Taking Mars’ Temperature – The ALH84001 Meteorite

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It might be four billion years old, but this meteorite which may have originated near the surface of Mars has a story to tell… one about a warmer and wetter history. Researchers at the California Institute of Technology (Caltech) have been analyzing the carbonate minerals contained within the Martian meteorite – ALH84001- and piecing together a climate history which showed the minerals formed at about 18 degrees Celsius (64 degrees Fahrenheit).

“The thing that’s really cool is that 18 degrees is not particularly cold nor particularly hot,” says Woody Fischer, assistant professor of geobiology and coauthor of the paper, published online in the Proceedings of the National Academy of Sciences (PNAS) on October 3. “It’s kind of a remarkable result.”

All recent studies, from rovers to spectroscopy, point to Mars having once had a much more temperate climate than its current average temperature of -63 degrees Celsius. Missions have photographed dry river beds, deltas, extinct lakes and more. Up until now, the one crucial point has been the lack of physical evidence. “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.

Of course, this mineralogical evidence is strictly one point – but it’s one point closer to knowing the full score. “It’s proof that early in the history of Mars, at least one place on the planet was capable of keeping an Earth-like 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.

Where did this new evidence come from? Try ALH84001, a Martian meteorite discovered in 1984 in the Allan Hills of Antarctica. While scientists cannot definitely prove where it came from, ALH84001 is theorized to have once originated several hundred feet below the Martian surface and was blown Earthward during an impact event. The Martian meteorite made headlines in 1996 when little inclusions that appeared to be fossilized bacteria were discovered. Even though the thought of simple life forms were quickly shot down, the pockets which contained carbonate minerals remained an enigma.

“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.

Deducing the temperature may help scientists to understand how the carbonates came to be, so a form of modeling called clumped-isotope thermometry was employed to help. It’s so sensitive it’s able to determine a dinosaur’s body temperature in relation to 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. As the temperature progressively lowers, the isotopes do their thing and clump. The degree to which this happens is directly related to 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 liquid water. “You can’t grow carbonate minerals at 18 degrees other than from an aqueous solution,” he explains.

Through this new information, it is also hypothesized the minerals may have come into existence inside the cavities of rock while it was below ground. “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.” A vessel for life? Well, chances aren’t good since any liquid water would have lasted for only a brief time – but it is a great indicator that this precious life-giver was once a part of Mars’ history.

Original Story Source: Caltech News Release.

Building Blocks of Life Can Form on Cold, Rocky Planets — Anywhere

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Our old friend and headline-maker is back in the news. Meteorite ALH84001 — the Mars rock that sent the world of astrobiology into a tizzy back in 1996 — hasn’t been just sitting around collecting dust. Researchers have been re-examining the famous meteorite in an effort to learn more about the early history of Mars. Not only did ALH84001 help determine that the building blocks of life actually did form on early Mars, but also that those same building blocks have the potential to form on a cold rocky planet anywhere in the Universe.

The meteorite, found in the Alan Hills region of Antarctica, grabbed the headlines over 11 years ago when scientists claimed to have found the remains of bacteria-like life forms within the rock from Mars. The claims have been hotly debated, with both sides still holding firm in their convictions.

But scientists at the Carnegie Institution’s Geophysical Laboratory took the research into ALH84001 a step further, and have shown for the first time that building blocks of life formed on Mars early in its history. Organic compounds that contain carbon and hydrogen form the building blocks of all life here on Earth. Previously, some scientists thought that organic material in ALH84001 was brought to Mars by meteorite impacts, and others felt the material might have originated from ancient Martian microbes, while still others thought any organics in the rock probably were introduced after it arrived on Earth.

The Carnegie-led team made a comprehensive study of the ALH 84001 meteorite and compared the results with data from related rocks found on Svalbard, Norway. The Svalbard samples came from volcanoes that erupted in a freezing Arctic climate about 1 million years ago — possibly mimicking conditions on early Mars.

“Organic material occurs within tiny spheres of carbonate minerals in both the Martian and Earth rocks,â€? said Andrew Steele, lead author of the study. “We found that the organic material is closely associated with the iron oxide mineral magnetite, which is the key to understanding how these compounds formed.”

“The results of this study show that volcanic activity in a freezing climate can produce organic compounds,” said Hans E.F. Amundsen, a co-author in the study from Earth and Planetary Exploration Services. “This implies that building blocks of life can form on cold rocky planets throughout the Universe.”

The organic material in the Allan Hills meteorite may have formed during two different events. The first, similar to the Svalbard samples, was during rapid cooling of fluids on Mars. A second event produced organic material from carbonate minerals during impact ejection of ALH84001 from Mars.

“Our finding sets the stage for the Mars Science Laboratory (MSL) mission in 2009,” said Steele, who is a member of the Sample Analysis on Mars (SAM) instrument team onboard MSL. “We now know that Mars can produce organic compounds. Part of the mission’s goal is to identify organic compounds, their sources, and to detect molecules relevant to life. We know that they are there. We just have to find them.”

This makes the MSL mission all the more exciting and anticipated. And perhaps the team of scientists who made the claims about microbes in ALH 84001 back in 1996 have something to strengthen their case.

Original News Source: Carnegie Institution For Science Press Release