Rogue waves. Floating magnetic islands. Charged particle showers. These are just some of the things NASA’s Parker Solar Probe witnessed during its first two close encounters with the sun.
Parker is on a nearly seven-year mission to repeatedly soar close to the sun. There, it will gather intel on mysteries that have stumped scientists for decades. A team of those scientists are flying the robotic craft through a tenuous plasma — a stream of charged particles — coming from the sun. The researchers hope to learn why the sun’s atmosphere is millions of degrees hotter than its surface. They’d also like to learn what powers the solar wind, the stream of charged particles that blows outward through the solar system.
Mission scientists do have data from the probe’s first two orbits. These were described online December 4 in four papers in Nature. They offer a sneak peek of what’s to come as the craft moves closer to the sun.
“We’re exploring a brand-new region,” says Russell Howard. He is a solar physicist at the U.S. Naval Research Laboratory in Washington, D.C. He also is in charge of the probe’s cameras. “Questions we would have formulated a year ago,” he says, “are just going to be blown away by the things that we’re actually seeing.”
Parker was launched in 2018. It is currently on an elliptical orbit that brings it near the sun about every five months. Its last close encounter was September 1. So, the probe has now completed three of those trips. Each time, the spacecraft flew within about 24 million kilometers (15 million miles) of the sun’s surface. That’s about twice as close as the planet Mercury ever gets to the sun.
Rogue waves and magnetic flips
Parker is already serving up plenty of surprises from its first two trips. “We’ve discovered some unexpected intense rogue [plasma] waves rattling through the sun’s atmosphere,” says Justin Kasper. This mission physicist works at the University of Michigan in Ann Arbor.
Bursts of plasma hurtling into space whacked Parker during its close encounters with the sun. Every so often, the speed of the plasma flowing away from the sun would jump by nearly 500,000 kilometers per hour (300,000 miles per hour) for up to a couple minutes. That’s nearly twice its normal speed.
“We’ve never seen anything quite like that,” says Philippa Browning. She is a solar physicist at the University of Manchester in England who is not involved with the mission.
Each plasma wave was also accompanied by a sudden reversal of the magnetic field around the probe. Magnets attract or repel one another. A magnetic field is an area of influence created by magnets or by the movement of electric charges. A compass measures magnetic fields. When the sun’s magnetic field reversed, “a compass on the spacecraft would have spun all the way around as a wave went past,” Kasper says. The scientists think that they are seeing S-shaped ripples in the magnetic field. It’s as if something near the surface of the sun grabbed a magnetic field line and snapped it like a whip.
Those S-shapes aren’t too surprising, according to Yannis Zouganelis. An astrophysicist at the European Space Astronomy Centre in Madrid, Spain, he is not involved with the Parker mission. “We should expect to see bended lines everywhere,” he says. The sun’s magnetic field gets wibbly-wobbly at times. It jiggles in response to fluid churning within the sun. “However, what is surprising is that we see them very frequently and very strong.”
The origin of these rogue waves is unclear. The spacecraft recorded about 800 over 11 days. That was during its first solar encounter alone. “That’s a very concrete thing we can try to connect to,” Kasper says. “What is the sun giving off 800 times in 11 days?”
The plasma where Parker gets close to the sun also whips around the star far faster than expected. Escaping plasma gets twirled off into space by the sun’s rotation. Researchers thought they’d clock that plasma’s lateral speeds at a few kilometers per second. Instead, they recorded speeds as high as 50 kilometers (30 miles) per second. “That’s really wild,” Kasper says.
Such high speeds might mean that researchers have to rethink how the sun — and all stars — evolve. As stellar winds spiral away, they carry with them rotational energy from the star. That gradually puts the brakes on its rotation. A faster wind spiral might mean stars spin down much faster than scientists thought, Kasper explains.
“This is really amazing, if true,” Zouganelis says. However, the researchers are not yet ready to rewrite the textbooks on stellar physics. These measurements need to be confirmed at lower altitudes. That is one of the many things Parker will watch for on future orbits, Kasper says.
Solving old mysteries
Parker has been busy raising new questions. But it also may have helped solve one mystery: the origin of the “slow” solar wind. The flood of particles from the sun is a blend of two flows. One moves up to twice as fast as the other. Researchers already showed that the fast flow originates near the sun’s poles. It flows through funnellike openings in the sun’s magnetic field. These openings are known as coronal holes. Now, Parker’s data suggest that the slow wind flows from small coronal holes near the sun’s equator.
“It hasn’t always been clear that coronal holes can generate the slow wind,” says Stuart Bale. “But now we can see this very clearly.” Bale is a mission scientist and a solar physicist at the University of California, Berkeley.
Parker cameras also caught magnetic “islands” forming. These tubes of plasma had been predicted. They are entangled in a nest of magnetic fields. Those magnetic fields cart energy and matter into space.
The researchers think that they also may be seeing hints of a clearing in the interplanetary dust near the sun. They aren’t quite sure yet how it happens. But they are excited, since they’d thought it was there for decades.
The spacecraft recorded small bursts of energetic particles coming from the sun. These are mostly protons. The bursts might provide the seeds for more voluminous waves of particles. Such particle tsunamis are sometimes carried up as part of the solar wind, says David McComas. A solar physicist in New Jersey at Princeton University, he is in charge of one of Parker’s particle detectors. The smaller bursts had not been seen by any other spacecraft. That means Parker is getting an up-close view of particle acceleration that would otherwise have been missed.
“We know that energetic particles come from the sun, but we seem to be seeing many more near the sun,” Browning says. “That tells us that particle acceleration might be much more common than perhaps we thought.”
More mysteries to come
That fire hose of information from Parker’s initial orbits is sure to keep researchers occupied for years to come. These new data have “created more questions than they answered,” Zouganelis says. “Most of all, these papers show that the instruments work really well, and we’ll have great measurements as they go closer to the sun.”
Parker’s next big maneuver is a series of 18 orbits. During these, the spacecraft will use the gravity of Venus to inch a little closer to the sun. Its last three orbits, starting in December 2024, will bring Parker even closer — to within just 6 million kilometers (3.7 million miles) of the sun’s surface. That’s more than seven times closer than any previous mission. And it will put all of Parker’s special protective technology to the test.
Nour Raouafi is confident in the solar probe’s future. He is Parker’s mission lead and works at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “We’ll never see the solar wind the same way,” he says. “Parker is going to rewrite the textbooks for us.”