The two moons of Mars, Phobos and Deimos, may have been created billions of years ago during a massive impact, according to a new research. The object which collided with Mars would have been almost 500 miles in diameter, roughly the size of Ceres, the largest member of the asteroid belt.
Phobos and Deimos are both very small, just 14 and 7.5 miles across, compared to our own moon, which is over 2,100 miles in diameter.
Other moons may have also been formed during such an impact, although they were likely short-lived.
Doctor Julien Salmon, a research scientist at the Southwest Research Institute explains a likely scenario:
“The outer portions of the disk accumulate into Phobos and Deimos, while the inner portions of the disk accumulate into larger moons that eventually spiral inward and are assimilated into Mars.”
For decades, astronomers have questioned the origin of the dual moons of Mars, but no theory fully explained all the data seen in the composition and behavior of the satellites.
Most astronomers believe our own moon was created during a similar, but much larger, event in the distant past.
In 2029, the Japanese space agency, JAXA, will send a mission to explore the moons of Mars, and return a sample of the surface of Phobos to Earth for examination.