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Mars’ largest moon, Phobos, is showing signs of being torn apart by the extreme gravitational forces exerted on it by the red planet, according to a new study. Researchers have revealed that the unusual grooves covering the surface of Phobos, which were previously thought to be scars from an ancient asteroid impact, are actually dust-filled canyons that widen as the moon stretches under the effect of gravitational forces.
Phobos measures about 17 miles (27 kilometers) at its widest point and its orbits March at a distance of 3,728 miles (6,000 km), making a full rotation around the red planet three times a day, according to Nasa (opens in a new tab). For comparison, Earth moon is about 2,159 miles (3,475 km) wide, 238,855 miles (384,400 km) from our planet, and takes about 27 days to complete an orbit.
However, unlike the moon, Phobos’ orbit around Mars is not stable: the tiny satellite is trapped in a death spiral and slowly falls towards the Martian surface at a rate of 1.8 meters every 100 years, according to NASA. .
But perhaps the most unusual feature of Phobos is its mysterious striped surface. Parallel grooves, or surface ridges, cover the moon. The most widely accepted theory suggests that the streaks formed when an asteroid slammed into Phobos at some point in the past, leaving behind a 6-mile-wide crater, known as Stickney, on the side of the moon.
But a new study, published on November 4 in the The Journal of Planetary Science (opens in a new tab)suggests that the grooves may actually be the result of the moon being slowly ripped apart by Mars’ intense gravity as Phobos spins closer and closer to the planet’s surface.
Related: A brand new mini ‘moon’ discovered in the outer solar system
The idea behind the new study is that as a body, in this case Phobos, gets closer to a larger body, such as Mars, the smaller one will begin to stretch in line towards the larger body. This is called tidal force.
In the case of Phobos, the tidal force on the moon is expected to increase as Phobos gets closer to the Martian surface, until eventually the tidal force becomes greater than the gravity holding the satellite together. At this point, Phobos will be completely torn apart, and the debris will likely form a small ring around the planet, like Saturn’s rings, according to the study.
While previous research suggested that tidal forces produced the tiger stripes of Phobos, the theory has been largely dismissed due to the moon’s powdery or “fluffy” composition, making it too soft for such cracks to form. .
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In the new study, the researchers used computer simulations to test the idea that the moon’s fluffy surface might sit on a somewhat cohesive underlayer. A buried hard shell would have potentially formed deep canyons into which surface dust could fall, creating visible grooves on the surface, according to the simulation.
“By modeling Phobos as a rubble pile interior covered by a cohesive layer, we find that tidal strain could create parallel fissures with regular spacing,” the researchers wrote in the paper.
At its current rate, Phobos will complete its death spiral and strike Mars in about 40 million years. But if tidal forces were already tearing the moon apart, the satellite could be completely destroyed long before that, the researchers wrote.
In 2024, the Japanese Space Agency, JAXA (opens in a new tab), will launch a new mission, known as Martian Moons eXploration (MMX), to land a spacecraft on Phobos and Deimos. Samples returned in 2029 should reveal what’s going on with Phobos’ striped surface.
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