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A weird powder puzzle on the Mars moon Phobos can be resolved

The Stickney Crater on Mars’ moon Phobos. New research suggests that the red and blue areas on the surface of the moon pointing the way to the understanding of the formation. (Credit: NASA/JPL-Caltech/University of Arizona)

The eccentric orbit of the Mars moon Phobos may be the flow of powder over the surface of the moon, a new study shows, shedding light on Phobos’ mysterious origin.

Dark gray, potato-shaped Phobos is only about 14 miles (22.5 km wide, but it is by far the largest of Mars ‘ two moons, is more than seven times the mass of its companion, Deimos. Phobos orbits just 3,700 miles (6,000 km) from the Martian ground, closer to the planet than any known moon; as a result of this tight orbit, Phobos zips around Mars three times per day of the Earth.

Previous work revealed a strange dichotomy on the surface of Phobos. Some areas are reddish while others are bluish, Ron Ballouz, lead author of the new study and an astrophysicist at the Japan Aerospace Exploration Agency (JAXA), told Space.com.

Related: European Probe Snaps Color Photos of Mars Moon Phobos

The origin of these red units and blue units, as these regions are called, was uncertain. Solving this puzzle may shed light on the origin of Phobos and the way it interacts with its environment, the researchers said.

To help solve this mystery Ballouz, the group examined the grains of dust and rock, known as regolith, which drift around the surface of Phobos due to the moon is slightly elongated orbit.

Although Phobos’ orbit is nearly round, it is quite a bit eccentric, or oval-shaped. This eccentricity “is large enough to change the relative strength between Phobos and Mars’ gravity on each job. The closer you get to the Red Planet, the stronger the force of attraction and vice versa,” study co-author Nicola Baresi, an astrodynamicist at JAXA, said Space.com.

As such, Phobos wobble a bit if the orbits of Mars, making the slopes on the moon to vary by up to 2 degrees in the course of the natural satellite 7 hours and 39 minutes to orbit the Red Planet. This slight tilt back and forth enough to draw beads of regolith downhill on Phobos.

Computer simulations showed that the amount of grain that flows ” depends on where you are on Phobos,” Ballouz said. When the researchers compared their data with photos of the surface of Phobos taken by the Mars Reconnaissance Orbiter, they found that the sites where they expected that the highest amount of surface area of the motion was found to correspond to the blue regions of Phobos.

The movement on the surface of Phobos “is a very gradual,” Ballouz said. “There is not a landslide on Phobos for every job. We call this a ‘cold flow’ process, in contrast to the rapid movement of a landslide.”

“This process is not really expected to create new ‘sand’ or regolith,” study co-author Sarah Crites, a planetary scientist at JAXA, said Space.com. Instead, the cold flow moves the existing particles around, she explained.

The researchers suggest that the blue units consist of relatively fresh, unweathered material of Phobos has been excavated by the rocking of the moon experiences during its orbit around the earth. In contrast, the scientists suggested that the red units consist of regolith that, for the most part remained stuck in the time and was weathered by being exposed to solar radiation.

These findings may shed light on the uncertain origin of Phobos. “One of the biggest mysteries around Phobos is the origin — it is made of a giant impact on Mars that created a debris disk around the planet that eventually coalesced into Phobos, or was it ever an asteroid that was captured by Mars gravity?” Ballouz said.

If Phobos was formed from a giant impact on Mars, the blue units should be similar on Mars rock, because the blue units represent pristine material from the Red Planet. However, the most recent data suggest that the near-infrared signature of the blue units is different from that seen so far of Mars rock, one of the researchers said.

The group to take part in a future international mission led by JAXA called the Moons of Mars Exploration (MMX) probe, which is set to launch in 2024 and return samples of Phobos to Earth in 2029. These samples may eventually help resolve the debate about Phobos’ origin, Ballouz said.

The scientists detailed their findings online March 18 in the journal Nature Geoscience.

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Original story on Space.com.

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