Mars has two moons, but not for long. One of them, Phobos, will either crash into the planet or break up and become a ring in about 10 to 50 million years. Which will it be? Below are excepts on the future fatal fate of phobos.
The Martian moon Phobos orbits only a few thousand miles above the Red Planet’s surface. Its proximity to its planet is one of the reasons astronomers were unable to see the satellite until the late 19th century. In fact, the moon is getting closer to Mars over the centuries …
Phobos, the larger moon, is spiraling inward and expected to crash into the planet within the next 10 million years. And so, in the future, Mars will only have a single Moon, Deimos.
The moon [Phobos] (with a mean radius of 11 km) is slowly dropping in altitude due to tidal forces. In about 11 million years it will either crash into Mars or be ripped apart through gravitational shear. Either way, Phobos is a doomed moon.
Phobos may become a Saturn style ring around Mars.
As Phobos slowly inches toward Mars, the planet’s gravity tugs on the moon’s crust, distorting it as it spins. Eventually, in 20 to 40 million years, the dust-coated pile of rubble could completely fall apart from all that stress.
If that happens, the debris could create a ring around the planet, according to calculations published today in Nature Geoscience. Saturn is thought to have gotten its iconic rings in a similar fashion. Mars’s ring would linger for up to 100 million years.
In a paper appearing online this week in Nature Geoscience, UC Berkeley postdoctoral fellow Benjamin Black and graduate student Tushar Mittal estimate the cohesiveness of Phobos and conclude that it is insufficient to resist the tidal forces that will pull it apart when it gets closer to Mars. …
Just as earth’s moon pulls on our planet in different directions, raising tides in the oceans, for example, so too Mars tugs differently on different parts of Phobos. As Phobos gets closer to the planet, the tugs are enough to actually pull the moon apart, the scientists say. This is because Phobos is highly fractured, with lots of pores and rubble. Dismembering it is analogous to pulling apart a granola bar, Black said, scattering crumbs and chunks everywhere.
The resulting rubble from Phobos – rocks of various sizes and a lot of dust – would continue to orbit Mars and quickly distribute themselves around the planet in a ring.
The grooves in this moon may be signs that it is already pulling apart.
Phobos’ grooves were long thought to be fractures caused by the impact that formed Stickney crater. That collision was so powerful, it came close to shattering Phobos. However, scientists eventually determined that the grooves don’t radiate outward from the crater itself but from a focal point nearby.
More recently, researchers have proposed that the grooves may instead be produced by many smaller impacts of material ejected from Mars. But new modeling by Hurford and colleagues supports the view that the grooves are more like “stretch marks” that occur when Phobos gets deformed by tidal forces.
The gravitational pull between Mars and Phobos produces these tidal forces. Earth and our moon pull on each other in the same way, producing tides in the oceans and making both planet and moon slightly egg-shaped rather than perfectly round.
The same explanation was proposed for the grooves decades ago, after the Viking spacecraft sent images of Phobos to Earth. At the time, however, Phobos was thought to be more-or-less solid all the way through. When the tidal forces were calculated, the stresses were too weak to fracture a solid moon of that size.
The recent thinking, however, is that the interior of Phobos could be a rubble pile, barely holding together, surrounded by a layer of powdery regolith about 330 feet (100 meters) thick.
“The funny thing about the result is that it shows Phobos has a kind of mildly cohesive outer fabric,” said Erik Asphaug of the School of Earth and Space Exploration at Arizona State University in Tempe and a co-investigator on the study. “This makes sense when you think about powdery materials in microgravity, but it’s quite non-intuitive.”
If you plan to visit Phobos, start packing soon … some time before the year 2018+2 million years, just to play it safe.
HiRISE acquired two dramatic views of the Martian moon, Phobos, on 23 March 2008 … The two images were taken within 10 minutes of each other and show roughly the same features, but from a different angle so that they can be combined to yield a stereo view. (Watch a short clip of both observations: 204KB, QuickTime.)