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The diameter of Mars is 6,792 km. That makes the Red Planet about 53% of the diameter of Earth. In addition to a smaller diameter, Mars has only 10% of Earth’s mass. Those are interesting pieces of information to have, but only give a small picture of what Mars is like. Here are some more facts about Mars.
The gravity on Mars is only 38% of that on Earth. That would present some interesting issues for any visitors to the planet as well as some challenges to long term colonization. The low gravity can also be connected to the near absence of a Martian atmosphere and the cold, dry environment. Gravity helps atmospheric gases to cling to a planet’s surface. Mars can only cling tenuously. What atmosphere that is present is high in carbon dioxide, so if the planet retained more of it, the surface would warm quickly through a greenhouse effect. The greenhouse effect would melt the subsurface ice that the Mars Express spacecraft has found, thus moistening the surface. There are many indications from different spacecraft that Mars was at one time a warmer, wetter world.
Mars is often perceived as a dead planet. Scientists had begun to accept that possibility until methane was detected in its atmosphere. The methane is most likely from a geologic source, but it has to be a large source. Methane is quickly destroyed in the Martian atmosphere in a variety of ways, so discovery of substantial methane indicates that an ongoing process is releasing it. The presence of the gas is of interest to scientists because organisms release much of Earth’s methane; however, other processes, like oxidation of iron, also release methane.
Mars lacks any tectonic plate movement. That may allow the source of the methane to release it in plumes. The lack of plate tectonics is also the reason that the largest mountain in the Solar System was able to form. Olympus Mons, on Mars, is a shield volcano that is 27 km tall and about 550 km across. The absence of plate tectonics allowed a single hotspot to pour molten material onto the surface uninterrupted for millions of years.
You started out wondering what the diameter of Mars is and, now, you have several interesting facts to ponder. Be sure to double check our facts on the NASA website and, hopefully, you will find much more to pique your interest.
And just in case you’ve heard this hoax going around, Mars will never look as big as the Moon in the sky. That’s a myth that got started back in 2003, and just won’t go away.
Here’s a 1928 research article where the diameter of Mars was accurately calculated. And then the sophisticated gravity measurement instrument on board NASA’s Mars Reconnaissance Orbiter, that can make extremely accurate gravity measurements of Mars.
Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.