Friday, August 26, 2005

NASA scientists say liquid water formed recent gullies on Mars

SpaceRef - Your Space Reference: "'Our model indicates that these fluvially-carved gullies were formed in the low temperature and low pressure conditions of present-day Mars by the action of relatively pure liquid water,' said Heldmann. The science team found that the maximum length of gullies simulated in the computer models were comparable to the martian gullies studied. 'We find that the short length of the gully features implies they did form under conditions similar to those on present-day Mars, with simultaneous freezing and rapid evaporation of nearly pure liquid water,' Heldmann said. In addition, images taken by the Mars Global Surveyor spacecraft show 'geologically young' small-scale features on the red planet that resemble terrestrial water-carved gullies, according to scientists. 'The young geologic age of these gullies is often thought to be a paradox, because liquid water is unstable at the martian surface,' Heldmann said. At present martian air pressure and temperature, water will boil and freeze at very rapid rates, the scientists reported. Team scientists noticed that images of some of Mars' gullies show that they taper off into very small debris fields ? or no debris fields at all - suggesting that water rushing through the gullies rapidly froze and/or evaporated. 'In the martian case, fluid well above the boiling point (which is a very low temperature at Mars' low atmospheric pressure and air temperature) is suddenly exposed to the atmosphere,' said Heldmann. 'The difference between the vapor and ambient pressures relative to the ambient pressure is large, and flash boiling can occur, leading to a violent loss of fluid.' "