What Is A Near-Earth Object (NEO)? What Is The Purpose Of The Near-Earth Object Program? How Many Near-Earth Objects Have Been Discovered So Far? What Are Asteroids And Comets? What Are The Differences Between An Asteroid, Comet, Meteoroid, Meteor and Meteorite? Why Study Asteroids? Why Study Comets? What Are Atiras, Atens, Apollos and Amors? What Is A Potentially Hazardous Asteroid (PHA)? What Is A Great Comet? What Spacecraft Are We Sending To Asteroids & Comets?

Also, see our FAQ on Impact Risk Assessment.

What Is A Near-Earth Object (NEO)?

Near-Earth Objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood. Composed mostly of water ice with embedded dust particles, comets originally formed in the cold outer planetary system while most of the rocky asteroids formed in the warmer inner solar system between the orbits of Mars and Jupiter.

What Is The Purpose Of The Near-Earth Object Program?

The purpose of the Near-Earth Object Program is to coordinate NASA-sponsored efforts to detect, track and characterize potentially hazardous asteroids and comets that could approach the Earth. With over 90% of the near-Earth objects larger than one kilometer already discovered, the NEO Program is now focusing on finding 90% of the NEO population larger than 140 meters. In addition to managing the detection and cataloging of Near-Earth objects, the NEO Program office will be responsible for facilitating communications between the astronomical community and the public should any potentially hazardous objects be discovered.

How Many Near-Earth Objects Have Been Discovered So Far?

As of June 29, 2015, 12863 Near-Earth objects have been discovered. Some 872 of these NEOs are asteroids with a diameter of approximately 1 kilometer or larger. Also, 1597 of these NEOs have been classified as Potentially Hazardous Asteroids (PHAs).

What Are Asteroids And Comets?

Asteroids and comets are believed to be ancient remnants of the earliest years of the formation of our solar system more than four billion years ago. From the beginning of life on Earth to the recent spectacular impact of Comet Shoemaker-Levy 9 with Jupiter, these so-called "small bodies" play a key role in many of the fundamental processes that have shaped the planetary neighborhood in which we live.

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