A mysterious vertical rock formation, akin to the monolith in Arthur C. Clarke’s novel and Stanley Kubrick’s film 2001: A Space Odyssey, towers above the surface of Mars’ 17-mile-wide and deeply-grooved moon Phobos. The origin of the monolith and even Phobos itself, which means “fear” in Greek, is unknown. The monolith may explain Russia’s almost mystical obsession with Phobos. First the Soviet Union, then more recently, Russia, made three attempts to reach the enigmatic object, but software errors and launch disasters have aborted each attempt.
In 2016 the BBC reported to the public that a mysterious monolithic object was spotted several years earlier on Phobos by a NASA probe, and to this day nobody is quite sure what it is or how it got there. “When people find out about that they are going to say, ‘Who put that there? Who put that there?’” said Buzz Aldrin, the second man to walk on the Moon, in 2009 about the peculiar and solitary large rock that sits on the surface of Phobos.
Japan’s MMX Mission
Back to the present: Japan is on deck, planning to launch its MMX mission to Phobos in 2024 for rock samples to decode the chemistry of the odd moon and decipher its origin as well as providing clues to the existence of life on ancient Mars, reports Robin George Andrews for the New York Times. Meteors crashing into Mars could have coated Phobos in a layer of Martian dust that may be both very young and extremely old, “showing how Mars may have progressed from a habitable world to an uninhabitable one,” says Tomohiro Usui, a robotic planetary exploration expert with the Japan Aerospace Exploration Agency, currently working at NASA’s Johnson Space Center.
“They’re super weird, confusing and interesting,” said Abigail Fraeman, a planetary scientist studying Mars, Phobos and its tiny sister moon Deimos at NASA’s Jet Propulsion Laboratory. “They check all of the boxes that are consistent with them being these captured asteroids,” said Fraeman — “rubbly patchworks that drifted too close to Mars long ago and became trapped in the planet’s orbit. “They just shouldn’t exist,” added Fraeman. “They don’t make any sense.”
Primitive Captured Asteroids?
The debate over the origin of the two moons has split scientists for decades, since the early days of planetary science. In visible light, Phobos and Deimos look much darker than Mars, resembling the primitive asteroids of the outer solar system, suggesting the moons might be asteroids caught long ago in Mars’ gravitational pull. But the shapes and angles of the moons’ orbits do not fit the capture hypothesis, with some scientists suggesting the moons must have formed at the same time as Mars, or resulted from a massive impact on the planet during its formative millennia.
Stickney Crater Clues
A 2018 Brown University study suggests that the strange distinctive grooves crisscrossing the surface of Phobos were made by rolling boulders blasted free from an ancient asteroid impact that created the Stickney crater, a huge 9-kilometer gash on one end of Phobos’ oblong body shown at top of the page. Computer models show that boulders rolling across the surface in the aftermath of the Stickney impact could have created the puzzling patterns of grooves, first glimpsed in the 1970s by NASA’s Mariner and Viking missions. Some scientists suggest that Mars’ gravity is slowly tearing Phobos apart, and the grooves are signs of structural failure.
In fewer than 100 million years, said Matija Ćuk, a research scientist at the SETI Institute in Mountain View, Calif., Phobos, which may have been assembled just 200 million years ago, will get so close to Mars that its gravity will tear the moon apart, transforming into a mini Saturn-like system of rings.
“It won’t be the first time, some scientists say,” reports the New York Times “Recent calculations suggest that Phobos was once 20 times more massive. But, as one hypothesis goes, it drifted toward Mars and shattered into ring material, much of it raining onto Mars. The remaining ring material clumped together into a new, smaller Phobos. This cycle has repeated several times over billions of years, with Phobos shrinking with every completed cycle.”
Scientists may get their answer to Phobos’ origins in the next couple of years, when the Martian Moon eXploration spacecraft completes its mission to collect samples and return them to Earth for analysis.
Image credit: NASA/JPL/University of Arizona