A CHUNK of rock some 50 metres across has been found circling the Sun in an orbit close to Earth’s. The object, which was discovered on 10 February by an automated asteroid-hunting telescope in New Mexico called Linear, is probably a chip off the Moon, say astronomers.
After six nights of observations, Gareth Williams of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, calculated that it circles the Sun every 1.09 years. Its nearly circular orbit is just nine million kilometres farther from the Sun than the Earth’s.
The object’s orbit is extremely unusual. Comets and asteroids that cross the Earth’s orbit normally have eccentric orbits. There is only one asteroid-like object, called 1991 VG, that has a similar orbit to that of the Earth. When it was discovered, eight years ago, astronomers thought it might be a spacecraft that had escaped the Earth’s gravity.
The new object, designated 1999 CG9, is considerably brighter than 1991 VG, indicating that it is much larger. Brian Marsden of Harvard-Smithsonian estimates it to be between 30 and 50 metres across, too big to be the final stage of a rocket. “The most likely explanation is that it’s a chip off the Moon,” he says.
Although the Moon is small, its low gravity makes it easy to blast debris into orbit. “We have seen there are chips off the Moon,” says Marsden. “Twelve small lunar meteorites have been found on the Earth.”
“If you can shoot things off the Moon, they would continue to go around the Sun in an orbit not too different from the Moon,” Marsden adds. So far, astronomers do not know the object’s composition, which could cast light on its origins. However, the astronomers hope to analyse the rock’s spectrum to see how it compares with that of the Moon.
UK CONTACT -- Claire Bowles, New Scientist Press Office, London Tel: 44-171-2751 or firstname.lastname@example.org US CONTACT -- Barbara Thurlow, New Scientist Washington Office Tel: 202-452-1178 or email email@example.com EMBARGOED FOR RELEASE: February 24, 1999, 2 p.m. EST Author: Jeff Hecht, Boston New Scientist issue 27th Feb 99