To date, astronomers have confirmed the existence of 4,152 extrasolar planets in 3,077 star systems. While the majority of these discoveries involved a single planet, several hundred star systems were found to be multi-planetary. Systems that contain six planets or more, however, appear to be rarer, with only a dozen or so cases discovered so far.
This is what astronomers found after observing HD 158259, a Sun-like star located about 88 light-years from Earth, for the past seven years using the SOPHIE spectrograph. Combined with new data from the Transiting Exoplanet Space Satellite (TESS), an international team reported the discovery of a six planet system where all were in near-perfect rhythm with each other.
The international team responsible for this discovery was led by Dr. Nathan Hara, a postdoctoral researcher at the University of Geneva (UNIGE), a member of the Swiss PlanetS institute, and a Fellow with the European Space Agencys (ESA) CHaracterising ExOPlanets Satellite (CHEOPS) mission. The study that describes their findings recently appeared in the journal Astronomy & Astrophysics.
Using SOPHIE, astronomers have been conducting velocity measurements of many stars in the northern hemisphere to determine if they have exoplanets orbiting them. This method, known as the Radial Velocity Method (or Doppler Spectroscopy), consists of measuring the spectra a star to see if it is moving in place which is an indication that the gravitational force of one or more planets is working on it.
Interestingly enough, it was SOPHIEs predecessor (the ELODIE spectrograph) that led to one of the earliest exoplanet discoveries in 1995 the hot Jupiter 51 Peg b (Dimidium). After examining HD 158259 for seven years, SOPHIE succeeded in obtaining high-precision radial velocity measurements that revealed the presence of a six planet system.
This system consists of an innermost large rocky planet (a super-Earth) and five small gas giants (mini-Neptunes) that have exceptionally regular spacing between them. As Franois Bouchy, a professor of astronomy and science at UNIGE and the coordinator of the observation program, explained in a UNIGE press release:
The discovery of this exceptional system has been made possible thanks to the acquisition of a great number of measurements, as well as a dramatic improvement of the instrument and of our signal processing techniques.
These planets range from being 2 (the innermost super-Earth) to 6 times (the mini-Neptunes) as massive as Earth. The system is also very compact, with all of six planets orbit closely to the star and the outermost being just 0.38 times as distant as Mercury is from the Sun. This places the planets well inside the stars habitable zone (HZ), which means none are likely to have water on the surfaces or dense enough atmospheres to support life.
Meanwhile, TESS monitored HD 158259 for signs of transits (aka. the Transit Method) and observed a decrease in the stars brightness as the innermost planet passed in front of the star. According to Isabelle Boisse, a researcher at the Marseille Astrophysics Laboratory and co-author of the study, the TESS readings (combined with the radial velocity data) allowed them to constrain the properties of this planet (HD 158259 b) further.
The TESS measurements strongly support the detection of the planet and allow to estimate its radius, which brings very valuable information on the planets internal structure, she said. But as noted earlier, the most impressive feature of this system is its regularity. Basically, the planets in the system have an almost exact 3:2 orbital resonance
This means that for every three orbits the innermost planet makes, the second one will complete about two. In the time it takes the second planet to complete three orbits, the third will complete about two. This ratio applies to all six planets in the system and came as quite a surprise to Hara and his colleagues.
When describing the planets orbits, Hara compared it to an orchestra playing music, though the arrangement is not quite perfect:
This is comparable to several musicians beating distinct rhythms, yet who beat at the same time at the beginning of each bar. Here, about is important. Besides the ubiquity of the 3:2 period ratio, this constitutes the originality of the system.
Resonances, even imperfect ones, are of interest to astronomers because of how they provide hints to a star systems formation and evolution. In astronomical circles, there is still considerable debate about how star systems come together and change over time. A particularly contentious point is whether planets form close to their final position in the system, or if they change their orbits after forming.
This latter scenario (known as planetary migration) has been gaining traction in recent years thanks to the discovery of exoplanets like Hot-Jupiters, leading many astronomers to question if planetary shake-ups occur. This theory would appear to explain the formation of the six planets in the HD 158259 system. Said Stephane Udry, a professor of astronomy and science at UNIGE:
Several compact systems with several planets in, or close to resonances are known, such as TRAPPIST-1 or Kepler-80. Such systems are believed to form far from the star before migrating towards it. In this scenario, the resonances play a crucial part.
The fact that HD 158259s planets are close to a 3:2 resonance, but not exactly within one, suggests that they were trapped in one in the past. However, they would have subsequently undergone synchronous migration and moved away from the resonance. According to Hara, thats not all that this system can tell us.
Furthermore, the current departure of the period ratios from 3:2 contains a wealth of information, he said. With these values on the one hand, and tidal effect models on the other hand, we could constrain the internal structure of the planets in a future study. In summary, the current state of the system gives us a window on its formation.
The more we learn about this multi-planet system and others like it, the more we can learn about how star systems like our own came to be. The resolution of these and other questions about the formation and evolution of planetary systems will put us one step closer to knowing how life can emerge (and perhaps where to look for it!)
Further Reading: University of Geneva, Astronomy & Astrophysics
Like Loading...
See the original post here:
Astronomers Find a Six-Planet System Which Orbit in Lockstep With Each Other - Universe Today
- Rotational spectra of isotopic species of methyl cyanide, CH_3CN, in their ground vibrational states up to terahertz frequencies - November 8th, 2009 [November 8th, 2009]
- Cosmological parameter extraction and biases from type Ia supernova magnitude evolution - November 8th, 2009 [November 8th, 2009]
- Continuous monitoring of pulse period variations in Hercules X-1 using Swift/BAT - November 8th, 2009 [November 8th, 2009]
- Constraining the ortho-to-para ratio of H{_2} with anomalous H{_2}CO absorption - November 8th, 2009 [November 8th, 2009]
- A photometric and spectroscopic study of the new dwarf spheroidal galaxy in Hercules - Metallicity, velocities, and a clean list of RGB members - November 8th, 2009 [November 8th, 2009]
- Luminosities and mass-loss rates of SMC and LMC AGB stars and red supergiants - November 8th, 2009 [November 8th, 2009]
- Electron beam – plasma system with the return current and directivity of its X-ray emission - November 8th, 2009 [November 8th, 2009]
- The propagation of the shock wave from a strong explosion in a plane-parallel stratified medium: the Kompaneets approximation - November 8th, 2009 [November 8th, 2009]
- Analysis of hydrogen-rich magnetic white dwarfs detected in the Sloan Digital Sky Survey - November 8th, 2009 [November 8th, 2009]
- Letter: Centaurus A as TeV \gamma-ray and possible UHE cosmic-ray source - November 8th, 2009 [November 8th, 2009]
- Young pre-low-mass X-ray binaries in the propeller phase - Nature of the 6.7-h periodic X-ray source 1E 161348-5055 in RCW 103 - November 8th, 2009 [November 8th, 2009]
- Radiative rates and electron impact excitation rates for transitions in Cr VIII - November 8th, 2009 [November 8th, 2009]
- Solar granulation from photosphere to low chromosphere observed in Ba II 4554 Å line - November 8th, 2009 [November 8th, 2009]
- Does the HD 209458 planetary system pose a challenge to the stellar atmosphere models? - November 8th, 2009 [November 8th, 2009]
- Effect of asymmetry of the radio source distribution on the apparent proper motion kinematic analysis - November 8th, 2009 [November 8th, 2009]
- Destriping CMB temperature and polarization maps - November 8th, 2009 [November 8th, 2009]
- Search for cold debris disks around M-dwarfs. II - November 8th, 2009 [November 8th, 2009]
- Precise data on Leonid fireballs from all-sky photographic records - November 8th, 2009 [November 8th, 2009]
- An X-ray view of 82 LINERs with Chandra and XMM-Newton data - November 8th, 2009 [November 8th, 2009]
- Radio observations of ZwCl 2341.1+0000: a double radio relic cluster - November 8th, 2009 [November 8th, 2009]
- Candidate free-floating super-Jupiters in the young \sigma Orionis open cluster - November 8th, 2009 [November 8th, 2009]
- The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies - November 8th, 2009 [November 8th, 2009]
- XMMSL1 J060636.2-694933: an XMM-Newton slew discovery and Swift/Magellan follow up of a new classical nova in the LMC - November 8th, 2009 [November 8th, 2009]
- The inner rim structures of protoplanetary discs - November 8th, 2009 [November 8th, 2009]
- The solar Ba{\sf II} 4554 Å line as a Doppler diagnostic: NLTE analysis in 3D hydrodynamical model - November 8th, 2009 [November 8th, 2009]
- Magnetic evolution of superactive regions - Complexity and potentially unstable magnetic discontinuities - November 8th, 2009 [November 8th, 2009]
- Low-mass protostars and dense cores in different evolutionary stages in IRAS 00213+6530 - November 8th, 2009 [November 8th, 2009]
- PMAS optical integral field spectroscopy of luminous infrared galaxies - I. The atlas - November 8th, 2009 [November 8th, 2009]
- First AGILE catalog of high-confidence gamma-ray sources - November 8th, 2009 [November 8th, 2009]
- Radiative hydrodynamics simulations of red supergiant stars - I. interpretation of interferometric observations - November 8th, 2009 [November 8th, 2009]
- Extrasolar planets and brown dwarfs around A–F type stars - VII. \theta Cygni radial velocity variations: planets or stellar phenomenon? - November 8th, 2009 [November 8th, 2009]
- Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 - II. The magnetic field structure - November 8th, 2009 [November 8th, 2009]
- Physical structure and water line spectrum predictions of the intermediate mass protostar OMC2-FIR4 - November 8th, 2009 [November 8th, 2009]
- The bright galaxy population of five medium redshift clusters - II. Quantitative galaxy morphology - November 8th, 2009 [November 8th, 2009]
- Dust in brown dwarfs and extra-solar planets - II. Cloud formation for cosmologically evolving abundances - November 8th, 2009 [November 8th, 2009]
- The quiet Sun magnetic field observed with ZIMPOL on THEMIS - I. The probability density function - November 8th, 2009 [November 8th, 2009]
- Complexity in the sunspot cycle - November 8th, 2009 [November 8th, 2009]
- Properties and nature of Be stars - 26. Long-term and orbital changes of \zeta Tauri - November 8th, 2009 [November 8th, 2009]
- The massive Wolf-Rayet binary LSS 1964 (=WR 29) - II. The V light curve - November 8th, 2009 [November 8th, 2009]
- Supernova progenitor stars in the initial range of 23 to 33 solar masses and their relation with the SNR Cassiopeia A - November 8th, 2009 [November 8th, 2009]
- The Hertzsprung-Russell Diagram of Star Clusters - November 8th, 2009 [November 8th, 2009]
- Table of the 10 Brightest stars within 10 Parsecs of the Sun - November 8th, 2009 [November 8th, 2009]
- The Hertzsprung-Russell Diagram of the Nearest Stars - November 8th, 2009 [November 8th, 2009]
- Magnitude and Color in Astronomy - November 8th, 2009 [November 8th, 2009]
- Stellar Types - November 8th, 2009 [November 8th, 2009]
- Brown Dwarfs - November 8th, 2009 [November 8th, 2009]
- Spotting the Minimum - November 8th, 2009 [November 8th, 2009]
- The Structure and Evolution of Brown Dwarfs - November 8th, 2009 [November 8th, 2009]
- No Bang from the Big Bang Machine - November 8th, 2009 [November 8th, 2009]
- The Sizes of the Stars and the Planets - November 8th, 2009 [November 8th, 2009]
- An Implausible Light Thrust - November 8th, 2009 [November 8th, 2009]
- the Masses of Degenerate Objects - November 8th, 2009 [November 8th, 2009]
- Degeneracy Pressure - November 8th, 2009 [November 8th, 2009]
- Introduction to Degenerate Objects - November 8th, 2009 [November 8th, 2009]
- The Radii of Degenerate Objects - November 8th, 2009 [November 8th, 2009]
- The Inevitability of Black Holes - November 8th, 2009 [November 8th, 2009]
- Scientific Pig-Out - November 8th, 2009 [November 8th, 2009]
- The Neutrino Cooling of Degenerate Dwarfs - November 8th, 2009 [November 8th, 2009]
- The Neutrino Cooling of Neutron Stars - November 8th, 2009 [November 8th, 2009]
- Overview of Supernovae - November 8th, 2009 [November 8th, 2009]
- Energetics of Thermonuclear Supernovae - November 8th, 2009 [November 8th, 2009]
- Thermonuclear Supernovae - November 8th, 2009 [November 8th, 2009]
- Nuclear Reactions in Thermonuclear Supernovae - November 8th, 2009 [November 8th, 2009]
- Core-Collapse Supernovae - November 8th, 2009 [November 8th, 2009]
- Neutrinos and SN 1987A - November 8th, 2009 [November 8th, 2009]
- Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R Coronae Austrinae - December 13th, 2009 [December 13th, 2009]
- Probing the dust properties of galaxies up to submillimetre wavelengths - I. The spectral energy distribution of dwarf galaxies using LABOCA - December 13th, 2009 [December 13th, 2009]
- On the physical origin of the second solar spectrum of the Sc II line at 4247 Å - December 13th, 2009 [December 13th, 2009]
- On detecting the large separation in the autocorrelation of stellar oscillation times series - December 13th, 2009 [December 13th, 2009]
- Imaging the spotty surface of Betelgeuse in the H band - December 13th, 2009 [December 13th, 2009]
- Chandra observation of Cepheus A: the diffuse emission of HH 168 resolved - December 13th, 2009 [December 13th, 2009]
- A planetary eclipse map of CoRoT-2a - Comprehensive lightcurve modeling combining rotational-modulation and transits - December 13th, 2009 [December 13th, 2009]
- The chemical composition of carbon stars. The R-type stars - December 13th, 2009 [December 13th, 2009]
- Flow instabilities of magnetic flux tubes - IV. Flux storage in the solar overshoot region - December 13th, 2009 [December 13th, 2009]
- Fragmentation of a dynamically condensing radiative layer - December 13th, 2009 [December 13th, 2009]
- Temporal variations of the CaXIX spectra in solar flares - December 13th, 2009 [December 13th, 2009]
- Deuterium chemistry in the Orion Bar PDR - “Warm” chemistry starring CH_{2}D^+ - December 13th, 2009 [December 13th, 2009]
- Metal abundances in the cool cores of galaxy clusters - December 13th, 2009 [December 13th, 2009]
- The nature of the X-ray binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift observations - December 13th, 2009 [December 13th, 2009]
- Relating basic properties of bright early-type dwarf galaxies to their location in Abell 901/902 - December 13th, 2009 [December 13th, 2009]