Scientists discover new insights into Mars’ structure from meteorites

The Chassigny meteorite in cross-polarized light. This meteorite is dominated by the mineral olivine. Grains are roughly 0.5 millimeters across. Credit: UC San Diego.

Researchers at the Scripps Institution of Oceanography at UC San Diego have uncovered new information about the structure of Mars by studying meteorites that originated from the red planet.

These meteorites, which formed about 1.3 billion years ago, provide crucial data on how Mars developed and evolved.

Geologist James Day and his team analyzed the chemical compositions of these meteorites, which were collected from Antarctica and Africa.

Their findings, published on May 31 in the journal Science Advances, offer valuable insights into Mars’ mantle and crust.

“Martian meteorites are the only physical materials we have from Mars,” said Day. “They allow us to make precise measurements and understand the processes that occurred within Mars and near its surface.

This information is essential for current NASA missions like Insight and Perseverance.”

Day’s team focused on two types of meteorites: nakhlites and chassignites. These meteorites all originated from the same Martian volcano.

Approximately 11 million years ago, a large impact on Mars sent these rocks into space, and some eventually landed on Earth. The first of these meteorites was discovered in Chassigny, France, in 1815, followed by another in Nakhla, Egypt, in 1905.

More meteorites have since been found in places like Mauritania and Antarctica. Scientists can identify them as Martian due to their young age, distinct oxygen compositions, and the fact that they contain the same atmospheric composition as measured by the Viking landers in the 1970s.

The nakhlite meteorites are similar to basaltic lavas found in Iceland and Hawaii, rich in a mineral called clinopyroxene. Chassignites, on the other hand, are composed almost entirely of olivine. On Earth, basalts are common in the crust, especially under the oceans, while olivines are abundant in the mantle. The same appears to be true for Mars.

The team discovered that these rocks are related through a process called fractional crystallization within the Martian volcano where they formed.

This process involves the separation of minerals as the molten rock cools. The researchers also found that some nakhlites incorporated parts of the crust near the surface, which had interacted with Mars’ atmosphere.

“By determining that nakhlites and chassignites come from the same volcanic system and interacted with the Martian crust, we can identify a new rock type on Mars,” said Day.

“With the existing collection of Martian meteorites, all of which are volcanic, we can better understand the internal structure of Mars.”

The unique chemical characteristics of nakhlites and chassignites, along with other Martian meteorites, reveal that Mars’ upper crust has been altered by atmospheric interactions. They also show a complex deeper crust and mantle, where plumes from deep within Mars have reached the base of the crust.

“What’s remarkable is that Mars’ volcanism has both similarities and differences to Earth’s,” said Day. “Nakhlites and chassignites formed in ways similar to recent volcanism in places like Oahu in Hawaii, where newly formed volcanoes generate tectonic forces that produce more volcanism.”

“However, the reservoirs in Mars are extremely ancient, separating from each other shortly after Mars formed. On Earth, plate tectonics has remixed these reservoirs over time. In this sense, Mars provides a glimpse into what the early Earth might have looked like.”

This study, which included contributions from Marine Paquet of Scripps Oceanography and colleagues from the University of Nevada Las Vegas and the French National Center for Scientific Research, enhances our understanding of Mars and its geological history. It also offers valuable data for ongoing and future Mars missions.

Source: UC San Diego.