SUPERFLARE­S: Earth un­der threat

The risk to our planet from coro­nal mass ejec­tions may have been se­ri­ously un­der­es­ti­mated, as Mar­cus Chown dis­cov­ers

Sky at Night Magazine - - SUPERFLARE­S -

The en­ergy of the Sun pow­ers all liv­ing things on Earth, along­side all the ad­vances in hu­man tech­no­log­i­cal civil­i­sa­tion. But what the Sun has so gen­er­ously given us it could take away in an in­stant. Ac­cord­ing to two as­tronomers in the US, a ‘su­per­flare’ could send us back to the pre-elec­tri­cal age or, at worst, trig­ger a global mass ex­tinc­tion.

Manasvi Lingam and Abra­ham Loeb of the Har­vard-Smith­so­nian Cen­ter for Astrophysi­cs say much at­ten­tion has been paid by sci­en­tists and gov­ern­ments to the threat of an as­ter­oid im­pact on Earth but very lit­tle to the threat posed by a vi­o­lent erup­tion from the Sun. And they be­lieve the lat­ter is at least as se­ri­ous a threat as the for­mer.

What has brought this threat into sharp fo­cus is the ob­ser­va­tion of around 100,000 Sun-like stars by NASA’s Ke­pler satel­lite in Earth or­bit. To ev­ery­one’s sur­prise, such stars are not as sta­ble as pre­vi­ously thought but in­stead prone to ex­traor­di­nar­ily vi­o­lent out­bursts, and the ob­vi­ous in­fer­ence is that the Sun may be no dif­fer­ent.

If the Sun were merely a hot ball of gas, it would be dull and bor­ing, its be­hav­iour easy to un­der­stand and pre­dict. In fact, in the 1920s, the ven­er­a­ble English as­tronomer Sir Arthur Ed­ding­ton was able to de­vise a the­ory of what was go­ing on in the so­lar in­te­rior de­spite hav­ing no knowl­edge of the nu­clear re­ac­tions that are the Sun’s ul­ti­mate power source.

The Sun, how­ever, is not merely a hot ball of gas: what changes ev­ery­thing – and makes it ca­pa­ble of launch­ing deadly so­lar flares into space – is the pres­ence of its mag­netic field.

The Sun of all fears

The Sun’s mag­netic field, which is not un­like that of a bar mag­net, is gen­er­ated by elec­tri­cally charged cur­rents of matter that are constantly churn­ing deep within its in­te­rior. Be­cause the Sun is not a solid body, its in­te­rior ro­tates at a dif­fer­ent rate to its sur­face and its ro­ta­tion speed also varies with lat­i­tude. This causes the so­lar mag­netic field ‘lines’ to wind up, stor­ing up en­ergy like twisted rub­ber bands.

When the ten­sion be­comes too great, th­ese field lines ‘re­con­nect’ to a lower-en­ergy state. High-en­ergy pro­tons and elec­trons, which were formerly con­fined by the field, are sud­denly

set free and vi­o­lently cat­a­pulted off into space. This is what is known a so­lar flare.

The big­gest flare in the age of science was recorded by English ama­teur as­tronomer Richard Car­ring­ton on 1 Septem­ber 1859. Now dubbed a ‘coro­nal mass ejec­tion’, the ‘Car­ring­ton event’ in­volved the Sun eject­ing so­lar ma­te­rial com­pa­ra­ble to the mass of Mount Ever­est at about 1,000 times the speed of a pas­sen­ger jet. When the mag­netic field it car­ried reached the Earth, it sliced through elec­tri­cal con­duc­tors, in­duc­ing cur­rents so mas­sive they were enough to elec­tro­cute tele­graph op­er­a­tors.

What is wor­ry­ing about Ke­pler’s ob­ser­va­tions is that they re­veal flares on so­lar, or G-type, stars up to 20,000 times big­ger than the Car­ring­ton event. For­tu­nately for us, such enor­mous flares ap­pear to oc­cur only ev­ery 20 mil­lion years or so on any given star. How­ever, Lingam and Loeb point out that there is some ev­i­dence of a 26 mil­lion-year pe­ri­od­ic­ity in ter­res­trial ex­tinc­tion events. They spec­u­late that, if this is real, it could be ex­plained by superflare­s.

A flare es­sen­tially cre­ates high-ve­loc­ity pro­tons and high-en­ergy ul­tra­vi­o­let light. Both have the abil­ity to de­stroy the ozone shield that pro­tects life on the sur­face of the Earth from deadly so­lar ul­tra­vi­o­let ra­di­a­tion. Not only can such ul­tra­vi­o­let di­rectly dam­age the DNA of or­gan­isms but it can re­duce the abil­ity of phy­to­plank­ton to pho­to­syn­the­sise, a process on which life in the oceans de­pends. As such or­gan­isms de­cline, so too does their abil­ity to suck the green­house gas car­bon diox­ide from the at­mos­phere, re­sult­ing in ris­ing

A dra­matic vis­ual of a coro­nal mass ejec­tion (CME) com­pos­ited from two images cap­tured by the So­lar and He­lio­spheric Ob­ser­va­tory (SOHO) – one of the Sun, the other of the CME – taken at roughly the same time in Jan­uary 2002

A sketch of the sunspots seen by Richard Car­ring­ton on 1 Septem­ber 1859. He watched as the points of ac­tiv­ity marked A and B moved to points C and D over the course of five min­utes, then van­ished

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