Martian meteorites reveal Red Planet structure
Mars has a distinct structure in its mantle and crust, with identifiable reservoirs, as revealed by meteorites analyzed by scientists at Scripps Institution of Oceanography at UC San Diego and their colleagues. These findings are crucial for understanding Mars’ formation and evolution and for providing precise data that can inform NASA missions like Insight, Perseverance, and the Mars Sample Return.
Meteorites formed around 1.3 billion years ago and ejected from Mars have been collected by scientists from Antarctica and Africa over recent decades. Scripps Oceanography geologist James Day and his team reported on May 31 in the journal Science Advances their analysis of these samples’ chemical compositions from Mars.
“Martian meteorites are the only physical materials we have available from Mars,” said Day. “They enable us to make precise and accurate measurements and then quantify processes that occurred within Mars and close to the martian surface. They provide direct information on Mars’ composition that can ground truth mission science, like the ongoing Perseverance rover operations taking place there.”
Day’s team studied meteorite samples from the same volcano, known as nakhlites and chassignites. About 11 million years ago, a large meteor impact on Mars ejected these rocks into space. Some landed on Earth, with the first discovered in 1815 in Chassigny, France, and another in 1905 in Nakhla, Egypt. Since then, more such meteorites have been found in places like Mauritania and Antarctica. Scientists can identify Mars as their origin because these meteorites are relatively young, have distinct oxygen compositions compared to Earth, and retain Mars’ atmospheric composition measured by the Viking landers in the 1970s.
The team analyzed the chemical compositions of nakhlite and chassignite meteorites, revealing insights into the structure and reservoirs within Mars. Nakhlites are basaltic rocks rich in clinopyroxene, similar to lavas found in Iceland and Hawaii. Chassignites, on the other hand, are primarily composed of olivine. On Earth, basalts and olivines are common in the crust and mantle, respectively, and the same applies to Mars.
The researchers showed that nakhlites and chassignites are connected through fractional crystallization within the same volcanic system. Interestingly, some molten nakhlites incorporated portions of the Martian crust that had interacted with the planet’s atmosphere, indicating the presence of a distinct, atmospherically altered upper crust on Mars.
“By determining that nakhlites and chassignites are from the same volcanic system, and that they interacted with martian crust that was altered by atmospheric interactions, we can identify a new rock type on Mars,” said Day. “With the existing collection of martian meteorites, all of which are volcanic in origin, we are able to better understand the internal structure of Mars.”
The distinctive chemical characteristics of nakhlites, chassignites, and other Martian meteorites reveal a complex, multi-layered structure within Mars:
- An atmospherically altered upper crust
- A complex deeper crust
- A mantle with plumes reaching the base of the crust
- Distinct volcanoes formed from melting of Mars’ interior early in its evolution
These findings shed light on the similarities and differences between Mars’ volcanic processes and those on Earth. While the formation of nakhlites and chassignites resembles recent volcanism on Earth, such as in Oahu, Hawaii, the reservoirs within Mars are extremely ancient, separating shortly after the planet’s formation, unlike the constant remixing of reservoirs on Earth due to plate tectonics.
