious gap in observations that date back to NASA's Voyager 1 spacecraft's first close flyby of Titan in 1980, during which it was discovered that many of the gases that make up Titan's brown haze were hydrocarbons, theoretically formed via the recombination of radicals created by the Sun's ultraviolet photolysis of methane.[38]

On October 24, 2014, methane was found in polar clouds on Titan.[49][50]

Titan's surface temperature is about 94K (179.2C). At this temperature, water ice has an extremely low vapor pressure, so the little water vapor present appears limited to the stratosphere.[51] Titan receives about 1% as much sunlight as Earth.[52] Before sunlight reaches the surface, about 90% has been absorbed by the thick atmosphere, leaving only 0.1% of the amount of light Earth receives.[53]

Atmospheric methane creates a greenhouse effect on Titan's surface, without which Titan would be far colder.[54] Conversely, haze in Titan's atmosphere contributes to an anti-greenhouse effect by reflecting sunlight back into space, cancelling a portion of the greenhouse effect and making its surface significantly colder than its upper atmosphere.[55]

Titan's clouds, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze.[19] The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto its surface.[57]

Clouds typically cover 1% of Titan's disk, though outburst events have been observed in which the cloud cover rapidly expands to as much as 8%. One hypothesis asserts that the southern clouds are formed when heightened levels of sunlight during the southern summer generate uplift in the atmosphere, resulting in convection. This explanation is complicated by the fact that cloud formation has been observed not only after the southern summer solstice but also during mid-spring. Increased methane humidity at the south pole possibly contributes to the rapid increases in cloud size.[58] It was summer in Titan's southern hemisphere until 2010, when Saturn's orbit, which governs Titan's motion, moved Titan's northern hemisphere into the sunlight.[59] When the seasons switch, it is expected that ethane will begin to condense over the south pole.[60]

The surface of Titan has been described as "complex, fluid-processed, [and] geologically young".[61] Titan has been around since the Solar System's formation, but its surface is much younger, between 100 million and 1 billion years old. Geological processes may have reshaped Titan's surface.[62] Titan's atmosphere is twice as thick as Earth's, making it difficult for astronomical instruments to image its surface in the visible light spectrum.[63] The Cassini spacecraft is using infrared instruments, radar altimetry and synthetic aperture radar (SAR) imaging to map portions of Titan during its close fly-bys. The first images revealed a diverse geology, with both rough and smooth areas. There are features that may be volcanic in origin, disgorging water mixed with ammonia onto the surface. There is also evidence that Titan's ice shell may be substantially rigid,[27][28] which would suggest little geologic activity.[64]

There are also streaky features, some of them hundreds of kilometers in length, that appear to be caused by windblown particles.[65][66] Examination has also shown the surface to be relatively smooth; the few objects that seem to be impact craters appeared to have been filled in, perhaps by raining hydrocarbons or volcanoes. Radar altimetry suggests height variation is low, typically no more than 150meters. Occasional elevation changes of 500meters have been discovered and Titan has mountains that sometimes reach several hundred meters to more than 1 kilometer in height.[67]

Titan's surface is marked by broad regions of bright and dark terrain. These include Xanadu, a large, reflective equatorial area about the size of Australia. It was first identified in infrared images from the Hubble Space Telescope in 1994, and later viewed by the Cassini spacecraft. The convoluted region is filled with hills and cut by valleys and chasms.[68] It is criss-crossed in places by dark lineamentssinuous topographical features resembling ridges or crevices. These may represent tectonic activity, which would indicate that Xanadu is geologically young. Alternatively, the lineaments may be liquid-formed channels, suggesting old terrain that has been cut through by stream systems.[69] There are dark areas of similar size elsewhere on Titan, observed from the ground and by Cassini; at least one of these, Ligeia Mare, Titan's second-largest sea, is almost a pure methane sea.[70][71]

The possibility of hydrocarbon seas on Titan was first suggested based on Voyager 1 and 2 data that showed Titan to have a thick atmosphere of approximately the correct temperature and composition to support them, but direct evidence was not obtained until 1995 when data from Hubble and other observations suggested the existence of liquid methane on Titan, either in disconnected pockets or on the scale of satellite-wide oceans, similar to water on Earth.[72]

The Cassini mission confirmed the former hypothesis. When the probe arrived in the Saturnian system in 2004, it was hoped that hydrocarbon lakes or oceans would be detected from the sunlight reflected off their surface, but no specular reflections were initially observed.[73] Near Titan's south pole, an enigmatic dark feature named Ontario Lacus was identified[74] (and later confirmed to be a lake).[75] A possible shoreline was also identified near the pole via radar imagery.[76] Following a flyby on July 22, 2006, in which the Cassini spacecraft's radar imaged the northern latitudes (that were then in winter), several large, smooth (and thus dark to radar) patches were seen dotting the surface near the pole.[77] Based on the observations, scientists announced "definitive evidence of lakes filled with methane on Saturn's moon Titan" in January 2007.[78][79] The CassiniHuygens team concluded that the imaged features are almost certainly the long-sought hydrocarbon lakes, the first stable bodies of surface liquid found outside of Earth.[78] Some appear to have channels associated with liquid and lie in topographical depressions.[78] The liquid erosion features appear to be a very recent occurrence: channels in some regions have created surprisingly little erosion, suggesting erosion on Titan is extremely slow, or some other recent phenomena may have wiped out older riverbeds and landforms.[62] Overall, the Cassini radar observations have shown that lakes cover only a few percent of the surface, making Titan much drier than Earth.[80] Most of the lakes are concentrated near the poles (where the relative lack of sunlight prevents evaporation), but several long-standing hydrocarbon lakes in the equatorial desert regions have also been discovered, including one near the Huygens landing site in the Shangri-La region, which is about half the size of Utah's Great Salt Lake. The equatorial lakes are probably "oases", i.e. the likely supplier is underground aquifers.[81]

In June 2008, the Visual and Infrared Mapping Spectrometer on Cassini confirmed the presence of liquid ethane beyond doubt in Ontario Lacus.[82] On December 21, 2008, Cassini passed directly over Ontario Lacus and observed specular reflection in radar. The strength of the reflection saturated the probe's receiver, indicating that the lake level did not vary by more than 3mm (implying either that surface winds were minimal, or the lake's hydrocarbon fluid is viscous).[83][84]

Specular reflections are indicative of a smooth, mirror-like surface, so the observation corroborated the inference of the presence of a large liquid body drawn from radar imaging. The observation was made soon after the north polar region emerged from 15 years of winter darkness.

On July 8, 2009, Cassini's VIMS observed a specular reflection indicative of a smooth, mirror-like surface, off what today is called Jingpo Lacus, a lake in the north polar region shortly after the area emerged from 15 years of winter darkness.[85][86]

Early radar measurements made in July 2009 and January 2010 indicated that Ontario Lacus was extremely shallow, with an average depth of 0.43m, and a maximum depth of 3 to 7m (9.8 to 23.0ft).[87] In contrast, the northern hemisphere's Ligeia Mare was initially mapped to depths exceeding 8m, the maximum discernable by the radar instrument and the analysis techniques of the time.[87] Later science analysis, released in 2014, more fully mapped the depths of Titan's three methane seas and showed depths of more than 200 meters (660ft). Ligeia Mare averages from 20 to 40m (66 to 131ft) in depth, while other parts of Ligeia did not register any radar reflection at all, indicating a depth of more than 200m (660ft). While only the second largest of Titan's methane seas, Ligeia "contains enough liquid methane to fill three Lake Michigans."[88]

During a flyby on 26 September 2012, Cassini's radar detected in Titan's northern polar region what is likely a river with a length of more than 400 kilometers. It has been compared with the much larger Nile river on Earth. This feature is connected to Ligeia Mare.[75] Later, a paper ("Liquid-filled Canyons on Titan"[89]) published on Geophysical Research Letters on 9 August 2016 reported about the May 2013 Cassini RADAR altimeter observation of Vid Flumina channels, defined as a drainage network connected to Titan's second largest hydrocarbon sea, Ligeia Mare. Analysis of the received altimeter echoes showed that the channels are located in deep (up to ~570m), steep-sided, canyons and have strong specular surface reflections that indicate they are currently liquid filled. Elevations of the liquid in these channels are at the same level as Ligeia Mare to within a vertical precision of about 0.7m, consistent with the interpretation of drowned river valleys. Specular reflections are also observed in lower order tributaries elevated above the level of Ligeia Mare, consistent with drainage feeding into the main channel system. This is likely the first direct evidence of the presence of liquid channels on Titan and the first observation of hundred-meter deep canyons on Titan. Vid Flumina canyons are thus drowned by the sea but there are few isolated observations to attest to the presence of surface liquids standing at higher elevations.

During six flybys of Titan from 2006 to 2011, Cassini gathered radiometric tracking and optical navigation data from which investigators could roughly infer Titan's changing shape. The density of Titan is consistent with a body that is about 60% rock and 40% water. The team's analyses suggest that Titan's surface can rise and fall by up to 10 metres during each orbit. That degree of warping suggests that Titan's interior is relatively deformable, and that the most likely model of Titan is one in which an icy shell dozens of kilometres thick floats atop a global ocean.[90] The team's findings, together with the results of previous studies, hint that Titan's ocean may lie no more than 100 kilometers (62mi) below its surface.[90][91] On July 2, 2014, NASA reported the ocean inside Titan may be as salty as the Dead Sea.[92][93] On September 3, 2014, NASA reported studies suggesting methane rainfall on Titan may interact with a layer of icy materials underground, called an "alkanofer," to produce ethane and propane that may eventually feed into rivers and lakes.[94]

In 2016, Cassini found the first evidence of fluid-filled channels on Titan, in a series of deep, steep-sided canyons flowing into Ligeia Mare. This network of canyons, dubbed Vid Flumina, range in depth from 240 to 570m and have sides as steep as 40. They are believed to have formed either by crustal uplifting, like Earth's Grand Canyon, or a lowering of sea level, or perhaps a combination of the two. The depth of erosion suggests that liquid flows in this part of Titan are long-term features that persist for thousands of years.[95]

Radar, SAR and imaging data from Cassini have revealed few impact craters on Titan's surface.[62] These impacts appear to be relatively young, compared to Titan's age.[62] The few impact craters discovered include a 440-kilometer-wide (270mi) two-ring impact basin named Menrva seen by Cassini's ISS as a bright-dark concentric pattern.[97] A smaller, 60-kilometer-wide (37mi), flat-floored crater named Sinlap[98] and a 30km (19mi) crater with a central peak and dark floor named Ksa have also been observed.[99] Radar and Cassini imaging have also revealed "crateriforms", circular features on the surface of Titan that may be impact related, but lack certain features that would make identification certain. For example, a 90-kilometer-wide (56mi) ring of bright, rough material known as Guabonito has been observed by Cassini.[100] This feature is thought to be an impact crater filled in by dark, windblown sediment. Several other similar features have been observed in the dark Shangri-la and Aaru regions. Radar observed several circular features that may be craters in the bright region Xanadu during Cassini's April 30, 2006 flyby of Titan.[101]

Many of Titan's craters or probable craters display evidence of extensive erosion, and all show some indication of modification.[96] Most large craters have breached or incomplete rims, despite the fact that some craters on Titan have relatively more massive rims than those anywhere else in the Solar System. There is little evidence of formation of palimpsests through viscoelastic crustal relaxation, unlike on other large icy moons.[96] Most craters lack central peaks and have smooth floors, possibly due to impact-generation or later eruption of cryovolcanic lava. Infill from various geological processes is one reason for Titan's relative deficiency of craters; atmospheric shielding also plays a role. It is estimated that Titan's atmosphere reduces the number of craters on its surface by a factor of two.[103]

The limited high-resolution radar coverage of Titan obtained through 2007 (22%) suggested the existence of nonuniformities in its crater distribution. Xanadu has 29 times more craters than elsewhere. The leading hemisphere has a 30% higher density than the trailing hemisphere. There are lower crater densities in areas of equatorial dunes and in the north polar region (where hydrocarbon lakes and seas are most common).[96]

Pre-Cassini models of impact trajectories and angles suggest that where the impactor strikes the water ice crust, a small amount of ejecta remains as liquid water within the crater. It may persist as liquid for centuries or longer, sufficient for "the synthesis of simple precursor molecules to the origin of life".[104]

Scientists have long speculated that conditions on Titan resemble those of early Earth, though at a much lower temperature. The detection of argon-40 in the atmosphere in 2004 indicated that volcanoes had spawned plumes of "lava" composed of water and ammonia.[105] Global maps of the lake distribution on Titan's surface revealed that there is not enough surface methane to account for its continued presence in its atmosphere, and thus that a significant portion must be added through volcanic processes.[106]

Still, there is a paucity of surface features that can be unambiguously interpreted as cryovolcanoes.[107] One of the first of such features revealed by Cassini radar observations in 2004, called Ganesa Macula, resembles the geographic features called "pancake domes" found on Venus, and was thus initially thought to be cryovolcanic in origin, until Kirk et al. refuted this hypothesis at the American Geophysical Union annual meeting in December 2008. The feature was found to be not a dome at all, but appeared to result from accidental combination of light and dark patches.[108][109] In 2004 Cassini also detected an unusually bright feature (called Tortola Facula), which was interpreted as a cryovolcanic dome.[110] No similar features have been identified as of 2010.[111] In December 2008, astronomers announced the discovery of two transient but unusually long-lived "bright spots" in Titan's atmosphere, which appear too persistent to be explained by mere weather patterns, suggesting they were the result of extended cryovolcanic episodes.[22]

In March 2009, structures resembling lava flows were announced in a region of Titan called Hotei Arcus, which appears to fluctuate in brightness over several months. Though many phenomena were suggested to explain this fluctuation, the lava flows were found to rise 200 meters (660ft) above Titan's surface, consistent with it having been erupted from beneath the surface.[112]

A mountain range measuring 150 kilometers (93mi) long, 30 kilometers (19mi) wide and 1.5 kilometers (0.93mi) high was also discovered by Cassini in 2006. This range lies in the southern hemisphere and is thought to be composed of icy material and covered in methane snow. The movement of tectonic plates, perhaps influenced by a nearby impact basin, could have opened a gap through which the mountain's material upwelled.[113] Prior to Cassini, scientists assumed that most of the topography on Titan would be impact structures, yet these findings reveal that similar to Earth, the mountains were formed through geological processes.[114] In December 2010, the Cassini mission team announced the most compelling possible cryovolcano yet found. Named Sotra Patera, it is one in a chain of at least three mountains, each between 1000 and 1500m in height, several of which are topped by large craters. The ground around their bases appears to be overlaid by frozen lava flows.[115]

Most of Titan's highest peaks occur near its equator in so-called "ridge belts". They are believed to be analogous to Earth's fold mountains such as the Rockies or the Himalayas, formed by the collision and buckling of tectonic plates, or to subduction zones like the Andes, where upwelling lava (or cryolava) from a melting descending plate rises to the surface. One possible mechanism for their formation is tidal forces from Saturn. Because Titan's icy mantle is less viscous than Earth's magma mantle, and because its icy bedrock is softer than Earth's granite bedrock, mountains are unlikely to reach heights as great as those on Earth. In 2016, the Cassini team announced what they believe to be the tallest mountain on Titan. Located in the Mithrim Montes range, it is 3,337 m tall.[116]

If volcanism on Titan really exists, the hypothesis is that it is driven by energy released from the decay of radioactive elements within the mantle, as it is on Earth.[22] Magma on Earth is made of liquid rock, which is less dense than the solid rocky crust through which it erupts. Because ice is less dense than water, Titan's watery magma would be denser than its solid icy crust. This means that cryovolcanism on Titan would require a large amount of additional energy to operate, possibly via tidal flexing from nearby Saturn.[22] The low-pressure ice, overlaying a liquid layer of ammonium sulfate, ascends buoyantly, and the unstable system can produce dramatic plume events. Titan is resurfaced through the process by grain-sized ice and ammonium sulfate ash, which helps produce a wind-shaped landscape and sand dune features.[117]

In 2008 Jeffrey Moore (planetary geologist of Ames Research Center) proposed an alternate view of Titan's geology. Noting that no volcanic features had been unambiguously identified on Titan so far, he asserted that Titan is a geologically dead world, whose surface is shaped only by impact cratering, fluvial and eolian erosion, mass wasting and other exogenic processes. According to this hypothesis, methane is not emitted by volcanoes but slowly diffuses out of Titan's cold and stiff interior. Ganesa Macula may be an eroded impact crater with a dark dune in the center. The mountainous ridges observed in some regions can be explained as heavily degraded scarps of large multi-ring impact structures or as a result of the global contraction due to the slow cooling of the interior. Even in this case, Titan may still have an internal ocean made of the eutectic waterammonia mixture with a temperature of 176K (97C), which is low enough to be explained by the decay of radioactive elements in the core. The bright Xanadu terrain may be a degraded heavily cratered terrain similar to that observed on the surface of Callisto. Indeed, were it not for its lack of an atmosphere, Callisto could serve as a model for Titan's geology in this scenario. Jeffrey Moore even called Titan Callisto with weather.[107][118]

Many of the more prominent mountains and hills have been given official names by the International Astronomical Union. According to JPL, "By convention, mountains on Titan are named for mountains from Middle-earth, the fictional setting in fantasy novels by J.R.R. Tolkien." Colles (collections of hills) are named for characters from the same Tolkien works.[119]

In the first images of Titan's surface taken by Earth-based telescopes in the early 2000s, large regions of dark terrain were revealed straddling Titan's equator.[120] Prior to the arrival of Cassini, these regions were thought to be seas of liquid hydrocarbons.[121] Radar images captured by the Cassini spacecraft have instead revealed some of these regions to be extensive plains covered in longitudinal dunes, up to 330ft (100m) high[122] about a kilometer wide, and tens to hundreds of kilometers long.[123] Dunes of this type are always aligned with average wind direction. In the case of Titan, steady zonal (eastward) winds combine with variable tidal winds (approximately 0.5 meters per second).[124] The tidal winds are the result of tidal forces from Saturn on Titan's atmosphere, which are 400 times stronger than the tidal forces of the Moon on Earth and tend to drive wind toward the equator. This wind pattern, it was theorized, causes granular material on the surface to gradually build up in long parallel dunes aligned west-to-east. The dunes break up around mountains, where the wind direction shifts.

The longitudinal (or linear) dunes were initially presumed to be formed by moderately variable winds that either follow one mean direction or alternate between two different directions. Subsequent observations indicate that the dunes point to the east although climate simulations indicate Titan's surface winds blow toward the west. At less than 1 meter per second, they are not powerful enough to lift and transport surface material. Recent computer simulations indicate that the dunes may be the result of rare storm winds that happen only every fifteen years when Titan is in equinox.[125] These storms produce strong downdrafts, flowing eastward at up to 10 meters per second when they reach the surface.

The "sand" on Titan is likely not made up of small grains of silicates like the sand on Earth,[126] but rather might have formed when liquid methane rained and eroded the water-ice bedrock, possibly in the form of flash floods. Alternatively, the sand could also have come from organic solids produced by photochemical reactions in Titan's atmosphere.[122][124][127] Studies of dunes' composition in May 2008 revealed that they possessed less water than the rest of Titan, and are thus most likely derived from organic soot like hydrocarbon polymers clumping together after raining onto the surface.[128] Calculations indicate the sand on Titan has a density of one-third that of terrestrial sand.[129] The low density combined with the dryness of Titan's atmosphere might cause the grains to clump together because of static electricity buildup. The "stickiness" might make it difficult for the generally mild breeze close to Titan's surface to move the dunes although more powerful winds from seasonal storms could still blow them eastward.[130]

Titan is never visible to the naked eye, but can be observed through small telescopes or strong binoculars. Amateur observation is difficult because of the proximity of Titan to Saturn's brilliant globe and ring system; an occulting bar, covering part of the eyepiece and used to block the bright planet, greatly improves viewing.[131] Titan has a maximum apparent magnitude of +8.2,[7] and mean opposition magnitude 8.4.[132] This compares to +4.6[132] for the similarly sized Ganymede, in the Jovian system.

Observations of Titan prior to the space age were limited. In 1907 Spanish astronomer Josep Comas i Sol observed limb darkening of Titan, the first evidence that the body has an atmosphere. In 1944 Gerard P. Kuiper used a spectroscopic technique to detect an atmosphere of methane.[133]

The first probe to visit the Saturnian system was Pioneer 11 in 1979, which revealed that Titan was probably too cold to support life.[134] It took images of Titan, including Titan and Saturn together in mid to late 1979.[135] The quality was soon surpassed by the two Voyagers.

Titan was examined by both Voyager 1 and 2 in 1980 and 1981, respectively. Voyager 1's trajectory was designed to provide an optimized Titan flyby, during which the spacecraft was able to determine the density, composition, and temperature of the atmosphere, and obtain a precise measurement of Titan's mass.[136] Atmospheric haze prevented direct imaging of the surface, though in 2004 intensive digital processing of images taken through Voyager 1's orange filter did reveal hints of the light and dark features now known as Xanadu and Shangri-la,[137] which had been observed in the infrared by the Hubble Space Telescope. Voyager 2, which would have been diverted to perform the Titan flyby if Voyager 1 had been unable to, did not pass near Titan and continued on to Uranus and Neptune.[136]:94

Even with the data provided by the Voyagers, Titan remained a body of mysterya large satellite shrouded in an atmosphere that makes detailed observation difficult. The mystery that had surrounded Titan since the 17th-century observations of Christiaan Huygens and Giovanni Cassini was revealed by a spacecraft named in their honor.

The CassiniHuygens spacecraft reached Saturn on July 1, 2004, and began the process of mapping Titan's surface by radar. A joint project of the European Space Agency (ESA) and NASA, CassiniHuygens has proved a very successful mission. The Cassini probe flew by Titan on October 26, 2004, and took the highest-resolution images ever of Titan's surface, at only 1,200 kilometers (750mi), discerning patches of light and dark that would be invisible to the human eye.

On July 22, 2006, Cassini made its first targeted, close fly-by at 950 kilometers (590mi) from Titan; the closest flyby was at 880 kilometers (550mi) on June 21, 2010.[138] Liquid has been found in abundance on the surface in the north polar region, in the form of many lakes and seas discovered by Cassini.[77]

Same image with contrast enhanced

Huygens landed[139] on Titan on January 14, 2005, discovering that many of its surface features seem to have been formed by fluids at some point in the past.[140] Titan is the most distant body from Earth to have a space probe land on its surface.[141]

The Huygens probe landed just off the easternmost tip of a bright region now called Adiri. The probe photographed pale hills with dark "rivers" running down to a dark plain. Current understanding is that the hills (also referred to as highlands) are composed mainly of water ice. Dark organic compounds, created in the upper atmosphere by the ultraviolet radiation of the Sun, may rain from Titan's atmosphere. They are washed down the hills with the methane rain and are deposited on the plains over geological time scales.[142]

After landing, Huygens photographed a dark plain covered in small rocks and pebbles, which are composed of water ice.[142] The two rocks just below the middle of the image on the right are smaller than they may appear: the left-hand one is 15centimeters across, and the one in the center is 4centimeters across, at a distance of about 85centimeters from Huygens. There is evidence of erosion at the base of the rocks, indicating possible fluvial activity. The surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice. The "soil" visible in the images is interpreted to be precipitation from the hydrocarbon haze above.

In March 2007, NASA, ESA, and COSPAR decided to name the Huygens landing site the Hubert Curien Memorial Station in memory of the former president of the ESA.[143]

There have been several conceptual missions proposed in recent years for returning a robotic space probe to Titan. Initial conceptual work has been completed for such missions by NASA, the ESA and JPL. At present, none of these proposals have become funded missions.

The Titan Saturn System Mission (TSSM) was a joint NASA/ESA proposal for exploration of Saturn's moons.[144] It envisions a hot-air balloon floating in Titan's atmosphere for six months. It was competing against the Europa Jupiter System Mission (EJSM) proposal for funding. In February 2009 it was announced that ESA/NASA had given the EJSM mission priority ahead of the TSSM.[145]

The proposed Titan Mare Explorer (TiME) was a low-cost lander that would splash down in a lake in Titan's northern hemisphere and float on the surface of the lake for three to six months.[146][147][148] It was selected for a Phase-A design study in 2011 as a candidate mission for the 12th NASA Discovery Program opportunity,[149] but was not selected for flight.[150]

Another mission to Titan proposed in early 2012 by Jason Barnes, a scientist at the University of Idaho, is the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR): an unmanned plane (or drone) that would fly through Titan's atmosphere and take high-definition images of the surface of Titan. NASA did not approve the requested $715 million, and the future of the project is uncertain.[151][152][153]

A conceptual design for another lake lander was proposed in late 2012 by the Spanish-based private engineering firm SENER and the Centro de Astrobiologa in Madrid. The concept probe is called Titan Lake In-situ Sampling Propelled Explorer (TALISE).[154][155] The major difference compared to the TiME probe would be that TALISE is envisioned with its own propulsion system and would therefore not be limited to simply drifting on the lake when it splashes down.

A Discovery Program contestant for its mission #13 is Journey to Enceladus and Titan (JET), an astrobiology Saturn orbiter that would assess the habitability potential of Enceladus and Titan.[156][157][158]

In 2015, the NASA Innovative Advanced Concepts program (NIAC) awarded a Phase II grant[159] to a design study of a submarine to explore the seas of Titan.[160][161][162]

Titan is thought to be a prebiotic environment rich in complex organic chemistry[46] with a possible subsurface liquid ocean serving as a biotic environment.[163][164][165]

The CassiniHuygens mission was not equipped to provide evidence for biosignatures or complex organic compounds; it showed an environment on Titan that is similar, in some ways, to ones theorized for the primordial Earth.[166] Scientists surmise that the atmosphere of early Earth was similar in composition to the current atmosphere on Titan, with the important exception of a lack of water vapor on Titan.[167]

The MillerUrey experiment and several following experiments have shown that with an atmosphere similar to that of Titan and the addition of UV radiation, complex molecules and polymer substances like tholins can be generated. The reaction starts with dissociation of nitrogen and methane, forming hydrogen cyanide and acetylene. Further reactions have been studied extensively.[168]

It has been reported that when energy was applied to a combination of gases like those in Titan's atmosphere, five nucleotide bases, the building blocks of DNA and RNA, were among the many compounds produced. In addition, amino acids, the building blocks of protein were found. It was the first time nucleotide bases and amino acids had been found in such an experiment without liquid water being present.[169]

On April 3, 2013, NASA reported that complex organic chemicals could arise on Titan based on studies simulating the atmosphere of Titan.[46]

Laboratory simulations have led to the suggestion that enough organic material exists on Titan to start a chemical evolution analogous to what is thought to have started life on Earth. The analogy assumes the presence of liquid water for longer periods than is currently observable; several theories suggest that liquid water from an impact could be preserved under a frozen isolation layer.[170] It has also been theorized that liquid-ammonia oceans could exist deep below the surface.[163][171] Another model suggests an ammoniawater solution as much as 200 kilometers (120mi) deep beneath a water-ice crust with conditions that, although extreme by terrestrial standards, are such that life could survive.[164]Heat transfer between the interior and upper layers would be critical in sustaining any subsurface oceanic life.[163] Detection of microbial life on Titan would depend on its biogenic effects. That the atmospheric methane and nitrogen might be of biological origin has been examined, for example.[164]

It has been suggested that life could exist in the lakes of liquid methane on Titan, just as organisms on Earth live in water.[172] Such organisms would inhale H2 in place of O2, metabolize it with acetylene instead of glucose, and exhale methane instead of carbon dioxide.[165][172]

All living things on Earth (including methanogens) use liquid water as a solvent; it is speculated that life on Titan might instead use a liquid hydrocarbon, such as methane or ethane.[173] Water is a stronger solvent than methane.[174] Water is also more chemically reactive, and can break down large organic molecules through hydrolysis.[173] A life-form whose solvent was a hydrocarbon would not face the risk of its biomolecules being destroyed in this way.[173]

In 2005, astrobiologist Chris McKay argued that if methanogenic life did exist on the surface of Titan, it would likely have a measurable effect on the mixing ratio in the Titan troposphere: levels of hydrogen and acetylene would be measurably lower than otherwise expected.[172]

In 2010, Darrell Strobel, from Johns Hopkins University, identified a greater abundance of molecular hydrogen in the upper atmospheric layers of Titan compared to the lower layers, arguing for a downward flow at a rate of roughly 1028 molecules per second and disappearance of hydrogen near Titan's surface; as Strobel noted, his findings were in line with the effects McKay had predicted if methanogenic life-forms were present.[172][174][175] The same year, another study showed low levels of acetylene on Titan's surface, which were interpreted by McKay as consistent with the hypothesis of organisms consuming hydrocarbons.[174] Although restating the biological hypothesis, he cautioned that other explanations for the hydrogen and acetylene findings are more likely: the possibilities of yet unidentified physical or chemical processes (e.g. a surface catalyst accepting hydrocarbons or hydrogen), or flaws in the current models of material flow.[165] Composition data and transport models need to be substantiated, etc. Even so, despite saying that a non-biological catalytic explanation would be less startling than a biological one, McKay noted that the discovery of a catalyst effective at 95K (180C) would still be significant.[165]

As NASA notes in its news article on the June 2010 findings: "To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere."[174] As the NASA statement also says: "some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface."[174]

In February 2015, a hypothetical cell membrane capable of functioning in liquid methane in Titan conditions was modeled. Composed of small molecules containing carbon, hydrogen, and nitrogen, it would have the same stability and flexibility as cell membranes on Earth, which are composed of phospholipids, compounds of carbon, hydrogen, oxygen, and phosphorus. This hypothetical cell membrane was termed an "azotosome", a combination of "azote", French for nitrogen, and "liposome".[176][177]

Despite these biological possibilities, there are formidable obstacles to life on Titan, and any analogy to Earth is inexact. At a vast distance from the Sun, Titan is frigid, and its atmosphere lacks CO2. At Titan's surface, water exists only in solid form. Because of these difficulties, scientists such as Jonathan Lunine have viewed Titan less as a likely habitat for life, than as an experiment for examining theories on the conditions that prevailed prior to the appearance of life on Earth.[178] Although life itself may not exist, the prebiotic conditions on Titan and the associated organic chemistry remain of great interest in understanding the early history of the terrestrial biosphere.[166] Using Titan as a prebiotic experiment involves not only observation through spacecraft, but laboratory experiments, and chemical and photochemical modeling on Earth.[168]

It is hypothesized that large asteroid and cometary impacts on Earth's surface may have caused fragments of microbe-laden rock to escape Earth's gravity, suggesting the possibility of transpermia. Calculations indicate that these would encounter many of the bodies in the Solar System, including Titan.[179][180] On the other hand, Jonathan Lunine has argued that any living things in Titan's cryogenic hydrocarbon lakes would need to be so different chemically from Earth life that it would not be possible for one to be the ancestor of the other.[181]

Conditions on Titan could become far more habitable in the far future. Five billion years from now, as the Sun becomes a red giant, its surface temperature could rise enough for Titan to support liquid water on its surface making it habitable.[182] As the Sun's ultraviolet output decreases, the haze in Titan's upper atmosphere will be depleted, lessening the anti-greenhouse effect on the surface and enabling the greenhouse created by atmospheric methane to play a far greater role. These conditions together could create a habitable environment, and could persist for several hundred million years. This was sufficient time for simple life to spawn on Earth; the presence of ammonia on Titan would cause chemical reactions to proceed more slowly.[183]

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Titan (moon) - Wikipedia

smithsonian.com July 6, 2017

The hope for Martian life took another blow today. AsIan Sample at The Guardian reports, a new study suggests that in the presence of ultraviolet light, perchlorates, a class of chemical compounds widespread on Mars' surface, turn deadly for bacteria.

The presence of perchlorates isn't new. Viking 1 and 2 spacecraft detected perchlorates when they landed on the Martian surface in 1976,JeffreyKlugerreportsfor Time. Since then, other spacecraft have confirmed the presence of the compounds. The 2009 Phoenix lander found that perchlorates make upbetween 0.4 and 0.6 percentof the soil sample it collected.

While perchlorates, which are composed of chlorine and oxygen, are toxic to humans, microbes typically love the stuff. Andresearchers have beenoptimistic that their presencecould support bacterial life on Mars. AsKluger reports,some bacteria on Earth use naturally occurring perchlorate as an energy source. The compound also lowers the melting point of water, which could improve the chance ofliquid water existing on the Red Planet.

But the latest study, published in the journalScientific Reports, suggests thatin the presence of ultraviolet lightperchlorate is not so microbe-friendly. Mars has a thin atmosphere, which often leaves its surface bathed in UV rays. And when heated, chlorine-based molecules like perchlorates cause heavy damage to living cells, reportsSarahFechtat Popular Science.

Researchers at the University of Edinburgh wanted to see just how much damage those perchlorates would cause to any Martian bacteria. So theyexposed test tubes of a common bacteria, Bacillus subtilis, to conditions similar to ones they might encounter on Mars. They started with low temperatures and low oxygen in the presence of perchlorate. Bacteriaunder these conditions survived for up to an hour, Fecht reports. But when the researchers addedUV light to the mix, the test tube was completely sterilized within 30 seconds. The researcher also found that two other common Martian soil components, iron oxide and hydrogen peroxide, reacted with irradiated perchlorate to make the soil hostile to bacteria.

We knew before that any life would have an incredibly hard time to survive on the surface, and this study experimentally confirms that, Dirk Schulze-Makuch, an astrobiologist at Washington State University not involved in the study, tells Fecht.

That doesnt completely rule out the possibility that bacteria may exist on Mars. I cant speak for life in the past, co-author Jennifer Wadsworth tells Sample. As far as present life, it doesnt rule it out but probably means we should look for life underground where its shielded from the harsh radiation environment on the surface.As Sample reports, the ExoMars rover, scheduled to launch in 2020, will test this idea, digging about 12 feet into the Martian soil to look for bacteria.

Therestill remains some hope for surface microbes. As Kluger reports, the researchers found that the colder temperatures offersome small protection for thebacteria. And the average temperature on Mars is -67 Fahrenheit. Also, the concentrations of perchlorate are not uniform, meaning there may be some pockets where life could exist.

It's also possible that hypothetical Martian bacteria could be much tougher than the commonBacillus subtilis.On Earth, researchers have found all types of extremophile organisms with the ability to survive under intense heat and pressure, in the presence of acid, without water and even inside rocks. Life can survive very extreme environments, Wadsworth tells Fecth. The bacterial model we tested wasnt an extremophile so its not out of the question that hardier life forms would find a way to survive.

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Mars Surface May Be Too Toxic for Microbial Life - Smithsonian