After more than three years since its launch , NASA’s Parker solar probe has finally managed to “touch” the Sun, entering our star’s atmosphere and beginning to gather new information during the five hours it remained in the area.
The solar atmosphere has a proper name – “crown” – and the arrival in it resulted in a paper published in Physical Review Letters , in a publicly accessible manuscript and free download .
“This marks the achievement of the primary objective of the Parker mission, as well as a new era of understanding the physics around the crown,” said Justin C. Kasper, primary author of the paper and interim co-CTO at BWX Technologies.
“This achievement not only gives us a deeper understanding of the evolution of the Sun and its impacts on our system, but everything we learn about our own star also teaches us about the stars in the rest of the universe,” said Thomas Zurbuchen, associate administrator from NASA’s Science Mission Directory in Washington.
According to preliminary data from the probe’s navigation, the Sun’s outer edge begins at a point known as the “Alfvén surface” – a specific point where the star’s gravitational and magnetic forces exert direct control over the solar winds . Some people think that unexpected reversals in the Sun’s magnetic field – the “zigzag effect” (or, in English, “ solar switchbacks ”) – are born here.
“The concept of sending a spacecraft into the Sun’s magnetized atmosphere — close enough that the magnetic energy is greater than the thermal, ion, and kinetic energies — is older than NASA itself,” said Kasper.
According to mission scientists, “zigzags” were noticed more frequently above the Alfvén line and much less below it, suggesting that these effects do not originate within the solar corona. Either that, or low-frequency magnetic reconnection on the Sun’s surface threw less mass into the current observed by the probe, which would reduce the number of occurrences of the effect.
“We’ve been looking at the Sun and its corona for decades, and we know there’s a whole lot of interesting physics in the region that heats and accelerates the wind of solar plasma. Even so, we can’t say precisely what kind of physics this is,” said Nour E. Raouafi, lead scientist for the Parker Solar Probe project , which created the probe inside the mission coordinator, Johns Hopkins University. “With this probe now flying inside the corona dominated by the magnetic field, we will have long-awaited information about the inner workings of this mysterious region.”
Unlike Earth , the Sun doesn’t have a solid surface – that’s why it’s impossible to “land” on the star in the literal sense of the word. However, its superheated atmosphere is made of material attached to the star by its immense gravitational and magnetic forces. In the corona, as the temperature increases and exerts more pressure to push this material out of the Sun, there is a point where these two forces become too weak to contain this action – resulting in solar winds.
These winds are nothing more than extremely energetic storms, which carry part of the Sun’s magnetic force to the rest of the solar system, sometimes reaching the Earth and other planets . Here, the effects of this are varied, impacting electrical distribution networks, radio and GPS satellites and even electronic equipment.
This point, named “Alfvén’s critical surface”, has never been properly known to us. Before the probe actually “touched” the Sun, estimates indicated that it started at some position between 6.92 million and 13.84 million kilometers (km) from the Sun.
During its eighth pass, the Parker probe found the specific magnetic and particle conditions that hinted at the beginning of the Alfvén surface, at a distance of 13.03 million km, marking the first time in history that humanity has managed to “touch” the sun.
“We already expected that, sooner or later, we would find the solar corona for at least a short period of time,” said Justin Kasper, another author of the paper and co-CTO of BWX Technologies. “But even so, it’s really exciting to see that we’ve already hit it.”
An interesting finding is that Alfvén’s critical surface, contrary to popular belief, is not a “smooth” projection, but full of peaks and dips – like a roller coaster. The idea is that these deformations line up with solar activity at some point – we still need to figure out “where” – which should help us understand how events from the Sun affect its atmosphere and solar wind capacity.
“It’s truly exciting to see our advanced technologies succeed in bringing the Parker solar probe closer to the Sun than we’ve ever been, and giving us back all this spectacular science,” said Joseph Smith, Parker Program executive at NASA. “We’re excited to see what else this mission can discover as it approaches in the coming years.”