Mosaic of the Schiaparelli hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The images were acquired in 1980 during an early northern summer on Mars. USGS, Public domain, via Wikimedia Commons.

Researchers have shown that the Lafayette Meteorite was exposed to liquid water while located on Mars 742 million years ago.

An asteroid struck Mars 11 million years ago and sent pieces of the red planet hurtling through space.

One of these chunks of Mars eventually crashed into the Earth somewhere near Purdue, Illinois, and is one of the few meteorites that can be traced directly to Mars.

This meteorite was rediscovered in a drawer at Purdue University in 1931 and therefore named the Lafayette Meteorite. 

During early investigations of the Lafayette Meteorite, scientists discovered that it had interacted with liquid water while on Mars and 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.

Lead author Marissa Tremblay, assistant professor with the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at Purdue University, uses noble gases like helium, neon and argon, to study the physical and chemical processes shaping the surfaces of Earth and other planets.

She explained 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.

“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.”

Credit: Purdue University.

Interaction on Mars

Tremblay’s 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.

She said: “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.

“But we were able to demonstrate that none of these things affected the age of aqueous alteration in Lafayette.”

Co-author Ryan Ickert, senior research scientist with Purdue EAPS, 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.

He said: “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.”

Origin story

Through 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.

Tremblay said: “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.

“Many meteoroids are produced by impacts on Mars and other planetary bodies, but only a handful will eventually fall to Earth.”

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 displays as a fiery entrance visible in the night sky.

Tremblay said: “We can identify meteorites by studying what minerals are present in them and the relationships between these minerals inside the meteorite. 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.”

Nakhlites

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.

Tremblay said: “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.”

The research is published in Geochemical Perspective Letters.