Rogue plasma waves. Floating magnetic islands. Showers of
charged particles. These are just some of the things NASA’s Parker Solar Probe
witnessed during its first two intimate encounters with the sun.
Parker is on a
nearly seven-year mission to repeatedly soar near the sun and gather intel
on mysteries that have plagued solar physicists for decades (SN: 7/5/18).
By flying a robotic craft through the tenuous plasma emanating from the sun,
researchers hope to figure out such puzzlers as why the sun’s atmosphere is millions
of degrees Celsius hotter than its surface and what powers the solar wind, the
stream of charged particles that blows outward through the solar system.
Mission scientists aren’t ready to answer those questions
yet. But data from the probe’s first two orbits, published online December 4 in
four papers in Nature, offer a sneak peek at what’s to come as Parker moves
closer to the sun over the next several years.
“We’re exploring a brand-new region,” says Russell Howard, a
solar physicist at the U.S. Naval Research Laboratory in Washington, D.C., who
is in charge of the probe’s cameras. “Questions we would have formulated a year
ago are just going to be blown away by the things that we’re actually seeing.”
Launched in 2018, Parker
is currently on an elliptical orbit that brings it near the sun about every
five months (SN: 8/12/18). With its
latest close encounter September 1, the probe has now completed three of those
trips. Each time, the spacecraft flew within about 24 million kilometers of the
sun’s surface — about twice as close as the planet Mercury ever gets.
Parker is already serving up plenty of surprises from its
first two trips. For example, “we’ve discovered some unexpected intense rogue [plasma]
waves rattling through the sun’s atmosphere,” says mission scientist Justin
Kasper, a physicist at the University of Michigan in Ann Arbor.
of plasma hurtling into space whacked Parker during its close encounters
with the sun, data show. Every so often, the speed of the plasma flowing away
from the sun would jump by nearly 500,000 kilometers per hour — nearly doubling
in speed — for up to a couple of minutes.
“We’ve never seen anything quite like that,” says Philippa
Browning, a solar physicist at the University of Manchester in England who is
not involved with the mission.
Each of these plasma waves was also accompanied by a sudden
reversal of the magnetic field around the probe. “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, 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 to Yannis Zouganelis,
an astrophysicist at the European Space Astronomy Centre in Madrid who is not
involved with this mission. “We should expect to see bended lines everywhere,”
he says. The sun’s magnetic field gets wibbly-wobbly at times, jiggling in
response to fluid churning within the sun. “However what is surprising is that
we see them very frequently and very strong.”
While the origin of these rogue waves is unclear, the
spacecraft recorded about 800 of them over 11 days during the first 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 at Parker’s distance of about 24 million
kilometers above the solar surface also whips around the sun much faster than
expected. Researchers expected to clock lateral speeds of a few kilometers per
second as the escaping plasma gets twirled off into space by the sun’s
rotation. Instead, the spacecraft recorded speeds as high as 50 kilometers 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, gradually
putting the brakes on its rotation (SN:
8/2/19). A faster wind spiral might mean stars spin down much faster than
thought, Kasper says.
“This is really amazing, if true,” says Zouganelis, though
he cautions that before rewriting stellar physics textbooks, these measurements
need to be confirmed at lower altitudes. That is one of the many things that Parker
will watch for on future orbits, Kasper says.
While Parker was busy raising new questions, 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 moving as much as twice
as fast as the other. Researchers already knew that the fast component
originates near the sun’s poles through funnellike openings in the magnetic
field 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 mission scientist Stuart Bale, a solar physicist at the
University of California, Berkeley. “But now we can see this very clearly.”
The list of new tidbits goes on. Parker’s cameras caught the formation of
magnetic “islands,” long-predicted tubes of plasma ensnared by a nest of
magnetic fields carting energy and matter into space. And the researchers think
that they may also be seeing hints of a long-hypothesized but never-before-seen
clearing in interplanetary dust near the sun.
The spacecraft also recorded a number of small bursts
of energetic particles, mostly protons, coming from the sun. These might
provide the seeds for more voluminous particle tsunamis sometimes carried aloft
as part of the solar wind, says David McComas, a solar physicist at Princeton
University in charge of one of Parker’s particle detectors. These smaller
bursts were not seen by other spacecraft orbiting farther out, which means
Parker is getting an up-close look at particle acceleration that would
otherwise be 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.”
That fire hose of information from Parker’s initial orbits
is sure to keep researchers occupied for years to come. “They’ve 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 job is far from over. On each of its next 18
orbits, the spacecraft will use the gravity of Venus to inch a little closer to
the sun. Then its last three orbits, starting in December 2024, will bring
Parker within just 6 million kilometers of the sun’s surface, more than seven times
as close as any previous mission, putting all of Parker’s special
protective technology to the test (SN:
Mission lead Nour Raouafi of the Johns Hopkins University
Applied Physics Laboratory in Laurel, Md., is confident in the solar probe’s future.
“We’ll never see the solar wind the same way,” he says. “Parker is going to
rewrite the textbooks for us.”