Sterilisation of planets

Patrick Wilken (patrickw@cs.monash.edu.au)
Thu, 23 Sep 1999 23:43:27 +1000

Thursday, September 23, 1999 Published at 10:04 GMT 11:04 UK

Sci/Tech

Sterilisation of planets

By BBC News Online's Science Editor Dr David Whitehouse

Could our Sun suddenly experience a so-called "superflare" on its surface that could wipe out all life on Earth?

That is the possibility, albeit a remote one, that emerges from observations of nearby stars that are similar to our own Sun.

Bradley Schaefer of Yale University, along with Jeremy King of the Hubble Space Telescope Science Institute and Constantine Deliyannis of Indiana University, have documented nine cases of other stars, seemingly well-behaved like our Sun, that have suddenly erupted superflares.

Two events, seen on the stars K Ceti and pi-Uma, are especially significant because these two stars have been called solar analogues, that is they are almost exactly identical to our Sun.

Yet they have been observed to emit superflares, energetic explosions on their surfaces that spray radiation and charged particles out into space. The effect on any planets orbiting them would be catastrophic.

Sterilised planets

If a superflare occurred on our Sun, then the Earth would be subject to rapid heating, aurorae would ripple in every sky, the ionosphere would break up and the ozone layer would be destroyed.

This would allow lethal radiation and charged particles from the Sun to reach the ground, destroying all life-forms except those protected in the deep oceans.

However, all geolical data, suggests our Sun has never experienced a superflare. Although researchers cannot rule out the possibility entirely.

So what is going on? How can stars like our Sun exhibit such superflares but our own Sun seem well-behaved?

Squeezed and amplified

The answer may be given in an accompanying paper in a forthcoming issue of the Astrophysical Journal. Bradley Shaefer and Eric Rubenstein of Yale suggest that the superflares are caused by a large planet, the size of Jupiter or larger, orbiting these Sun-like stars.

What they believe happens is that the planet's magnetic field gets tangled up with the star's magnetic field and they both become squeezed and amplified, like pulling a knot tighter and tighter.

Something eventually gives and the pent-up magnetic energy is explosively released in a gigantic superflare. This is highly unlikely to happen in our Solar System, say these astronomers, because there is no large planet close enough to our Sun.

But their analysis has implications for the possibility of life in space.

In recent years, many Jupiter-class planets have been discovered closely orbiting some of the nearest stars to our Solar System, raising the possibility that some of these newly-discovered planetary systems may harbour life.

If superflares are common in these systems then they may sterilise the surfaces of accompanying planets, making life harder to develop. Alternatively, it may mean that life in these systems would evolve in protected regions such as deep caves or beneath the surface of an ocean.