14 Phobos Moon Facts | Great Facts about Phobos

Phobos is one of the two moons that orbit the planet Mars. It takes its name from the son of Ares, literally meaning “fear”. However, there is little to fear about Phobos, as most of the time it spends its days quietly orbiting Mars, and one day in the future, it will actually be destroyed. Not sure what I mean? Well, you’ll find out in some of these Phobos facts.


Phobos Moon Facts

  1. Phobos has a radius of 11.267km, which is very small when compared to other moons in the solar system.
  2. The Earth is more than 574x the size of Phobos. The two Martian moons, Phobos and Deimos, are relatively small when compared to the moons of Saturn and Jupiter.
  3. It orbits Mars at a distance of around 3,700 mi (6,000km). This is the closest proximity of any moon!
  4. Phobos was discovered all the way back in 1877 by American astronomer, Asaph Hall.
  5. When I said Phobos will be destroyed, I meant it! Due to its orbiting pattern, Phobos gets two meters closer to Mars every 100 years. So in 50 million years time, Phobos will crash into Mars!
  6. Ares is the Greek equivalent of the Roman God, Mars. Ares twin sons were named Phobos (Fear), and the other moon orbiting Mars is named after his other son, Deimos (literally meaning ‘dread’ or ‘terror’).
  7. Out of the two moons, Phobos is the larger object, and it orbits Mars at a closer proximity too.
  8. Astronomers believe that Phobos and its brother Deimos might actually be captured asteroids, due to Mars proximity to the Asteroid belt.
  9. Phobos is known for its strange shape that isn’t spherical, which is one of the reasons it’s believed to be an asteroid.
  10. Japan are going to launch a mission to Phobos in 2024, called the Martian Moon Exploration mission.
  11. The temperatures on Phobos can range anywhere from -4°c to more than -100°c.
  12. Phobos has an orbital period of approximately 7.6 hours, which is how long it takes to orbit Mars fully.
  13. Much like the surface of Mars, Both Phobos and its twin Deimos are both covered in craters from collisions with other objects.
  14. The largest crater on the moon Phobos is called Stickney, after the wife of the discoverer of Phobos. It has a 5.6 mile (9km) diameter., and is likely caused by a previous collision with an asteroid.

Common Questions about Phobos

Will Phobos crash into Mars?

Although nothing is certain, it is believed that one day Phobos will actually crash into Mars. This is because Phobos orbits Mars very quickly, much faster than Mars rotates, which brings it closer and close to the planet, however very, very slowly. It will continue to get closer and closer to Mars over the next millions of years, until it’s close enough to Mars that it will break apart. It may end up forming into Mars, or it may become a ring around Mars.

Is Phobos a dwarf planet?

Phobos isn’t actually large enough to be considered a dwarf planet. However, it is made up of the same materials as a dwarf planet, so it does have the right composition to be considered one if it was larger. The best example of a dwarf planet like Phobos is Ceres, which is a dwarf planet that’s located in the Asteroid belt.

Why is Phobos not round?

A common question about moons like Phobos is why are they so strangely shaped – they aren’t spherical like other moons. The answer is that with planets, they are spherical because gravity pulls from the center of the planet, and makes all of the edges of the planet equal, creating a sphere. Phobos does not have the mass to become spherical under it’s own gravity – if it was bigger, then it would likely be more shape like an ellipse.

Can I see Phobos from Earth?

If you’re trying to see Phobos from Earth, then you’re definitely going to need a telescope – it’s not visible to the naked eye. It is possible to see the tiny moon from Earth, but only at certain times.

How did Phobos form?

A commonly asked question about Phobos is how it formed and became one of the moons that orbits Mars. There are some astronomers that think that Phobos is just an asteroid that has got caught in the gravity of Mars. However, it may have also happened from a collision between two objects, with Phobos being part of the debris.


Hopefully this has helped you learn a little bit more about the moon Phobos. Although it is the larger of the two Mars moons, it’s still tiny in comparison to some of the bigger moons in our solar system, like our Moon or the biggest moon, Ganymede. It can pretty difficult to spot either of the Martian moons from Earth, though it is possible with a telescope that has a high aperture.