During early investigations of the Lafayette Meteorite, scientists discovered that it had interacted with liquid water while on Mars. Scientists have long wondered when that interaction with liquid water took place. An international collaboration of scientists including two from Purdue University's College of Science have recently determined the age of the minerals in the Lafayette Meteorite that formed when there was liquid water. The team has published its findings in Geochemical Perspective Letters.
Marissa Tremblay, assistant professor with the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at Purdue University, is the lead author of this publication. She uses noble gases like helium, neon and argon, to study the physical and chemical processes shaping the surfaces of Earth and other planets. She explains that some meteorites from Mars 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," she says. "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."
In this publication, her team 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 Lafayette 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," she says. "But we were able to demonstrate that none of these things affected the age of aqueous alteration in Lafayette."
Ryan Ickert, senior research scientist with Purdue EAPS, is a co-author of the paper. He uses heavy radioactive and stable isotopes to study the timescales of geological processes. He demonstrated that other isotope data (previously used to estimate the timing of water-rock interaction on Mars) were problematic and had likely been affected by other processes.
"This meteorite uniquely has evidence that it has reacted with water. The exact date of this was controversial, and our publication dates when water was present," he says.
Found in a drawer
Thanks to research, quite a bit is known about the Lafayette Meteorite's origin story. It was ejected from the surface of Mars about 11 million years ago by an impact event.
"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," Tremblay says. "Many meteoroids are produced by impacts on Mars and other planetary bodies, but only a handful will eventually fall to Earth."
But once Lafayette hit Earth, the story gets a little muddy. It is known for certain that the meteorite was found in a drawer at Purdue University in 1931. But how it got there is still a mystery. Tremblay and others made strides in explaining the history of the post-Earth timeline in a recent publication.
"We used organic contaminants from Earth found on Lafayette (specifically, crop diseases) that were particularly prevalent in certain years to narrow down when it might have fallen, and whether the meteorite fall may have been witnessed by someone," Tremblay says.
Meteorites: time capsules of the universe
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," says Tremblay. "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."
An international collab
The team involved with this publication included an international collaboration of scientists. The team also includes Darren F. Mark, Dan N. Barfod, Benjamin E. Cohen, Martin R. Lee, Tim Tomkinson and Caroline L. Smith representing the Scottish Universities Environmental Research Centre (SUERC), the Department of Earth and Environmental Science at the University of St Andrews, the School of Geographical and Earth Sciences at the University of Glasgow, the School of Earth Sciences at the University of Bristol, and the Science Group at The Natural History Museum in London.
"Before moving to Purdue, Ryan and I were both based at the Scottish Universities Environmental Research Centre, where the argon-argon isotopic analyses of the alteration minerals in Lafayette took place" Tremblay says. "Our collaborators at SUERC, the University of Glasgow, and the Natural History Museum have previously done a lot of work studying the history of Lafayette."
Dating the alteration minerals in Lafayette and, more generally, in this class of meteorites from Mars called nakhlites, has been a long-term objective in planetary science because scientists know that the alteration happened in the presence of liquid water on Mars. However, these materials are especially difficult to date, and previous attempts at dating them had either been very uncertain and/or likely affected by processes other than aqueous alteration.
"We have demonstrated a robust way to date alteration minerals in meteorites that can be applied to other meteorites and planetary bodies to understand when liquid water might have been present," Tremblay says.
Because of the Stahura Undergraduate Meteorite Fund, Tremblay and Ickert will be able to continue studying the geochemistry and histories of meteorites and undergraduates at Purdue EAPS will be able to assist in this research.
Research Report:Dating recent aqueous activity on Mars
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