The combined use of ESA’s Solar Orbiter missions and NASA’s Parker missions helps solve the mystery why the sun’s atmosphere is so hot relative to the surface.
The scientists used data collected when The Parker Solar Probe explored the Sun up close and the ESA/NASA Solar Orbiter observed it from further back.
The Sun’s atmosphere is called the corona. It consists of an electrically charged gas called plasma and has a temperature of about one million degrees Celsius.
Its temperature is an enduring mystery, as the sun’s surface is only about 6,000 degrees. The corona should be colder than the surface because the Sun’s energy comes from the nuclear furnace at its core, and things naturally cool the further they are from a heat source. However, the corona is more than 150 times hotter than the surface.
Another method must be to transfer energy to the plasma, but which one? It has long been suspected that turbulence in the solar atmosphere could lead to significant heating of the plasma in the corona. But when studying this phenomenon, solar physicists encounter a practical problem: it is impossible to collect all the data needed with a single space probe, explains the ESA it is a statement.
There are two ways to study the sun: Remote sensing and in-situ measurements. In remote sensing, the spacecraft is placed at a certain distance and uses cameras to observe the sun and its atmosphere at different wavelengths. During in-situ measurements, the space probe flies through the region it wants to examine and measures the particles and magnetic fields there.
Both approaches have their advantages. Remote sensing shows large-scale results, but not the details of the processes occurring in the plasma. In-situ measurements now provide very specific information about small-scale processes in the plasma, However, they do not show how this plays out on a large scale.
To have a full view, two spacecraft are required. That’s exactly what solar physicists currently have in the form of ESA’s Solar Orbiter spacecraft and NASA’s Parker solar probe. Solar Orbiter is designed to get as close to the Sun as possible while still conducting remote sensing operations and in-situ measurements. Parker Solar Probe largely foregoes remote sensing of the sun in order to get even closer for its in-situ measurements.
However, to take full advantage of the complementary approaches, the Parker Solar Probe would need to be within the field of view of one of Solar Orbiter’s instruments. This allowed Solar Orbiter to record the large-scale consequences of what Parker Solar Probe was measuring in the field.
Daniele Telloni, a researcher at the Italian National Institute of Astrophysics (INAF) at the Turin Astrophysical Observatory, is part of the team behind Solar Orbiter’s Metis instrument. Metis is a coronagraph that blocks light from the sun’s surface and takes photos of the corona. It’s the perfect instrument for large-scale measurements, so Daniele started looking for moments when the Parker Solar Probe would align.
He noted that the two spacecraft would be near the correct orbital configuration on June 1, 2022. Essentially, Solar Orbiter would be facing the sun and Parker Solar Probe would be right next to it. tantalizingly close, but out of sight of the Metis instrument.
As Telloni looked at the problem, he realized that all that was needed to bring the Parker Solar Probe into view was a 45-degree rotation of the sun’s orbit and then a slight orientation away from the sun.
The maneuver brought the Parker Solar Probe into view and together the spacecraft carried out the first simultaneous measurements of the large-scale configuration of the solar corona and the microphysical properties of the plasma.
By comparing the newly measured rate with theoretical predictions that solar physicists have made over the years, Telloni has shown that solar physicists almost certainly do They were right when they identified turbulence as a way to transfer energy.
The specific way turbulence does this is no different than what happens when you stir a cup of coffee. By exciting random movements of a fluid, whether gaseous or liquid, energy is transferred on smaller and smaller scales, culminating in the conversion of energy into heat. In the case of the solar corona, the liquid is also magnetized and therefore Stored magnetic energy can also be converted into heat.
This transfer of magnetic energy and motion from larger to smaller scales is the very essence of turbulence. On the smallest scales, this allows the fluctuations to eventually interact with individual particles, usually protons, and heat them up.