NASA’s Sun-Orbiting Probe Reveals New Secrets of Our Host Star
The first findings from the Parker Solar Probe change what we know about the workings of our nearest star
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In August 2018, NASA launched the Parker Solar Probe toward the sun to analyze and measure the G-type yellow dwarf star that makes life on Earth possible. Now, after the spacecraft completed 3 of 24 planned close orbits around the sun, researchers have released four papers published in the journal Nature detailing the probe's first findings.
The $1.5 billion probe has flown closer to the sun than any spacecraft in history, passing through the sun’s upper atmosphere, or corona, for the first time. The probe is loaded up with several suites of instruments that collect data about solar wind, plasma flows, the sun’s magnetic field and more, reports Alexandra Witze at Nature News & Comment.
Scientists at University of California, Berkeley led by plasma physicist Stuart Bale control the probe’s devices, fittingly dubbed FIELDS, that study the sun’s magnetic and electric fields. A second toolkit called SWEAP—or Solar Wind Electrons Alphas and Protons, operated by the University of Michigan and the Smithsonian Astrophysical Observatory—measures the particles of solar winds. The probe’s imaging instrument WISPR is led by the Naval Research Lab. Another group of devices—called the Integrated Science Investigation of the Sun suite, led by Princeton University—measures the sun’s outflow of energetic particles, like electrons and ions. Together, data from all of these instruments are revolutionizing what we know about the star.
Solar winds constantly wash over Earth, but studying the phenomenon from an earthly vantage point is like trying to understand the origin of a waterfall by standing halfway down the cliff, explains Bale. Expanding on the waterfall analogy, Bale tells Witze, “[i]f you want to know the source, you have to get up there and get closer—is it coming from one hole in the ground? From a bunch of seams in the rocks? Is there a sprinkler system up there?”
The so-called “fast solar wind,” which flows at 500 to 1,000 kilometers per second, emanates from large holes in the corona near the sun’s north and south poles, reports Hannah Devlin at The Guardian. However, the origin of the “slow solar wind,” which is denser and travels at about half that speed, is not understood, explains atmospheric physicist Tim Horbury of Imperial College London, who is part of FIELDS research team.
During each swoop toward the sun, the probe passes about 15 million miles above a coronal hole for up to a week at a time to measure the solar wind and magnetic fields, according to a Berkeley press release.
Parker Solar Probe is also investigating a mystery that has long baffled solar physicists: the extreme heat of the outer atmosphere. “The corona is a million degrees, but the sun’s surface is only thousands,” Horbury tells Devlin. “It’s as if the Earth’s surface temperature were the same, but its atmosphere was many thousands of degrees. How can that work? You’d expect to get colder as you moved away.”
Data from the spacecraft shows that the movement of plasma in the corona is extraordinarily complex. The measurements revealed that quick reversals in magnetic fields and fast-moving jets of plasma cause turbulence in the solar wind. The researchers dubbed one particularly dramatic type of magnetic field reversal a “switchback.”
As the solar wind flows away from the sun, the magnetic field lines would almost completely reverse for a few seconds or even a few minutes, causing abrupt changes in velocity. When the magnetic field snaps back to its previous orientation, it produces a spike in energy. While the researchers do not yet know what causes these magnetic reversals, the spacecraft's close observations will help them narrow down the possibilities.
“These switchbacks are probably associated with some kind of plasma jets," Bale says in the Berkeley release. “My own feeling is that these switchbacks, or jets, are central to the solar wind heating problem.”
The Parker probe was able to measure solar wind while it was still rotating with the sun, finding that the speed and strength of the rotation was ten times more powerful than current solar models predict.
Because the sun rotates, solar wind travels on a curved path. But after the energy is flung into space, its path eventually straightens out. Finding out the exact point at which that energy starts traveling in a straight line will tell researchers about the lifecycles of stars and the workings of protoplanetary disks, which will improve our understanding of how planets form.
The probe also observed the sun’s “dust-free zone.” Our solar system is full of dust particles remaining from the planet-forming process that occurred over billions of years. Researchers long ago predicted that the heat of the sun could vaporize this dust into gas creating an area with much less dust. The probe has finally found supporting evidence of this phenomenon and researchers suspect it will likely encounter less and less dust as it swings closer to the sun.
Scientists also used the probe’s data to measure the outflow of electrons and ions that sometimes produce solar flares or coronal mass ejections (CMEs). So far, the Parker probe has recorded several new types of particles and ejection events that researchers are unable to observe from Earth, explains Princeton’s David McComas who leads the Integrated Science Investigation of the Sun suite of instruments.
“It’s amazing—even at solar minimum conditions, the sun produces many more tiny energetic particle events than we ever thought,” says McComas in a NASA press release. “These measurements will help us unravel the sources, acceleration, and transport of solar energetic particles and ultimately better protect satellites and astronauts in the future.”
As Mike Wall at Space.com reports, this new data is really just a taste of what the probe will likely discover if its 4.5-inch-thick, carbon-composite shield can survive the remaining 21 dips closer and closer to the sun over the next five years. Eventually, the craft will fly as close as 3.83 million miles above the sun.
“We knew we were going into a region we've never been before. It is a voyage of discovery,” Nicola Fox, director of the NASA’s Heliophysics Division, tells Nell Greenfieldboyce at NPR. “It's going to the last sort of major region of our solar system to ever be visited by a spacecraft. And as we continue to get closer and closer, then I'm sure that we are going to continue to see more and more surprises."