COULD the Sun send out a monstrous flare powerful enough to melt the ice on
Jupiter鈥檚 moons, destroy much of Earth鈥檚 ozone layer and obliterate all our
satellites? It鈥檚 possible, say astronomers who have studied other Sun-like stars
in our Galaxy, which seem to produce enormous 鈥渟uperflares鈥� about once a
century. They are baffled by the fact that there are no records of similar solar
explosions.
Our Sun often sends flares towards Earth, and more energetic explosions can
spit out giant blobs of ionised gas called coronal mass ejections. Roughly once
or twice a decade, the eruption of stellar material is powerful enough to send
huge electric currents racing around the Earth鈥檚 upper atmosphere, disrupting
power grids and communications satellites. In 1989, one such explosion knocked
out a power grid in northern Quebec.
But at this week鈥檚 meeting, a team of three astronomers reported that this
kind of solar activity is mild compared with that of the Sun鈥檚 sister stars.
They studied records of lone stars in our Galaxy with roughly the same
brightness, size and composition as the Sun. They found that over the past
century, almost all these Sun-like stars had produced superflares that made them
dramatically brighter for minutes or even days.
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鈥淥ne of the cases I have is a star, S-Fornax, where for a 40-minute period it
was seen to be three magnitudes brighter than usual,鈥� says Brad Schaefer of Yale
University, a member of the team. The astronomers conclude that Sun-like stars
normally produce a bright superflare about once a century.
A superflare on the Sun would be about 10 000 times as powerful as the
explosion that caused the Canadian blackout. 鈥淚t would melt large flood plains
on the outer, icy satellites,鈥� says Schaefer. Although life on Earth would
survive, the atmosphere would glow very brightly and half the ozone layer would
be destroyed in the blink of an eye, not to mention spacecraft. 鈥淵ou鈥檇 probably
lose the entire satellite fleet,鈥� says Schaefer.
Why a superflare has not occurred on the Sun in recorded history is unclear.
鈥淚 think a consensus is emerging that our Sun is extraordinarily stable,鈥�
suggests Galen Gisler, an astronomer at the Los Alamos National Laboratory in
New Mexico. 鈥淲e seem to have found a star that is extremely stable and friendly
to life鈥攐r we are just on a star that happens to be stable right now and
will not always be so.鈥�