No spacecraft will ever land on the surface of the sun--it's a flaming ball of gas that reaches thousands of degrees even in its coolest regions. But next year, a ship from Earth will fly closer to its fires than ever before in a mission that represents a big development not just for scientists but, potentially, for everyone else.
In September 2018, NASA plans to launch a probe that will journey nearly 90 million miles, eventually flying within 3.8 million miles of the sun. The Parker Solar Probe is expected to reach the sun's outer envelope of fiery gases, known as the corona, by November of that year, providing new insights not only into our home star but into all stars--which is no small thing, given that the closest star system is an unreachable four light-years away. That's 24 trillion miles. The sun, just 93 million miles away, is well within our reach.
That doesn't mean getting there is easy. Even as NASA probes have sailed past Pluto and out of the solar system entirely, the sun has mostly been a no-go zone. Designing a spacecraft tough enough to take the sun's thermal punishment has proved difficult--not that that's stopped astronomers from trying. All the way back in 1958, Eugene Parker--a young physicist at the University of Chicago, whose name the new spacecraft bears--published a paper about what we now call solar wind: the high-speed storms of stellar particles and magnetism that stream from the sun. Ever since his discovery, Parker, now 89, has been campaigning for a close-up mission to the sun. At last the technology is available.
After its launch, the unmanned spacecraft will enter a preliminary solar orbit and then make seven flybys of Venus, using the planet's gravity to edge closer and closer to the sun. Ultimately, the ship will be so close that it will make a single trip around the sun in just 88 days--a quick trip compared with Earth's poky 365 days. At its peak speeds, the Parker Solar Probe will move fast enough to get from Philadelphia to Washington in a second.
While temperatures in the corona can reach 1 million°F, the probe will limit itself to regions where things get no hotter than 2,500°F. Still, that's four times as hot as the melting point of lead--a heavy heat load for a spacecraft that will cost $1.5 billion to build, launch and operate. But a 4.5-in. carbon-composite heat shield will allow the probe's camera and suite of scientific instruments to operate at a comfortable room temperature.
There are many reasons for the mission that go beyond bragging rights. For starters, scientists may learn why the million-degree coronasphere--which ought to be cooled by its direct contact with space--is up to 100 times as hot as the 10,000°F surface of the sun. Scientists have a number of theories as to why that might be. Some think it's due to the waves of plasma that rise from the sun and crash back down, causing localized superheating that warms the corona. Others think that sudden realignments in the sun's magnetism could be the cause. It's impossible to know for certain, however, until we get up close.
NASA says the data it collects could also provide insight into the physics of stars at large. Our sun may be special to us, but it's rather common in the sweep of space; the better we understand how it works, the better we understand all stars of its mass and color.
Perhaps most important is what the probe may reveal about the cause and nature of solar storms, stellar eruptions that can turn solar wind into a solar gale, wreaking havoc far beyond the perimeter of the sun. During solar storms, charged particles streaming through the solar system can disable communications satellites and shut down electrical grids over vast swaths of the planet.
A National Academy of Sciences study revealed that a particularly ferocious storm could cause up to $2 trillion in damage in the U.S. alone and black out the Eastern seaboard for a year. A better understanding of what causes the eruptions might enable us to predict them--and protect ourselves in advance. That could make even a mission with a billion-plus price tag one of NASA's great bargains.