An unexpected tool gives us new insight into the fine structure of Mars’ outer layers.
Using meteorites long ago broken off from the red planet about 11 million years ago and hurled into space to eventually land on Earth, scientists were able to study how volcanism shaped the crust and mantle of Mars to infer the presence of silicate reservoirs that fed their formation.
It’s really tricky research – we have new information about the structure and evolution of Mars without having to go all the way to it. Martian meteorites have proven to be of great value in understanding the planet’s history, and they have been delivered right here to our doorstep.
“Martian meteorites are the only physical material we have available from Mars,” says geologist James Day of the Scripps Institution of Oceanography.
“They allow us to make precise and accurate measurements and then quantify the processes that have occurred inside Mars and near the surface of Mars. They provide direct information about the composition of Mars that can ground the truth of a mission, such as the ongoing operations of the Perseverance rover that take place there.”
The meteorites examined by Day and his colleagues come in two forms; chassignites, according to a rock found in 1815 in Chassigny, France, and nakhlites, according to a specimen discovered in Nakhla, Egypt, in 1905.
The two rock types also have different compositions. Nakhlite is basalt, it contains inclusions of minerals augite and olivine. Chasignite is almost entirely olivine.
Here on Earth, basalts are 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 characteristics, the researchers were able to determine that they formed in the same volcano approximately 1.3 billion years ago. Their difference is due to a process called fractional crystallization, which is when different conditions cause liquid magma to solidify into different configurations.
The Nakhlites were part of the Martian crust; chassigniti were part of the mantle below. Moreover, some of the nakhlites were close enough to the crust to interact with and be modified by the Martian atmosphere.
“By determining that nakhlite and chassignite are from the same volcanic system, and that they interacted with 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, the two rocks show that volcanism on Mars is both similar and different from volcanism on Earth. Fractional crystallization appears to occur in the same way, producing basalt-dominant crustal rocks and olivine-dominant mantle rocks, just as with volcanic activity here.
“On the other hand, the reservoirs on Mars are extremely old, having separated from each other shortly after the formation of the red planet,” says Day. “On Earth, plate tectonics has helped re-mix reservoirs over time. In this sense, Mars provides an important link between what the early Earth may have looked like versus what it looks like today.”
The research was published in Scientific progress.