Astronomers studying observations acquired by NASA's WISE spacecraft have discovered the first known object, a tiny asteroid, moving around the Sun along Earth’s orbit. (WISE stands for Wide-field Infrared Survey Explorer.) Three other planets, Mars, Jupiter and Neptune, have orbital partners, small asteroids that orbit around particular points, along the planetary orbits.
Interestingly, asteroids sharing orbit with a planet are termed Trojan asteroids, after the Greek mythological Trojan War. (Many of the objects of the Solar System are named after mythological figures.) The Trojan asteroids always lead or lag behind their planet, without colliding with it.
Scientists had predicted the presence of Earth’s Trojans, but they have been difficult to find, since they are relatively small and located near the Sun in the sky.
"These asteroids dwell mostly in the daylight, making them very hard to see," said Martin Connors, principal author of a new research article on the discovery. "But we finally found one, because the object has an unusual orbit that takes it farther away from the Sun than what is typical for Trojans. WISE was a game-changer, giving us a point of view difficult to have at Earth's surface."
The WISE telescope surveyed the entire sky in infrared light, from January 2010 to February 2011. Connors and his team began their search for an Earth Trojan, through WISE data, which focused in part on near-Earth objects (NEOs), such as asteroids and comets. NEOs are bodies that come to within 45 million km of Earth's orbit. WISE observed more than 155,000 asteroids, orbiting between the orbits of Mars and Jupiter, and over 500 NEOs, including 132 new discovery.
The team found two Trojan candidates. One termed 2010 TK7 was confirmed as an Earth Trojan after follow-up observations, using the Canada-France-Hawaii Telescope, atop Mauna Kea Volcano in Hawaii.
2010 TK7 is roughly 300 m across. It is about 80 million km away. The asteroid's orbit is well-defined, and it will come no closer than 24 million km from Earth, for at least 100 years. An animation showing 2010 TK7’s orbit is available at the following link.
http://www.nasa.gov/multimedia/videogallery/index.html?media_id=103550791
"It's as though Earth is playing follow the leader," said Amy Mainzer, the principal investigator of NASA's Jet Propulsion Laboratory. "Earth always is chasing this asteroid around."
A few of other asteroids also orbit in the vicinity of Earth, with orbits similar to Earth’s. Such objects could be excellent targets for future robotic or human exploration. Asteroid 2010 TK7 is not a good destination, as it wanders too far above and below the plane of Earth's orbit, which would require large amounts of fuel to reach it.
References
NASA
www.nasa.gov/
Wikipedia