Phobos is the larger of the two Natural satellites March. It is also the closest to the planet (it orbits at a distance of 6000 km from the surface of Mars). At 27 km in diameter, it is relatively small compared to our Moon. Its surface is more or less heavily cratered as a result of meteorite bombardment. Because they share many characteristics Asteroids Type C, Phobos, and Deimos may come from the main asteroid belt. However, the geometry of their orbits does not support this hypothesis. These two moons could be remnants of an impact between Mars and another smaller object. At the moment, their origins remain a mystery, but the Mars Express probe provides some answers.

Examining the internal structure of Phobos

Launched on June 2, 2003, ESA designed the Mars Express probe to study the planet Mars (surface, atmosphere, ionosphere, internal structure) in detail. The mission was originally scheduled to end after two Martian years. Despite everything, it was extended several times considering the quality of data collected.

Mars Express loads the Marsis device (Advanced Radar of Mars for Surface and Ionosphere Sounding), now famous for his role Discovery of liquid water Hidden under the red planet’s south pole. This radar sends low-frequency radio waves to Mars through a 40-meter-long antenna. Most of these waves are reflected from the planet’s surface. However, many of them pass through the crust and reflect various layers of material below the surface, including ice, rock, and water.

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Analysis of these waves allows scientists to map the interior of Mars several kilometers deep and study the characteristics of each layer. But device-based software has benefited this year An important update, which gives him new abilities. It was originally designed for use within 250 km of Mars. Now it can be mined at much closer ranges.

During Mars Express’s first pass near Phobos, scientists on the mission were able to gather new information. ” During this flyby, we used Marsis to study Phobos from a distance of 83 km », Andrea Cicchetti says. He is a researcher at the Italian Institute of Astrophysics and a member of the MARSIS team.

Strange layered underground structures

Phobos is not only cratered on its surface. And strange scratches. Also, this object is closer to Mars. In a few million years it will disintegrate into a ring of debris. All these observations arouse the greatest interest of specialists.

The recent approach allowed them to study the structure of Phobos in more detail. They identified important features that could not be seen from further away. ” We are still only at the beginning of our analysis. However, we have already seen possible signs of previously unknown characteristics. Cicchetti said. In particular, the signals reflected by the moon suggested the presence of strange underground structures arranged in layers.

Observation path and “radargram” acquired by Marsis during its flyby of Phobos on September 23, 2022. The solid bright line shows the echo from the lunar surface (the brighter the signal, the stronger the echo). Bottom reflections are either “noise” caused by surface features or traces of structural features below the surface. The AC section was recorded using an older version of the MARSIS software. D to F successfully used the new version for the first time. Credits: ESA

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Combined with the material’s low density, irregular shape, and composition close to carbonaceous chondrites, Phobos is definitely an ancient asteroid captured by Mars. or is the result of a set of residues. ! So other observations and analyzes are needed to conclude the debate properly.

Future overflights within 40 km!

Of course Phobos and Deimos have many points in common with Type C asteroids, however, their orbits are enough to cast doubt. They both lie above the equator of Mars and are very round. This indicates that these moons orbit Mars. The two ancient asteroids that captured the planet would exhibit more elliptical orbits and different degrees.

We already have other close flybys of Phobos planned. The team believes that in the future it will be possible to get closer to a distance of less than 40 km! ” Between 2023 and 2025 we adjusted the orbit of Mars Express to bring us as close as possible to Phobos during a handful of flybys. This will give us good opportunities to try,” Cicchetti explains.

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La Mission Exploration of the Moons of Mars (MMX), in collaboration with the Japanese Space Agency, should also enable more data to be collected. The launch of this mission is scheduled for 2024. This included not only an overflight of Phobos and Deimos, but also the collection of regolith samples on Phobos. The second will return to Earth in 2029. Solving the mystery of the origin of the moons of Mars will allow scientists to revise the formation conditions of the planets in the Solar System.