Since it’s launch in 2018, NASA’s Parker Solar Probe has returned unprecedented data from near the Sun, culminating in new discoveries published on Dec. 4, 2019, in the journal Nature revealing that the dynamics of our star are even stranger than once imagined.
Among the findings the spacecraft observed during its first two flybys are new understandings of how the Sun’s constant outflow of material, the solar wind, behaves. Seen near Earth — where it can interact with our planet’s natural magnetic field and cause space weather effects that interfere with technology — the solar wind appears to be a relatively uniform flow of plasma. But Parker Solar Probe’s observations reveal a complicated, active system not seen from Earth.
“The Sun has fascinated humanity for our entire existence,” said Nour E. Raouafi, project scientist for Parker Solar Probe at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, which built and manages the mission for NASA. “We’ve learned a great deal about our star in the past several decades, but we really needed a mission like Parker Solar Probe to go into the Sun’s atmosphere. It’s only there that we can really learn the details of these complex solar processes. And what we’ve learned in just these three solar orbits alone has changed a lot of what we know about the Sun.”
“All of this brand-new information about how the way our star works is going to help us understand how the sun drives change in the space environment throughout our solar system,” said Nicola Fox, director of the heliophysics division at NASA, during a telephone news conference on Wednesday.
Meanwhile, Parker mission researchers at the University of Michigan in Ann Arbor, suggested that we’re missing something fundamental about the sun. The researchers provided important insights into two fundamental questions the mission was designed to answer: Why does the sun’s corona get hotter as your move further away from the surface? And what accelerates the solar wind–an outward stream of protons, electrons and other particles emanating from the corona. Both questions have ramifications for how we predict, detect and prepare for solar storms and coronal mass ejections that can have dramatic impacts on Earth’s power grid and on astronauts.
“Even with just these first orbits, we’ve been shocked by how different the corona is when observed up close,” said Justin Kasper, a professor of climate and space sciences and engineering at U-M who serves as principal investigator for Parker’s Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite. “These observations will fundamentally change our understanding of the sun and the solar wind and our ability to forecast space weather events.”
Solar wind acceleration findings
The spacecraft revealed that the sun’s rotation impacts the solar wind much farther away than previously thought. Researchers knew that close in, the sun’s magnetic field pulls the wind in the same direction as the star’s rotation. Farther from the sun, at the distance the spacecraft measured in these first encounters, they had expected to see, at most, a weak signature of that rotation.
“To our great surprise, as we neared the sun, we’ve already detected large rotational flows–10 to 20 times greater than what standard models of the sun predict,” Kasper said. “So we are missing something fundamental about the sun, and how the solar wind escapes.
“This has huge implications. Space weather forecasting will need to account for these flows if we are going to be able to predict whether a coronal mass ejection will strike Earth, or astronauts heading to the moon or Mars,” Kasper said.
Coronal heating findings
Parker Solar Probe’s findings regarding the sun’s magnetic field–which is believed to play a role in the coronal heating mystery–were equally surprising. From Earth’s vantage point, magnetic oscillations called “Alfvén waves” were detected in the solar wind long ago. Some researchers though they may be remnants of whatever mechanism caused the heating phenomenon.
Parker researchers were on the lookout for indications that might be the case, but found something unexpected.
“When you get closer to the sun, you start seeing these ‘rogue’ Alfvén waves that have four times the energy than the regular waves around them,” Kasper said. “They feature 300,000 mph velocity spikes that are so strong, they actually flip the direction of the magnetic field.”
Those polarity-reversing velocity spikes offer another potential candidate for what may cause the corona to get hotter moving away from the sun.
“All of this new information from Parker Solar Probe will cause a fundamental rethinking of how the magnetic field of the Sun behaves and is coupled to the acceleration of the solar wind,” said Lennard Fisk, the Thomas M. Donahue Distinguished University Professor of Climate and Space Sciences and Engineering.
Read more at Nature: “A step closer to the Sun’s secrets”
Image credits top of page: An artist’s depiction of NASA’s Parker Solar Probe gathering data about the sun.