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Earth and Mars

Mars Compared to Earth. Image credit: NASA/JPL

Mars Compared to Earth. Image credit: NASA/JPL

Earth and Mars are two of the rocky terrestrial planets that orbit within the inner Solar System. In some ways they are very similar, but in other ways, they couldn’t be more different. Let’s take a look at Earth and Mars and consider their similarities and differences.

The origin of Earth and Mars is the same for all of the planets in the Solar System. Scientists believe that the Sun, the planets and everything in the Solar System all formed at the same time within the solar nebula; a giant cloud of cold molecular hydrogen. The Sun formed in the middle of the Solar System, and its rapid rotation created a flattened disk of material surrounding it. It was from within this disk that Earth and Mars and all the planets formed.

Both Earth and Mars are terrestrial planets, made up of rock and metal. We know quite a bit about the internal structure of Earth, but can only guess at the structure of Mars. Scientists think that both planets have an inner core of metal surrounded by a mantle of rock. A thin crust covers the mantle. Since Mars is a smaller world, it’s believed that it cooled faster, so it’s crust is thicker. Mars lacks a magnetic field, so it probably doesn’t have a rotating liquid metal core like we have here on Earth.

Unlike Earth, Mars has no plate tectonics. Perhaps it was because of this rapid cooling, but the crust on Mars is one thick shell surrounding the entire planet. While plate tectonics are constantly resurfacing planet Earth, we can see that the surface of Mars is ancient, hammered by thousands of meteorite impacts. The lack of plate tectonics also allowed hotspots in the mantle to remain in the same position for billions of years. This was how the largest volcanoes in the Solar System, such as Olympus Mons, could get so big.

Mars is small. At only 6,792 km across, it’s about half the diameter of Earth, and has only 10% of the Earth’s mass. This means that it has a much lower surface gravity than Earth. If you could stand on the surface of Mars, you would only experience about 1/3rd the gravity you have on Earth. You would be able to jump 3 times higher than you could on Earth.

Earth and Mars also share water. But here on Earth, water is everywhere; the oceans account for 71% of the surface area of the planet. Mars looks dry and dusty, but there are vast deposits of water ice at the planet’s northern and southern poles. It’s thought that Mars had large quantities of water on its surface billions of years ago; there’s evidence of flooding and ancient river valleys. But that water is long gone. What water remains is locked as ice underneath the ground.

Of course, the biggest difference between Earth and Mars is life. Here on Earth, life is everywhere – you can see the green forests from space. Mars looks dry and dusty, and no spacecraft sent to Mars have found any life. Scientists think there could be life hiding underground with water, or inside rocks, but nothing has been found so far.

We have written many articles about Mars for Universe Today. Here’s an article about ancient groundwater flows on Mars, and here are some photos of the deepest canyon on Mars.

If you’d like more info on Mars, check out Hubblesite’s News Releases about Mars, and here’s a link to the NASA Mars Exploration home page.

We have recorded several podcasts just about Mars. Including Episode 52: Mars and Episode 92: Missions to Mars, Part 1.

NASA Solar System Exploration: Earth-Mars Comparison Chart
NASA: Earth and Mars


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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