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THE fear that a 鈥渟uperflare鈥� from the Sun will annihilate all life on Earth
has suddenly receded. 鈥淲e think such flares are triggered by giant planets
orbiting close to a star,鈥� says Eric Rubenstein of Yale University in New Haven,
Connecticut. 鈥淪ince we don鈥檛 have one in our Solar System, we should be OK.鈥�

Astronomers have seen superflares鈥攈uge bursts of high-energy
particles鈥攅xploding from Sun-like stars over recent decades. This did not
cause alarm back on Earth, because they believed that they either came from
young 鈥渁ctive鈥� stars or from stars that had been 鈥渟pun-up鈥� by companion stars.
Closer examination in recent years, however, has triggered concern. 鈥淲hat
changed everything was the discovery that this is not true for any of the
stars,鈥� says Rubenstein. 鈥淧eople began to worry about a superflare happening on
the Sun.鈥�

Superflares occur when the magnetic field of a star gets wound up like a
twisted elastic band. When the field abruptly changes to a less contorted shape,
the tension is released in a huge burst of energy.

Explosions are from 20 times to 100 million times as energetic as the biggest
flares observed on the Sun. Even a 鈥渓ow-end鈥� superflare on the Sun would knock
out power transmission grids on Earth. 鈥淎 鈥榟igh-end鈥� flare would destroy 80 to
90 per cent of the ozone layer, triggering a mass extinction,鈥� says
Rubenstein.

But a recent discovery should mean we can relax again, say Rubenstein and
Brad Schaefer of the University of Texas at Austin. Many planetary systems
around Sun-like stars have giant Jupiter-sized planets orbiting close to the
star. 鈥淗ot Jupiters can twist up a star鈥檚 magnetic field and cause a
superflare,鈥� says Rubenstein. 鈥淥ur prediction is that all the stars which have
had superflares also have close-in Jupiters, so we鈥檙e OK.鈥�

鈥淚t鈥檚 a very plausible explanation,鈥� says David Hough of Trinity University
in San Antonio, Texas.