Fact Impact - Mars
25 May 2011
Dominic Ford, Cambridge University
- Mars is the fourth planet from the Sun in the Solar System.
- It lies just outside the orbit of the Earth.
- In the night sky it appears red, a similar colour to a rusty nail...
- ... in fact, a very similar colour; a major constituent of Martian soil is iron oxide, which is better known as rust.
- It's the second smallest planet in the Solar System, half the size of the Earth.
- And yet it plays host to the largest mountain in the Solar System, a volcano known as Olympus Mons, which is three times higher than Mount Everest here on Earth.
- Its atmospheric pressure is less than a 100th of that on Earth.
- On the Earth that's equivalent to the pressure at an altitude of 100,000 feet.
- At such low pressure, liquid water would evaporate almost immediately.
- So while there's plenty of water on Mars, it's all locked up in ice reservoirs beneath the surface.
- And what little air there is on Mars is mostly carbon dioxide, with barely a trace of breathable oxygen.
- At the poles, this gets so cold that it forms frost. Not made of ice, but made of solid carbon dioxide at -120 C.
- So, the surface of Mars is a harsh place. Moreover, with no magnetic field to deflect it, Mars' surface receives the full brunt of the ionising radiation emitted by the Sun.
- But it might not always have been that way. The surface of Mars shows signs of past water erosion.
- So, it probably had a thicker atmosphere and a warmer climate in the past.
- And may well have been much more habitable back then.
- Mars has two moons, Phobos and Deimos, named after the sons of Mars in Greek mythology.
- But they're much smaller moons than our own, measuring less than 25 km across.
- They orbit so close to Mars that they're difficult to spot, even with a sizeable telescope.
- And it's quite a mystery where they came from. They may well once have been asteroids that slipped into orbit around Mars.
- More spacecraft have been sent to study Mars than any other planet.
- The success rate has been low; of 33 missions launched; only 15 have returned useful data.
- ... but the latest rovers to land on the Martian surface, Spirit and Opportunity, have lasted over six years, well beyond their 90-day design lifetime.