Phobos’ surface has deep grooves that run along its length that NASA’s Goddard Space Flight Center believes are early warning signs that it will soon be destroyed. Phobos orbits Mars at a distance of 3 ,700 mile (6 ,000 kilometers) from the Red Planet. It orbits Mars at a distance that is greater than any moon of the Solar System. It is comparable to the 238,900 mile (384,400km) distance between Earth and its Moon. Mars’ gravity is drawing Phobos (the larger moon, Deimos) in. It is approximately 6.6 feet (3 metres) closer every hundred years. Scientists believe Phobos will fall apart in the next 30 or 50million years. New modeling suggests that Phobos may have its grooves produced by tidal force. (Credits: NASA/JPL-Caltech/University of Arizona) Phobos has already begun to fail Terry Hurford, who works at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said: “We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves.” Hurford’s and colleagues’ findings were presented at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society at National Harbor, Maryland, on November 10th. Scientists believed that the grooves formed from an impact on Stickney crater for a while. The impact was so powerful that Phobos almost fell to the ground. NASA’s team discovered that the grooves don’t radiate from the crater, but rather from a central point nearby. Researchers suggest that the grooves may have been caused by tidal forces. Hurford’s team has done new modeling that supports the idea that these marks are more similar to’stretchmarks’ that result from tidal forces deforming Phobos. The gravitational forces that pull on Phobos and Mars cause these tidal effects. Earth and Moon pull together in a similar way, creating ocean tides that make both planet and moon slightly ovale (egg-shaped). After the Viking spacecraft returned images of Phobos, this explanation was put forth for the grooves decades ago. It was believed to have been more or less solid throughout. They found the stresses too weak to break down a solid mass this large when they calculated the tide forces. There are two Mars moons: Deimos (the bigger one) and Phobos (the smaller). Image: svs.gsfc.nasa.gov. Phobos has a heap of rubble. Scientists have recently come to believe that Phobos could actually be an interior made of rubble, with a layer of unconsolidated solid material (roughly meters thick) surrounding it. Erik Asphaug is co-investigator of the research. He works at Arizona State University’s School of Earth and Space Exploration in Tempe. It makes perfect sense when we think of powdery materials in microgravity. However, it is not intuitive. With such an interior, Phobos could easily be distorted. The interior is weak and the outer layer must adjust to any pull it receives. Researchers believe that Phobos’ outer layer acts elastically, and accumulates stress. However, it is so weak that it can fail. The surface can be fractured by the gravity and tidal pull (gravitational pulling) that Phobos experiences. The model predicts stress fractures which are very similar to the Phobos images. The model also predicts that certain grooves will be more recent than others if they are created by an ongoing process. Neptune’s Moon Triton is also slowly falling inward, and has a fractured top. It will likely end in the same manner. Their work has also implications for exoplanets according to the researchers. Exoplanets are planets that orbit stars outside of our Solar System. Hurford stated: “While we can’t see distant planets, this can be used to help understand them. Any kind of planet that falls into its star host could also get torn apart.”
NASA scientists say Mars’ Moon Phobos is slowly falling apart
