Today, scientists are releasing the surprising initial results from the Parker Solar Probe’s first two close encounters with the Sun.
From 36 solar radii away, it’s already clear that our Sun is a chaotic beast full of surprises, with solar winds circling it faster than expected, rapidly reversing magnetic fields, and blobs of plasma spewing from its corona. These first four papers have already generated new mysteries and demonstrate just how much science is yet to come from the Parker Solar Probe.
“I wasn’t counting on seeing surprising things this soon,” Justin Kasper, principal investigator of the Parker Solar Probe’s Solar Wind Electron Alphas and Protons (SWEAP) instrument, told Gizmodo. “There’s clearly not going to be a dull moment as we get closer and closer.”
The Parker Solar Probe launched in August 2018 to much fanfare. Its researchers are hoping to learn why the Sun’s outer atmosphere, also known as its corona, has temperatures over a million degrees Celsius while its surface is just a few thousand degrees Celsius. They also want to understand the process by which the corona emits the energetic particles we call the solar wind. The probe carries a suite of imaging, particle-measuring, and electromagnetic field-measuring instruments protected by an advanced carbon foam and ceramic heat shield.
The probe used Venus’s gravity to fling itself into an eccentric orbit that carries it faster and brings it closer to the Sun than any previous mission. After releasing data publicly last week, scientists are now presenting the results of the first two close encounters, which occurred in November 2018 and April 2019 and brought the spacecraft within 36 solar radii of the Sun. Their findings appear in four papers published today in Nature.
Perhaps the most dramatic discovery was the intricate details of the solar wind, which loses complexity as it travels toward Earth. The electromagnetic field-measuring FIELDS instrument observed jets of plasma punctuating a quieter solar wind emanating from a hole in the corona, producing regions where the magnetic field quickly whips around, according to the paper. In these regions, it’s as if you had entered a place where your compass needle begins flipping between south and north. The Sun is generating this solar wind structure even during the present solar minimum, when the Sun is supposed to be least active.
Observing the behaviours of the particles themselves with SWEAP revealed spikes in particle velocity associated with these magnetic field flips that occurred a thousand times over the course of one 11-day observation period. Furthermore, the particles’ rotational movement around the Sun peaked at between 35 and 50 kilometers per second, around 10 times faster than previously predicted based on the Sun’s own rotation, according to the paper. Imagine arriving at a merry-go-round and seeing the outermost animal travelling inexplicably fast; you’d be confused, too. Since the solar wind should be pulling energy away from the Sun, these high-velocity particles suggest that the Sun’s own rotation should be slowing down at a higher rate, too; it’s another mystery for scientists to figure out.
Imaging of the sunlight scattered by electrons and dust particles taken by the Wide-Field Imager for Parker Solar Probe instrument, or WISPR, mostly confirmed observations from Earth, with less scattering farther from the Sun. However, a drop-off in the scattering closer to the Sun seems to suggest evidence of a theorised but never observed “dust-free” zone. These observations also show evidence of the complex structure of the corona itself, with blobs of particles emanating from the corona. There was also evidence of twisted tubes of magnetic field called flux ropes, and, for the first time, evidence of ellipses of magnetic field called magnetic islands, which are generated by the energetic consequences of magnetic field lines crossing and rearranging, according to the research.
Finally, analysis of the particles above the corona using the Integrated Science Investigation of the Sun instrument, or ISʘIS, seems to show evidence of many more smaller particle emission events that we can’t see from the Earth. These smaller events may eventually cascade into the larger or higher-energy events that we do see, said David McComas, vice president of the Princeton Plasma Physics Laboratory. The team sees the particles accelerating in different ways, both directly from magnetic field lines reconnecting in the corona, from shocks, and even from smaller compression waves, the authors write. Accelerations from compression waves haven’t been seen before.
Overall, these results will help us understand the solar wind and space weather overall, as well as how particles are accelerated and move around the solar environment, Mitzi Adams, solar scientist at the NASA’s Marshall Space Flight Centre who was not involved in the work, told Gizmodo in an email.
And all of this is just from two flybys.
“This suggests that we can expect much more high-quality observations over the next six years of the Parker Solar Probe’s lifetime,” Reka Winslow, research assistant professor at the University of New Hampshire who was not involved in the analyses, told Gizmodo in an email. She explained that one of the biggest hindrances to understanding solar processes is the lack of data from the solar environment. “The more high-quality data we have, the higher the chance that we can conclusively answer some of the big questions still remaining in heliophysics.”
These missions show that a lot of information gets lost as particles make the journey between the Sun and Earth—data that the Parker Solar Probe will be able to record from its closer vantage point. Another mission from the European Space Agency, the Solar Orbiter, will soon join the Parker Solar Probe with its own suite of complementary instruments, Daniel Verscharen, senior research fellow at the University College London, noted in a Nature commentary. “These joint measurements will certainly close some of the remaining gaps in our knowledge of the Sun and the solar wind.”
The Sun will only grow more active as it continues from its current solar minimum to its maximum and back over an 11-year cycle, likely throwing even more surprises at the probe’s various instruments. Said Kasper: “I can’t even imagine what things are going to look like when we get three times closer.”