ET, Close Encounters, Mars Attacks… the movies are full of extra-terrestrial landings and contact with aliens. In fact, all cultures have represented alien beings in their art, stories and writing at some time or other. But what does science say?

Are we alone in this universe, or is it teeming with life?

We've been looking for extra-terrestrial life for years, but so far none has been found. A lot of attention has been focused on looking for life on Mars - first with telescopes, and then using more sophisticated techniques. In 1975 the remotely-controlled Viking probe was sent to Mars to search for life. The successful landing the following year was an amazing achievement, but despite hopes, no life was found.

Mars was barren of life … or was it?

A lot of excitement was generated in the 1990s when a team of scientists from the Natural History Museum and the Open University found that a meteorite that had fallen to Earth from Mars (called ALH 84001) contained a high concentration of organic compounds. They couldn't tell whether these compounds had formed on Mars or on Earth.

In 1996, a team from NASA examined the meteorite and discovered structures that resembled fossilised microbes. It was a discovery that caught the imagination of the whole world.

Could this be evidence of life on Mars?

Unfortunately, the huge excitement was crushed by further study, which revealed that the structures could easily have been formed by processes on Earth. It seemed that they probably hadn't come from space after all.

Despite this, the search for signs of life on Mars continues. There's evidence of water on Mars, past and present, and scientists believe that life could still exist... below the planet's surface. Scientists are also looking for life in other parts of the solar system…and beyond!

One current theory of how life emerged on Earth is that it evolved around hydrothermal vents deep in the oceans. Some researchers now think that Jupiter's moon Europa might also have hydrothermal vents at the bottom of its oceans, and if so, life might be found there.

NASA is planning to send a remote-controlled probe to Europa which will land on the surface ice, drill through to the oceans, dive to the bottom of the sea and look for signs of life!

Although we all think of aliens as big, multicellular creatures like ourselves, it's probable that if we do find extra-terrestrial life, it will be a lot simpler. We're far more likely to find a tiny, slimy microbial blob - if we're lucky! It's also possible that life might exist in a form that we simply do not - or cannot - recognise.

Despite this, scientists are still looking for life of an altogether more intelligent nature. The Search for Extra Terrestrial Intelligence - commonly known as SETI - is a world-wide collaboration in which radio-telescopes are used to scan the skies for signals from aliens that must not only be biologically complex, but technologically advanced.

It's highly unlikely that we'll ever detect such a signal from another, alien civilisation. But so what? It's a relatively cheap process to look for signals, and the impact of finding one would be momentous! So scientists are having a go. We can all get involved in looking for signals by joining Team SETI and downloading the SETI screensaver.

The BBC and the Open University are not responsible for the content of external websites.

    next > Page 1 of 2

Comments