Cosmic signs say `we may not be alone'
Monday 15 December 1997
The medieval astronomer Copernicus took us away from the centre of the universe, insisting the Earth orbits the Sun, not vice-versa. And successive cosmological discoveries have made us seem less important.
Now, British scientists at the Royal Observatory in Edinburgh have made new observations that make our solar system seem even less unusual: they have found other stars which have groups of planets orbiting them. But that also means that we are less likely to be alone, since such planets are ideal settings for life to start.
Investigating four young stars - Beta Pictoris, Fomalhault, Epsilon Eridani and Vega - which all lie less than a hundred light years from Earth, they found that there were haloes around the central star, and circular areas apparently swept clear of dust. One of the best examples is Fomulhaut which lies 22 light years from our sun. In cosmic terms, it's next door.
This pattern of haloes fits the predicted way that a sun and solar system would form from a diffuse interstellar cloud of gas and dust.
Matter begins to fall towards the centre as the cloud collapses through its own gravity; this will also tend to make the cloud spin. Over time, the matter and gas at the centre compresses into a star which achieves enough density to begin fusion. Meanwhile some of the dust around it has enough rotational momentum to keep orbiting, and form proto-planets, whose gravity attracts wandering dust as they enlarge - eventually leaving planets, and empty space between them.
One of the strongest predictions of this idea is that all the planets should orbit our sun in the same direction. And they do. The difference between these four stars and our own sun is age. While our sun is about half way through its 10billion-year life, these are only about 200 million years old.
"Our solar system probably looked like this 4 billion years ago: A halo of dust with planets orbiting inside it," said Professor Glenn White of Queen Mary and Westfield College in London. All that is then needed is for life to start - a process which scientists argue could either be caused by "seed chemicals" from passing comets, or by chemical reactions which catalyse themselves to create more complex molecules.
The new results were obtained using a pounds 1m camera called Scuba - sub-millimetre common user bolometry array - which is able to detect incredibly small heat emissions from distant objects. It is so sensitive that it has to be cooled almost to absolute zero, -273C, and mounted on a telescope 14,000 feet up in the unpolluted mountain air of Hawaii.
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