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But the sun could trigger the end of our planet much before that time. Solar flares may suddenly heat the earth, or the light from the sun may be blocked by dust, slowly freezing it (eg. the dust and vapour may come from a Kuiper belt disturbance).
A solar flare is a violent explosion in the Sun's atmosphere with an energy equivalent to tens of millions of hydrogen bombs. Solar flares (or coronal mass ejections) take place in the solar corona and chromosphere, heating the gas to tens of millions of kelvins and accelerating electrons, protons and heavier ions to near the speed of light. They produce electromagnetic radiation across the spectrum at all wavelengths from long-wave radio signals to the shortest wavelength gamma rays. Earth's atmosphere and magnetic field negate the potentially lethal effects of ordinary fares.
The most powerful flare of the last 500 years was believed to have occurred in September 1859: it was seen by British astronomer Richard Carrington and left a trace in Greenland ice in the form of nitrates and beryllium-10, which allow its strength to be measured today. (New Scientist, 2005). Similar stellar flares have also been observed to varying degrees on other stars in modern times.
It was long thought that solar flares send out streams of highly energetic solar wind that can present a radiation hazard to spacecraft outside of a planetary magnetosphere and can disrupt radio signals on Earth. They were also thought to be a primary contributor to the aurora borealis and aurora australis and to Solar proton events. However, it is now thought that Coronal Mass Ejections (CMEs) ,which frequently accompany flares, are the main cause of such effects on and around the Earth.
Solar flares release a cascade of high energy particles known as a proton storm. Protons can pass through the human body, doing bio-chemical damage. Most proton storms take two or more hours from the time of visual detection to reach Earth. A solar flare on January 20, 2005 released the highest concentration of protons ever directly measured, taking only 15 minutes after observation.
The radiation risk posed by solar flares and CMEs is one of the major concerns in discussions of manned missions to Mars or to the moon. Some kind of physical or magnetic shielding would be required to protect the astronauts. Originally it was thought that astronauts would have two hours time to get into shelter. Based on the Jan. 20 event, they may have as little as 15 minutes in which to reach shelter.
Scientists have found evidence that some perfectly normal-looking, sunlike stars can brighten briefly by up to a factor of 20. They believe these stellar flickers are caused by superflares, millions of times more powerful than their common cousins. Within a few hours, a superflare on the sun could fry Earth and begin disintegrating the ozone layer. Although there is persuasive evidence that our sun doesn't engage in such excess, scientists don't know why superflares happen at all, or whether our sun could exhibit milder but still disruptive behavior. Decreased solar activity may have contributed to 17 of the 19 major cold episodes on Earth in the last 10,000 years.
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