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Planet Mars's Moons: The Oddness Of Phobos And Deimos

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Published on April 7th, 2011 | by Yellow Magpie


Planet Mars’s Moons: The Oddness Of Phobos And Deimos


Planet Mars

Many of our ancestors have gazed upon our Moon and wondered if other planets had their own satellites. But the planet that people wondered about the most was planet Mars. Did it have its own moon and was it like our? What would it be like to set foot on Mars and gaze up at Planet’s Mars’s moons.

Over a century ago, people had their answer and planet Mars revealed that not only had it one Moon it had two. These moons were completely different to that of the Earth, both in size and appearance. What’s more their origin presented even more problems.

The Moons Of Planet Mars

Phobos is Mars’s largest moon. Nonetheless, it is tiny in comparison to our the Moon, at just 22 kilometres in diameter (13 miles). It is so small that Phobos is not spherical in shape. Phobos also orbits very close to the Martian planet at just 9,300 kilometres (5,800 miles) away.

Phobos Planet Mars's Largest Moon

Unlike the Moon, which is receding from the Earth, Phobos is slowly being drawn closer to Mars where it will eventually be ripped apart before crashing onto the surface. This will probably occur 11 million years from now.

The Strange Orbit Of Planet Mars’s Moon: Phobos

Because Phobos is so close to planet Mars, its orbit is very strange. It travels around Mars twice a Martian day which is very unusual for a moon. This is unlike our own Moon and the Earth which orbits around out planet once every day. This is called a synchronous orbit.

The International Space Station has a non synchronous orbit although, because it is much closer to the Earth, it goes around our planet every 90 minutes or so.

Viking Probe Undergoing Tests

Phobos’s orbit puzzled many scientists during the 1950’s and 60’s. Data that was gathered suggested that the moon was much lighter than was previously realised. This led some astrophysicists to speculate that the satellite was artificial and created by alien life.

Phobos Passing Across The Sun (Transit) As Seen From Planet Mars

Some time later it was revealed that the data was erroneous. Although it is believed that the moon is largely porous.

The Viking probes of the 1970’s revealed pictures that clearly showed the satellite to be entirely natural and not created by Martians.

Deimos: Planet Mars’s Moon

The second-largest Martian moon is Deimos at 15 kilometres (nine miles) in width. However, Deimos orbits much farther out at 23,500 kilometres (14,580 miles).

Deimos Planet Mars Second Moon

Only two of Deimos’s geological features have been named. These are the Swift and Voltaire craters named after people who wrote about the possibility of Mars having its own moons.

Asteroid Origin?

Phobos and Deimos’s irregular shapes have led astronomers to speculate that both moons were once stray asteroids that were captured by Mars’s gravity.

The Asteroid Belt

The only problem with this theory is that in order to capture an asteroid a lot of energy must be somehow dissipated (the speed of the asteroid must be reduced).

Currently, it has been calculated that the Martian atmosphere is too thin to aid with dissipation, or slowing down the asteroid. Another offshoot of the asteroid hypothesis suggests that the moons were created as a result of Mars capturing a binary asteroid. These two asteroids would have been slowed down by the Martian tides.

An alternative theory to the asteroid origin is that there was a collision between a large body called a planetesimal that created the irregular shaped moons.

Hall’s Discovery

Both Phobos and Deimos were discovered on the same day by the American astronomer, Asaph Hall, on August 12, 1877. Unlike, many other discoveries that were accidental, Hall was purposefully looking for planet Mars’s moons.

Now that we have discovered planet Mars’s moons perhaps the next biggest challenge would be to land on them. A feat that no doubt would enthuse future dare-devils. It would also be an event that would make the Moon landing of 1969 pale into significance, such is the difficulty required.

Although Phobos and Deimos have now been given names and faces, thanks to space probes that have amassed pictures, we still have yet to see them in the flesh. Who knows what great things these two moons will inspire in the future.

Highly Recommended Reading

Check out Yellow Magpie’s The Planet Mars: Our Infatuation With The Red NeighbourMars’s Volcanoes: A Stunningly Mysterious World With Colossal VentsTerraforming Mars: How To Create Another Home PlanetThe Planet Mars And The Valles Marineris: A Wonderland Of Canyons and The Red Planet And Water: Is There Life On Mars? for a more in-depth look at the Red Planet.

You may also like to take a gander at The Solar System And Beyond: A Guide To The Cosmos.

Cosmos is a highly recommended book. It contains large, full-page pictures of Mars and writing on the subject by the highly competent author, Giles Sparrow.

For people living in Ireland or the United Kingdom, you can access: Cosmos from here.

For those who live in Canada, you can obtain: Cosmos here.

For Germany: Cosmos.

For France: Cosmos.

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