Dear friends Of Science and Astronomy,

Water flowed 'recently' on Mars : Nasa says it has found "compelling" evidence
that liquid water flowed recently on the surface of Mars.

Gullies like this could have been cut by water, Nasa says
The finding adds further weight to the idea that Mars might harbour the right
conditions for life. The appearance of gullies, revealed in orbital images from
a Nasa probe, suggests that water could have flowed on the surface in the last
few years. But some scientists think these fresh gullies could also have been
cut by liquid carbon dioxide (CO2). The latest research emerged when Nasa's Mars
Global Surveyor (MGS) spacecraft spotted gullies and trenches that scientists
believed were geologically young and carved by fast-moving water coursing down
cliffs and steep crater walls. Scientists at the San Diego-based Malin Space
Science Systems, who operate a camera aboard MGS decided to retake photos of
thousands of gullies in search of evidence for recent water activity. Two
gullies that were originally photographed in 1999 and 2001, and imaged again in
2004 and 2005, showed changes consistent with water flowing down the crater
walls, according to the study. In both cases, scientists found bright,
light-coloured deposits in the gullies that were not present in the original
photos. They concluded that the deposits - possibly mud, salt or frost - were
left there when water recently cascaded through the channels. Other scientists
think it possible that gullies like this were caused not by water but by liquid
carbon dioxide. One of the reasons for favouring CO2 was that computer models of
the Martian crust indicated water could exist only at depths of several
kilometres. Liquid carbon dioxide, on the other hand, could persist much nearer
the surface where temperatures can drop as low as -107C.

Prospects for life


We're now realising Mars is more active than we previously thought, and that
the mid-latitude section seems to be where all the action is Phil Christensen,
Arizona State University
Oded Aharonson, an assistant professor of planetary science at the California
Institute of Technology (Caltech) said that while the interpretation of recent
water activity on Mars was "compelling," it was just one possible explanation.
Aharonson said further study was needed to determine whether the deposits could
have been left there by the flow of dust rather than water. Deciding what was
responsible for the features is a pressing question that has important
consequences for the likelihood of life on Mars. Scientists have proposed that
reservoirs of liquid water could exist beneath the Martian surface, providing a
habitat for microbial life. "This underscores the importance of searching for
life on Mars, either present or past," said Bruce Jakosky, an astrobiologist at
the University of Colorado at Boulder, who had no role in the study. "It's one
more reason to think that life could be there." Mars Global Surveyor abruptly
lost radio contact with Earth last month. Attempts to locate the spacecraft,
which has mapped the Red Planet since 1996, have failed, and scientists fear it
is lost. Nasa's Mars rovers, which landed in 2004, have sent scientists back
equally strong evidence that liquid water flowed on the surface in ancient
times, based on observations of alterations in ancient rocks. "We're now
realising Mars is more active than we previously thought, and that the
mid-latitude section seems to be where all the action is," said Arizona State
University scientist Phil Christensen, who was not part of the current research.


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