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Thank our lucky star

Thank our lucky star

作者:隗痛  时间:2019-03-08 05:11:03  人气:

By Charles Seife COULD the Sun send out a monstrous flare powerful enough to melt the ice on Jupiter’s moons, destroy much of Earth’s ozone layer and obliterate all our satellites? It’s possible, say astronomers who have studied other Sun-like stars in our Galaxy, which seem to produce enormous “superflares” 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’s 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’s meeting, a team of three astronomers reported that this kind of solar activity is mild compared with that of the Sun’s 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. “One 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,” 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. “It would melt large flood plains on the outer, icy satellites,” 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. “You’d probably lose the entire satellite fleet,” says Schaefer. Why a superflare has not occurred on the Sun in recorded history is unclear. “I think a consensus is emerging that our Sun is extraordinarily stable,” suggests Galen Gisler,