From: Patrick Wilken (patrickw@cs.monash.edu.au)
Date: Thu Sep 23 1999 - 07:43:27 MDT
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.
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