WATERWORKS: This crater-wall gully in Mars's Promethei Terra region offers strong evidence of liquid water flowing on the Red Planet's surface in recent geologic times.
Image: NASA/JPL/UNIVERSITY OF ARIZONA
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A new analysis of puzzling gullylike features on Mars offers further evidence that water flowed on the Red Planet's surface, perhaps as recently as several hundred thousand years ago. The findings bolster the case that melting snow from a departed Martian ice age carved these gullies, rather than shifting sands or other "dry" phenomena.
The paper, published today in the journal Geology, examines one of the many gullies on crater and valley walls visible in satellite images of the Martian surface. The cause and age of these channels are the subject of debate.
To help settle the matter, the paper's authors relied on a bit of geologic good luck to date one of the features. Images snapped by the HiRISE (High Resolution Imaging Science Experiment) camera onboard the Mars Reconnaissance Orbiter showed a typical gully system about 0.62 mile (one kilometer) long with a deltalike fan at its bottom—similar to features on Antarctic Dry Valleys and on dry mountains after rain in the U.S. Southwest.
The researchers noticed an array of craters dotting the delta's western portion [lower left in the photograph] and suspected that a large meteorite impact had peppered the area with ejected rocks to form these so-called secondary craters. Sure enough, the pattern of pockmarks led like a trail of bread crumbs to a large impact crater some 62 miles (100 kilometers) southwest. Infrared imaging assisted in matching the impact events.
"We had hoped to find the source of these secondary craters, and voilà, we found a link to this big crater," says lead study author Samuel Schon, a graduate student at Brown University's Planetary Geosciences Group.
To estimate the age of planetary surfaces, geologists look to craters. Earth, with its active tectonics and dynamic weather, has few impact craters on its relatively young surface; Earth's weatherless, geologically dead moon, however, is heavily cratered and has very old surfaces (except where ancient lava flows formed large, flat, dark areas called maria, or "seas"). Because much of the rest of the studied Martian gully system is craterless [at right in the photograph], those areas are believed to be geologically younger than the cratered portions, Schon says.
By dating the primary Martian crater that sprayed the gully to 1.25 million years old—which qualifies as very young in Mars's 4.6-billion-year history—Schon and his colleagues demonstrated that an estimated three subsequent outflows in the gully system must be younger than the first, which was bombarded by ejecta.
"Dating these gullies has been a big problem," says Michael Meyer, lead scientist for NASA's Mars Exploration Program. "But because these guys dated the nearby crater, you have proof that the water activity is recent."
Today, virtually all water on Mars is believed to be trapped underground or frozen near the poles, where the Phoenix lander found ice mere inches under the soil this past summer. Unresolved research, though, has hinted at very recent water activity on Mars—within the past decade. A tantalizing ribbon of light-colored material mimicking water flow appeared in satellite images of a crater wall sometime between 1999 and 2005. But materials scientists have shown that avalanching sands can also create this effect, and later studies cast doubt on water as the culprit.
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8 Comments
Add CommentPeople used to think those were canals built by intelligent Martians to carry water. :)
Reply | Report Abuse | Link to thisI fell asleep watching Sagans Cosmos last night. Had a big dream about prehistoric mars. I can't help but wonder if there's a possibility that life was knocked off Mars during it's inhabitable period and arrived on earth. Possibly by a cosmic collision, or possibly by experimenting scientists of that era, from there or elsewhere. If our sun was fading and our planet was about to freeze and lose its atmosphere, would we not try to send off the seeds of life to any nearby planet that may be habitable? Hm. It's not immediately productive to think about such things, but it is entertaining.
Reply | Report Abuse | Link to thisThe gullies are quite a bit smaller (kilometer-scale) than the valley networks (many hundreds of kilometers). While valley networks strongly suggest pluvial activity and integrated catchments early in Mars history (>3 billion years ago), the gullies seem to represent transient/ephemeral flows of water in the very recent past.
Reply | Report Abuse | Link to thisThe original article in Geology is here:
http://geology.gsapubs.org/cgi/content/full/37/3/207
The assumption here is that the secondary craters once covered a larger area of the photo but were washed away by the later water flow. I don't see any craters on the far side of the gully. Is it possible that the craters we see in the picture simply represent the farthest extent of the area where the material was ejected from the meteor strike? In that case, the craters could be the more recent feature.
Reply | Report Abuse | Link to thisIt's clear, from the photo, that the major cities and other infrastructures were washed away in the thaw!
Reply | Report Abuse | Link to thisImagine the loss to humanity: If only Great Library of Mars had survived!
What wonders we could learn. Shame it's gone.
Since Mars and Earth are the same age, early life might have been "knocked off" Mars (to the Earth), but how did it start on Mars?? Also, When the Sun "fades", it will swell up and incinerate the Earth, we won't have to worry much about freezing.
Reply | Report Abuse | Link to thisResponding to Josh83 :
Reply | Report Abuse | Link to thisInteresting suggestion but from the text: the gully system is ~1km in size but the crater which generated the impacting rocks is ~100km away (~100 times as large; meaning the rocks rained down over an area at least 200km wide). It's very unlikely that such a widely-dispersed rain of rocks would happen to end partway across such a relatively small feature - you'd expect a gradual dropoff not a sudden one, and any sudden dropoff would be very unlikely to occur at that exact location.
Yes Cosmos gets like that :-)
Reply | Report Abuse | Link to thisThe obvious response is that we know that life arose (somehow) on Earth but we have no convincing evidence that this happened on Mars or that life which did arise there was transferred (the famous ALH84001 meteorite results which suggested that at least Martian fossils could reach Earth are generally regarded as unreliable).
By Occam's Razor which Carl Sagan was fond of (basically "All other things being equal, the simplest explanation consistent with the facts is likely to be the right one") it makes more sense to assume that life found on Earth started on Earth, until proven otherwise.
As far as humans seeding life elsewhere goes : this is a very good reason to colonise other lifeless planets, but alas I don't think we'll live to see it.