NASA spacecraft ‘Touches’ the Sun

The Parker Solar Probe has crossed a threshold and entered the Sun’s atmosphere, obtaining information that will aid scientists in their understanding of stars.

A NASA spacecraft has officially “touched” the sun, plunging through the unexplored solar atmosphere known as the corona. https://t.co/gNH6diBHG6

— The Associated Press (@AP) December 15, 2021

The long-awaited achievement, which occurred in April but was only revealed on December 14, is a significant achievement for the Parker Solar Probe, which is travelling closer to the Sun than any other mission in history.

“We’ve finally arrived“, said Nicola Fox, the director of NASA’s heliophysics division, which is based in Washington, DC. “Humanity has made contact with the Sun“.

During a press conference at this week’s American Geophysical Union meeting in New Orleans, Louisiana, she and other team members talked. Physical Review Letters published a paper explaining the findings.

Using this new opportunity, scientists will be able to explore some of the biggest questions about the Sun, including how it generates the solar wind and how its corona gets heated to temperatures much higher than those on its surface.

“This is a huge milestone“, says Craig DeForest, a solar physicist at the Southwest Research Institute in Boulder, Colorado, who is not involved with the mission. Flying into the solar corona represents “one of the last great unknowns”, he says.

Into the unknown

On April 28th, the Parker probe entered the Sun’s atmosphere at 9:33 a.m. Universal Time. 

It took mission scientists several months to download and analyse the data acquired, and to confirm that the spacecraft had crossed the much-anticipated Alfvén surface.

The interface between the Sun’s atmosphere and an outer region of space dominated by the solar wind is marked by this surface. 

It was the Swedish physicist Hannes Alfvén who proposed the underlying theory of the boundary in a paper in Nature in 1942, and scientists have been trying to discover it ever since.

But it took the $1.5 billion Parker Solar Probe to get there in the first place. It has been orbiting the Sun since its launch in 2018, looping closer to the solar surface with each pass.

Its instruments are protected by a carbon-composite heat shield against temperatures that will eventually reach 1,370 °C.

When the spacecraft reached 14 million kilometres away from the Sun’s surface, or just under 20 solar radii, it crossed the Alfvén boundary.

Some researchers had predicted that the boundary would be ‘fuzzy,’ but it was crisp and wrinkled instead. The spacecraft spent over five hours in the corona before returning to Earth, and it may have gone through it twice more.

The solar wind speed and plasma concentrations both decreased inside the corona, indicating that the boundary had been crossed. “We are learning new things that we did not have access to before“, Raouafi says.

Switchbacks

The Parker probe passed through a ‘pseudostreamer‘ of electrically charged material as it reached the Alfvén surface, where circumstances were quieter than the roiling environment outside.

The spacecraft also analysed strange twists in the magnetic field of the solar wind known as switchbacks while inside the corona.

Scientists have previously known about switchbacks, but the Parker Solar Probe data allowed them to track their origins all the way down to the solar surface.

The mission will make its closest approach to the sun in 2025, at a distance of only 6.2 million kilometres from the surface, well within Mercury’s orbit.

“Being this close to the Sun is allowing us to make really interesting and new connections we wouldn’t be able to do from afar”, he said.