Mars meteorite, ALH84001. Credit: NASA

Mars meteorite, ALH84001.
Credit: NASA

It’s the Mars rock that keeps on giving!

Snowmobilers plucked from an Antarctic ice field 30 years ago this month the infamous, controversial, and tell-all Alan Hills meteorite – later identified as ALH84001.

Those making the find on December 27, 1984 were part of the ANSMET (Antarctic Search for Meteorites), a program funded by the Office of Polar Programs of the National Science Foundation.

Credit: Case Western Reserve University

Credit: Case Western Reserve University

Based on chemical analyses, the meteorite is believed to have originated on Mars from a period when liquid water existed on the now bleak planet’s surface.

In 1996, a group of scientists at NASA Johnson Space Center, led by the late David McKay, Everett Gibson and Kathie Thomas-Keprta, published an article in Science announcing the discovery of biogenic evidence in the ALH84001 meteorite.

Jump to today, according to one of those NASA researchers – Everett Gibson – he remains steadfast that, even after 18 years, “there were signatures of possible biogenic activity within selected Martian samples,” he told Inside Outer Space.

An elongated structure resembling a fossil microorganism (centre of image), revealed in a photomicrograph of a sample of the Martian meteorite ALH84001. The finding has been used in support of a controversial suggestion by some scientists that the meteorite contains microscopic and chemical evidence of ancient life indigenous to Mars. Credit: NASA

An elongated structure resembling a fossil microorganism (centre of image), revealed in a photomicrograph of a sample of the Martian meteorite ALH84001. The finding has been used in support of a controversial suggestion by some scientists that the meteorite contains microscopic and chemical evidence of ancient life indigenous to Mars.
Credit: NASA

Ancient chemistry

The new analysis of the Martian rock reveals a record of the planet’s climate billions of years ago, back when water likely washed across its surface and any life that ever formed there might have emerged.

“Minerals within the meteorite hold a snapshot of the planet’s ancient chemistry, of interactions between water and atmosphere,” said Robina Shaheen, a project scientist at University of California, San Diego and the lead author of a new work reported in the early online edition of the Proceedings of the National Academy of Sciences: “Carbonate Formation Events in ALH 84001 Trace the Evolution of the Martian Atmosphere.”

ALH84001 is the oldest meteorite found on Earth from Mars, a chunk of solidified magma from a volcano that erupted four billion years ago. Since that period something liquid, probably water, seeped through pores in the rock and deposited globules of carbonates and other minerals.

Ozone signal

In the new study, scientists from the UC San Diego, NASA and the Smithsonian Institution report detailed measurements of minerals within the meteorite.

This team measured a pronounced ozone signal in the carbonates within the meteorite, suggesting that although Mars had water back then, vast oceans were unlikely. Instead, the early Martian landscape probably held smaller seas.

As noted in a UC San Diego press statement, carbonates can be deposited by living things that scavenge the minerals to build their skeletons. “But that is not the case for the minerals measured by this team.”

“The carbonate we see is not from living things,” Shaheen said. “It has anomalous oxygen isotopes that tell us this carbonate is abiotic,” she said, that is, factors that are essentially non-living components.

By measuring the isotopes in multiple ways, the chemists found carbonates depleted in carbon-13 and enriched in oxygen-18. That is, the atmosphere of Mars in this era — a period of great bombardment — had much less carbon-13 than it does today.

The change in relative abundances of carbon and oxygen isotopes may have occurred through extensive loss of Martian atmosphere. A thicker atmosphere would likely have been required for liquid water to flow on the planet’s chilly surface.

Mars life: Yes, no, maybe, could be, might have been. Credit: NASA/USGS

Mars life: Yes, no, maybe, could be, might have been.
Credit: NASA/USGS

A family of four?

For NASA’s Gibson, basically, the new research “does not change our earlier hypothesis.”

“From the published literature, there are now four unique Martian meteorites with possible signatures of past Martian biogenic activity,” Gibson said. Along with ALH84001, he points to Nakhla, Yamato 000593, and Shergotty meteorites.

In fact, Gibson said, that micro tunnels found in Yamato 000593 – reported by Lauren White at the Jet Propulsion Laboratory — are identical to those produced by microbial bacterials in terrestrial submarine basalts and glasses – and adds evidence for potential biogenic activity on Mars in moderate times.

“Yes, Charlotte, there are reduced carbon phases present on Mars. No surprise that the Curiosity SAM instrument has recently re-discovered ‘reduced carbon compounds’ that terrestrial laboratory studies have shown from the study of Martian meteorites,” Gibson said.

“Perhaps the Curiosity team members should look at the Martian meteorite literature about what has been done,” research that has, he said, laid the foundation for understanding reduced organic materials on Mars.

“I have said for a long time, we can solve a lot of Mars’ problems by studying Martian meteorites,” Gibson concluded.

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