Melissa Weiss / CfA
Artist’s concept of the boundary in the solar atmosphere, where the speed of the outer solar wind becomes greater than the speed of magnetic waves.
Scientists have created and validated the first two-dimensional maps of the Sun’s outer surface, offering unprecedented insight into how and where the star “loses control” over its outer atmosphere.
A team of astronomers from the Center for Astrophysics | Harvard & Smithsonian (CfA) produced the first continuous, two-dimensional maps of the outer limit of the solar atmosphere — an ever-changing boundary, frothy and turbulentwhich marks the point at which the solar wind escapes the domain of the Sun’s magnetic field.
By combining these maps with proximity measurements, scientists showed that this border becomes biggerrougher and more “spiky” as the Sun enters a phase of greater activity.
The results of the study, presented in a published last week in The Astrophysical Journal Letterscould help improve models on how the Sun influences Earth and better predict the atmospheric complexity of other stars.
“The Parker Solar Probe data collected well below the surface of Alfvén can help answer big questions about the Sun’s corona, like why it’s so hot. But to answer these questions, we first need to know exactly where the border is,” he said. Sam Badmanastrophysicist at the CfA and main author of the article, in a CfA.
Scientists directly validated these maps using deep forays into the solar atmosphere carried out by NASA’s Parker Solar Probe. The results are published today in Astrophysical Journal Letters (ApJL).
A boundary in the Sun’s atmosphere at which the outward solar wind speed becomes greater than the speed of magnetic wavesdesignated by astronomers as surface of Alfvénand the “point of no return” for material that escapes the Sun and enters interplanetary space: once it passes this point, that material can no longer return to the Sun.
This surface works, in practice, as the “margin” of the solar atmosphere and provides scientists with an active laboratory to study and understand how solar activity affects the rest of the Solar System, including life and technology on and near Earth.
Using Parker’s Solar Wind Electrons Alphas and Protons (SWEAP) instrument, developed by the CfA in conjunction with the University of California, Berkeley, the team collected data in the deep interior of the sub-Alfvénic region of the solar atmosphere.
“There are still several fascinating questions of physics about the Sun’s corona that we don’t fully understand,” said Michael StevensCfA astronomer and principal investigator for Parker’s SWEAP instrument.
“This work shows, without a doubt, that the Parker Solar Probe is diving deeply, with each orbit, into the region where the solar wind originates. We are now entering an exciting periodin which the probe will directly observe how these processes change as the Sun advances to the next phase of its activity cycle”, he added.
Scientists already knew that this frontier varies dynamically throughout solar cycles, moving away from the Sun and becoming larger, more structured and more complex during solar maximum, and the reverse during solar minimum. However, until now, there was no confirmation on the exact aspect of these changes.
“As the Sun goes through cycles of activity, what we are seeing is that the formal form of Alfvén’s superfícies around the Sun they are enlarging and becoming spikier. This is precisely what we predicted in the past, but now we have been able to confirm it directly”, concludes Badman.
