TCS Daily

Too Hot to Handle

By Sallie Baliunas - November 12, 2003 12:00 AM

The Sun is the origin of deadly hazards in near space, which begins approximately 60 miles above earth's surface. An extreme flare that erupted from the sun on November 4 showed that the Sun's ferocity knows few limits. This extraordinarily powerful flare proved how difficult it is to predict flare hazards.


Humans have threaded low-earth orbit with electronic equipment used for navigation, communication and science aboard satellites. The gear can be damaged by bursts of swift particles ejected from the sun during a flare.


Flares occur over relatively small regions on the sun, and sometimes burst in the direction of the earth. When they do, their fast-moving protons, electrons, and nuclei of heavy atoms bombard the earth's environment. The charged particles may smash into the earth's magnetic field, releasing energy that temporarily excites the air's oxygen atoms. The atoms quickly emit the energy, often as visible greenish or reddish light seen shaped as shimmery curtains, called aurorae, washing across the night sky.


The Nov. 4 flare was of the highest energy class known -- the X-class -- and was off-scale compared to flares recorded systematically by satellite observations since the 1970s. The flare barely touched the earth because the magnetically disturbed area had been carried away from direct line of sight to the earth by the sun's spin. Still, the ensuing aurorae were spectacular, and spacecraft measurements observed the might of the flare. The flare's offset punch perhaps meant sparing some spacecraft electronics.


The sun has exhibited surprising flare activity this year. In general flares tend to occur at times when sunspots appear in the greatest number -- that is, when the sun is most heavily covered by intense regions of intense magnetic field. The sunspot cycle brings high magnetism and the possibility for flares roughly every 11 years. The cycle last peaked in 2000-2001, and the number of sunspots has been dropping to the cycle's expected low around 2005. Despite the low number of sunspots, some that have appeared have been unusually large. There is no good explanation why large spots have been recently appearing.


The unusual Nov. 4 flare probably ranks with a few great flares of the past for which satellite monitoring was unavailable, but whose strengths can be inferred from supporting observations.


On the afternoon of Thursday, Sept. 1, 1859, Richard Carrington and Richard Hodgson independently observed what is thought to be the first recorded flare in visible light. Carrington, observing the projected image of the sun, saw "a ray of light" whose "brilliancy was fully equal to that of direct Sun-light" that persisted for about five minutes. Some 17 hours later the plasma bombarded the earth so violently that aurorae were seen over much of the Northern Hemisphere, even as far south as Havana and the region of Mahastra, India, according to D. Kimball of the University of Alaska who compiled the 1859 aurora information in 1960. The ejected material had to be speeding at approximately 5 million miles per hour to cross the 93 million miles from the sun to the earth in so brief a time.


Because satellites have been destroyed during solar particle eruptions, satellites are now built to withstand the hardest-hitting known flares, with excess margin for the super events. As humans travel to the moon or Mars, they will also need to be protected from powerful flares.


Now that societies of earth have crossed the threshold of space they will have to comprehend the bizarre and dangerous environment of space. In this next phase of humankind, the cosmos will remain entirely unchanged but humans will be irrevocably altered by our experience. Knowledge of solar hazards must be advanced because they are of the first magnitude of importance among near-space hazards.


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