Fitted with a select set of instruments, Solar Probe Plus will address two questions that solar physicists have tussled with for decades: How does the corona, that ghostly, spiked halo seen during a total solar eclipse, heat to more than a million degrees, far hotter than the sun's surface? And what powers the solar wind, the stream of charged particles that flows from the corona?
An up-close look at the sun may ultimately help scientists predict solar flares, as well as coronal mass ejections — "solar storms" like those launched at Earth last week. These events send a barrage of high-energy particles crashing against the Earth's magnetic field, at times disabling satellites, wiping out power grids, forcing airlines to reroute flights and potentially exposing astronauts to fatal doses of radiation.
Scientists have sent probes to the solar system's edge, but never so near its heart. Coming within 3.7 million miles of the sun's surface — 25 times closer than Earth — the 1,350-pound unmanned spacecraft will heat to 2,600 degrees Fahrenheit and endure 512 times the sunlight of vessels orbiting Earth. It is expected to make its first approach from that distance in 2024.
The mission "will undoubtedly have impact on our ideas about how life operates throughout the universe — if life does operate throughout the universe — how our planet evolved and how we're going to contend with the further exploration of space," said Richard Fisher, director of NASA's heliophysics division.
Half a century in the making, with an estimated price tag of $1.2 billion and barely 88 pounds allotted to experimental hardware, the project spawned fierce competition among heliophysicists for a piece of the action.
In September 2010, Kasper learned that his proposal to count the electrons, protons and helium ions in the solar wind had won one of five coveted spots. He happily ripped open boxes filled with commemorative copies of the proposal — he'd let them gather dust for months, afraid to jinx his chances — and passed them out to his team.
Now, with the instruments selected and the project's next phase underway, some researchers are elated while others tussle with a mix of emotions: sadness at being left out and excitement at what their field stands to learn.
Other spacecraft have ventured toward the sun before: In 1976 the Helios 2 mission came within 27 million miles. The European Space Agency plans to launch a solar orbiter in 2017 that will come as close as 26 million miles.
But Solar Probe Plus, to be built by the Johns Hopkins University Applied Physics Laboratory, is more ambitious by far, venturing seven times closer.
Scientists have talked of such a journey since the 1950s, but plans were always logistically fraught and prohibitively expensive.
They had wanted to study the solar poles because the sun's magnetic field would be strongest there. But this meant flying over and under the sun rather than girdling its middle like the planets, requiring huge amounts of energy.
The proposed solution: Send the probe to Jupiter, whose gravity would twice lob it back toward the sun, over its north pole and under its south pole.
But sending a probe to such cold, dark reaches of space would require nuclear power — not just solar — and thus a heavy cooling system. Costs mounted.
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