An unexpected tool gives us new insight into the fine structure of Mars’ outer layers.
Using meteorites that were long ago chipped off the red planet 11 million years ago and ejected into space to eventually land on Earth, scientists were able to study the way volcanism shaped the crust and mantle of Mars to infer the presence of silicate reservoirs that fueled their formation.
It’s really quite sophisticated research – we have new information about the structure and evolution of Mars without having to go all the way there to get it. It turns out that Martian meteorites are a great asset to understanding the planet’s history, and they’re being delivered right here to our own doorstep.
“Martian meteorites are the only physical materials we have from Mars,” says geologist James Day of the Scripps Oceanography Institute.
“They allow us to make precise and accurate measurements and then quantify the processes that have occurred on and near the surface of Mars. They provide direct information about the composition of Mars that can inform mission-truth science, such as the Perseverance rovers’ ongoing operations there .” “
The meteorites studied by Day and his colleagues come in two forms; chassignites, after a rock found in 1815 at Chassigny, France, and nakhlites, after a specimen discovered at Nakhla, Egypt, in 1905.
The two types of rock also have different compositions. Nachlite is basaltic, contains inclusions of minerals augite and olivine. Chassignite is almost all olivine.
Here on Earth, basalt is more abundant in the crust and olivine in the mantle. Mars is no different.
By carefully examining and comparing the two types of rock and their unique chemical properties, scientists were able to determine that they formed in the same volcano about 1.3 billion years ago. Their difference is due to a process called fractional crystallization, where different conditions cause liquid magma to harden into different configurations.
The Nakhlites were part of the Martian crust; chassignites were part of the mantle below. Additionally, some of the nachlites were close enough to the crust to interact with and be modified by the Martian atmosphere.
“By finding that nakhlites and chassignites are from the same volcanic system and that they interacted with the Martian crust that has been altered by atmospheric interactions, we can identify a new type of rock on Mars,” says Day.
“With the existing collection of Martian meteorites, all of which are of volcanic origin, we are able to better understand the internal structure of Mars.”
Interestingly, these two rocks show that volcanism on Mars is both similar and different from volcanism on Earth. Fractional crystallization appears to occur in the same manner, forming a basalt-dominant rock in the crust and an olivine-dominant rock in the mantle, just like volcanic activity here at home.
“On the other hand, the reservoirs on Mars are extremely old and separated from each other shortly after the red planet formed,” says Day. “On Earth, plate tectonics helped to re-mix the reservoirs over time. In this sense, Mars provides an important link between what the early Earth might have looked like and what it looks like today.”
The research was published in Scientific advances.