In the first volume of his Mars trilogy Red Mars, science fiction writer Kim Stanley Robinson has the larger of Mars’ two moons, Phobos, destroyed after it had been weaponized. Which would be a tragedy IRL, since Phobos may well be a stepping stone to exploring the Red Planet. It could also give us information about the planet remotely and act as a base to guide remote vehicles on the surface of Mars.
Phobos is tiny, just 15 miles in diameter, although the word “diameter” implies a spherical shape — the moon is more potato than ball, too small for gravity to smooth out all its bulges and wrinkles. In the color-enhanced image above, note the large crater on the right. That’s Stickney Crater, named for mathematician and suffragist Angeline Stickney Hall, the wife of Phobos’ discoverer. In 1875, the discoverer Asaph Hall was given responsibility for what was then the largest refracting telescope in the world at the U.S. Naval Observatory in Washington, D.C. He later wrote, “The chance of finding a satellite [of Mars] appeared to be very slight, so that I might have abandoned the search had it not been for the encouragement of my wife.”
Mars and Earth were particularly close in August of 1877, which is when Hall found not one but two tiny moons of Mars, named for the twin sons of Ares (god of war) and Aphrodite (god of love): Deimos (meaning terror) and Phobos (panic). Deimos is even smaller than Phobos, about 8 miles across, so it’s astonishing that Hall was able to spot the two tiny objects.
Phobos is unique in the solar system in that it zips around its parent planet faster than the planet rotates. So fast, in fact, that to someone on the surface of Mars, Phobos would rise in the west, race across the sky and set in the east just four hours later — twice a day. It’s also odd in that its density is uncannily low, so it’s more like a pile of rubble than solid rock. Its low density led Russian astronomer Iosif Sklovsky to suggest, in the late 1950s, that Phobos was artificial: a thin metal skin enclosing a hollow interior. Nice idea, but no alien outpost, as subsequent measurements have shown.
Phobos has attracted the interest of would-be Mars explorers since it would be much easier to land on and take off from the moon than Mars itself due to the moon’s very low gravity. Indeed, if we can figure out how to reliably land on our moon — with many projects currently underway, including NASA’s Artemis program — Phobos should be a snap. The difficulty of landing on and taking off from another body is usually expressed at “delta-v,” essentially the amount of effort to change a spacecraft’s velocity. The delta-v to land on and leave Phobos is less than that for the moon, despite Phobos being over 100 times farther away.
One idea is to establish a base on Phobos and use that as a way station to the surface of the planet. Another is to exploit the resources of the moon, which, according to some, is rich in water and organic compounds, the feedstock of rocket fuel. From the point of view of planetary scientists, who are more interested in knowledge than exploration, potentially there’s a huge benefit in obtaining samples of rock and dust from Phobos and returning them to Earth for analysis. Three previous Russian attempts at doing this failed, but a Japanese probe to Phobos, the Martian Moons exploration (MMX), is scheduled to launch next year, returning to Earth in 2031. Samples from Phobos should include some small percentage of dust from Mars itself, giving cosmochemists a glimpse into the stuff that the planet’s made from and, with a great deal of luck, telling us if it was ever home to extraterrestrial life. All without actually landing on Mars.
Barry Evans (he/him, barryevans9@yahoo.com, planethumboldt.substack.com) notes that Carl Sagan drove an orange Porsche with license plate PHOBOS.
This article appears in Global Solidarity at the Mouth of the Klamath.
Moving about in extremely low gravity? Yikes! would not take much to just fly away into the great abyss. Perhaps it could become an art project for heavy sculpture.