The moons of Mars – Deimos and Phobos – are both weird and fascinating at the same time. Their size and orbits meant that their discovery was rather delayed, but when they did happen, they were found within a week of each other. And despite plenty of time having now passed since their discovery, we are still looking to learn more about them and the secrets they hold.
Much before their discovery in 1877, German astronomer Johannes Kepler speculated in the 17th Century that since Earth had one moon and Jupiter had four known moons (during his time), Mars, which orbits the sun between Earth and Jupiter, might have two moons. This might have influenced Anglo-Irish satirist Jonathan Swift, who wrote that the scientists of Laputa discovered “two lesser stars, or satellites, which revolve about Mars” in “Gulliver’s Travels”.
Their real discovery, however, had to wait much longer. The credit for that goes to Asaph Hall, an American astronomer who didn’t always have it easy.
Born into a once prosperous family in 1829, the death of Hall’s father left the family in trying circumstances. He started out as a carpenter’s apprentice at the age of 16 and worked as a carpenter himself three years later. He put the skills he acquired here to good measure when supervising construction of observation shelters during astronomical expeditions in his later life.
As his formal schooling wasn’t regular, Hall was largely self-taught and excelled in mathematics. He met Chloe Angeline Stickney, who taught Mathematics while still studying, and they married in 1856.
Stepping stones
Determined to become an astronomer, Hall started out in a minor position at the Harvard University observatory by 1858. He became an assistant astronomer in the U.S. Naval Observatory and even though his first years at Washington were blighted by the Civil War, he was able to become a professor of Mathematics with the institute a year later.
Hall spent the following years as the assistant observer of telescopes that were large during that age, observing asteroids and comets. He travelled to observe and record eclipses and the transit of Venus, before eventually taking charge of a larger 26-inch telescope in 1875.
Using this, Hall was able to discover a white spot on Saturn, observing which he was able to give a reliable period of Saturn’s rotation, the first such update regarding Saturn’s period in decades. And then, the unusually close approach of Mars in August 1877 set the stage for Haul’s best remembered work.
Never give up
Theoretical predictions suggested Mars’ satellites, if any, should be close to the planet. Based on this, Hall started a systematic search for the moons of Mars. Even though Hall wanted to give up on occasions, Angeline, his wife and an astronomy enthusiast, wouldn’t hear of it.
The perseverance and backing paid off as Hall finally caught a glimpse of Deimos on August 11, 1877. Bad weather meant that he had to wait for a few days before confirming that Deimos was indeed a satellite of Mars. And on August 17, Hall found Mars’ second satellite as well and named it Phobos.
Hall informed his discoveries to Simon Newcomb, the scientific head of the discovery, who took an undeserved claim for these finds. After giving interviews where he claimed responsibility, he later retracted and eventually apologised to Hall, whose role as the discoverer was recognised.
Hall continued as a voluntary observer even after his retirement in 1891. His love for astronomy and mathematics never abated and he taught for another five years at Harvard from 1896-1901, before his death in 1907.
Lots more to learn
The two moons that Hall discovered have maintained a sense of mystery despite the growing tools at our disposal. There is a theory that Phobos will be torn apart by Mars’ gravity in a few hundred million years and transform into a system of rings. Some suggest this would not even be the first time this happens, and posit that it alternates between being a ring and a moon. Deimos, which is smaller than Phobos (which in itself is much smaller than our moon), might, however, have remained the same for a billion years or more.
Our current best bet with finding out more lies with Japan. Japan’s Martian Moons eXploration (MMX mission) plans to arrive at Mars in 2025 and study both of Mars’ small moons. The mission also aims to grab some sample rocks from one of the moons and return it to Earth. If that is successful, it will not only go a long way in unravelling the truths about these moons, but might also help us understand our own Earth better.
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What’s in a name?
The two moons of Mars – Deimos and Phobos – are named after the mythological sons of Ares.
Ares, the Greek god of war, is the Greek counterpart of the Roman god of war. No prizes for guessing what is the name of the Roman god of war. (It is Mars, in case you are wondering.)
Deimos means dread and Phobos means fear (phobias now make more sense, don’t they?)
Deimos and Phobos are brothers, making them an apt choice for Mars’ moons.
Mars’ satellites, however, inspire neither dread nor fear. They are rather small on an astronomical scale and are more like space potatoes going around Mars.
