The two lumpy months, Phobos and Deimos, were discovered in 1877 and named the sons of Ares from Greek mythology (Mars is named after the Roman god of war, Ares in Greek). Phobos means fear or panic and Deimos means fear.
They have long been thought to actually be asteroids captured by the planet’s gravity. Both appear similar in composition to blackish carbonaceous chondrite asteroids. But scientists have realized that the moons are about the same plane as the Martian equator. This indicates that they were formed around the same time that Mars did around 400 billion years ago.
While they are both irregular, Deimos is little more than an oddball than Phobos – its orbit is tilted by two degrees.
“The fact that Deimos̵7;s orbit is not exactly in the plane of the Mars equator is considered insignificant, and nobody cares to try to explain it,” said Matija Ćuk, lead author of the study of lead and research scientist at SETI Institute. “But once we had a big new idea and we looked into it with new eyes, Deimos’s orbital tilt revealed its big secret.”
A cycle of fortune for the month of Mars?
Researchers looked at Phobos, who lost height while interacting with the Martian extreme over time. Eventually, its orbit becomes too low and Mars essentially rips it into pieces that form a ring around the planet. It is estimated to occur within 50 million years.
What if Mars had other months that met the same fate? Over time, the rings will form a new, smaller moon in a seemingly endless cycle.
Something pushed Deimos away from the planet and caused him to tilt – like contacting another, larger moon.
Phobos, slightly larger than Deimos, is only about 3,700 miles above the Martian surface – no known moon in our solar system is closer to its planet. Being so close, Phobos completes three orbits around Mars on one Earth Day, while Deimos, farther away, takes about 30 hours of Earth to complete an orbit.
But what if Phobos isn’t always, well, Phobos? How can it sometimes be bigger and go through a few cycles where it went from a month to a ring, and back again?
Researchers believe that Phobos used to have a grandmother 3 billion years ago when they called proto-Phobos – probably 20 times as big as small moons today. Over the course of a few cycles of the moon, it became Phobos – which explains why some researchers believe it was formed only 200 million years ago.
A prominent ring around Mars will push out proto-Phobos, away from the planet. It will also affect the effect of the proto-Phobos orbital on Deimos and also push it from Mars.
The Japanese space agency, JAXA, plans to send a spacecraft to Phobos in 2024 to collect samples from the surface and return it to Earth. It may reveal more about the past of the month.