Mars, the fourth planet from the Sun, is a reddish brown world, dry and dusty with a thin atmosphere, covered mostly by freezing cold deserts. But it also one of the most exciting places humans have ever studied. Mars is about half the size of the Earth, and about one tenth of its mass. This means that if you were standing on Mars you would feel about half as heavy as you do on the Earth. It is about one and a half times further from the Sun than the Earth, and so the Sun appears about half as bright on Mars.

The surface of Mars is a tough place. At night it can be colder than the coldest places in Antarctica and during the day it is never warmer than about 68 F. Days and nights last about the same as on Earth – a complete day and night on Mars is 24 hours and 40 minutes. A Martian year lasts for about 687 Earth days. One of the biggest differences from the Earth is that the Martian atmosphere is much thinner than the Earth’s. Standing on Mars is like being twenty miles up in the air on Earth (about four times higher than Mt. Everest). The other big difference from the Earth is that there is almost no oxygen in Mar’s atmosphere. It is mostly Carbon Dioxide (95%) and a little bit of Nitrogen (3%) and about 1% Argon. The Argon on Mars, just like the Argon on the Earth, comes from the radioactive decay of a type of Potassium.

Think about it

Although there is frozen water on Mars, at the North and South Poles, and there is water vapor in the atmosphere, there is no liquid water anywhere on the surface. This is because Mars has such a thin atmosphere. Water can’t exist as a liquid for very long when the pressure of the atmosphere is as low as it is on Mars, so it changes from a gas to a solid and vice-versa, without ever being liquid. Because liquid water is key for life then it may be that any life on Mars is underground, where it can be warmer and where the pressure might be high enough for water to stay liquid.

Image of the thin Martian atmosphere seen from orbit


Climate on Mars

One of the biggest questions about Mars is whether millions or billions of years ago it used to be more like the Earth, with oceans and a thick atmosphere, and possibly with life on the surface. Today Mars is covered with craters from meteorites and other objects that have crashed into it. The thin atmosphere doesn’t protect Mars as much from these things as our thick atmosphere on Earth does. Mars is also incredibly dusty. With little or no water on the surface, and harsh chemicals, then the Martian rocks have been worn down into fine dust that is blown around the planet, sometimes in huge dust storms.

Image of Mars taken by the Hubble Space Telescope.
The white patches of frozen water ice, together with frozen carbon dioxide ice at the north and south poles of Mars also show the brownish haze of giant dust storms that cover half the planet.


Martian Geology

Scientists are very interested in the geology of Mars – the study of its rocks, their composition, ages, and the study of its mountains, volcanoes and other features. Geology can tell us about the history of Mars, and give use clues to why Mars is so different from the Earth, and what it might have been like millions and billions of years ago. By looking at the types of rocks and minerals, and the way the Martian landscape has been shaped, scientists think that billions of years ago Mars may have had much more water, in liquid form on the surface.

At three times the height of Mt. Everest on Earth then Mar’s giant volcanic mountain Olympus Mons is the tallest feature on Mars, and the tallest such object in the Solar System!

Image of Olympus Moons – looking down from space


Mars also has the largest canyon know in the Solar System. This is Valles Marineris, a great rift or “crack” in the surface of Mars that is an incredible 2,500 miles long, 120 miles wide and at its deepest going down 4 miles!

Image of Valles Marineris from space



Mars has two small moons called Phobos and Deimos, about 13 and 10 miles across. They are lumpy and not at all spherical because they are too small for their gravity to squash them into a round shape. They are both probably asteroids that were captured into orbits around Mars when they came too close tens of millions of years ago.


Humans have been sending robotic probes to Mars for over 40 years. Many of these either flew by Mars or orbited it and took images and other scientific data to measure things like magnetic fields and the chemicals in the atmosphere and on the surface. Some probes have actually landed on the surface of Mars and have studied the rocks and soil and sent back thousands of pictures. Two of the most successful probes have been the twin robotic rovers Spirit and Opportunity, each exploring a different part of Mars. Unfortunately, no human has visited Mars yet. Many scientists and engineers are busy planning for a trip to the planet, and think that this could be a first step towards human exploration of the rest of space. If getting to the Moon was tough, getting to Mars is even harder! But some people think that the first person to set foot on Mars is already somewhere on Earth today. Could it be you? No one has gone yet, so that historic chance to be the first man or woman to visit another planet is still open!

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