Phobos will be torn apart by Mars' gravitational pull in millions of years

Now they believe they're the first signs of the moon being under stress

They thought they were left over from a massive impact

Grooves on the surface of Mars’ largest moon suggest it is being destroyed by its parent planet.

While scientists have long suggested it is doomed to be destroyed, the ‘extensive system of grooves’ the first signs that the rocky satellite is gradually been torn apart.

They were first spotted in the 1970s, but new analysis shows the grooves match up with regions being put under stress.

Doomed: Grooves on the surface of Mars’ largest moon suggest it is being destroyed by its parent planet. While scientists have long suggested it is doomed to be destroyed, the ‘extensive system of grooves’ the first signs that the rocky satellite is gradually been torn apart

Experts have predicted Phobos, perhaps aptly named after the character fear and panic in Greek mythology, will eventually be destroyed because it us so close to Mars that the planet’s tidal pull is shrinking its orbit.

In millions of years, it is expected these forces will rip the moon apart before its pieces smash into Mars.

Experts first learned of the moon’s long, parallel grooves measuring 328 to 656 feet (100-200 metres) wide and 33 to 98 feet (10-30metres) long when the area was surveyed by the Mariner 9 and Viking orbiters in the 1970s.

They assumed they were cracks made by a large impact, or rows of debris on a homogenous lump of rock.

The grooves (shown) were first spotted in the 1970s, but new analysis shows they match up with regions being put under stress. Some believe the linear features are the result of an impact that formed Stickney crater

THE MARKINGS OF PHOBOS Phobos is the larger and closer of Mars' two moons, the other being Deimos. They were both discovered in 1877. Irregularly-shaped Phobos has an average radius of seven miles (11km) and is seven times larger than Deimos. Phobos is 3,700 miles (6,000km) from Mars and has the closest orbit of any known planetary moon. It is so close that it orbits Mars faster than Mars rotates, and completes an orbit in just 7 hours and 39 minutes. Due to tidal interactions, Phobos is drawing closer to Mars by one meter every century, and it is predicted that in 50 million years it will collide with the planet or break up into a planetary ring. It was thought that mysterious grooves on the moon were markings as the result of an impact, but nor scientists say they are the first sign the rocky body is under stress. Advertisement

But in 2008, the Mars Express spacecraft revealed that Phobos is really a ball of rubbish stuck together by a thick layer of dust, meaning the grooves were unlikely to have been caused by a massive impact, which could have blown the rocky body apart.

Terry Hurford, of Nasa’s Goddard Space Flight Centre in Greenbelt, Maryland, calculated the effect of stress tidal forces on Phobos using a computer model.

‘We calculate the surface stress field of the de-orbiting satellite and show that the first signs of tidal disruption are already present on its surface,’ his team write in the study.

‘Most of Phobos’ prominent grooves have an excellent correlation with computed stress orientations,’ it says, meaning that the marks are aligned with regions under the most stress.

Dr Hurford, who will present the results at a meeting of the Geological Society of America, said: ‘The grooves are the first sign of tearing it apart.’

There is a theory that the grooves may be faults, which could explain why some of them seem to cross each other’s paths.

Experts first learned of the moon’s long, parallel grooves measuring 328 to 656 feet (100-200 metres) wide and 33 to 98 feet (10-30metres) long when the area was surveyed by the Mariner 9 and Viking orbiters in the 1970s. An illustration showing the larger of Mars' two moons near its parent planet is shown

The study says: Our model results applied to surface observations imply that Phobos has a rubble pile interior that is nearly strengthless.

It suggests the moon is held together by a flexible outer layer of dust.

‘This outer layer behaves elastically and can experience significant tidal stress at levels able to drive tensile failure.

‘Fissures can develop as the global body deforms due to increasing tides related to orbital decay.’

The researchers write: ‘Phobos may have an active and evolving surface; an exciting target for further exploration.’

They believe their findings could help the study of another satellite in our solar system – Triton, which is one of Jupiter’s moons and one of the few known to be geologically active.

While the study may seem dramatic, Dr Hurford believes Phobos will survive for millions of years.