Geologically, Mars is very reminiscent of the moon. But it also looks a lot like the Earth. It all depends on who you ask.
Current understanding of Mars' evolution is based on spacecraft measurements and meteorite analysis. Those meteorites were ejected from Mars and traversed space before landing on Earth, where they were discovered primarily in African deserts and Antarctica. They come in two categories: shergottites and nakhlites. Each paints a distinctly different picture of Mars' geologic history.
In a study published in the Proceedings of the National Academy of Sciences, LLNL researchers argue that samples retrieved from known locations on Mars by sample return missions could solve this conundrum.
"We are currently using samples that are often smaller than the tip of your thumb to extrapolate the entire evolutionary history of a planet. You would not predict the existence of the Himalayas from a sample collected in the ocean basin," LLNL researcher Lars Borg said. "We need to be able to determine if the characteristics we see are part of a large-scale feature or just some small local anomaly."
Shergottites are 200- to 600-million-year-old basaltic rocks that have geochemical and isotopic characteristics similar to the moon. These meteorite samples suggest that Mars formed a core, mantle and crust very early in its history and then sat quietly. In contrast, nakhlites are 1.3 billion years old and indicate that Mars formed a core, mantle and crust even earlier and, like the Earth, experienced ongoing geologic activity. No other planet presents such a confusing combination of clues.
Measurements and dating of many Martian meteorites have been done at LLNL by the Cosmochemical & Isotopic Signatures group. They are currently updating their facilities in anticipation of NASA's Mars Sample Return Campaign, which would bring samples collected by the Perseverance rover to Earth.
"This is part of a much broader agenda for LLNL to contribute our unique analytical capabilities to upcoming sample return missions, which importantly include the return of humans to the moon through the Artemis program," LLNL researcher Thomas Kruijer said.
By studying Martian samples (and their known locations), Borg and his team hope to construct a unified model for the formation and evolution of the red planet.
Understanding the history of Mars could inform studies on Earth's formation and the earliest evolution of terrestrial planets in general.
"Obtaining samples from the only place in the solar system that even remotely looks like Earth could illuminate how our world came to be, explain how civilization formed and examine whether we are alone in the universe," Borg said.
This publication was funded by the NASA Solar System Exploration Research Institute.
