First close flyby of Phobos, one of Mars’ mysterious moons

First close flyby of Phobos, one of Mars' mysterious moons

Bobos is the larger of the two Natural satellites In the month of March. It is the closest to the planet (it orbits at a distance of 6000 kilometers from the Martian surface). At 27 kilometers in diameter, it is relatively small compared to our Moon. Its surface is more or less covered with large craters, the result of meteorite bombardments. 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 theory. Both of these moons are remnants of an impact between Mars and another smaller object. For now, their origins remain a mystery, but the Mars Express probe offers some answers.

Exploring the internal structure of Phobos

Launched on June 2, 2003, ESA designed the Mars Express probe to study Mars in detail (surface, atmosphere, ionosphere and internal structure). The mission was originally planned to be completed after two years, the equivalent of one Martian year. In spite of everything, in terms of the quality of data collected, it has been extended several times.

Mars Express carries the Marsis instrument (Mars Advanced Radar for Surface and Ionosphere Sounding), now famous for his role Discovery of liquid water Hidden under the red planet’s south pole. This radar transmits low-frequency radio waves to Mars through its 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 the various layers below the surface, including ice, rock, and water.

Phobos, Mars, Moon, Exploration

Illustration of Mars Express with the MARSIS antenna, two arms 20 meters long, fully extended. Credits: NASA/JPL/Corby Waste

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Analysis of these waves allows scientists to map the internal structure of Mars at a depth of several kilometers and study the properties of each layer. But tool-based software has benefited this year A major upgrade, which gives him new abilities. It was originally designed to be used within 250 kilometers of Mars. It can now be cut to a very close range.

On the occasion of Mars Express’s first pass near Phobos, the mission’s scientists were able to gather new information. ” During this trip, we used MARSIS to study Phobos from a distance of 83 km ยป, says Andrea Cicchetti. He is a researcher at the Italian Astrophysical Institute and a member of the MARSIS group.

Strange layered underground structures

Not only are craters on the surface of Phobos, But strange scratches. Additionally, the object is approaching Mars. Within a few billion years it will disintegrate into a ring of debris. All these observations arouse the great interest of experts.

A recent approach allowed the structure of Phobos to be studied in more detail. They identify important features that cannot be seen from a distance. ” We are still only at the beginning of our analysis. However, we have already seen potential signs of previously unknown properties. said Cicchetti. In particular, signals reflected by the Moon suggested the presence of strange subterranean structures arranged in layers.

Phobos, Mars, Moon, Exploration

Tracking trajectory and “radargram” obtained by MARSIS during the Phobos flyby 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 signs of structural features below the surface. AC segmentation was recorded using an older version of MARSIS software. The new version D to F was successfully used for the first time. Credits: ESA

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This type of structure, combined with the material’s low density, its irregular shape, and its composition close to carbonaceous chondrites, may indicate that Phobos is actually an ancient asteroid captured by Mars… or the result of debris accumulation. ! Other observations and analyzes are necessary to conclude the discussion conclusively.

Future flights within 40 km!

Certainly Phobos and Deimos have many points in common with the C-type asteroids, however, and their orbits are enough to cast doubt. They both lie above the Martian equator and are very round. These moons are said to have formed around Mars. Two ancient asteroids captured by the planet show highly elliptical orbits and different planes.

We are already planning other close flybys of Phobos. In the near future, the team thinks it will be possible to get closer to less than 40 kilometers! ” During a few flybys between 2023 and 2025, we’ve got Mars Express’ orbit as close to Phobos as possible. This gives us good opportunities to experiment,” explains Cicchetti.

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Mars Moon Exploration Mission (MMX), in collaboration with the Japanese Space Agency, should make it possible to collect more data. The start of this work is planned in 2024. This includes not only overflights of Phobos and Deimos, but also the collection of regolith samples from Phobos. The latter should return to Earth in 2029. Solving the mystery of the origin of Mars’ moons will allow scientists to refine the solar system’s planet formation scenario.

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