NASA solar probe 'touches' the sun, uncovers solar wind mysteries
The first science results from the Parker Solar Probe shine a light on the sun's strange magnetic fields and energetic particles.
The Parker Solar Probe is in orbit around the sun and will continue to examine the star from close up.
NASA has a myriad of robots patrolling the solar system, all equally deserving of our love and attention, but perhaps the most badass of them all is the Parker Solar Probe. The spacecraft, about the size of a small sedan, is circling the sun, kitted out with revolutionary tech that allows it to "touch" the sun. On Wednesday, NASA investigators released the first set of science data from the mission, detailing the first measurements from one of the solar system's most extreme environments.
"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," said Nour E. Raouafi, project scientist at Johns Hopkins Applied Physics Laboratory. "What we've learned in just these three solar orbits alone has changed a lot of what we know about the Sun."
The space agency launched the Parker Solar Probe on Aug. 12, 2018, and was able to insert the heat-resistant spacecraft into an elliptical orbit around the sun. The orbit slingshots the probe at such a pace that it's already earned the title of "fastest-ever human-made object" and, using Venus for a gravity assist, the probe will continue to decrease its distance to the solar system's big heater.
In a suite of four papers, published in the journal Nature on Wednesday, researchers detail the first measurements taken by the Parker Solar Probe from inside the sun's aura of plasma, a region known as the corona, and analyze data from the PSP's first two close approaches, which occurred in November 2018 and April 2019. Temperatures in the corona hover between 2 million and 5 million degrees Fahrenheit, but how it's heated and how subatomic particles behave within has remained something of a puzzle for astronomers.
The corona also generates the solar wind, streams of energetic particles that emanate out into the solar system. In the past, astronomers have been able to measure these streams closer to Earth, but thanks to state-of-the-art tools aboard the PSP (hidden behind an impressive heat shield), some of the sun's secrets are beginning to be unraveled.
Parker has four instruments on board: a wide-field imager and three separate devices measuring the particles in the solar wind, in addition to the electric and magnetic fields surrounding the sun. The four papers presented in Nature outline the first measurements from each instrument and analyze the dynamics in a region of space that's never been probed before.
WISPR dust
The Wide-field Imager for Solar Probe acts as the probe's "eyes" and allows researchers to image structures formed by the solar wind in the corona. The WISPR delivered a stunning first-light image in September 2018 and then followed it up with a mind-blowing image from inside the sun's atmosphere in December of that year.
Russ Howard, principal WISPR investigator, examined pictures taken by the instrument to identify structures in the solar wind. The images reveal new dynamics in coronal "streamers," magnetic loops that brightly beam from the sun, and offer a look at faint coronal rays. The team also observed the intensity of dust-scattered light in the region around the sun, confirming observations made from Earth. However, they were surprised to see unusual intensity profiles closer to the sun.
The change in intensity could demonstrate a "dust-free zone" closer to the sun's surface, a hypothesis dating back as far as the Helios spacecraft experiments in the 1970s. Howard and colleagues caution in their study that the WISPR didn't directly observe the hypothesized dust-free zone, and alternate explanations could be a change in the properties or intensity of the dust, rather than quantity. Confirmation of this long-sought environment should come as the PSP decreases its distance to the sun over the coming years.
WISPR is able to capture images of the material flowing away from the sun, as seen in the large, white streaks emanating from the left of the image.
The solar wind isn't acting as predicted
A second unexpected finding was discovered by a team of researchers led by Justin Kasper. Using the Solar Wind Electrons Alphas and Protons instruments on board the PSP, Kasper and colleagues gathered information about how electrons, hydrogen ions and helium ions are moving through the solar wind. When the sun belches out these particles, they eventually collide with the SWEAP, which can record their properties -- a feat that occurs typically more than four times per second.
With an abundance of particles smashing into the SWEAP instruments, and supported by data from the FIELDS instrument aboard the PSP, Kasper and his team discovered that the near-sun solar wind is acting strangely as a result of magnetic field reversals. During a reversal, the velocity of the solar wind seems to spike, and the team thinks the streaming particles may follow an S-like curve as they move away from the sun.
Previously, scientists have measured solar wind particles streaming away from the sun like bullets, on straight trajectories across past the Earth. But Kasper's team discovered a surprising increase in the "rotational flow" of the solar wind that doesn't match any previous models of how the solar wind should rotate. Closer to the Sun, the wind is still rotating but the reason for this remains unknown.
"The large rotational flow of the solar wind seen during the first encounters has been a real surprise," said Kasper in a press release. "While we hoped to eventually see rotational motion closer to the Sun, the high speeds we are seeing in these first encounters is nearly ten times larger than predicted by the standard models."
As Parker continues to orbit, researchers will get a better look at the near-sun solar wind flows. The authors note this will "be essential for understanding how the sun loses angular momentum and spins down as it ages."
What's next?
On Dec. 26, the probe will perform its second flyby of Venus, using the planet's gravity to shrink its orbit even more and get even closer to the sun. The flyby will also see the Parker Solar Probe pick up even more speed, zipping around the sun at 109 kilometers per second, until a third Venus flyby in July 2020 kicks it up another gear again.
The PSP's activities will continue for the next five years, until 2025, and on closest approach the craft will be within 7 million kilometers (4.3 million miles). Mercury, the closest planet to the sun, is approximately 46 million kilometers from the star at its closest approach. Closing the distance, slowly, over the next five years will be crucial to understanding the complexities of the sun's corona, its surface, how solar wind is blasted out into the cosmos and the ways it affects the rest of the solar system.
In 2020, the PSP will be joined on its mission by another spacecraft, the European Space Agency's Solar Orbiter. Scheduled to launch in February, the spacecraft will also get up close and personal with the sun, swinging around in a highly elliptical orbit that brings it within approximately 42 million kilometers of the ultrahot plasma ball. With the two spacecraft patrolling the solar system's nuclear fusion reactor well into the next decade, scientists will begin to shine a light on the brightest object in our solar system and discover more surprises lurking within.
Updated 12:05 p.m. PT: Additional details, clarity from NASA's press event.