Earth trojan asteroid

The orbit of 2010 TK₇, the first Earth trojan to be discovered, and the only one so far

Earth trojans are asteroids that orbit the Sun on a similar orbital path as that of Earth in the vicinity of the Earth–Sun Lagrangian points L₄ (leading 60°) and L₅ (trailing 60°). They are named after the trojan asteroids that are associated with the analogous Lagrangian points of Jupiter.

Their location in the sky as observed from Earth's surface would average about 60° east or west of the Sun. Because people tend to search for asteroids at much greater elongations, few searches have been done in these locations.

The 300-meter-diameter asteroid 2010 TK₇ has been determined to be associated with the Earth L₄ Lagrangian point, leading Earth's orbit, by Martin Connors and colleagues of Athabasca University using the Wide-field Infrared Survey Explorer (WISE) satellite. It is the first confirmed Earth trojan.^[1][2]

List

2010 TK7, the first known (and so far only) Earth trojan, is located in the annotated green circle in the lower right

L₄

• 2010 TK₇

L₅

• Currently, there are no confirmed objects, nor are there any objects suspected of being L₅ trojans of Earth.

Significance

The orbits of Earth trojans could make them less energetically costly to reach than the Moon, even though they are hundreds of times more distant. Such asteroids could one day be useful as sources of elements that are rare near the Earth's surface. On Earth, siderophiles such as iridium are difficult to find, having largely sunk to the core of the planet shortly after its formation. A small asteroid could be a rich source of such elements even if its overall composition is similar to Earth's; because of their small size, such bodies would lose heat much more rapidly than a planet once they had formed, and so would not have melted, a prerequisite for differentiation. Their weak gravitational fields also would have inhibited significant separation of denser and lighter material; a mass the size of 2010 TK₇ would exert a surface gravitational force of less than 0.00005 times that of Earth.

Other companions of Earth

Earth has a second companion, asteroid 3753 Cruithne, about 5 km across, in a peculiar type of orbital resonance called an overlapping horseshoe. It is probably only a temporary liaison.^[3] Several other small objects have been found in similar orbits. Although these objects are in 1:1 orbital resonance, they are not Earth trojans because each of them does not librate around a definite Sun–Earth Lagrangian point, either L₄ or L₅.

See also

• 3753 Cruithne
• Earth's second moon
• Natural satellite
• Quasi-satellite
• 6Q0B44E
• 2006 RH120
• 2003 YN107

References