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Rebooted Mars Express instrument peers inside martian moon Phobos

A nearly 20-year-old instrument on the European Space Agency (ESA)’s Mars Express orbiter recently received a software upgrade which has enabled it to study the martian moon Phobos in greater detail than ever before. The Mars Advanced Radar for Subsurface and Ionosphere Sounding or MARSIS instrument was originally designed to study the interior of Mars, but in a recent flyby, it was able to gather close-up data on one of Mars’s two moons.

MARSIS was updated from its Windows 98-based software earlier this summer, allowing it to collect and process data more efficiently. That let it take a deep look at Phobos. “We didn’t know if this was possible,” said ESA’s Simon Wood, who oversaw the upload of the new software, in a statement. “The team tested a few different variations of the software, with the final, successful tweaks uploaded to the spacecraft just hours before the flyby.”

Mars Express HRSC image of Phobos, taken on 7 March 2010.
Mars Express HRSC image of Phobos, taken on 7 March 2010. ESA/DLR/FU Berlin (G. Neukum)

Mars Express made its flyby of Phobos on 23 September, with the craft coming within around 50 miles of the moon. The MARSIS instrument was designed to operate from a much greater distance, as it typically passes over 150 miles from Mars.

“During this flyby, we used MARSIS to study Phobos from as close as 83 km,” said Andrea Cicchetti from the MARSIS team at the Italian National Institute for Astrophysics. “Getting closer allows us to study its structure in more detail and identify important features we would never have been able to see from further away. In future, we are confident we could use MARSIS from closer than 40 km. The orbit of Mars Express has been fine-tuned to get us as close to Phobos as possible during a handful of flybys between 2023 and 2025, which will give us great opportunities to try.”

The MARSIS instrument on ESA's Mars Express spacecraft uses its recently upgraded software to peer beneath the surface of the martian moon Phobos.
The MARSIS instrument on ESA’s Mars Express spacecraft uses its recently upgraded software to peer beneath the surface of the martian moon Phobos. INAF - Istituto Nazionale di Astrofisica

The data collected by MARSIS should help reveal the interior structure of Phobos. The researchers are still analyzing the data, but according to Cicchetti, they have already seen indications of previously unknown features beneath the surface. Understanding the moon’s structure can help to answer questions such as how Mars’s moon formed — whether they were asteroids which got too close to the planet and were captured by its gravity or chunks of the planet  blown off by an impact.

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