Space.com (December 31, 2009)
"The moon may not be made of Swiss cheese, but it appears to have at least one deep hole, a vertical skylight that could serve as a protective lunar base for future astronauts.
" 'We discovered a vertical hole on the moon,' an international team of scientists recently announced.
"The gaping, dark pit on the near side of the moon is as big as a city block and deep as a modest skyscraper. It is thought to be a collapsed lava tube, created perhaps billions of years ago when the moon was warmer and volcanically active. The moon, overall, is more than 4 billion years old.
"The discovery, detailed in the journal Geophysical Research Letters in October, was made using data from the moon-orbiting Japanese SELENE spacecraft. It was not widely reported at the time, and the journal announced it today. The work was led by Junichi Haruyama of the Japanese Space Agency JAXA...."
According to the article, the hole is "213 feet (65 meters) across with a depth of 262 to 289 feet (80-88 meters)." The working assumption now is that it's a place where the roof of a lava tube collapsed.
Between radiation - particularly when the sun's acting up - and rocks shooting in at odd angles now and again, setting camp at the bottom of a deepish hole seems a bit more attractive than it would in a spot like, say, Yosemite.
A fair-sized base could be set up in that city-block-sized hole. What's exciting about this particular hole in the ground is that features like this aren't one-of-a-kind here on Earth. It's not unreasonable to assume that where there's one hole in the ground on the moon - there are others that haven't been spotted yet.
And maybe lava tubes that'd be a trifle easier to get in and out of than this one apparently would be.
- "The Caves of Mars"
(October 26, 2009)