For the First Time Ever, a NASA Spacecraft Has ‘Touched’ the Sun

Scientists announced yesterday that NASA's Parker Solar Probe became the first spacecraft to "touch" the sun this past April when it reached the sun's upper atmosphere, known as the corona, Leah Crane reports for New Scientist. 

NASA set a goal to reach the sun around 60 years ago to answer fundamental questions about the center of our solar system, and it launched the Parker Solar Probe in 2018, Ashley Strickland reports for CNN.

"Parker Solar Probe 'touching the sun' is a monumental moment for solar science and a truly remarkable feat," Thomas Zurbuchen, the associate administrator for NASA's Science Mission Directorate, says in a press release. "Not only does this milestone provide us with deeper insights into our Sun's evolution and it's impacts on our solar system, but everything we learn about our own star also teaches us more about stars in the rest of the universe.”

Scientists announced this milestone yesterday at a meeting of the American Geophysical Union and published their findings in the journal Physical Review Letters.

NASA's Parker Solar Probe Touches The Sun For The First Time

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Since the Parker Solar Probe launched in 2018, it's been orbiting the sun and inching closer with every loop. On April 28, the probe finally crossed into the outer atmosphere and stayed there for about five hours, Alexandra Witze reports for Nature.

The probe crossed the Alfvén critical surface, which is the boundary between the end of the sun's atmosphere and the start of solar winds, which are streams of charged particles that radiate from the corona and carry a magnetic field. Researchers at the Harvard-Smithsonian Center for Astrophysics (CfA) built and monitor a key instrument on the spacecraft called the Solar Probe Cup, which collects particles from the sun's atmosphere, per a CfA press release. The Solar Probe Cup's data shows that the Parker Solar Probe dipped into the corona three times on April 28, at one point staying in the outer atmosphere for approximately five hours. To resist the sun's intense temperatures, the device is made of heat-tolerant chemicals like tungsten, niobium, molybdenum and sapphire. 

"The goal of this entire mission is to learn how the Sun works. We can accomplish this by flying into the solar atmosphere," says Michael Stevens, an CfA astrophysicist, in a statement. "The only way to do that is for the spacecraft to cross the outer boundary, which scientists call the Alfvén point. So, a basic part of this mission is to be able to measure whether or not we crossed this critical point."

Scientists previously calculated that the boundary was between 4.3 and 8.6 million miles away from the sun's surface. The Parker Solar Probe confirms that their estimates were close, crossing the threshold at 8.1 million miles away, Elizabeth Howell reports for Space.com.

The probe also confirmed scientists' hypotheses that the boundary wasn't a smooth sphere, but instead has "spikes and valleys." How these wrinkles line up with solar activity could help scientists understand the dynamics between the sun, its atmosphere and solar wind, according to the press release.

Additionally, the spacecraft offered new revelations about switchbacks, or structures in solar wind shaped like zigzags. Though scientists already knew about them, data collected by the probe suggests that they originate in the photosphere, the sun's visible surface, and have higher concentrations of helium, Space.com reports.

The Parker Solar Probe helped locate some of the switchbacks, but scientists are still debating between theories on how they're formed. Study coauthor Stuart Bale, an astrophysicist at the University of California, Berkeley, is hopeful that the spacecraft's data collection will help solve the conundrum.

"My instinct is, as we go deeper into the mission and lower and closer to the sun, we're going to learn more about how magnetic funnels are connected to the switchbacks," he says in the press release. "And hopefully resolve the question of what process makes them."

Though the Parker Solar Probe has already offered a glimpse into the sun's atmosphere, its work isn't done yet. It will approach the sun 24 times over its lifetime, and in 2025, it will get closer than ever before—only 4 million miles away, Nature reports. It sounds far, but experts say if the sun is at the endzone of a football field, Parker will be at the four-yard line, CNN reports.

"I’m excited to see what Parker finds as it repeatedly passes through the corona in the years to come," Nicola Fox, division director for NASA's Heliophysics Division, says in the press release. "The opportunity for new discoveries is boundless."

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Rasha Aridi is a science journalist based in Richmond, Virginia. She has written for Science magazine and Science News for Students. You can find her portfolio at rashaaridi.com.