Tuesday, August 16

A NASA spacecraft ‘touches’ the Sun for the first time




For the first time in history, a spaceship has touched the Sun. This is the Parker Solar Probe, the NASA ingenuity that these days has flown through the fiery upper atmosphere of our star, the corona, to take samples of particles and measure its intense magnetic fields.

The achievement is a milestone and a breakthrough in our understanding of the Sun. Just as landing on the Moon allowed scientists to unravel the mysteries of its formation, directly ‘touching’ the solar material will help researchers discover new ones. data on the star that dominates the Solar System and to which we owe our existence.

“Touching the Sun is a monumental moment for solar science and a truly remarkable feat,” says Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington.

This milestone not only provides us with more in-depth information about the evolution of our Sun and its impacts on the Solar System, but everything we learn about our own star also teaches us more about stars in the rest of the universe. “

As it has approached the solar surface, Parker has discovered things that other spacecraft could not. In 2019, for example, he discovered that the solar wind’s zig-zag magnetic structures, called curves, abound near the Sun. But how and where they form remained a mystery. Now, half the distance from the Sun than then, the spacecraft has passed close enough to identify one of the places where they originate: the solar surface itself.

This first pass through the corona, and those to come, will continue to provide new data on phenomena that are impossible to study from afar.

The Parker Solar probe passes through a series of massive structures in the solar corona
The Parker Solar probe passes through a series of massive structures in the solar corona – NASA / Johns Hopkins APL / Naval Research Laboratory

Parker Solar Probe was launched in 2018 with the goal of getting much closer to the Sun than any previous spacecraft. And now, three years after launch and several decades after the mission was conceived, it has finally arrived. Unlike Earth, the Sun does not have a solid surface. But it has a superheated atmosphere, made of material that binds to the Sun thanks to gravity and magnetic forces. As increasing heat and pressure push that material away from the star, it reaches a point where gravity and magnetic fields are too weak to contain it.

That point, known as the ‘critical surface of Alfvén’, marks the end of the solar atmosphere and the beginning of the solar wind. Solar material with enough energy to cross that boundary becomes the solar wind, which carries the Sun’s magnetic field as it moves toward Earth and beyond. It is important to note that beyond the critical Alfvén surface, the solar wind moves so fast that on the other side, the wind that has crossed the critical limit will never be able to travel fast enough to return to the Sun, so the connection between the two is cut off.

Until now, researchers weren’t sure where exactly Alfvén’s critical surface was located. Based on remote images of the corona, estimates had placed it between 10 and 20 solar radii from the Sun’s surface: between 6.9 and 13.8 million km. But Parker’s spiral path is slowly bringing it closer to the Sun and during the last few passes, the spacecraft was well below 20 solar radii, putting itself in a position to cross the boundary, if the estimates were correct.

On April 28, 2021, during its eighth flyby of the Sun, Parker Solar Probe encountered the specific boundary conditions at 18.8 solar radii (about 13.3 million miles) above the solar surface. And that was what allowed the scientists to know that it had crossed the critical surface of Alfvén and that it was entering the solar atmosphere for the first time.

“We were looking forward to meeting the crown sooner or later for at least a short period of time,” said Justin Kasper of the University of Michigan and lead author of a new paper on the milestone published in
‘Physical Review Letters
‘-. But it is very exciting that we have already achieved it. “

In the eye of the hurricane

During its flyby, Parker Solar Probe went in and out of the crown several times. So she was able to check for herself the predictions that Alfvén’s critical surface is in the shape of a smooth ball. Nothing could be further from the truth. In fact, it has peaks and valleys that crinkle its surface. Finding out where these bulges align with activity from the solar surface can help scientists learn how events on the Sun affect the atmosphere and the solar wind.

At one point, when Parker Solar Probe dived just below 15 solar radii (about 10.4 million km) from the Sun’s surface, it passed through a characteristic massive corona structure rising above the surface of the Sun and that can be seen from Earth during eclipses.

Passing through some structures, known in English as pseudostreamers (pseudo streamers) was like flying into the eye of a storm. Inside, conditions calmed down, particles slowed down, and the number of bends decreased, a dramatic change from the busy barrage of particles the spacecraft typically encounters in the solar wind.

At that time, and for the first time, the spacecraft found itself in a region where magnetic fields were strong enough to dominate particle motion. These conditions were the definitive proof that the spacecraft had passed the critical Alfvén surface and entered the solar atmosphere.

The first pass through the crown, which lasted only a few hours, is one of many planned for the mission. Parker will continue to get even closer to the Sun in a spiral path, eventually reaching 8.86 solar radii (6.1 million km) from the surface. The upcoming flybys, the next of which will take place in January 2022, will likely carry Parker Solar Probe through the crown again.

“I am eager to see what Parker finds as he repeatedly passes for the crown in the coming years,” said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. “The opportunity for new discoveries is limitless.”

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