Mars was Wet, but was it Warm?

May 31, 2010 by Leslie Mullen
Scientists have proposed that the lowlands of Mars's northern hemisphere were once covered in water. Image Credit: NASA

Mars is frozen today, but when it was young there may have been liquid water on its surface. What does the latest evidence indicate about the ancient martian climate? Understanding the past environment of Mars can help future missions "follow the water" in the search for alien life.

On today, is frozen solid. The average temperature of the is negative 55 degrees Celsius (-67 F), and when the temperature rises -- the highest recorded temperature is a balmy 20 degrees C (68 F) -- this ice turns directly into a gas, skipping the liquid phase entirely because of the low .

Mars may have had a thicker atmosphere and on its surface between 3.5 and 4 billion years ago. Satellites orbiting Mars have taken images of ancient ocean shorelines, river beds and canyons - features all thought to be caused by flowing water. The chemistry of the also suggests that liquid water may have been present once on the surface. If so, then perhaps life could have emerged on Mars during this time in its history.

Many scientists think Mars was cold when it was young - cold enough so that surface water should have been frozen solid. One way around this problem is if the chemistry of the water was such that it could remain liquid at lower temperatures. On Earth, the salt in prevents it from freezing at the same temperature as freshwater. For early Mars to be cold but still wet, however, the water would have had to be much saltier than seems likely.

Another possibility is that Mars was warmer in the past. At first glance this idea doesn’t make sense -- the Sun was fainter back then, so the planet should have been even colder in the past and then gradually warmed up as the Sun grew brighter. But sunlight is not the only way to warm a planet; an atmosphere also can help keep conditions toasty. Just look at Venus -- its thick greenhouse atmosphere has raised its average surface temperature to a searing 464 degrees Celsius (867 F).

Could Mars also once have had a greenhouse atmosphere that warmed the planet enough to keep water flowing across its surface?

Jim Kasting of Penn State and Brian Toon of the University of Colorado discussed the possibility of a warm and wet Mars at the recent NASA Astrobiology Science Conference in League City, Texas.

Surface features of Venus can not be seen in visible light by orbiting spacecraft, due to the thick greenhouse atmosphere. Could Mars also once have had a thick greenhouse atmosphere that kept the planet warm? Image credit: NASA

Kasting explained that the climate models haven’t found a solution for warming early Mars, because the greenhouse effect is “self-limiting.” Adding different types of gases to the atmospheric models can help increase the temperature, but these same gases create clouds which reflect sunlight back into space, cooling the planet. The two effects compete with each other up to a point, but then eventually you end up with a colder planet because the added gases develop so much cloud cover. Climate modelers have looked at greenhouse gases like methane, carbon dioxide, sulfur dioxide, and water vapor, but so far have not hit upon a good way to warm ancient Mars.

"We've spent 30 years on the greenhouse effect and no one has solved the problem in a credible way so far,” noted Toon. “On the greenhouse problem, we're just drifting into deeper and deeper complexity."

Why does the greenhouse climate work so well to heat up Venus but not Mars? The thick clouds of Venus also bounce a lot of sunlight off into space, and that reflection is why we’re not able to see the surface of Venus in the visible light spectrum. One answer is that Venus is much closer to the Sun, so it receives substantially more sunlight than Mars does. According to Toon, another reason is that Mars is little. The lower gravity of a less massive world reduces the rate that air cools with altitude. On Earth this rate is about 10 degrees Kelvin per kilometer, but on Mars the rate is about half that. “This makes it harder to get a greenhouse effect, giving you less ‘bang for the buck’ for your greenhouse gases,” Toon said. “Mars is hard to warm up because it’s so small.”

Toon believes that, rather than a greenhouse atmosphere keeping Mars warm and wet, the canyons and river beds we see on Mars formed due to periodic asteroid and comet impacts. In this scenario, impacts would have filled the atmosphere with vaporized rock and ice and resulted in several years of rainfall and flooding that created the erosion features on Mars.

“We know the impacts occurred - we can see the craters there,” said Toon. “It's pretty much impossible to avoid there being large amounts of water coming from them.”

Kasting, however, doesn’t agree that impact events created the features seen on Mars. He pointed to Nanedi Valles on Mars, which he said was "essentially a Grand Canyon, on a slightly smaller scale." Kasting estimates it took roughly 5 million meters of water to form the Grand Canyon on Earth over 17 million years. The same amount of rainfall would have been needed to form a feature like Nanedi Valles on Mars, ten to one hundred thousand times more water than an impact could generate.

Kasting also noted that features in Warrego Valles looked similar to oxbow lakes on Earth, which are made slowly over time by meandering rivers. If the formations on Mars were made by a similar process, then the water must have been flowing persistently, rather than quickly and catastrophically as would have been the case from impact-related flooding.

This artist's depiction shows the disappearance of Mars’s magnetic field, which may have triggered the loss of much of its atmosphere. Image credit: NASA

Toon countered this by pointing to features on Earth that formed quickly, such as the Salton Sea flood in California where a river was carved in approximately nine months to a similar depth and length as some of the channels on Mars. “You can certainly carve significant terrain in nine months,” he said.

Scientists disagree on how long it might take such features to form on Mars because of the lack of absolute age data. To get that information, we would need to analyze rock samples from the features in the laboratory. “All our age dates come from crater counts, and that is not an accurate science by any means, especially when you’re trying to resolve issues of how long it took to form valleys,” said Kasting. “The only thing we know how long it takes to form are impact craters, because they’re created instantaneously.”

The quality of the soil may provide some clues to the time it took features to form on Mars. If the soil is looser, in the manner of loamy sand rather than bedrock, it would erode much more quickly. Kasting said the surface of Mars is mainly basalt - a hard crust that would be comparatively resistant to erosion. “The surface of Mars may be somewhat more erodible than rocks on Earth, but not by a factor of ten to the fourth," he said.

Toon disagreed. "If you have all these large impacts, you're going to create about a kilometer of regolith,” he said. “This is loosely consolidated material that's covering the planet about a kilometer deep, and that's very likely where these rivers formed due to impacts."

The chemical make-up of the soil is another avenue for trying to understand early Mars. On Earth, carbon dioxide in the atmosphere reacts with water and silicate rocks and is converted into calcium carbonate (limestone). The martian atmosphere today is primarily composed of carbon dioxide, and scientists have long wondered why we could never find evidence for carbonates in the soil. NASA’s Phoenix mission finally found carbonates on Mars, but in very low amounts.

Warrego Valles is a suite of branching valleys located in the martian southern hemisphere. The valleys are old, and many have been modified by later processes that obscure the original geologic features related to their origin. Image Credit: NASA/JPL/Malin Space Science Systems

Earth’s carbonates tend to form in shallow warm waters like the sea near the Bahamas, rather than in colder areas like the North Sea. The low abundance of carbonates on Mars may indicate the planet has always been cold.

However, the carbonates found by Phoenix are not thought to have formed in standing water. Instead, scientists think they formed through the chemical interaction of carbon dioxide and water vapor as minute particles of basalt blew on the wind.

The paucity of carbonates may tell us something about the composition of the early atmosphere. If, for instance, sulfur dioxide was ever part of the martian atmosphere, carbonates would have had a hard time forming.

“Sulfate in rain would prevent carbonates on surface, but you don’t even need that,” said Kasting. “If you had a 3 bar carbon dioxide atmosphere on Mars, rainwater would be pH 3.7 and would dissolve any carbonates.”

In the end, Kasting and Toon were in perfect agreement on one point: the environment of ancient Mars remains a mystery. Every new bit of information is another piece of the puzzle, and eventually we’ll fit enough of these pieces together to construct a clear picture of the Red Planet’s earliest days.

Explore further: 'Cold' Mars Could Have Harbored Liquid Water

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not rated yet May 31, 2010
This is a nice, interesting article, but I wonder how important it is for the planet to be both warm and wet. Is there any indication that you can't have life at low temperatures?
1 / 5 (1) Jun 01, 2010
This is bad news. Mars can never be terraformed, because there is no combination of gases that would make it warm enough for liquid water to exist.
1 / 5 (4) Jun 01, 2010
The assumption that water is needed for the formation of life is questionable. We now know clearly that the life-building block amino acids of proteins quickly dis-associate in the presence of water. So how can life have formed in water unless there was some kind of shielding that kept the water in check?
Basically, life forming spontaneously in water remains a highly improbable event - and biologists KNOW this. You need enzymes to stitch together the amino acids - but the enzymes themselves are proteins!!! A terrible chicken and egg situation to resolve.

I'm glad to see the two prominent scientists disagreeing on structures and possible processes. This is healthy and most welcome in a world dominated by a particular "scientific" point of view.
5 / 5 (2) Jun 01, 2010
We now know clearly that the life-building block amino acids of proteins quickly dis-associate in the presence of water. So how can life have formed in water unless there was some kind of shielding that kept the water in check?
Who told you that was at all relevant? If anything the fact they disassociate in water is vital.

Our form of life requires water otherwise lipids wouldn't be able to polymerize giving rise to cell walls and allowing for single monomer osmosis, wherein the amino acids would then polymerize and become trapped giving rise to karyotic cells as we now know them.

A little knowledge, misplaced, leads one down the wrong path.
1 / 5 (1) Jun 01, 2010
The article presents a number of facts, suggests and rejects numerous features and possible mechanisms, et c- so it basically summarizes the current state of our knowledge of Mars.

The one flaw that I can see is that the assumption has been made that all factors have remained static. But how do they know that Mars' orbit, for instance, has remained constant over the last 4.5 billion years?

Before you laugh, remember, it was an object roughly the size of Mars, that is supposed to have collided with Earth, and ejected the mass that formed our Moon.

Well? What we know for certain is that many things have changed- suddenly, and frequently catastrophically- in the solar system, so what I'm saying is that it may be profitable to think in terms of a bigger picture to explain the mystery of liquid water on Mars.
1 / 5 (1) Jun 01, 2010
This is bad news. Mars can never be terraformed, because there is no combination of gases that would make it warm enough for liquid water to exist.

Who needs terraforming? That costs too much and takes too long...

You simply build contained environments on the surface, and vaccuum up what little atmosphere there is and compress it into the living quarters.

With larger compressors running non stop, and with (soon) extremely automated mining and construction robots, a planet-wide mega-structure for housing, farming, and manufacturing could be completed in a fraction of the time required for the mythical "terraforming" project...
not rated yet Jun 01, 2010
Significant changes in the orbit of Mars will greatly change the conditions on the early Earth. That's a fairly improbable cause.
1 / 5 (2) Jun 01, 2010
Well? What we know for certain is that many things have changed- suddenly, and frequently catastrophically- in the solar system, so what I'm saying is that it may be profitable to think in terms of a bigger picture to explain the mystery of liquid water on Mars.

No disagreement here. Catastrophism does provide insights into planetary formation/evolution.

First, I believe there is evidence to support the notion that most of Mars' water is still there, locked up in planetary glaciers. There is also evidence that Mars thaws out periodically for geologically long periods. And there is evidence of localized thawing, hot springs and volcanic vents. You wanna look for life like ours? Look there.

Then there is the question of Mars' unstable rotation. Apparently the poles of the planet are often flipped 90 degrees to the orbital plane, much like Uranus, causing each pole to face the Sun for six months a years. Talk about wrecking havoc on a weather cycle.

As for the atmosphere?
1 / 5 (2) Jun 01, 2010
Just a guess, but the impact that created Hellas Basin blew the majority of the original Atmosphere off the planet.

At around this same time (early Hesperian) the Tharsis volcanic province was created and the planetary magnetic field shut down. So ended the warm/wet Mars.
1 / 5 (2) Jun 01, 2010
Information on the thermal history of planets is important because that may shed light on energy source that sustains the Sun.

With kind regards,
Oliver K. Manuel

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