Thursday, July 28, 2011

Earth has 'secondary moon': So-called Trojan asteroid was hard to spot because of its angle with sun -- what else lurks out there?

The moon isn't the only hunk of space rock that has been travelling around the sun alongside the Earth for ages.

Canadian scientists have discovered that the Earth is also accompanied by a "Trojan" companion — an asteroid that stays just a few steps ahead of it at all times, sharing nearly the same orbit around the sun.

Similar objects have been found travelling with other planets in our solar system, including Mars, Jupiter and Neptune.

"In a way, these are sort of like secondary moons," said Martin Connors, the Alberta scientist who led the discovery published in Thursday's issue of Nature.

Like the moon, the asteroid known as 2010 TK7 is under the control of Earth's gravity and has been orbiting stably with the Earth for at least 10,000 years. Viewed from the Earth, the asteroid sits 60 degrees from the sun, so that it forms an equilateral triangle with the Earth and the sun.

"You would think that the gravity of the planet would just like to pull the asteroid in," said Connors. "But when it does do that, it moves closer to the sun, and then the sun's gravity makes it go faster, and it pulls away from the planet again." (more)