Joe, I'm just remembering some basic high school physics, but you're right - standing water can't exist on the surface of Mars under today's conditions due to low atmoshperic pressure. However, I don't recall that anyone has yet put a timeline to these features. If recent, the water scenario is difficult to explain. If ancient, perhaps not. I believe the November S&T recounted a reasonable alternate theory that suggests, as you do, that superheated volcanic flows such as Earth's pyroclastic flows (I hope I spelled that right) may have caused the phenomena. However, this raises a new question for me: don't the pyroclastic flows on Earth require superheated water also, or are they possible without water? Anyone know? -----Original Message----- From: Joe Bauman [mailto:bau@desnews.com] Sent: Thursday, December 11, 2003 10:44 AM To: Utah Astronomy Subject: [Utah-astronomy] Mars closeup pics A new subject for discussion, if anyon'e interested. In pictures like this -- http://www.msss.com/mars_images/moc/2003/12/11/index.html -- we see evidence of channels on Mars that look as if water flowed fairly recently from the side of a crater. If the scale is accurate, the longest of these gullies seems to be about 800 meters long, or about half a mile. Much speculation has centered on the idea that these features, which seem to be fairly common, are evidence of water from some underground layer. The questions I have are: if water were to thaw out, wouldn't the extremely thin atmosphere cause it to evaporate immediately? Or if it somehow flowed, wouldn't it quickly freeze again? And yet whatever it is continues for half a mile. Maybe it's really water. Maybe parts of Mars are just saturated with frozen underground water that can thaw out and flow in copious quantities. But here's another possibility I've come up with -- maybe it's fine solid material that happens to be extremely slippery and flows like water. What if it's a powdery volcanic ash layer? Would that flow well enough to look like water? Or could there be a field of big round boulders that periodically come loose and go tumbling downhill? My problem with the water theory is mainly that Mars' atmospheric pressure is so low that I suspect water would boil at a very low temperature. Could anyone who knows the facts do some calculations? Any thoughts the group would like to share would interest me greatly. Thanks, friends -- Joe _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy