- NASA’s Parker Solar Probe has become the first spacecraft to touch the sun.
- Researchers announced the milestone December 14 in a virtual press conference held by the American Geophysical Union Conference.
- Results from the probe's journey could answer big picture questions about our sun and other stars.
NASA’s Parker Solar Probe has passed through the sun’s atmosphere—a feat no other spacecraft has achieved. Data from these flybys could help researchers answer critical questions about how the star generates solar wind and shed light on the inner workings of distant stars across the universe.
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“I’m thrilled to say that we've officially touched the sun,” Justin Kasper, a researcher at BWX Technologies, Inc. and the University of Michigan, said December 14 in a virtual press conference held by the American Geophysical Union.
The spacecraft, which launched from Florida’s Cape Canaveral Space Force Station in 2018, is designed to withstand incredible amounts of heat and radiation. The record-breaking probe—built and operated by John’s Hopkins University Applied Physics Laboratory (JHUAPL)—is also the single fastest object humans have ever constructed, with an orbital speed of about 430,000 miles per hour.
Understanding the Alfvén Critical Surface
During Parker’s eighth flyby on April 28, 2021, the probe passed in and out of a region called the Alfvén critical surface, the team announced. This boundary marks the separation between the sun’s atmosphere, or corona, where solar material is still trapped by gravitational and magnetic forces, and the surrounding layer of solar wind.
Researchers have worked to map the extent of this boundary for more than half a century, with recent estimates placing it somewhere between 4.3 to 8.6 million miles from the surface of the sun.“We have been wondering about this for six decades now," Nour Raouafi, a project scientist for the Parker Solar Probe Mission at JHUAPL, said during the press conference. "But now, we are there."
Data collected during the April 28 flyby, which took the craft within 8.1 million miles of the Sun’s surface, revealed that conditions within the sun’s atmosphere were dramatically different than those outside it.
“Inside the corona, the sun’s magnetic field grew much stronger and then dominated the movement of the particles there,” said Kasper, who is the lead investigator for the spacecraft's Solar Wind Electrons Alphas and Protons (SWEAP) project and one of the authors of a paper in Physical Review Letters about the discovery. "Instead of waves just gushing out from the sun, which is what we normally see in the solar wind, waves there were moving back and forth.”
The team is hopeful the data will eventually help solve three outstanding questions about the sun.
First, scientists have long known that the sun’s corona is millions of degrees hotter than its surface, which hovers around 6,000 degrees Fahrenheit. This temperature spike seems to defy the laws of physics. As Parker passes through the sun’s corona, it could shed light on how this heating occurs.
Another quirk: The magnetic field in the sun’s corona is so strong it slows down the rate at which the sun spins. Scientists suspect the rate at which this spin down occurs could be related to the location of the Alfvén critical surface, Kasper explained. “Now that we know the location of the [Alfvén critical surface], this will allow us to determine how solar activity changes over long timescales as the sun ages and slows down,” he said.
These measurements could also provide insight about the origins of solar wind and reveal how different types of solar wind form. Understanding these processes could help researchers better predict dangerous solar weather events which could disable Earth-orbiting satellites and wreak havoc on our planet's power grid. (See: the Carrington Event of 1859.)
The flyby revealed clues about the shape of the boundary layer, too. Since the spacecraft passed through the Alfvén critical surface multiple times, researchers can infer that it doesn’t uniformly wrap about the star. Instead, it appears to be made up of a kaleidoscope of twirling peaks and troughs, likely shaped by solar activity.
Finally, during this flyby, the spacecraft sped through a feature called a pseudostreamer. These massive tendrils of solar material are the same features seen emanating from the blotted sun during a solar eclipse. “Flying through this region was like flying through the eye of the storm,” Kasper said. “The conditions quieted, the density of the atmosphere dropped significantly, and the sun's magnetic field was stronger.”
Parker has also shed light on the origins of a solar feature called switchbacks. Since scientists first observed these curly-cue structures in the mid-90s, researchers have sought to understand their origins, including how and where exactly they form.
Now, scientists can begin to piece together answers to these questions. Measurements collected by Parker’s instruments during this latest flyby revealed an usually high number of helium ions within the switchbacks, which suggest that they could originate on or near the sun’s surface. The spacecraft also spotted a magnetic funnel-like feature, which emanates from the sun’s photosphere and appears to align with the switchbacks. The team theorized that these magnetic funnels may also generate the solar winds that sweep across the solar system.
On the Horizon
Parker is just getting started. The spacecraft’s next flyby will occur in January, 2022. (The closest flyby of the entire mission will take the spacecraft as close as 4 million miles from the sun’s surface and is scheduled for 2025.) And it’s perfect timing, too, because the sun is entering the height of its activity cycle and will likely generate more space weather.
“The data to come will allow us a glimpse into the region that’s critical for superheating the corona and pushing the solar wind supersonic speeds,” Kelly Korreck, a program scientist and Parker Solar Probe team member at NASA’s headquarters, said during the press conference. “These types of measurements from the corona will be critical for understanding and forecasting extreme space weather events that can disrupt telecommunications and damage satellites around the Earth.”