One of the biggest puzzles about our sun is a strange one: you might think that it would be hottest right at the surface, but in fact, that isn’t the case. The corona, or the sun’s outer atmosphere, is hundreds of times hotter than its surface. It’s still not clear exactly what that should be the case, so it’s an issue that solar missions are keen to research.
Recent results from the European Space Agency (ESA)’s Solar Orbiter mission give some clues. Solar Orbiter worked together with another mission, NASA’s Parker Solar Probe, to get data on both close-up in-situ measurements and a big-picture overview of the sun’s activity. Using Solar Orbiter’s Metis coronagraph instrument, researchers were able to get data from the sun’s corona at the same time that Parker Solar Probe passed within its field of view on 1 June 2022.
However, getting the two spacecraft into position required some finagling, as Parker Solar Probe travels close to the sun to take measurements of the immediate environment around it, while Solar Orbiter sits further away from the sun to observe it in totality. Even when both spacecraft were in the right locations, they still needed to be pointed in just the right direction.
In the end, Solar Orbiter had to perform a 45-degree role and change its angle slightly so both could work together to make their observations. This allowed the researchers to collect detailed data on what was happening in the plasma (the charged gas in the corona) while simultaneously seeing the corona as a whole.
The results support a long-held theory that the corona becomes so hot due to turbulence in the atmosphere. “The specific way that turbulence does this is not dissimilar to what happens when you stir your morning cup of coffee,” ESA explains. “By stimulating random movements of a fluid, either a gas or a liquid, energy is transferred to ever smaller scales, which culminates in the transformation of energy into heat. In the case of the solar corona, the fluid is also magnetized and so stored magnetic energy is also available to be converted into heat.”
This helps provide scientists with a greater understanding of the puzzle of the hot corona and also shows how the two spacecraft were able to work together to get data that neither could accomplish on their own.
The research is published in The Astrophysical Journal Letters.
