An artist's rendering of the Solar Probe Plus on its approach to the Sun.
On September 1, 1859, a British astronomer named Richard Carrington was sketching the shapes of sunspots projected from his telescope onto a screen when two spots flared into view and brightened still further, only to fade a few minutes later. Less than 24 hours after that, says Harvard astronomer Justin Kasper, “everything went to hell on Earth.” The sky lit up with Northern Lights so bright, he says, that people could read newspapers outside at 2 A.M. in New York’s Central Park. More ominously, says Kasper, “the telegraph network—the Victorian internet—went completely down.”
What scientists now call the “Carrington event” was the most violent solar storm in recorded history, and there’s no reason something like it, or even worse, couldn’t happen again, shutting down communications and power grids for weeks or even months.
That’s one reason NASA is hard at work on a spacecraft known as Solar Probe One—the first mission designed to dip into the Sun’s outer atmosphere—and, more impressively, live to tell the tale. Slated for a 2018 launch, the craft will try to figure out why solar storms happen and how they send blasts of particles out to threaten Earth with electronic disaster.
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But that’s only one focus of the mission. Another is to answer the 60-year-old mystery of how the Sun’s surface can hover at around 10,000°F (5,500°C) while the thin gas immediately above, known as the corona, is at least a hundred times hotter. Nobody fully understands how this can be. It might be caused by the Sun’s powerful magnetic fields, says Kasper, lead scientist for one of Solar Probe’s five instruments. Or it might have to do with the Sun’s turbulent, roiling surface, which triggers pressure waves that that dissipate their energy in the corona “like waves crashing on the beach.”
In theory, Solar Probe One should be able to provide some clues. But those, along with observations that might make disruptive solar eruptions easier to predict, won’t come along right away. The spacecraft will need some eight years after launch to reach the Sun, using no fewer than seven Venus flybys to adjust its trajectory until it finally dips to within 3.7 million miles (6 million km) of the solar surface.
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That sounds pretty far away, but the Sun itself is a million miles across, and even at that distance, its rays are 500 times brighter than they are on Earth, and temperatures will soar to 2,500°F (1,400°C). To protect the probe, NASA engineers plan to toughen the already impressive heat-shielding techniques used to keep the MESSENGER probe from getting fried during its observations of Mercury.
By the mid 2020’s, therefore, assuming all goes well, scientists might finally have a reasonably complete understanding of the biggest, most obvious target for Solar System exploration. It’s the reason all of the other objects are here at all—and it’s been neglected for far too long.
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