Cosmic alignment and some spacecraft gymnastics yielded groundbreaking measurements that helped solve the 65-year-old cosmic mystery of why the Sun’s atmosphere is so hot. The Sun’s atmosphere is called corona. It consists of an electrically charged gas known as plasma and its temperature is approximately one million degrees Celsius.

Since the Sun’s surface is only around 6,000 degrees, its temperature remains a mystery. The corona must be cooler than the surface because solar energy comes from the nuclear furnace in its core, and objects naturally cool as they move away from the heat source. However, the corona is 150 times hotter than the surface.

Another method of transferring energy to the plasma would probably work, but which one?

It has long been assumed that turbulence in the solar atmosphere could lead to significant heating of the plasma in the corona. But when it comes to studying this phenomenon, solar physicists face a practical problem: it is impossible to collect all the necessary data with a single spacecraft.

There are two ways to study the Sun: remote sensing and in situ measurements. In remote sensing, a spacecraft is positioned at a certain distance and cameras are used to look at the sun and its atmosphere at different wavelengths. In in situ measurements, a spacecraft flies over the area it wants to study and takes measurements of the particles and magnetic fields in that area.

Both approaches have advantages. Remote sensing shows large-scale results but not the details of the processes occurring in the plasma. Meanwhile, in situ measurements provide very specific information about small-scale processes in the plasma but do not show how they affect large scales.

Two spacecraft are needed to see the whole picture. That’s exactly what solar physicists now have in the form of the ESA-led Solar Orbiter spacecraft and NASA’s Parker Solar Probe. Solar Orbiter is designed to get as close to the sun as possible and perform remote sensing as well as in situ measurements. The Parker Solar Probe largely forgoes remote sensing of the sun in favor of getting closer for in-situ measurements.

However, to take full advantage of their complementary approaches, the Parker Solar Probe must be in line of sight with one of the Solar Orbiter instruments. In this way, Solar Orbiter was able to capture the large-scale effects of what Parker Solar Probe was measuring in situ.

Daniele Telloni, a researcher at the Italian National Institute for 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 photographs of the corona. Since it is an ideal tool for large-scale measurements, Daniel began looking for when the Parker Solar Probe was aligned.

“Heating rate of the corona in the slow solar wind” by D. Telloni et al. It was published in Astrophysical Journal Letters.

He found that on June 1, 2022, the two spacecraft will be in nearly the correct orbital configuration. Essentially, as the Solar Orbiter faces the sun, the Parker Solar Probe will be off to the side, extremely close but completely out of view of the Metis instrument. After examining the problem, Daniele realized that all that was needed to turn on the Parker Solar Probe was to do a little gymnastics with the Solar Orbiter: rotate it 45 degrees and then point it slightly away from the sun.

But since every maneuver of a space mission is carefully planned in advance, and the spacecraft itself is designed to point only in very specific directions, especially in the scorching heat of the sun, it was not clear whether the spacecraft operations team would allow such a maneuver. deflection. But once everyone realized the potential scientific return, the verdict was a resounding yes.

The rolling and sliding guide has gone forward; The Parker Solar Probe was revealed, and together the spacecraft performed the first simultaneous measurements of the large-scale configuration of the solar corona and the microphysical properties of the plasma.

“This work is the result of the contributions of many people,” says Daniele, who led the analysis of the datasets. Working together, they were able to make the first combined observational and in situ estimate of the coronal warming rate.

“Being able to use both the Solar Orbiter and the Parker Solar Probe really added a whole new dimension to this research,” says Gary Zanck of the University of Alabama in Huntsville, US, and co-author of the final paper.

By comparing the newly measured velocity with theoretical predictions that solar physicists have been making for years, Daniele showed that solar physicists were almost certainly correct in identifying turbulence as a mode of energy transfer.

The way turbulence does this is not unlike what happens when you stir your morning coffee. By stimulating random motions of a liquid, gas or liquid, energy is transferred to increasingly smaller scales, resulting in the conversion of energy into heat. In the case of the solar corona, the liquid is also magnetized so that the stored magnetic energy is also ready to be converted into heat.

The transfer of magnetic energy and kinetic energy from larger scales to smaller scales is the essence of turbulence. At the smallest scales, this allows the fluctuations to eventually interact with individual particles (mostly protons) and heat them. More work is needed to say that the solar heating problem has been solved, but now, thanks to Daniele’s work, physicists have made the first measurement of this process.

“This is the first scientific study. This study represents an important step forward in solving the problem of coronal heating,” says Daniel Muller, one of the project’s researchers. Source