This weekend, in the dark hours before dawn, NASA plans to send a spacecraft to touch the sun.
The Parker Solar Probe, which could blast off from Cape Canaveral Air Force Station as early as 12:33 a.m. Pacific on Saturday, will dip down to within 4 million miles of the solar surface — or nearly 10 times as close as sun-scorched Mercury.
Each of its 24 orbits will provide an extraordinary glimpse at the sun’s ethereal corona and offer a taste of the solar wind.
Each pass also comes with terrible risk, forcing the spacecraft to face powerful electric and magnetic fields, speeding-bullet dust grains and obliterating heat.
The years of work building a spacecraft tough enough to survive this environment — and sophisticated enough to send back valuable data — are well worth the effort, scientists say.
“We’re going to explore unknown territory,” said Marco Velli, a UCLA space physicist and the probe’s observatory scientist.
“People are hugely excited about this,” said Robert Rosner, a computational physicist at the University of Chicago who was not involved in the mission. Talk of such a solar probe, he said, “probably goes back at least 40 years.”
A combination of Icarus-like daring and Daedalian planning, the Parker spacecraft seeks to answer fundamental questions about our nearest star that have stymied space physicists for decades.
Among them: Why does the corona — the ghostly halo of plasma, or ionized gas, surrounding the sun — reach temperatures higher than 2 million degrees Fahrenheit, hundreds of times hotter than the sun’s broiling surface? And what powers the solar wind, the stream of charged particles that flows outward from the corona at speeds on the order of a million mph?
No human efforts to study our home star — telescopes that scan the surface, X-ray observations of the corona, spacecraft that pass over the poles — have fully answered these questions, said Justin Kasper, a space scientist at the University of Michigan and leader of a particle-sampling instrument suite.
“We can’t agree on what’s actually going on,” Kasper said. “When you look at what gets to Earth or to these spacecraft, it’s ambiguous.”
The answers that Parker finds would not just help scientists understand the behavior of the sun, Kasper and his colleagues said. They could potentially shed light on coronal structures around massive galaxies, the jets from powerful black holes and accretion disks where young planets are forming.
“What we learn here, we apply to other astrophysical systems,” said Stuart Bale, a space plasma physicist at UC Berkeley and leader of an experiment measuring electric and magnetic fields.
These findings could also help researchers better understand coronal mass ejections — enormous bursts of high-energy particles that can erupt from the sun’s surface. This subatomic tsunami can potentially knock out satellites and disable power grids on Earth.
With a fuller portrait of our sun, scientists may also be able to better shield both our infrastructure as well as future space travelers, said David McComas, a Princeton University space physicist who leads an instrument suite studying energetic particles.
“If you go out to the moon or if you’re planning on going out to Mars or elsewhere, these solar energetic particles provide potentially a very dangerous radiation environment for astronauts,” McComas said.
The Parker probe, which is managed by the Johns Hopkins University Applied Physics Laboratory in Maryland, has four suites of instruments.
The Fields experiment’s antennas will measure the sun’s electric and magnetic fields. The Integrated Science Investigation of the Sun experiment will observe extremely energetic electrons, protons and heavy ions for insight into the solar wind and corona. The Wide-field Imager for Parker Solar Probe’s telescopes will take snapshots of the corona and inner heliosphere — the huge region of space affected by the solar wind. And the Solar Wind Electrons Alphas and Protons Investigation’s sensors will survey the most abundant solar wind particles: electrons, protons and helium ions.
But many of the phenomena that the spacecraft seeks to measure are the same ones that could destroy it.
The Parker probe will get so close that the pressure from mere sunlight will be enough to flip the spacecraft around in less than a minute, Kasper said. And without shielding, most of its instruments would quickly melt. That’s not to mention the remote but still real possibility that high-speed dust particles could slam into the spacecraft from the opposite direction at a relative speed of 400 kilometers per second.
“We call that a hyperkinetic impact,” Kasper said. “A dust grain moving that fast would blow a hole the size of a quarter through a metal plate.”
So the team’s scientists and engineers have gone to extraordinary lengths to protect their instruments. They’ve built a roughly 8-foot-wide carbon-composite shield that will always face the sun. That heat shield will bear the brunt of the solar onslaught, rising to 2,500 degrees Fahrenheit, while the instruments it protects will hover at a balmy 85 degrees. Meanwhile, the spacecraft’s powerful reaction wheels will work overtime to keep the spacecraft stable and the shield in place.
“It was all an act of heroic thermal engineering,” Bale said.
Testing the spacecraft and its instruments for such a grueling environment forced the scientists to think outside the box, the researchers said.
Years ago, Kasper’s team had to devise a system that could expose a test model to sun-like torment. They ended up simulating the sun using older-model IMAX projectors purchased on EBay, because their bulbs had roughly the same effective temperature as the solar surface.
At first, the test model didn’t quite work. A cable snapped; the high voltage broke down. They adjusted parts, changed out materials and tried again.
“And then ... it ran beautifully,” Kasper recalled. “It ran overnight thinking it was close to the sun, this light just roasting it — and that’s probably the biggest moment when I was like, ‘OK … fundamentally, this thing is going to work.’ ”
After launch, the spacecraft will head toward Venus, whose gravity will bend its path into the correct orbit. After that late September flyby, the Parker should make its first close approach to the sun on Nov. 1 — the first of about two dozen solar passes and seven gravity assists from Venus. Its final encounter with the sun’s atmosphere will come in June 2025.
Scientists who study the sun say they are eager for the data that Parker could send back.
Rosner, of the University of Chicago, recalled the first time he witnessed a total solar eclipse in person, after years of studying it from afar.
“It was breathtaking, breathtaking,” he said.
The chance to get up close and personal with the sun thanks to the Parker probe, he said, evoked that same awe.
“Being able to get at something that you’ve been working at for years, and finally saying, ‘Oh my god, I’m going to get this data, wow,’ is just awesome,” he said.
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