Space probe brushed past Martian moon to peek inside: ScienceAlert

The long-running mystery of the origin of the Martian moons may be about to be solved.

A space probe has approached tens of kilometers from the larger of the two satellite brothers to capture data on what lies under its scratched and cratered surface.

“Whether the two small moons of Mars are captured asteroids or made of material torn from Mars in a collision is an open question,” says astronomer Colin Wilson of the European Space Agency (ESA). “Their appearance suggests they were asteroids, but the way they orbit Mars probably suggests otherwise.”

Phobos, named after the ancient Greek deity of fear and panic, is the larger of the two moons at 22.2 kilometers (13.8 miles) across and orbits Mars at an average distance from the surface approximately 6000 km.

Deimos, after the Greek god of terror and dread, is only 12.6 kilometers (7.8 miles) in diameter and has a much greater average orbital distance of around 20,000 kilometers from Mars.

They are both rather particular objects, rather different from our own companion in many respects. There are also some interesting differences between the two.

As Deimos slips away and may one day escape Mars completely, Phobos is heading for Mars in a decaying orbit that shrinks by 0.7 inches (1.8 cm) every year, a journey that could see it tear apart to form a ring in the next 100 million years or so.

We also don’t know where they come from. Several compelling lines of evidence suggest that our Moon broke away from Earth in a giant collision, but Mars and its moons, millions of miles away, aren’t as easy to study.

Compositionally, Phobos and Deimos appear quite similar, suggesting that they may have come from the same source; and this composition is also similar to a group of asteroids. But they also have similar ordered orbits that are nearly circular and stick quite tightly to Mars’ equator, a feature not typical of captured asteroids.

One way to search for answers is to look under the hood, so to speak – to find out what lies beneath the moons surface. So ESA sent its Mars Express orbiter for a flyby of Phobos, hovering within 83 kilometers (about 51 miles) of the potato-like satellite. For context, the Karman Line that separates Earth’s atmosphere from interplanetary space is about 100 kilometers above sea level. A flyover just 83 kilometers away is close.

“We didn’t know if it was possible,” says ESA’s Mars Express flight controller Simon Wood. “The team tested a few different variations of the software, with the final successful adjustments uploaded to the spacecraft just hours before the flyby.”

Data obtained by MARSIS during the flyby of Phobos in September 2022. (ESA)

The flyby itself took place towards the end of September. The goal: to use an instrument called Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) to probe beneath the surface of Phobos.

It is a radar instrument that sends low frequency radio waves to Mars; the way these waves bounce off different materials below the surface helps scientists understand what might be there.

This is how scientists figured out that there could be lakes of liquid water (or deposits of clay, or deposits of volcanic rocks, or layers of rock and ice) buried under the ice sheet. Martian south polar. Now the instrument is preparing to demystify the internal structure of Phobos.

“We are still at an early stage of our analysis,” says astronomer Andrea Cicchetti of the National Institute of Astrophysics in Italy, which operates MARSIS. “But we’ve already seen possible signs of previously unknown features below. that of the moon surface. We are excited to see the role MARSIS could play in finally solving the mystery surrounding the origin of Phobos.”

Over the next few years, Mars Express will perform even closer flybys of the small, lumpy moon. From 2023 to 2025, the probe will dive, the team hopes, up to 40 kilometers from the surface of Phobos. This will provide opportunities to collect even more data on its interior structure.

Additionally, space agencies around the world are collaborating on the Martian Moons eXploration mission. This ambitious project aims to send a probe to both Phobos and Deimos and study them in detail – and to collect a sample from Phobos and bring it back to Earth for detailed analysis.

Perhaps we will finally have an answer on the birthplace of the two tiny eccentric Martians.

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