A space probe skimmed past a Martian moon to take a closer look: ScienceAlert

The long-standing mystery about the origin of the Martian moons could be one step closer to solving it.

A space probe has come within tens of kilometers of the larger of the two satellite brothers to record data on what lies beneath the grooved and cratered surface.

“Or Mars“The two small moons are captured asteroids or made of material ripped 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 suggests otherwise.”

Phobos, named after the ancient Greek deity of fear and panic, is the larger of the two moons, measuring 22.2 kilometers (13.8 miles) in diameter and orbiting Mars at an average distance from the surface of about 6,000 kilometers.

Deimos, after the Greek god of fear and terror, is only 12.6 kilometers (7.8 mi) wide and has a much larger mean orbital distance of about 20,000 kilometers from Mars.

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

As Deimos moves away and may one day escape Mars altogether, Phobos moves toward Mars in a decaying orbit that shrinks by 1.8 centimeters (0.7 inches) every year, a journey it could see tear apart to form a ring within the next 100 million years or so.

It is also unclear where they came from. Multiple compelling evidence suggests that our moon broke off from Earth in a giant collisionbut Mars and its moons, millions of miles away, are not so easy to study.

Compositional, Phobos and Deimos look very similar, suggesting they may have come from the same source; and that composition is also similar to a group of asteroids. But they also have similar neat orbits that are nearly circular and stay fairly close to the Martian equator, a feature not typical of captured asteroids.

One way to look for answers is to look under the hood, so to speak – to find out what lurks beneath the surface of the moons. So ESA sent them Mars Express orbiter for a Phobos flyby, skimming 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 flyby at only 83 kilometers is close to.

“We didn’t know if this was possible”, says Mars Express flight controller Simon Wood from ESA. “The team tested a few different variants of the software, with the final, successful tweaks uploaded to the spacecraft several hours before the flyby.”

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

This is a radar instrument that sends low-frequency radio waves to Mars; the way these waves bounce off various materials below the surface allows scientists to figure out what could be there.

This is how scientists got a hunch that there might be liquid water lakes (or clay depositsor volcanic rock depositsor layers of rock and ice) buried under Mars’ southern polar ice sheet. Now the instrument is set to demystify the internal structure of Phobos.

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

In the coming years, Mars Express will fly even closer to the lumpy little moon. From 2023 to 2025, the probe will dive in, the team hopes, as far as 40 kilometers from the surface of Phobos. This offers opportunities to collect even more data about the internal structure.

In addition, 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 – collecting a sample from Phobos and returning it to Earth for detailed analysis.

We may finally have an answer to the birthplace of the two little Martian aliens.