NASA’s Parker Solar Probe has made history after becoming the first spacecraft to plunge into the Sun’s atmosphere.
The milestone journey was made on 28 April 2021, nearly three years after the probe’s launch in August 2018, during its eighth flyby. It spent a total of five hours travelling amidst the plasma and solar winds in the Sun’s upper atmosphere, or corona.
The landmark event was not announced until 14 December as the data recorded by the probe took several months to reach the Earth and then several more to be processed and analysed by scientists.
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“We were fully expecting that, sooner or later, we would encounter the corona for at least a short duration of time,” said Justin Kasperdeputy chief technology officer at BWX Technologies, Inc. and University of Michigan professor. “But it is very exciting that we’ve already reached it.”
"This marks the achievement of the primary objective of the Parker mission and a new era for understanding the physics of the corona.”
Parker spent five hours exploring the Sun’s atmosphere beneath a boundary known as the Alfvén critical surface – the point at which the star’s powerful gravitational and magnetic fields are no longer strong enough to prevent solar winds from escaping out into the Solar System, to Earth and beyond. During this time, it passed above and below the boundary a total of three times.
“We have been observing the Sun and its corona for decades, and we know there is interesting physics going on there to heat and accelerate the solar wind plasma. Still, we cannot tell precisely what that physics is,” said Nour E Raouafi, the Parker Solar Probe Project Scientist at JHU/APL. “With Parker Solar Probe now flying into the magnetically-dominated corona, we will get the long-awaited insights into the inner workings of this mysterious region.”
Until now, researchers were unsure exactly where the Alfvén critical surface lay. Preliminary results from Parker show that it lies about 13 million km from the Sun’s surface. The data show it is wrinkled and suggest that these wrinkles may be caused by a pseudostreamer – a giant magnetic formation that rises above the Sun’s surface and can be seen from Earth during solar eclipses.
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This first passage through the corona is just one of many planned for the mission. It is hoped that the probe will continue to spiral ever closer to the Sun, eventually coming within 6 million km of its surface.
Upcoming flybys, the next of which is happening in January 2022, will likely bring Parker Solar Probe through the corona again.
“I’m excited to see what Parker finds as it repeatedly passes through the corona in the years to come,” said Nicola Fox, division director for the Heliophysics Division at NASA Headquarters. “The opportunity for new discoveries is boundless.”
The size of the corona is also driven by solar activity. As the Sun’s 11-year activity cycle reaches its peak, the outer edge of the corona will expand, giving Parker Solar Probe a greater chance of being inside the Sun’s atmosphere for longer periods of time.
“It is a really important region to get into because we think all sorts of physics potentially turn on,” Kasper said. “And now we're getting into that region and hopefully going to start seeing some of these physics and behaviours.”