NASA Spacecraft 'Touches' The Sun For First Time In 'Monumental Moment' For Solar Science

Parker Solar Probe entered the Sun's corona and sampled particles and magnetic fields there, which proved to be a major milestone for solar science.

New Delhi: A NASA spacecraft has touched the Sun for the first time in history. The spacecraft, called the Parker Solar Probe, entered the Sun's upper atmosphere, or the corona, and sampled particles and magnetic fields there.

This proves to be a major milestone for solar science. The feat is as phenomenal as the Moon landing, because touching the solar surface will help scientists obtain important information about Earth's closest star, and its influence on the solar system.

Quoting Thomas Zurbuchen, the associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, a NASA statement said that the Parker Solar Probe "touching the Sun" is a monumental moment for solar science and a truly remarkable feat. He said the milestone provides deeper insights into the Sun's evolution, and everything learnt about our star will help scientists know more about stars in the rest of the Universe.

Parker has made significant discoveries such as information about the flow of particles from the Sun that can influence people on Earth. The fact that magnetic zigzag structures in the solar wind, called switchbacks, are quite close to the Sun, was discovered by Parker in 2019. Now that Parker has halved the distance to the Sun since then, and has touched the solar corona, the probe can identify the origin of these structures, NASA said on its website.

Nour Raouafi, the Parker project scientist at the Johns Hopkins Applied Physics Laboratory, said the Parker Solar Probe now senses conditions in the magnetically dominated layer of the solar atmosphere, as it is flying close to the Sun. He added that NASA can actually see the spacecraft flying through coronal structures observed during a total solar eclipse.

Parker Solar Probe Closer To Sun Than Ever Before

Launched in 2018, the Parker Solar Probe explores the mysteries of the Sun by traveling closer to it than any spacecraft before. Parker has finally arrived at the Sun three years after launch. 

The Sun does not have a solid surface but a superheated atmosphere made of solar material bound to the Sun by gravity and magnetic forces. Since rising heat and pressure push that material away from the Sun, it reaches a point where gravity and magnetic fields are too weak to contain the material. 

That point is called the Alfven critical surface, and marks the end of the solar atmosphere and beginning of the solar wind. When solar material and solar energy make it across the boundary, they become the solar wind, which drags the magnetic field of the Sun with it. The solar wind moves very fast beyond the Alfvén critical surface.

Researchers estimated that the Alfvén critical surface lies somewhere between 10 to 20 solar radii, or 4.3 to 8.6 million miles from the surface of the Sun. Parker, which has a spiral trajectory, was consistently below 20 solar radii during the last few passes towards the Sun. This distance is 91 per cent of Earth's distance from the Sun, and put Parker in the position to cross the boundary, according to NASA.

On April 28, 2021, Parker made its eighth flyby of the Sun, and encountered the specific magnetic and particle conditions at 18.8 solar radii, which is around 8.1 million miles, above the solar surface. This meant Parker had crossed the Alfvén critical surface for the first time, and finally encountered the solar atmosphere.

A paper about the milestone was recently published in the journal Physical Review Letters. Justin Kasper, the lead author of the study, said it is very exciting that NASA has already reached the corona.

Parker Looks Into The Eye Of The Storm

Parker passed in and out of the corona several times during its eighth flyby. Some scientists had predicted that the Alfvén critical surface is not shaped like a smooth ball, and Parker's movements proved this. The surface has spikes and valleys that wrinkle the surface.

Scientists will try to discover where the protrusions line up with solar activity coming from the surface to learn how solar events affect the atmosphere and solar wind.

There was a point when the Parker Solar Probe dipped to just beneath 15 solar radii below the Sun's surface. The probe transited a feature in the corona called a pseudostreamer, which is a massive structure that rises above the Sun's surface and can be seen during solar eclipses.

When Parker passed through the pseudostreamer, it was like flying into the eye of a storm. The conditions quieted and particles slowed inside the pseudostreamer. Also, a number of switchbacks dropped, which is a dramatic change from the busy barrage of particles the spacecraft usually encounters in the solar wind. 

This was the first time Parker found itself in a region where the magnetic fields were strong enough to dominate the movement of particles there. All this proved that Parker had passed the Alfvén critical surface and entered the solar atmosphere where magnetic fields shape the movement of everything in the region. 

However, Parker's mission does not end here. The spacecraft's first passage through the corona lasted only a few hours. Parker will continue spiraling close to the Sun, and is expected to eventually reach as close as 8.86 solar radii from the solar surface, according to NASA. Parker will pass through the corona again in January 2022.

Solar activity drives the size of the corona. At the end of the solar cycle, which is the Sun's 11-year activity cycle, the outer edge of the corona will expand. This will give Parker a greater chance of being inside the corona for longer durations.

Kasper said that Parker entering the solar corona will help scientists see some of the physics and behaviours of solar particles.

Scientists think that the magnetic tunnels might be where one component of the solar wind — the faster variety — originates.  

Stuart Bale from the University of California said the structure of the regions with switchbacks matches up with a small magnetic funnel structure at the base of the corona. 

Parker's closer passes are expected to reveal more clues about switchbacks and other solar phenomena, and will give scientists a glimpse into a region that is critical for understanding extreme space weather events that can disrupt telecommunications and damage satellites around Earth.

Parker Solar Probe is a part of NASA's Living With a Star program. It's goal is to explore aspects of the Sun-Earth system that directly affect life and society.