National
Geographic: Earth's first Trojan asteroid,
2010 TK7, has been discovered. About 1000 feet wide,
it travels with Earth around the Sun at a distance of about 50
million miles, writes Ker Than for
National Geographic. Trojans are bodies that exist in
orbital "sweet spots" between Lagrange points—spots where
the gravitational pull of the planet and that of the Sun
combine to allow the Trojan to maintain its position relative
to both of them. Trojan asteroids have been found around Mars,
Jupiter, and Neptune; although it had long been thought that
Earth should also have them, they proved difficult to find
because any Trojan, from the perspective of an observer on
Earth, will reside in the general direction of the Sun. Martin
Connors, an astronomer at Athabasca University in Canada, and
colleagues
made
the discovery with
NASA's
Wide-field Infrared Survey Explorer (WISE)
telescope. Connors likened the asteroid's orbit to the path
of an orange held at arm's length by a person riding a Ferris
wheel.
