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In this section: MARS | Europa | Titan
- Mars is the planet in our Solar System that is most similar to the Earth
- Primitive life could survive around hydro-thermal vents near the planet's surface
- Nowadays it may be too cold for life to exist there. But organisms may have thrived in the past
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The Beagle 2 Probe |
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In June 2003, the Mars Express probe set out for the Red Planet, searching for
life. Sadly, it was lost in action.
 Artist's impression of the Beagle 2 probe |
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In science fiction stories, Mars is the favourite home of aliens. No one has found any green Martians wandering over the planet. But many scientists believe that Mars may be the best place to look for simpler forms of life.
Of all the planets in the Solar System, Mars is the most similar to Earth.
Why is Mars like Earth?
- It has a similar temperature
At present, it's too cold for liquid water to exist on the surface. But the planet may have been warmer in the past.
- It has an atmosphere
The atmosphere is much thinner than on Earth. Plus there's not much ozone to protect the planet from the Sun's harmful UV rays. But the atmosphere may have been thicker millions of years ago.
- It has a rocky surface
This makes it easier for life to get a foothold. On rocky planets, all the necessary chemicals for life can collect in one place, rather than floating freely through a gassy atmosphere.
- It has polar ice caps
These expand and contract with the planet's seasons. Although the ice is mostly frozen carbon dioxide, there is probably water there too. So like the Earth, Mars could also have a water cycle.
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Percival Lowell's drawings of canals on Mars |
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Canals on Mars?
When 19th century astronomers looked at Mars, many saw lines criss-crossing the planet.
Percival Lowell was convinced that these lines were canals, built by a race of intelligent Martians. In fact, they were just an optical illusion.
 Find out more about the surface of Mars in our travel guide to the Solar System
Will we find life on Mars?
 | | Were these gullies formed by liquid water? |
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Although it's probably too cold for life to exist on the surface of Mars, it could exist in warmer pockets below ground. Micro-organisms could be living around hydro-thermal vents near the planet's surface.
In the past, Mars was a very different world. The Mars Global Surveyor probe found evidence that there was running water on the planet's surface. This would have made the planet much more hospitable to life.
Why is water essential for life?
A change in Mars' climate may have killed off primitive life forms early in the planet's history. If so, we may find fossilised evidence of life on Mars. Only time will tell.
The Martian meteorite
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Are these fossilised bacteria - or just mineral deposits? |
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In 1996, NASA scientists announced that they may have proof of life on Mars. They had found what looked like fossilised bacteria in a meteorite that had once been part of the Red Planet.
The scientists knew the meteorite was from Mars because it contained traces of gas similar to that found in the Martian atmosphere. By studying it, there were able to tell that it had once had liquid water flowing through it. They also detected organic chemicals similar to those found when bacteria decay.
But many experts are still not convinced that the objects in the meteorite are fossils. They are a lot smaller than bacteria on Earth. They are also a similar shape to many naturally occurring mineral deposits. The argument rages on.
Explore Europa, Jupiter's moon, for more signs of life | 
