This summer, humanity embarks on its source mission to touching on the Sun: Influenza A virus subtype H5N1 spacecraft volition endure launched into the Sun's outer atmosphere.
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| The solar air current blows past times basis inwards this illustration [Credit: NASA's Goddard Space Flight Center/ Scientific Visualization Studio/Greg Shirah] |
The solar air current fills our entire solar system. When gusts of solar air current larn far at Earth, they tin mail away prepare off dazzling aurora -- but every bit good expose astronauts to radiation, interfere amongst satellite electronics, too disrupt communications signals similar GPS too radio waves. The to a greater extent than nosotros sympathise the primal processes that campaign the solar wind, the to a greater extent than nosotros tin mail away mitigate some of these effects.
In 1958, Parker developed a theory showing how the Sun's hot corona -- past times too so known to endure millions of degrees Fahrenheit -- is so hot that it overcomes the Sun's gravity. According to the theory, the cloth inwards the corona expands continuously outwards inwards all directions, forming a solar wind. Influenza A virus subtype H5N1 twelvemonth later, the Soviet spacecraft satelite 1 detected solar air current particles inwards space, too 3 years after that, the observations were confirmed past times NASA's Mariner 2 spacecraft.
All those years ago, Mariner 2 detected ii distinct streams of solar wind: a ho-hum current travelling at only about 215 miles per instant too a fast current zipping through infinite at twice that speed. Then, inwards 1973, the origins of the fast solar air current were identified. X-ray images of the corona taken from Skylab -- the U.S.'s source manned infinite station -- revealed that the fast air current spews from coronal holes, which are dark, comparatively cool regions on the Sun.
"The ho-hum solar air current is, inwards many respects, a larger mystery," said Jim Klimchuk, solar physicist at NASA's Goddard Space Flight Center inwards Greenbelt, Maryland. "It offers neat hope for revealing primal novel understanding."
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| Dark coronal holes rotate into sentiment inwards this picture of the Sunday inwards extreme ultraviolet low-cal [Credit: NASA/SDO] |
But we're non without clues. NASA's Ulysses mission, launched inwards 1990 to wing about the Sun's poles, observed that during periods of minimum solar activity, the ho-hum solar air current is confined to the Sun's equator -- correct where Parker Solar Probe volition fly. As the solar bike progresses toward its maximum, the construction of the solar air current changes from two-distinct regimes -- fast at the poles too ho-hum at the equator -- to a mixed, inhomogeneous flow.
The combat virtually the origins of the ho-hum solar air current hinges on a distinction betwixt what's known every bit the closed too opened upwardly corona. The closed corona refers to regions of the Sunday where its magnetic champaign lines are closed -- that is, connected to the solar surface at both ends. Bright helmet streamers -- large loops that shape over magnetically active regions, shaped similar a knight's pointy helmet -- are ane such example. The plasma, or ionized gas, travelling along the closed loops of a helmet streamer is for the most business office confined to the surface area close the Sun.
The opened upwardly corona, on the other hand, refers to regions where the magnetic champaign lines anchor to the Sunday at solely ane end, stretching out into infinite on the other, hence creating a highway for solar cloth to escape into space. Coronal holes -- the cooler regions at the source of the fast solar air current -- are the habitat of opened upwardly champaign lines.
By the fourth dimension the ho-hum solar air current leaves the solar corona, it is every bit good flowing on opened upwardly magnetic champaign lines, every bit that's the solely means to larn so far from the Sun. But theories differ on whether it started off there, or was instead born on closed champaign lines solely to switch to opened upwardly champaign lines somewhere along the way.
The expansion factor theory, for example, claims the ho-hum solar air current originates on opened upwardly champaign lines, only similar the fast wind. Its (comparatively) ho-hum speed results from the expanding path it takes on its means out of the corona, every bit magnetic champaign lines skirt the borders of helmet streamers. Just every bit H2O coursing through a pipage slows to a trickle every bit the pipage expands, plasma traveling along these widening magnetic paths slows down, forming the ho-hum wind.
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| Closed magnetic champaign lines loop dorsum to the Sunday to shape helmet streamers, surrounded past times opened upwardly champaign lines that make out into space, every bit depicted inwards this illustration [Credit: NASA's Goddard Space Flight Center/Lisa Poje/Genna Duberstein] |
The thought that ho-hum solar air current plasma was ane time on closed champaign lines is supported past times show that it ane time faced the kinds of extreme heating nosotros know happens there.
"It's non virtually the temperature of the plasma when nosotros stair out it; it's virtually the temperature history of that plasma," said Aleida Higginson, a University of Michigan enquiry scientist working at Goddard. "We tin mail away nation that the ho-hum solar air current was much hotter inwards the past." In addition, the exceptional mix of elements that brand upwardly the ho-hum solar air current matches good amongst those seen inwards the closed corona -- but non amongst plasma that nosotros know has ever been on opened upwardly champaign lines.
Current efforts to assay these theories past times spacecraft close basis are stymied past times the neat distance betwixt their measurements too the solar wind's origins (a lot tin mail away hap inwards 93 1000000 miles). The key is getting closed up, tracing the solar air current dorsum to its source -- too Parker Solar Probe volition create only that.
"If nosotros tin mail away stair out the ho-hum solar wind, too discover it comes from the boundary betwixt opened upwardly too closed magnetic fields, too so that supports the thought that magnetic reconnection gives ascent to the ho-hum solar wind," Klimchuk said.
Parker Solar Probe's instruments volition collect downstream show of magnetic reconnection -- a tell-tale sign that the closed-field-to-open-field theory is at play. Specific kinds of reconnection twist the resulting magnetic champaign inwards unlike ways, too Parker's instruments volition stair out the twists inwards these fields early on, earlier they create got had much fourth dimension to endure distorted. In addition, close-up images of the nascent solar air current volition nation us how coronal structures evolve every bit they propagate outward. This volition aid us respond a long-standing inquiry whether the solar air current is a continuous or intermittent flow.
For scientists who crave information to assay their theories, accurate measurements of the solar corona's magnetic fields volition endure invaluable. "That's why Parker's mission is so important," Higginson said. "It all traces dorsum to agreement the detailed magnetic construction on the Sun."
Author: Miles Hatfield | Source: NASA/Goddard Space Flight Center [July 31, 2018]
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