Europe leads space race to hunt down ET

Europe leads space race to hunt down ET

Europe leads space race to hunt down ET

It is a view that astronomers would die for: a shimmering, blue, alien world with oceans and continents and vegetation changing colour with seasons. A vision like this, across the galactic void, would be unambiguous proof of the existence of extraterrestrial life.

Planets outside our solar system are many hundred thousand billion miles distant, however, and the prospect of observing them has been considered utterly remote by most scientists.

But European researchers have now begun work on a research programme that could culminate in such an instrument, a flotilla of orbiting mirrors that could return clear pictures of exo-planets, worlds that circle other stars.

‘It is the one irrefutable way of deciding if another world has life on it,’ said Professor Antoine Labeyrie, of the Observatoire de Haute Provence, in France. ‘If you can see there is chlorophyll and vegetation that changes colour as plants die or flourish as the planet swings round its sun, then you have found a world with life on it. Whether this has evolved to a complex level is a different matter.’

Labeyrie’s space telescope is unlikely to be built for decades, although preliminary optical tests have already begun. In the meantime, the European Space Agency (Esa) is preparing to launch a programme aimed at developing less complex missions for pinpointing stars with life-bearing planets. If these succeed, the Exo-Earth Imager could follow them.

The main message is clear, however: European astronomers intend to be world leaders in the hunt for ET. ‘This is our territory,’ said David Southwood, head of Esa’s science programme. ‘The first astronomers to find a planet in orbit round another star were European – Michel Mayor and Didier Queloz. who discovered a planet in orbit round 51 Pegasi in 1995. We want to keep this lead and be the first not just to find planets but also to discover those bearing life. That will tell us whether we are alone in the galaxy or just one of many other lifeforms. Either way the information will be crucial.’

This view is shared by most other European scientists. Earlier this year Esa asked Europe’s scientists – not only astronomers but also biologists, chemists, botanists and others – what goals they wanted their space scientists to pursue. The search for life-bearing planets received widespread support.

A programme called Cosmic Visions was launched. This will see the construction of several major space telescopes, designed to spot exo-planets, over the next 20 years and could ultimately lead to the con struction of an Exo-Earth Imager, though this is not yet part of the programme.

‘Planets are tiny objects compared to stars,’ said Dr Catherine Turon, of the Paris Observatory, Meudon, and head of Cosmic Visions. ‘They reflect a billionth of the light that a star emits. Yet we have to spot them from across the galaxy. It’s like spotting a candle beside a lighthouse 1,000 kilometres away.’

Nevertheless, European astronomers have devised several ingenious missions. All require telescopes to be blasted above the distorting effects of Earth’s atmosphere.

The first, Gaia, will use a single telescope to create an extraordinarily precise three-dimensional map of a billion stars throughout our galaxy and will reveal exo-planets by the disturbing effect they have on their parent stars’ movements. To date, more than a hundred exo-planets have been discovered by Earth-based telescopes. Gaia, to be launched in 2011, should find thousands.

But only planets that can support life are of real interest. These will lie in a star’s ‘Goldilocks zone’, orbits where temperatures are not too hot and not too cold. To find these, a more ambitious mission, Darwin, will launch a flotilla of eight spacecraft in 2015.

These will look for Earth-like planets round stars near our solar system. By combining light from several telescopes, Darwin will cancel out the image of a central star, allowing its planets to appear as pinpricks of light. Analysis of this light with a spectrometer will then reveal the presence of gases in the planet’s atmosphere. Combinations of oxygen, ozone, methane and carbon dioxide would suggest life there.

After that, a mission, provisionally called super-Gaia, would study stars even further into space, and pinpoint Earth-like planets at distances of 300 to 400 light years. Similarly, Nasa is planning to launch its Terrestrial Planet Finder in 2018, using techniques similar to Darwin’s, while the French are planning their own mission Corot, which is to be put in orbit in 2008. If ET is up there, he will have his work cut out heading from Earthly attentions.

And if these missions find promising alien worlds, ones with Earth-like atmospheres, then the Exo-Earth Imager – or a mission very like it – will become the next logical project. It will operate like Darwin, but instead of eight orbiting telescopes, Labeyrie is envisaging a system made up of 10,000 mirror-telescopes, each with a 3m diameter. This will create a camera that has an effective aperture of 100 kilometres: not enough to pin point ET in his bath, but big enough to study his home planet.

In short, if there are alien worlds with life on them in our galactic neighbourhood, then scientists – led by Europe – will find them, even if these life-forms are no more than humble plants or bacteria, a point stressed by David Southwood.

‘We have yet to find sign of alien life, although it now seems that exo-planets are fairly common,’ he said. ‘It may be that our planet is special and that, for some as yet unknown reason, life was lucky to survive here. Or it may be that simple life, like bacteria, is common, but complex life like ours is very rare. If so, we want to know why. The issue is of fundamental interest to everyone, after all.’