An asteroid struck Mars 11 million years ago and sent pieces of the planet hurtling through space; one of these chunks eventually crashed into the Earth. During early investigations of this object, named Lafayette meteorite, scientists discovered that it had interacted with liquid water while on Mars. Now, researchers from the United States and the United Kingdom have determined the age of the minerals in the meteorite that formed when there was liquid water.
The Lafayette meteorite was chipped off the surface of Mars and then sped through space for roughly 11 million years. It eventually found its way into a drawer at Purdue University in 1931 and has since been teaching scientists about Mars. Image credit: Purdue Brand Studio.
Meteorites are solid time capsules from planets and celestial bodies from our Universe.
They carry with them bits of data that can be unlocked by geochronologists.
They set themselves apart from rocks that may be found on Earth by a crust that forms from its descent through our atmosphere and often form a fiery entrance visible in the night’s sky.
“We can identify meteorites by studying what minerals are present in them and the relationships between these minerals inside the meteorite,” said Dr. Marissa Tremblay, a researcher at Purdue University.
“Meteorites are often denser than Earth rocks, contain metal, and are magnetic.”
“We can also look for things like a fusion crust that forms during entry into Earth’s atmosphere.”
“Finally, we can use the chemistry of meteorites (specifically their oxygen isotope composition) to fingerprint which planetary body they came from or which type of meteorite it belongs to.”
According to the authors, some Martian meteorites, such as a 0.8-kg nakhlite meteorite called the Lafayette meteorite, contain minerals that formed through interaction with liquid water while still on Mars.
“Dating these minerals can therefore tell us when there was liquid water at or near the surface of Mars in the planet’s geologic past,” Dr. Tremblay said.
“We dated these minerals in the Martian meteorite Lafayette and found that they formed 742 million years ago.”
“We do not think there was abundant liquid water on the surface of Mars at this time.”
“Instead, we think the water came from the melting of nearby subsurface ice called permafrost, and that the permafrost melting was caused by magmatic activity that still occurs periodically on Mars to the present day.”
The researchers demonstrated that the age obtained for the timing of water-rock interaction on Mars was robust and that the chronometer used was not affected by things that happened to the Lafayette meteorite after it was altered in the presence of water.
“The age could have been affected by the impact that ejected the Lafayette meteorite from Mars, the heating Lafayette experienced during the 11 million years it was floating out in space, or the heating Lafayette experienced when it fell to Earth and burned up a little bit in Earth’s atmosphere,” Dr. Tremblay said.
“But we were able to demonstrate that none of these things affected the age of aqueous alteration in Lafayette.”
“This meteorite uniquely has evidence that it has reacted with water,” said Dr. Ryan Ickert, also from Purdue University.
“The exact date of this was controversial, and our publication dates when water was present.”
“We know this because once it was ejected from Mars, the meteorite experienced bombardment by cosmic ray particles in outer space, that caused certain isotopes to be produced in Lafayette,” Dr. Tremblay said.
“Many meteoroids are produced by impacts on Mars and other planetary bodies, but only a handful will eventually fall to Earth.”
The findings were published this month in the journal Geochemical Perspective Letters.
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M.M. Tremblay et al. 2024. Dating recent aqueous activity on Mars. Geochemical Perspectives Letters 32; doi: 10.7185/geochemlet.2443