An illustration showing how Mars’s rings might look following the destruction of its moon Phobos. Image by Tushar Mittal using Celestia 2001-2010, Celestia Development Team.
While the demise of Mars’s largest moon is not anticipated for another twenty to forty million years, new research suggests Phobos will eventually be torn apart by the gravitational forces that are pulling it towards the Red Planet.
Just as Earth pulls our Moon in different directions – a force that contributes to tides on our planet – so too is Mars’s gravity pulling Phobos inwards, according to a new study.
But because Phobos is fractured and made up of porous rubble, rather than crashing into the Red Planet the moon will likely be torn apart in its atmosphere, potentially creating rings around Mars, like those around Saturn, that could last from one to one hundred million years.
Two earth scientists at the University of California, Benjamin Black and graduate student Tushar Mittal, conducted the research.
They say the largest chunks would crash into the Red Planet and create craters on the Martian surface, while much of the debris would remain in Mars’s orbit and circle the planet for millions of years before dropping to the surface in moon showers.
Mars’s other moon, Deimos, would remain.
“While our moon is moving away from Earth at a few centimetres per year, Phobos is moving toward Mars at a few centimetres per year, so it is almost inevitable that it will either crash into Mars or break apart,” Black says.
“One of our motivations for studying Phobos was as a test case to develop ideas of what processes a moon might undergo as it moves inward toward a planet.”
The researchers say this work is important in studying the planets of our early Solar System, which likely hosted many more moons that have since disintegrated into rings.
Black and Mittal examined data of fractured rocks on Earth and meteorites that have struck Earth that have a density and composition similar to Phobos.
They also looked at results from simulations of the Stickney impact crater on Phobos, which formed when a rock smashed into the Martian moon.
The crater is huge, spanning about one sixth of the lunar circumference.
The duo then modelled the predicted evolution of the ring that might form around Mars following Phobos’s demise.
“If the moon broke apart at 1.2 Mars radii, about 680 kilometres above the surface, it would form a really narrow ring comparable in density to that of one of Saturn’s most massive rings,” Mittal says.
“Over time it would spread out and get wider, reaching the top of the Martian atmosphere in a few million years, when it would start losing material because stuff would keep raining down on Mars.”
It is, however, not clear whether the rings would be visible from Earth, but they might reflect enough light to make Mars appear brighter.
“Standing on the surface of Mars a few tens of millions of years from now, it would be pretty spectacular to watch,” Black says.