Martian atmospheric oxygen, carbon, nitrogen and argon ions have been escaping Mars for billions of years and could be preserved inside the uppermost hundreds of nanometers of Phobos’ nearside regolith grains, which may be brought back to Earth by future sample return missions.
The High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter captured this image of the larger of Mars’ two moons, Phobos, on March 23, 2008. The image was taken from a distance of about 6,800 km (about 4,200 miles). It is presented in color by combining data from the camera’s blue-green, red, and near-infrared channels. The illuminated part of Phobos seen in the image is about 21 km (13 miles) across. The most prominent feature is the large crater Stickney in the lower right. With a diameter of 9 km (5.6 miles), it is the largest feature on Phobos. Image credit: NASA / JPL-Caltech / University of Arizona.
The Japan Aerospace Exploration Agency (JAXA) is preparing to send the Martian Moons Exploration (MMX) probe to Phobos in 2024 to collect the first samples from its surface and deliver them to Earth.
“But those samples could reveal a lot more than the origin of Phobos if MMX were to land on the nearside of the moon, or the side that always faces Mars,” said Dr. Quentin Nénon, a researcher in the Space Sciences Laboratory at the University of California, Berkeley.
Phobos is currently tidally locked on its orbit, always showing its nearside to the Red Planet, and has probably kept this configuration for at least tens of millions of years.
As a result, the nearside rocks have been bathed for millennia in Martian atoms and molecules.
To measure the Martian ions in Phobos’ orbit, Dr. Nénon and colleagues analyzed data collected by the Suprathermal and Thermal Ion Composition (STATIC) instrument on board NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter.
They found that the uppermost surface layer of Phobos’ nearside has been subjected to 20 to 100 times more wayward Martian ions than its far side.
“We knew that Mars lost its atmosphere to space, and now we know that some of it ended up on Phobos,” Dr. Nénon said.
“So hopefully this finding will have an impact on the scientific activities of the MMX mission.”
“With a sample from the nearside 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,” he added.
The study was published in the journal Nature Geoscience.
Q. Nénon et al. Implantation of Martian atmospheric ions within the regolith of Phobos. Nat. Geosci, published online February 1, 2021; doi: 10.1038/s41561-020-00682-0
This article is based on text provided by the National Aeronautics and Space Administration.