Could a controversial meteorite help scientists better understand how habitable Mars was in the ancient past? New studies of Allan Hills 84001 — a piece of cosmic debris named for the site in Antarctica where it was found, and which is best known for stirring up claims of Martian life in the 1990s — show that its origin story does at least include a lot of water.
While various space missions are orbiting Mars and roving its surface to search for ancient signs of water, scientists are also scouring the only pieces of Mars that they can get their hands on: meteorites. ALH84001 (as the meteorite is typically abbreviated) was found in 1984 and has a similar composition to other meteorites from Mars. With today's more sophisticated analytical tools, meteorites are regularly revisited for new hints of their history. This latest investigation of Allan Hills is just one example.
"Our study, and previous ones on the oldest Martian meteorites, are just showing the tip of the iceberg," said Josep Trigo-Rodriguez, a tenured scientist at Spain's Institute of Space Sciences, in an e-mail to Seeker. Trigo-Rodriguez co-authored a new paper on ALH84001 that was recently published in the journal Meteoritics & Planetary Science.
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"Mars can surprise us and certainly we need to go there, and implement sample-return missions to sample and study in our labs the oldest Martian rocks," he added. "I'm particularly convinced that Mars could have developed the right conditions to create a biosphere, but the question to ask is if that environment lasted long enough to create simple living organisms."
Credit: Wikimedia Commons
ALH84001 received widespread public attention in 1996 when a NASA-funded team found "several mineral features characteristic of biological activity, and possible microscopic fossils of primitive, bacteria-like organisms," according to a press release from the time, which was dramatically headlined: "Meteorite Yields Evidence of Primitive Life on Early Mars."
But subsequent studies suggested that these features could have resulted from Earth contamination, or even from abiotic (non-life) processes, dampening the enthusiasm of the initial announcement. Most scientists today would look for more convincing evidence to suggest that this or any other meteorite once hosted life.
Trigo-Rodriguez's research study, funded by the Spanish Ministry of Sciences, is studying some of the oldest Martian meteorites to learn about the early stages of the Red Planet's evolution. ALH84001, which is about 4.5 billion years old, meets the qualification. The research was initiated by a 2013 thesis from then-Ph.D. student Carles Moyano-Cambero, who was interested in Mars' atmosphere and climactic evolution.
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"We were particularly interested in understanding aqueous alteration and describing the secondary minerals created in this rock by the action of water," Trigo-Rodriguez said of the latest study. "The goal was trying to gain insight into the first processes occurred in Mars, and the action that water had in such environment. In particular, we also studied the effect of shock and corrosion to learn about the meteorite."
There was a lot of water where ALH84001 was — enough to dissolve carbon, iron, and magnesium. The dissolution created carbonate globules abiotically. The researchers found that carbonate globules were formed at least two times, but there are likely more formation "events," as they see many different layers of carbonate globules with different compositions of magnesium and iron. The meteorite also shows evidence of the atmosphere and periodic volcanism that was happening on Mars at the time, Trigo-Rodriguez noted.
The researchers are also looking at more recent meteorites on Mars to learn more about the planet's Amazonian geological period, which began about three billion years ago and had arid conditions similar to what we see on the Red Planet today.
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