Phobos (Moon of Mars)

Phobos Facts

Phobos is a moon of Mars and is about 4.5 billion years old, about the same age as Mars. It is heavily cratered and looks a bit like a potato, with a prominent crater on one end of it.

The crater is named Stickney. This was the maiden name of Asaph Hall’s wife. He was the one who discovered Mars’ moons in 1877!


Phobos Overview

Diameter: Its diameter is only 14 miles (22km). That’s pretty small.

Distance from Mars: It is 5,827 miles (9,377km) away from Mars.

Orbit around Mars: It orbits around Mars every 7 hours and 39 minutes.

Temperature: The surface temperature is -124.7°F (-40.15°C)

The Orbit of Phobos

  • Phobos orbits closer to Mars than any other Moon in the solar system. That means, of all the moons orbiting Jupiter, Saturn, and Neptune and beyond, none are closer to their planets than Phobos is to Mars.
  • Phobos’ orbit is so fast that if you were looking at it on the planet it would look as if it was rising in the west and setting in the east each Martian day.

Phobos facts

Phobos and Mars

  • Every single time Phobos orbits around Mars it is getting closer and closer. Eventually it will be destroyed by Mars’ tidal forces. This will probably only happen in several tens of millions of years. We sure won’t be seeing this in our time.
  • It is quite likely that it will break up in orbit and its pieces will be scattered onto the surface of Mars and also spread out across its orbit. This might cause a ring, that won’t last too long.
  • The shadow of Phobos has been photographed from the surface of Mars by quite a number of spacecraft.

What does Phobos look like?

  • We already know that Phobos looks a bit like a potato, with the large crater being called Stickney. What you might not know is that most of its largest features are named after places from the book Gulliver’s Travels.
  • No one really knows where Phobos was formed. It has the same make up and characteristics of an asteroid. It’s quite possible that it’s a captured asteroid. There is however some debate over whether this is true or not.
  • The moon has a fine dusty layer on the surface called ‘regolith’. Some astronomers have predicted that this material drifts away and leaves behind a very faint tail.
  • Phobos has sure had its turn in being studied. Nearly all of the missions that have gone to Mars have studied this moon.

phobos falling apart

Photographs of Phobos

  • The first real photograph of Phobos was taken by the Mariner 9 spacecraft in 1971. Since then, it has been photographed eight more times by Viking 1, the Mars Global Surveyor and the Mars Reconnaissance Orbiter. Two probes were sent to Phobos by the Soviet Union in 1988, but neither was able to gather any information.

A mission to Phobos?

  • There has never been a direct mission to explore Phobos; however they’ve been looking into it for a long time. There is a recently funded project called Phobos and Demos and Mars Environment (PADME) and they will launch to Mars and be expected to land in about 2021.
  • There has been talk of at least one human mission to Phobos, using it as the staging area for missions that would later go to Mars’ surface. It would be interesting to see what they find.

Martians on Phobos?

  • In the 1950s, some astronomers believed that Phobos might be hollow. It turned out to be false, but for about ten years, some very prominent scientists believed that Phobos could have been created by Martians.

Phobos is certainly an interesting moon, with a very interesting shape. We hope you enjoyed these facts about this moon of Mars!

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