Moons of Mars - Facts for Kids

Moons of Mars - Facts for Kids
Phobos (the large moon) and Deimos captured together by ESA’s Mars Express Orbiter. [Credit: ESA/DLR/FU Berlin]

Earth's moon is the Moon because it was the only moon anyone had ever seen until 1610. That's when Galileo discovered moons orbiting Jupiter. It took until 1877 to discover the moons of our neighbor Mars.

American astronomer Asaph Hall discovered the two Martian moons.
Hall chose the names Phobos and Deimos (Fear and Panic), because they were the sons of Ares. Ares was the Greek name for the god the Romans called Mars. Phobos and Deimos drove Ares's chariot into battle to terrify the enemy. Even today, if you have a great fear of something like high places or spiders, it's called a phobia.

Phobos is bigger than Deimos, but they're both tiny.
The moons are too small for their own gravity to pull them into a rounded shape. They're shapeless and lumpy with lots of craters. Phobos is only 22 km (14 mi) across on average and tiny Deimos is about 12 km (8 mi) across.

Why did it take so long to find the Martian moons?
Besides being small, they also orbit very near to Mars. Until Asaph Hall searched, no one had looked that close to the planet. For example, the Moon is 384,000 km (240,000 miles) from Earth. However Deimos is just 23,500 km (14,600 mi) from Mars. Phobos is even closer at 9400 km (5800 mi) – Earth has artificial satellites in higher orbits than that.

Phobos has a crater that's over six times as wide as Earth's famous Meteor Crater in Arizona, USA.
In the distant past, something big hit Phobos. It was so big that it nearly smashed the moon to bits. The impact left a crater which has been named Stickney after Hall's wife Angeline Stickney.

The moons orbit so close to the surface of Mars that an astronaut on Mars couldn't see them from the polar regions.
Since the moons are in circular orbits around the Martian equator, the equator is where you'd get the best view. You could see a full Phobos as big as one-third the size of a full Moon, and Deimos might look about the size Venus does from Earth. If you started traveling away from the equator, you'd see the moons lower and lower in the sky, until they were hidden below the horizon.

Moonrises and moonsets on Mars aren't like the ones we're used to.
Our Moon orbits from west to east in about 27 days. Earth turns on its axis in 24 hours, so the Moon doesn't get very far in a day. As we turn eastward and first see the Moon, it seems to rise in the east. Then as we leave it behind, we see it set in the west.

Mars takes a bit more than 24 hours to turn once on its axis, but its moons don't dawdle for weeks getting around it. Deimos takes about 30 hours to orbit, so it doesn't quite keep up with Mars. From Mars, Deimos seems to move very slowly, taking 66 hours to rise in the east and set in the west.

Phobos, on the other hand, orbits much faster than the planet turns. It's moving so much faster than Mars, it seems to be going backwards. Looking up from Mars, you could see it rising in the west and setting in the east, maybe three times a day.

Astronomers used to think that the shapeless little moons were captured asteroids.
Many astronomers now think that it's more likely that the moons were created in a collision between Mars and another large body. The impact sent material flying away into an orbiting ring where it clumped together to make the two moons.

In the distant future, Mars won't have any moons.
The gravitational forces between planets and their moons cause tidal effects. The rotation of Mars is slowing a tiny bit, and Deimos is slowly moving into a higher orbit. Millions of years in the future, it will escape Mars to become an asteroid.

Poor Phobos is another story. It's dangerously close to Mars and is being slowly pulled closer. It could eventually crash into Mars. However, the tidal forces will probably pull it apart before then. It will once again become a ring of debris orbiting the red planet, making Mars the only inner planet with a ring. That would be a sight worth seeing if anyone's around about 50 million years from now.

You Should Also Read:
Jupiter's Moons - Facts for Kids
Mars - Facts for Kids
Saturn's Moons - Facts for Kids

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