IS THE MOON ACTIVE?
Searches for activity on the Moon began with Galileo almost 400 years ago and have continued ever since. Observers have claimed to see mists obscuring craterlets on Plato's floor, a glow on the central peak of Alphonsus, and the "disappearance" of the Linne crater, to name just a few examples. Are these transient lunar phenomena (TLPs) the result of meteorite strikes or gaseous escapes from the Moon's interior—or are| they merely tricks of the light and an over-eager imagination?
Many TLP reports grew troin the long-standing belief that the Moon's features were wholly or largely volcanic in origin. Since volcanoes are always erupting somewhere on Earth, it was natural to expect similar activity on the Moon.
But scientists now know that lunar features, especially craters, are overwhelmingly the result of impacts. The Moon's real volcanic activity mainly produced the maria, and research has shown that even the youngest mare has been cold, hard rock for at least a billion years. Instruments left by Apollo astronauts reported that the Moon's interior is seismically quiet, indicating that there is no volcanic activity.
While the Moon's geological engine may have shut down ages ago, it is no less interesting a place. In fact, its surface records something of great value: a history ot the Solar System's earliest days. The record of this period on Earth has all but vanished, thanks to erosion. But in the Moon, nature has conveniently placed a veritable geo-museum in our cosmic backyard.