February 10, 2021 New research suggests that particles escaping from Mars’ atmosphere have been accumulating on the surface of the planet’s largest moon Phobos for billions of years. They could provide important new details about the history of both worlds. Mars’ largest moon Phobos, as seen by NASA’s Mars Reconnaissance Orbiter spacecraft on March 23, 2008. Image via NASA/ JPL-Caltech/ University of Arizona. A new study suggests that Mars’ larger moon Phobos orbits through a stream of charged particles flowing off the planet’s atmosphere. The findings, published February 1, 2021, in the peer-reviewed journal Nature Geoscience, suggest that the ions of oxygen, carbon, nitrogen, and argon charged particles smashing into Phobos have been accumulating on the moon’s surface for billions of years. The researchers say analysis of Phobos’ soil could provide important new details about the history of both worlds.