Believe it or not, humanity has never fired a probe directly into the Sun. By 2015, NASA hopes to check that interstellar bucket list item with Solar Probe+ (pronounced Solar Probe plus), a heat-resistant spacecraft "designed to plunge deep into the sun's atmosphere where it can sample solar wind and magnetism first hand." At first the mission sounds like a tough break for the little probe, especially as its older cousins play in a sandbox and tool around Saturn, but once you dig a bit deeper there's actually quite a bit left to learn about our parent star's lingering mysteries.
According to NASA, at its closest approach Solar Probe+ will be about 7 million km from the sun (image below). At that point, the probe's incredibly important carbon-composite heat shield must withstand temperatures greater than 1400 C. Oh, and there's the incessant blasts of radiation at "levels not experienced by any previous spacecraft" to contend with too.
And those mysterious alluded to earlier? NASA spells them out thusly:
- Mystery #1—the corona: If you stuck a thermometer in the surface of the sun, it would read about 6000o C. Intuition says the temperature should drop as you back away; instead, it rises. The sun's outer atmosphere, the corona, registers more than a million degrees Celsius, hundreds of times hotter than the star below. This high temperature remains a mystery more than 60 years after it was first measured.
- Mystery #2—the solar wind: The sun spews a hot, million kph wind of charged particles throughout the solar system. Planets, comets, asteroids—they all feel it. Curiously, there is no organised wind close to the sun's surface, yet out among the planets there blows a veritable gale. Somewhere in between, some unknown agent gives the solar wind its great velocity. The question is, what?
"To solve these mysteries, Solar Probe+ will actually enter the corona," said program scientist Lika Guhathakurta of NASA Headquarters. "That's where the action is." No kidding. Just be sure to bring the SPF 10,000, little guy. [NASA]