GROUND TRUTH: NASA's Opportunity rover is now investigating Endeavour Crater on Mars, where clay minerals have been detected from orbit.
Image: NASA/JPL-Caltech/Cornell/ASU
-
The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
Read More »
When Mars orbiters decades ago spotted valleys and other fluvial landforms on the surface of the Red Planet, a tantalizing idea came to the fore. Perhaps, planetary scientists ventured, ancient Mars was blanketed by a thick atmosphere that kept the planet much warmer and wetter than it is now, with flowing water, lakes and maybe even an ocean covering at least part of its surface. And if Mars had water some three billion to four billion years ago, they wondered, why not life?
But recent mineralogical data have put a twist on that idea, according to a new study. For although Mars indeed seems to have passed through a warm, wet phase, the bulk of the action looks to have occurred in the crust, beneath a surface that remained mostly dry and frigid. In this scenario, Mars's valleys and lakebeds would have been shaped by ephemeral, episodic flows, rather than by long-lived bodies of water. But belowground the environment may have been very different—warm, watery and possibly even hospitable to life.
That is the thrust of a review article published in the November 3 issue of Nature. (Scientific American is part of Nature Publishing Group.) The study's authors examined how clay minerals, which form in the presence of liquid water and have been detected at sites all over Mars, came to exist on the surface. The evidence, the researchers argue, suggests that the clays formed belowground rather than in rocks near the surface exposed to liquid water, as they often do on Earth. The minerals would have been churned up to the surface by meteor impacts in the billions of years since their formation.
"The more information we saw, the more it looked like clays weren't forming in the way that they did on Earth," says lead study author Bethany Ehlmann, a planetary scientist at the California Institute of Technology. "I think it's interesting that the warmer, wetter early Mars may be beneath the surface." In the first billion or so years of Mars's history, ample heat was available in the crust, due to extensive volcanism and bombardment by large impactors.
One line of evidence for subsurface clay formation comes from the chemical composition of those minerals, which closely resembles that of the volcanic rocks that reacted with water to form the clays. That similarity points to an enclosed system without much inflow or outflow of chemical elements due to flowing water or atmospheric exchange. "There hasn't been a lot of water moving in and out of the system, and if you're on the surface, it's hard to imagine how that would happen," Ehlmann notes. "The clays and the basalts are of similar chemical composition."
Another important point is that some of the clay minerals identified on Mars form in high-temperature environments of up to 400 degrees Celsius, indicating pockets of hydrothermal activity rather than open-air bodies of water as the source of the clays.
If the geochemical evidence for water on Mars indeed traces a hydrologic history dominated by subsurface activity, that would mean that the flows that carved valleys and floodplains on the Red Planet are mere outliers in the planet's watery past. "There's sort of a disconnect between the morphological evidence and the mineralogical evidence for water," Ehlmann says. The morphological features may have been carved by brief, episodic floods of melting ice during anomalously warm periods in Mars's unstable climate. "The evidence is consistent with the fact that those were very short in time," Ehlmann says.
Although Martian landforms suggestive of water have been recognized since the 1970s, that morphological evidence does not tell the whole story, says Raymond Arvidson, a planetary scientist at Washington University in Saint Louis who did not contribute to the new study. "What we're finding when you combine that with the mineralogical evidence is: 'Whoa. Take off your Earth-colored glasses,'" he says, "because this is a planet where there has been extensive water activity, but nowhere near as extensive as on Earth."
A cold, dry Martian exterior agrees well with some climate models for the planet, which struggle to reproduce a temperate paleoclimate. "We no longer, based on our modeling, believe in a warm, wet scenario for Mars," Robin Wordsworth, a postdoctoral researcher at the Laboratory of Dynamic Meteorology (LMD) in Paris, said at a planetary science conference in France last month.
If Mars was once blanketed by a thicker atmosphere than it has today, the models indicate that it would indeed have been somewhat warmer. "In spite of that, we found that whatever the thickness of the atmosphere, the climate would have been too cold to sustain a long-term, Earth-like, warm and wet climate," says Wordsworth's LMD colleague Francois Forget. "Overall, our climate simulations point toward a cold early Mars where ice and snow would have played a major role," he says, with localized or episodic melts providing liquid water.
"The real Mars, I think, is beginning to stand up," Arvidson says. "Mars was occasionally warm on the surface and occasionally wet on the surface, but far more in the subsurface." Understanding where and when liquid water existed for long periods on Mars is the key to designing targeted searches for signs of past life on the Red Planet. "It will eventually lead us to the right place to see if Mars had the right stuff to sustain a habitable environment," Arvidson says.
See what we're tweeting about
11 Comments
Add CommentCareful, steady, plodding, painstaking, methodical, humble geology pursued by generations of hardworking scientists with their noses to the grindstone and their hands in the dirt is now bearing astronomical fruit in our present ability to decipher and infer conditions on neighboring planets and their moons through optical and geochemical data from orbiters and landers. Nice going, champions!
Reply | Report Abuse | Link to thisThis is why the Martians, in the golden age of Barsoom, lived underground in their huge, sprawling cities.
Reply | Report Abuse | Link to thisOne of the new propositions being offered up by our scientific community is that the water on Mars, in bulk, resided within the crust of the outer shell of the planet. This is offered up in contrast to the prevailing concept that Mars like Earth had it major reservoirs of water on its surface, in the forms of lakes, seas, and oceans. One of the major dynamics of our water is its evaporation and cloud making abilities. If Mars did hold its main reservoirs of water within the crust of the shell of the planet, it would see much less of the dynamics of evaporation, and condensation. If this were the case the geological development of erosion would also be significantly impacted; to a point that much of what our research has shown would not be there. In consideration of the direct and secondary effects of holding its water resources beneath the surface, I have to reject the proposal, and label it as not likely.
Reply | Report Abuse | Link to thisJohn Matson
Reply | Report Abuse | Link to thisIt is an interesting alternative, the only comment I would present is that you are wrong. Read the logic listed above and you will see your error.
Jack
Is there anything that prevents Mars from still being wet on the inside even today?
Reply | Report Abuse | Link to thisThere is a prediction that there will be remnants of ancient humanoid cities. Less developed than ours. The source looks reliable ,so far.
Reply | Report Abuse | Link to thiswhy should there be any measures to prevent Mars from being wet on the inside? Does it matter a lot if not?
Reply | Report Abuse | Link to thisThe thin atmosphere will lead to evaporation of the bulk of the water unless that water is buried under unbroken rock formations with no fractures reaching the surface. Even if the water is in the form of ice there will be loss of mass due to the lack of atmospheric pressure.
Reply | Report Abuse | Link to thisYou should stop listening to the crazy voices in your head.
Reply | Report Abuse | Link to thisMost of the Martians lived in the (yet to be discovered) underground cities. They are accessed by the elevators.
Reply | Report Abuse | Link to thisOnce we find the elevators, the cities will be easy to spot. They start at level 27. Really.
Where there is disconnect is between researchers who study the early Earth and early Mars.
Reply | Report Abuse | Link to thisConsidering that quite a few who study Earth say that early on Earth was much cooler, due to the sun being cooler, and some even postulate that early on there was a global ice age, it strikes me as odd that during the same overlapping time frames that while significant research indicates the Earth was substantially cooler during that time that Martian theorists would postulate that Mars was so warm, relatively speaking.
This recent theorizing makes much more sense, because it matches up with much of what is being theorized regarding the climate of early Earth.
If they didn't make an effort they should make an effort to draw in what is known of Earth from that time to help shape the understanding of what was going on on Mars at the same time.