American Geophysical Union Journal Highlights - 12 April 2010
Changes in Martian gullies indicate liquid water
Evidence for present day gully activity on the Russell crater dune field, MarsPresent-day gully activity on Mars provides new evidence for transient liquid water. Reiss et al. study images of the Russell crater dune field on Mars taken by the High Resolution Imaging Science Experiment from November 2006 to May 2009. The authors observe that the length of a 2-meter (6.56 feet) wide gully channel had increased by about 50 m (164 ft) in one year and about 120 m (394 ft) within the second year. On the basis of the morphology of the channel and other factors, the researchers believe that these changes in the length of the gully are best explained by erosional processes triggered by the melting of small amounts of water ice.
- Geophysical Research Letters, 37, doi: 10.1029/2009GL042192, 26 March 2010
Initial results for the north pole of the Moon from Mini-SAR, Chandrayaan-1 missionWater ice exists in large quantities in many small craters near the Moon's north pole, according to a new study. Spudis et al. present initial results from the miniature synthetic aperture radar (Mini-SAR) experiment on board the Indian Chandrayaan 1 spacecraft, which mapped most of the area near the north pole of the Moon between February and April 2009. The Mini-SAR instrument collected data on the polarization of radio waves reflected off the lunar surface. These data give the researchers insight into lunar surface features. For instance, high values of the circular polarization ratio (CPR) indicate either surface roughness or ice.
The observations suggest that water ice exists in many of the small craters in permanent darkness near the north pole of the Moon. According to the scientists' analysis, the CPR values recorded indicate that this ice must be at least 2–3 meters (6.5-9.8 feet) thick. The researchers note that the ice is not distributed evenly over the lunar surface, suggesting that it may have been deposited through an episodic deposition process such as comet or asteroid impact. Because these lunar craters near the north pole are in permanent shadow, ice would remain stable there indefinitely. The new study supports and extends other recent discoveries of water on the Moon.
- Geophysical Research Letters, 37, doi: 10.1029/2009GL042259, 31 March 2010