MOON TURNS TO BLOOD?

Reports of curious flashes and fleeting clouds on the Moon may not be figments of wild imaginations, astronomers say. A new look at observations by the American satellite Clementine show that a small area on the Moon's surface darkened and *REDDENED in April 1994. Why this happened remains a mystery.

For hundreds of years, people have reported seeing flashes, short-lived clouds and other brief changes on the Moon's surface. But astronomers have never been able to confirm the sightings. "The events were observed on many occasions, but most astronomers don't believe in them," says Bonnie Buratti of NASA's Jet Propulsion Laboratory in Pasadena, California.

On 23 April 1994, around a hundred amateur astronomers reported seeing a possible darkening of the Moon, lasting 40 minutes, near the edge of the bright lunar crater Aristarchus. At the same time, the US Department of Defense's Clementine satellite was mapping the lunar surface.

Intrigued by the amateur reports, Buratti's team has taken a close look at the Clementine data to see if the satellite also recorded the event. Sure enough, they found that the crater looked different before and after the amateur reports. "After the event, it looks redder," says Buratti, who announced the findings at a meeting of the American Astronomical Society in Padua, Italy, last week.

Winifred Cameron, a retired astronomer who worked at the Lowell Observatory in Arizona, thinks that brief colour changes might be caused by small gas eruptions throwing dust around. We know that there are pockets of gas in the lunar soil, and the gas may occasionally escape. "I'm pretty sure that some of these changes are due toemanations of gas that are more dense than usual," says Cameron. "The Aristarchus region is the source of about a third of all of these.

Charles Seife
From New Scientist, 23 October 1999

CHIP OFF THE MOON

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.

From New Scientist, 27 February 1999. By Jeff Hecht, Boston.