Light in Moon's Permanently Dark Craters

I have friend who has been trapped in a mostly underground research facility at the South Pole since early winter. She recently broke her foot, which is just tough luck because nobody gets out of there until spring, which is, I think, in October.

This will remind you of the stroy of Dr. Jerri Nielsen, who was at an Antarctic research station and diagnosed herself of having breast cancer, and was rescued rather dramatically back in 1999. Nielsen died, by the way, Tuesday. (Of breast cancer.)

Well, my friend at the South Pole is not going to die of a broken foot. (Though perhaps other people will. Die of her broken foot, that is.) But what is eventually going to happen is that the sun is going to come up.

But on the moon, there are places where, for all practical purposes, the sun never comes up. Just as with the earth, the polar regions receive oblique sun. Now think about that for a second. A crater is essentially a round cliff. While a cliff may blot out the sun from one direction, the sun will eventually be on the other side of the cliff and any shadowed area will be visible. But if the cliff circumscribes an area steeply enough, that area will never, ever have sunlight.

Between the round-cliff effect and the polar oblique sunlight effect, there are craters in the Moon's polar regions that are not visible. Well, the crater is visible, but not the inside.

Fearing that these dark places may be where Moon Dwellers have set up extensive cities invisible from outer space¹, NASA has figured out a way of imaging these craters using radar.

Details from the press release:

PASADENA, Calif. -- A new lunar topography map with the highest resolution of the moon's rugged south polar region provides new information on some of our natural satellite's darkest inhabitants -- permanently shadowed craters. The map was created by scientists at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who collected the data using the Deep Space Network's Goldstone Solar System Radar located in California's Mojave Desert. The map will help Lunar Crater Observation and Sensing Satellite (LCROSS) mission planners as they target for an encounter with a permanently dark crater near the lunar South Pole.

"Since the beginning of time, these lunar craters have been invisible to humanity," said Barbara Wilson, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and manager of the study. "Now we can see detailed topography inside these craters down to 40 meters [132 feet] per pixel, with height accuracy of better than 5 meters [16 feet]."

The terrain map of the moon's south pole is online here.

Scientists targeted the moon's south polar region using Goldstone's 70-meter (230- foot) radar dish. The antenna, three-quarters the size of a football field, sent a 500- kilowatt-strong, 90-minute-long radar stream 373,046 kilometers (231,800 miles) to the moon. Signals were reflected back from the rough-hewn lunar terrain and detected by two of Goldstone's 34-meter (112-foot) antennas on Earth. The roundtrip time, from the antenna to the moon and back, was about two-and-a-half seconds.

The scientists compared their data with laser altimeter data recently released by the Japanese Aerospace Exploration Agency's Kaguya mission to position and orient the radar images and maps. The new map provides contiguous topographic detail over a region approximately 500 kilometers (311 miles) by 400 kilometers (249 miles).

______________
¹I'm joking about the invisible cities.