Wet and mild: Researchers take the temperature of Mars's past

Oct 12, 2011 by Marcus Woo
The meteorite called ALH84001 is sliced to show its interior. Found in the Allan Hills ice field in Antarctica in 1984, the four-billion-year-old rock is one of the oldest in the world. The meteorite likely originated just below the surface of Mars. About 16 million years ago, another meteorite struck the area, blasting it off into space before it landed on Earth about 13,000 years ago. [Credit: NASA]

(PhysOrg.com) -- Researchers at the California Institute of Technology (Caltech) have directly determined the surface temperature of early Mars for the first time, providing evidence that's consistent with a warmer and wetter Martian past.

By analyzing carbonate minerals in a four-billion-year-old that originated near the surface of , the scientists determined that the minerals formed at about 18 degrees Celsius (64 degrees ). "The thing that's really cool is that 18 degrees is not particularly cold nor particularly hot," says Woody Fischer, assistant professor of and coauthor of the paper, published online in the (PNAS) on October 3. "It's kind of a remarkable result."

Knowing the temperature of Mars is crucial to understanding the planet's history—its past climate and whether it once had liquid water. The Mars rovers and orbiting spacecraft have found ancient deltas, rivers, lakebeds, and mineral deposits, suggesting that water did indeed flow. Because Mars now has an average temperature of 63 degrees Celsius, the existence of liquid water in the past means that the climate was much warmer then. But what's been lacking is data that directly points to such a history. "There are all these ideas that have been developed about a warmer, wetter early Mars," Fischer says. "But there's precious little data that actually bears on it." That is, until now.

The finding is just one data point—but it's the first and only one to date. "It's proof that early in the history of Mars, at least one place on the planet was capable of keeping an Earthlike climate for at least a few hours to a few days," says John Eiler, the Robert P. Sharp Professor of Geology and professor of geochemistry, and a coauthor of the paper. The first author is Itay Halevy, a former postdoctoral scholar who's now at the Weizmann Institute of Science in Israel.

This photograph shows globules of orange-colored carbonate minerals found in the Martian meteorite dubbed ALH84001. The origin of the carbonate minerals has long puzzled scientists, but by determining that the carbonate formed at about 18 degrees Celsius, Caltech researchers say they might have an answer. The mild temperature is also consistent with the theory that Mars was once warmer and wetter than it is today. [Credit: NASA]

To make their measurement, the researchers analyzed one of the oldest known rocks in the world: ALH84001, a Martian meteorite discovered in 1984 in the Allan Hills of Antarctica. The meteorite likely started out tens of meters below the Martian surface and was blown off when another meteorite struck the area, blasting the piece of Mars toward Earth. The potato-shaped rock made headlines in 1996 when scientists discovered tiny globules in it that looked like fossilized bacteria. But the claim that it was extraterrestrial life didn't hold up upon closer scrutiny. The origin of the globules, which contain carbonate minerals, remained a mystery.

"It's been devilishly difficult to work out the process that generated the carbonate minerals in the first place," Eiler says. But there have been countless hypotheses, he adds, and they all depend on the temperature in which the carbonates formed. Some scientists say the minerals formed when carbonate-rich magma cooled and crystallized. Others have suggested that the carbonates grew from chemical reactions in hydrothermal processes. Another idea is that the carbonates precipitated out of saline solutions. The temperatures required for all these processes range from above 700 degrees Celsius in the first case to below freezing in the last. "All of these ideas have merit," Eiler says.

Finding the temperature through independent means would therefore help narrow down just how the carbonate might have been formed. The researchers turned to clumped-isotope thermometry, a technique developed by Eiler and his colleagues that has been used for a variety of applications, including measuring the body temperatures of dinosaurs and determining Earth's climate history.

In this case, the team measured concentrations of the rare isotopes oxygen-18 and carbon-13 contained in the carbonate samples. Carbonate is made out of carbon and oxygen, and as it forms, the two rare isotopes may bond to each other—clumping together, as Eiler calls it. The lower the temperature, the more the isotopes tend to clump. As a result, determining the amount of clumping allows for a direct measurement of temperature.

The temperature the researchers measured—18 ± 4 degrees Celsius—rules out many carbonate-formation hypotheses. "A lot of ideas that were out there are gone," Eiler says. For one, the mild temperature means that the carbonate must have formed in . "You can't grow carbonate minerals at 18 degrees other than from an aqueous solution," he explains. The new data also suggests a scenario in which the minerals formed from water that filled the tiny cracks and pores inside rock just below the surface. As the water evaporated, the rock outgassed carbon dioxide, and the solutes in the water became more concentrated. The minerals then combined with dissolved carbonate ions to produce carbonate minerals, which were left behind as the water continued to evaporate.

Could this wet and warm environment have been a habitat for life? Most likely not, the researchers say. These conditions wouldn't have existed long enough for life to grow or evolve—it would have taken only hours to days for the water to dry up. Still, these results are proof that an Earthlike environment once existed in at least one particular spot on Mars for a short time, the researchers say. What that implies for the global geology of Mars—whether this rock is representative of Martian history or is just an isolated artifact—is an open question.

The research described in the PNAS paper, "Carbonates in the Martian meteorite Allan Hills 84001 formed at 18 ± 4 °C in a near-surface aqueous environment," was supported by a Texaco Postdoctoral Fellowship, NASA, and the National Science Foundation.

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User comments : 11

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Nanobanano
not rated yet Oct 12, 2011
Because Mars now has an average temperature of 63 degrees Celsius, the existence of liquid water in the past means that the climate was much warmer then.


Ok, that should be "-63", and 18 celsius is actually COOLER than the modern summer high of 20 celsius.

Apparently, these conditions still exist during the summer at the base of canyons. They just found the "suspected water" the other day, remember? Of course, lasting a few days at a time and then vanishing.

Now that they've as much as proven "liquid" exists on Mars at least some of the time, even today, then we can postulate that during the day time high in the summer, the conditions to meet this are probably still present.
TMEubanks
5 / 5 (1) Oct 12, 2011
I think that there is a lot of confusion about liquid water on Mars. It's not magic - if the pressure is about the triple point (roughly 1/2 of the surface area of Mars) and the temperature is high enough (most places in the daytime) and there is frozen water available (again, many if not most places), you will have liquid water, if only for a while. Note that the surface temperature can be 20 C while the air temperature 10 cm up can be -20 C, so lander temperature measurements can be misleading. For example, Viking Lander 2 saw snow or frost, and had a pressure well above the triple point, and surface temperatures > 0 C, so there should have been liquid water there, at least as the frost melted.
dub1
1 / 5 (1) Oct 12, 2011
How much thrust would it take to propel the appropriate amount of mining equipment to Mars to make it temporarily habitable? Don't get me wrong, I think we(they) should go, it just seems like a technical nightmare at this point. Unless you just want to go to 'say we did it'.
Nanobanano
not rated yet Oct 12, 2011
How much thrust would it take to propel the appropriate amount of mining equipment to Mars to make it temporarily habitable?


Um, incalculable, if I understand your question correctly.

Maybe you mean like landing a habitat on the surface with several months or years worth of "self sufficient hydroponics," like in the "Red Planet" Val Kilmer, Carrie-Anne Moss movie.

Well, this would take several times as many rockets and total thrust as a "mere" manned orbiter mission, or even a "mere" walk on the surface in space suits.

Descent stage alone of the Lunar Module is 10 metric tons.

Landing a pre-fab habitat and hydroponics on the surface of a planet would probably require a DESCENT stage far, far bigger than that. The LEM was like a big truck size machine. An actual habitat with sufficent hydroponics to last for several months would be the size of a large house, with like a couple dozen tons of water, air, and nutrients. 6100 pounds food and water per person, minimum.
dub1
1 / 5 (1) Oct 12, 2011
I was under the impression that solar radiation was lethal on the surface of Mars and necessitated the need to go underground. You think humans in relatively sparse shelters can survive on the surface?
Pirouette
1 / 5 (1) Oct 12, 2011
"The meteorite likely originated just below the surface of Mars."
I hate these ambiguous statements that include words like "likely, possibly, might be, etc. etc.
If they have any doubt whatsoever about the origin of the rock, then why can't they just admit that they really have no idea where it came from, instead of trying to lead us into believing in something non-absolute? They are scientists, while I am not. I may use such terms because I am not trained in those disciplines that they are researching, although I do have my own research concerning Mars. I prefer my politicians and science with a smattering of honesty and lucidity, but that's me
Pirouette
1 / 5 (1) Oct 12, 2011
Perhaps the early Mars, just like the early Earth received at least some of its water from comets bearing H2O in the form of ice. In a warmer, primordial Mars, the comets slamming into the surface of the planet would have released the water which would have poured through the sandy soil and gone underground into aquifers. The aquifers full of water may still be there and rarely emerge onto the surface. Carbonate of itself doesn't necessarily indicate the potential for life in its presence. Calcium Carbonate would, at least for life as we know it.
PinkElephant
5 / 5 (3) Oct 12, 2011
If they have any doubt whatsoever about the origin of the rock, then why can't they just admit that they really have no idea where it came from
Hold your horses, cowboy. Lacking absolute certainty is not the equivalent or even the analogue of having no idea whatsoever. There are precious few things in science (and in life generally) that are known with near-absolute certainty. The rest merely gets endowed with a certain particular level of confidence. Only hypocrites and the Sith deal in absolutes...
instead of trying to lead us into believing in something non-absolute?
Science is not religion. It does not require you to believe in anything, much less in anything "absolute". It merely concludes that some things are more plausible and likely than others (whereas certain things that blatantly contradict known laws and facts, or are internally paradoxical, are altogether impossible.)
ROBTHEGOB
1 / 5 (1) Oct 13, 2011
Nobody knows where these rocks came from.
Ricochet
not rated yet Oct 13, 2011
I was under the impression that solar radiation was lethal on the surface of Mars and necessitated the need to go underground. You think humans in relatively sparse shelters can survive on the surface?

I'm thinking Biodome...
Pirouette
1 / 5 (1) Oct 15, 2011
I would advise the NASA to grow samples of human skin cells, bone and other human body cells in something like a nutrient-rich Petri dish, or whatever will suffice. Then place the resulting mass into the next spacecraft carrying a rover for the trip to Mars, along with a method of keeping the mass (or mess) alive. When the rover lands on Mars at or near the equator for a warmer climate, have the cells examined by instruments on the rover for any deterioration, radiation, unusual changes in growth, strange colorations, every test required to see what happens to human skin and bone cells while in outer space and on the surface of Mars. If all of the cells are unchanged after a certain amount of time, then it may be safe for humans to walk on Mars with a bio-suit for outdoors. Obviously, they would still need some sort of body suit protection even underground in the event that radiation is emitted from below the surface, just as radon is emitted from Earth's surface.

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