Since the discovery of gullies on Mars in 2000, NASA has endeavored to re-image areas known to have them. Now for the first time, using before and after images taken of the same region on Mars, a dune gully flow is shown to have happened very recently. On September 20, 2005, NASA held a media teleconference addressing recent changes on Mars that have been observed with the Mars Global Surveyor spacecraft, which has been orbiting Mars successfully since 1997. Among the highlights of the teleconference were before and after images shown of rock falls, a new impact crater, a receding south polar region, and a sand dune that appears to have recently formed gullies running from its crest to its base, suggesting fluid flow. Finding gullies on Mars is nothing new, thousands of them have been found to date, lining the sun-facing walls of impact craters and sand dunes located at latitudes poleward of 30 deg. First reported by Malin and Edgett in 2000, they published that the gullies were evidence of ground-water seepage from dust-mantled snowpacks on Mars but that they could not tell if the gullies themselves were recent or thousands to millions of years old.
展开▼
