Mars' moon Phobos is slowly being pulled apart by tidal forces and scientists expect it to be destroyed in 30 to 50 million years, a new study has found.

The larger of Mars' two moons Phobos is closer to the planet than any other in the solar system, orbiting at only 3,700 miles (6,000 kilometers) above the surface and being pulled closer by two metres every hundred years, reported Space Coast Daily.

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Scientists say Phobos has already begun showing signs of its eventual demise, with imagery showing grooves in the moon's surface that indicate stress marks caused by the forces produced in the gravitational pull between Mars and the moon.

"We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves," said Terry Hurford of NASA's Goddard Space Flight Centre.

According to Science Daily, the grooves were originally thought to be fractures from an asteroid impact, as Phobos was more-or-less solid the entire way through, meaning that the tidal forces were not strong enough to pull the moon apart.

But new modelling indicated the grooves were actually "stretch marks" that occur when the moon is deformed by forces, and Phobos could actually be a rubble pile that is barely being held together and surrounded by a layer of powdery rock, dust and soil about 100 metres thick.

Researchers also noted that the grooves did not radiate from the impact crater but rather from a focal point nearby, further strengthening their theory, reported ABC News.

The same grim fate may also await Neptune's moon Triton, which has a similarly fractured surface and is collapsing inward.

Dr Hurford said the findings have implications for extrasolar planets, or planets outside our own solar system.

"We can't image those distant planets to see what's going on, but this work can help us understand those systems, because any kind of planet falling into its host star could get torn apart in the same way," he said.

TagsMars' moon Phobos, NASA's Goddard Space Flight Centre, NASA, Phobos, NASAs space center, Phobos Craft, Space flight Centre, Mars