An international team of scientists has teased apart the secrets hidden inside a meteorite from Mars.
A meteorite that fell in Morocco last year might contain the freshest evidence for water on Mars, according to a study published this week in Science.
The meteorite, named Tissint after the town nearest its landing site, was identified as a Mars rock in January. Now, Hasnaa Chennaoui Aoudjehane (Hassan II University of Casablanca, Morocco) and her colleagues report that Tissint contains evidence of Martian soil — and that soil appears to have been altered by water.
Meteorites from Mars are nothing new. Over the last 4 billion years, giant meteorites have struck the Red Planet, blasting Martian rocks into space. Many of these rocks eventually hit Earth, where researchers can identify them as Martian based on the bubbles of atmosphere trapped inside. Meteorite hunters have found roughly 100 Mars rocks that have landed on Earth in this way.
But Tissint is special. Most Mars meteorites sat for months or years on Earth’s surface, encountering rain and humidity that confuse any evidence of Mars water they might contain.
Tissint is fresh. Eyewitnesses saw it fall to Earth at 2 a.m. on July 18th, 2011, and, because the Moroccan desert is dry and rainless, Tissint likely touched no water during the 2 months it took to recover all the pieces. This makes Tissint the freshest, least-contaminated sample of Mars that we have.
So if Tissint records evidence of liquid water, it’s Mars’s water — not Earth’s. Aoudjehane and her team believe they see just that.
Tissint originally formed when lava erupted onto the surface of Mars and cooled quickly in the cold Martian air. Then 700,000 years ago, an impact blasted Tissint from Mars, melting some of the rock into tiny veins of black glass that now crisscross the meteorite. (Similar rocks from Mars are also roughly 700,000 years old, suggesting the same event ejected them into space.)
When the team performed chemical analyses of these veins, they found evidence of melted soil, perhaps melted by the heat of the impact. The chemical signature they found could only be explained by water interacting with the soil at some point before the rock was blasted off Mars.
Interestingly, Aoudjehane’s team found chemical signatures that indicate the water was unlike most Earth water – it was highly acidic. Researchers working on the Spirit and Opportunity rovers, and several satellite spacecraft, have come to the same conclusion: past water on Mars was acidic, at least for a time. Why all the Red Planet’s water became acidic, when, and for how long is still unknown.
With Tissint, though, researchers finally have what all of the Mars rovers, satellites, and meteorites could not deliver: a pristine rock to study — and one that is actually on Earth.
Guest blogger Selby Cull is a planetary geologist at Bryn Mawr College and studies the mineralogy and geochemistry of the Martian surface. She is also a former intern at Sky & Telescope.