The Most Interesting Star
BY ADRIAN BERRY
Posted: October 8, 2008

"Imagine if spectroscopic analysis revealed a blue planet with an oxygen atmosphere just four light-years away orbiting Alpha Centauri. The demand to build a warp drive would start right away!'' Daniel S. Goldin, former administrator of NASA.

There is an astonishing contrast between the efforts we put in to exploring dim and obscure star systems while we ignore the most brilliant one that is closest to us of all.

There has been tremendous excitement, for example, about the faint star Gliese 581, some 20 light-years away in the north-east part of the constellation of Libra, which has in its orbit three admittedly interesting worlds, a gas-giant about the size of Neptune and two much smaller rocky planets, one of which may well be habitable.

But we seem to pay little attention to the much brighter star system Alpha Centauri, the nearest star to the Sun, a mere fifth of this distance away from us, and to the all important question of whether it possesses any habitable planets.

The discovery of any such worlds would be much more interesting – five times more interesting, in fact, going by distance, than the rocky worlds of Gliese 581 – because Alpha Centauri is only 4.3 light-years away. It is easy to feel Mr Goldin's excitement with which to explore it.

The neglect of Alpha Centauri is all the more remarkable when we reflect that two of its the stars, known as Alpha Centauri A and B, are almost identical to the Sun. Their respective masses are 1.1 and 0.9 of the Sun's. And they never come closer to each other than a billion miles, 11 times the distance between Earth and Sun, so there would be a suitable environment for a habitable planet around each of them.

There seems to be nothing particularly "alien" about these stars. They have the same spectral signature as the Sun, suggesting that they are composed of the same elements and that they were created at the same time. It may be that all three stars coalesced from the same supernova explosion that formed the Solar System five billion years ago. They even share with the Sun the unlikely ratio of one atom of iron to 31,620 atoms of hydrogen, a ratio that no other star is known to possess.

And quite apart from the search for planets, one can make interesting speculations about the real nature of the Alpha Centauri system itself, and how it may have affected our own history.

Some extreme binary systems consist of stars separated by distances of up to three light-years. Might it not even be that the Sun and Alpha Centauri, at a distance of only 4.3 light-years, are gravitationally bound and are members of the same binary system, circling each other every hundred million years or so?

It is often suggested that the Sun has a hidden companion star. After all, most stars are doubles, trebles or quadruples. It seems inexplicable that ours seems to be an exception. But maybe we have a companion star that it not hidden! Might it not be a bright star like Alpha Centauri? I know of no reason to think this is true, but it might be a hypotheses worth pursuing.

Both for science and for the sake of the technological future of mankind, Alpha Centauri deserves far more attention than it is now receiving.

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Visit Adrian Berry's website at www.adrianberry.net He is Consulting Editor (Science) of the Daily Telegraph.