An image of Phobos from March 23, 2008, taken by the High Resolution Imaging Science Experiment camera on NASA’s Mars Reconnaissance Orbiter. Credits: NASA/JPL-Caltech/University of Arizona

SSL researcher Quentin Nénon is lead author of a study which says that as Mars spent billions of years sloughing off its once-thick atmosphere—a continuous stream of oxygen, carbon, nitrogen and argon ions—its moon Phobos regularly passed through this cast-off flow and could bear witness to the past. A tiny tidally-locked moon, Phobos’ Mars-facing side was struck repeatedly by charged particles that likely remain embedded in its surface. If the soil of Phobos could be analyzed in Earthly labs, it should reveal answers to some mysteries of Martian evolution and atmosphere loss. Nénon’s team analyzed data from NASA’s Mars Atmosphere and Volatile EvolutioN, or MAVEN, spacecraft to reach this conclusion. “We knew that Mars lost its atmosphere to space, and now we know that some of it ended up on Phobos,” says Quenon, in the paper published on Feb. 1 in Nature Geoscience.

“What Quentin has done is take investigations we’ve done at the Moon and at other moons of the solar system and applied the same methods to Phobos for the first time,” said Andrew Poppe, associate research scientist at the Space Sciences Laboratory and co-author of the paper. “What we’ve seen in Apollo samples is that the Moon has been patiently recording individual atoms coming from the Sun and from Earth,” Poppe said. “It’s a really cool historical record.”

JAXA is readying a probe called Martian Moons Exploration (MMX) which will arrive at Phobos in 2024 to collect the first samples from its surface. “With a sample from the near side,” Nénon said, “we could see an archive of the past atmosphere of Mars in the shallow layers of grain, while deeper in the grain we could see the primitive composition of Phobos.”

See the full NASA article and Nature Geoscience paper here.