NASA is preparing to launch a historic probe to "touch the sun" — which scientists hope will crack decades-long mysteries about our star — in early August.
The spacecraft's daunting flight plan isn't just a daring lark; it's a necessity to answer questions about the sun that have stumped scientists for decades. In some cases, their answers will affect our lives on Earth. But scientists are also taking advantage of convenient access to the sun to understand all stars by proxy.
"We need to go to the corona because we have done so much science by looking at the star," project scientist Nicola Fox, a solar scientist at Johns Hopkins University, said on July 20 during a NASA news conference about the upcoming mission. "We've looked at it in every single different way you can imagine, every wavelength; we've traveled beyond the orbit of Mercury even. But we need to get into this action region and into the region where all of these mysteries are really occurring." [New Look Inside Sun's Atmosphere Yields Clues About Mysterious Solar Wind]
Solving three mysteries
First, the mission will help scientists understand the corona itself — in particular, how heat moves through the sun's atmosphere. Right now, that heat flow seems counterintuitive: The corona can reach temperatures about 300 times hotter than the surface of the sun, despite being farther away from the reactions powering the star.
"It's a very strange, unfamiliar environment for us," Alex Young, a solar scientist at NASA, said during the news conference. "We're used to the idea that if I'm standing next to a campfire and I walk away from it, it gets cooler — but this is not what happens on the sun."
The probe's second task is to study what scientists call the solar wind — a flood of highly charged particles that streams out of the sun and crosses the entire solar system, forming the bubble that marks our neighborhood of space.
But scientists are still working to try to understand exactly how it works, and again, there's something very weird happening — the solar wind somehow speeds up to supersonic. "The solar wind goes from sort of a steady breeze to an actual supersonic flow from the corona going to millions of miles an hour," Young said. Scientists hope that the probe's measurements as it flies both straight into the solar wind and along its current will help them solve that mystery.
Finally, the probe will investigate an even more dramatic consequence of living near our star, which occasionally burps out knots of plasma into space. "The sun can blast out these huge blobs of material — billions of tons of solar atmosphere threaded with solar magnetic field traveling away from the sun at millions of miles an hour," Young said.
These tantrums cause a collection of phenomena scientists call space weather, and if they're dramatic enough, the outbursts can be dangerous to astronauts and satellites in their path — and particularly strong ones could knock out power grids here on Earth. Scientists have some techniques for predicting the space-weather equivalent of tornadoes and hurricanes, but they hope the mission will make those predictions more accurate.
And if you're just here for the pretty pictures, don't worry; NASA has arranged for some of those as well. The probe contains a camera that will show project scientists the spacecraft's view flying through the corona. That will mean pictures not of the sun's surface but of the corona itself, with images more closely resembling those produced on Earth during a total solar eclipse. [Watch the Sun's Elusive Corona Appear in Time-Lapse Solar Eclipse Video]
Delayed for technology
Scientists have been grappling with these questions for decades, but without the resources to actually reach for the stars. For that, they needed to wait for technology to turn the Parker Solar Probe into a reality.
The most important part of that technology is the heat shield, which most of the spacecraft's instruments rely on as protection from the staggering heat of the sun. It's an oddly shaped, unassuming-looking slab of carefully engineered carbon materials, but it does its job: When temperatures on the front of the shield hit 2,500 degrees Fahrenheit (1,370 degrees Celsius), its back is just 600 degrees F (315 degrees C) — and the instruments themselves stay at a balmy 85 degrees F (30 C).
The spacecraft's instruments will be powered by solar panels, but those panels had to be adapted to manage the overpowering input available so close to the sun. "Solar cells need to stay cool; they don't like to overheat, and if they do, they don't work," Fox said. That meant designing self-cooling panels that the spacecraft can adjust on its own, tucking most of the panels behind the heat shield when needed.
A third important advance was making sure the probe could take care of itself without much human input. The probe will be on the far side of the sun during its closest approaches, with no way of calling home if something goes wrong — and even when it can get a signal out, it will face a 16-minute round-trip communication lag.
"I like to think of her [Parker] as an independent spacecraft," Fox said. "She is highly, highly autonomous. She has to look after herself when she is in this coronal region; there is no person in the loop." That means the spacecraft can automatically determine when it needs to shift its position in space because of how much sun individual parts of the spacecraft are receiving. [Touching the Sun: NASA Mission Renamed 'Parker Solar Probe']
The Parker Solar Probe is at NASA's Kennedy Space Center, packed and ready for launch, despite small issues delaying the launch by a week, including the addition of a second, backup set of temperature sensors after concerns the original set would malfunction.
Now, the spacecraft is ready to go. "We have done all the work, all the checks; she finally looks exactly like I expected her to look from all those PowerPoint presentations I saw 10 years ago," Fox said. "She is buttoned up, looking beautiful and totally ready to take her flight."
The spacecraft is now scheduled for a launch window that opens on Aug. 6 at 4:08 a.m. EDT (0808 GMT) and closes on Aug. 19. It will leave Earth aboard a United Launch Alliance Delta IV rocket with two stages, and a third stage of acceleration will be triggered in space.
All that power is necessary to set the spacecraft's path toward the sun. "We need to go so fast because we have to lose the influence of the Earth," Fox said. "We do not want to travel around with the Earth; we want to be able to go in towards the sun."
Once the spacecraft has escaped Earth's pull, it will fly toward Venus, looping the planet about six weeks after launch in order to slow down and home in on the sun. Then, it's on to the sun. The probe will make 24 orbits around the sun, interspersed with six more adjustments that use Venus' influence to inch the probe closer to the star.
The orbits are shaped like flower petals, with the probe gathering most of its data in 11-day spurts while it is within a quarter of the distance to Earth, then sending that information home during the distant part of its loop. During its closest approach, the probe will fly just 3.83 million miles (6 million kilometers) above the sun's surface at a speed of 430,000 mph (700,000 km/h), which will make it the fastest human-made object.
Finally, about seven years after launch, the spacecraft will run out of the fuel it uses to adjust its body and keep sensitive instruments out of the brunt of the sun's heat. And that will be the beginning of the end for the Parker Solar Probe.
"At that point, parts of the body that are not designed to see the full solar environment will then see it, the spacecraft will start to break apart into large pieces, and then it will get gradually and gradually smaller," Fox said. "I romantically like to think that she will become part of the corona and orbit the sun forever."