This image from Solar Orbiter’s Metis instrument shows the sun’s outer atmosphere, known as the corona, extending into space. Metis is a multiwavelength device that operates at visible and ultraviolet wavelengths. It is a coronagraph, meaning it blocks out bright sunlight from the sun’s surface and leaves visible the weaker light scattered from particles within the corona. In this image, the blurred red disk represents the coronagraph, and the white disk is a mask to compress the image size and reduce the amount of unnecessary data that is downlinked. Credit: ESA & NASA/Solar Orbiter/Metis team. D. Terroni et al. (2023)
Cosmic alignment and a little spacecraft gymnastics have yielded groundbreaking measurements that help solve a 65-year-old cosmic mystery: why the sun’s atmosphere is so hot.
The sun’s atmosphere is called the corona. It consists of an electrically charged gas known as . plasma And its temperature is about 1 million degrees Celsius.
The sun’s surface temperature is only about 6,000 degrees Celsius, so its temperature remains an eternal mystery. The sun’s energy comes from a nuclear reactor at its core, and the corona should be cooler than the surface because it naturally cools as you move away from the heat source. However, the corona is more than 150 times hotter than the surface.
There must be another way of transferring energy to the plasma at work, but what?
Theory and research questions
It has long been suspected that turbulence in the solar atmosphere can significantly heat the plasma in the corona. However, solar physicists encounter practical problems when trying to investigate this phenomenon. It is impossible for him to collect all the necessary data with just one rover.
There are two ways to study the Sun: remote sensing and in situ measurements. In remote sensing, spacecraft are positioned at a fixed distance and use cameras to observe the sun and its atmosphere at different wavelengths. For in-situ measurements, the spacecraft flies over the area you want to investigate and takes particle and magnetic field measurements in that part of space.
Both approaches have their advantages. Remote sensing shows large-scale results but does not show details of the processes occurring within the plasma. In situ measurements, on the other hand, provide very specific information about small-scale processes within the plasma, but do not show how this affects large-scale processes.
Double spacecraft investigation
To get the full picture, we need two spacecraft. This is exactly what heliophysicists are currently achieving in the form of the ESA-led Solar Orbiter spacecraft and NASA’s Parker Solar Probe. Solar Orbiter is designed to perform remote sensing operations along with in-situ measurements while getting as close as possible to the Sun. The Parker Solar Probe largely omits remote sensing of the Sun itself, as it gets even closer to the Sun itself to take measurements in situ.
But to take full advantage of their complementary approaches, the Parker Solar Probe must be within the field of view of either Solar Orbiter instrument. In doing so, Solar Orbiter was able to record large-scale results from measurements made in situ by the Parker Solar Probe.
![Solar Orbiter and Parker Solar Probe](https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-777x437.jpg 777w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-400x225.jpg 400w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-768x432.jpg 768w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-1536x864.jpg 1536w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-2048x1152.jpg 2048w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-180x101.jpg 180w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-260x146.jpg 260w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-373x210.jpg 373w,https://scitechdaily.com/images/Solar-Orbiter-and-Parker-Solar-Probe-120x67.jpg 120w)
ESA’s Solar Orbiter is one of two complementary spacecraft to study the Sun at close range, joining NASA’s Parker Solar Probe, which was already engaged in that mission. Credits: Solar Orbiter: ESA/ATG Media Lab; Parker Solar Probe: NASA/Johns Hopkins APL
astrophysical adjustment
Daniele Terroni, 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 to photograph the corona. This is the perfect instrument to use for large-scale measurements, so Daniele started looking for when the Parker Solar Probe would be in the lineup.
He found that on June 1, 2022, the two spacecraft will be in approximately the correct orbital configuration. Basically, the Solar Orbiter will be observing the Sun, and the Parker Solar Probe will be right next to it, tantalizingly close but just outside the field of view of the Metis instrument.
As Daniele looked at the problem, she realized that a little gymnastics with the Solar Orbiter was enough to bring the Parker Solar Probe into view. That is, rotate it 45 degrees and point it slightly away from the sun.
But if every maneuver of a space mission is carefully planned in advance, and the spacecraft itself is designed to face only in very specific directions, especially when dealing with the terrifying heat of the sun, spacecraft operations It wasn’t clear whether the team would allow such a thing. Deviation. But once everyone was clear on the potential scientific benefits, the decision was a clear yes.
![Solar probe reaches first perihelion](https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-777x437.jpg 777w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-400x225.jpg 400w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-768x432.jpg 768w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-1536x864.jpg 1536w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-180x101.jpg 180w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-260x146.jpg 260w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-373x210.jpg 373w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion-120x67.jpg 120w,https://scitechdaily.com/images/Solar-Orbiter-Reaches-First-Perihelion.jpg 1920w)
At its closest approach, ESA’s Solar Orbiter mission will face the sun from within Mercury’s orbit.Credit: ESA/ATG Media Lab
groundbreaking observation
Roll and offset pointing advanced. The Parker Solar Probe came into view, and together the spacecraft made the first simultaneous measurements of the large-scale composition of the solar corona and the microphysical properties of the plasma.
“This research is the result of the contributions of so many people,” says Daniele, who led the analysis of the dataset. Together, they were able to produce the first combined observational and in-situ estimates of the rate of coronal heating.
“The ability to use both the Solar Orbiter and the Parker Solar Probe opens up a whole new dimension to this research,” said Gary Zank of the University of Alabama in Huntsville, USA, and co-author of the paper. .
By comparing the newly measured speed with theoretical predictions made by solar physicists over the years, Daniele found that solar physicists were almost certainly correct in identifying turbulence as the method of energy transfer. It was shown that
![Parker solar probe approaches the sun](https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-777x437.jpg 777w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-400x225.jpg 400w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-768x432.jpg 768w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-1536x864.jpg 1536w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-2048x1152.jpg 2048w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-180x101.jpg 180w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-260x146.jpg 260w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-373x210.jpg 373w,https://scitechdaily.com/images/Parker-Solar-Probe-Spacecraft-Approaching-Sun-120x67.jpg 120w)
Artist’s concept of the Parker Solar Probe spacecraft approaching the sun.Credit: NASA/Johns Hopkins APL/Steve Gribben
The specific way turbulence causes this is similar to what happens when you stir your morning coffee. By stimulating the random motion of a gas or liquid fluid, energy is transferred to a smaller scale and ultimately the energy is converted into heat. In the case of the solar corona, the fluid is also magnetized, so the stored magnetic energy can also be converted into heat.
This transfer of magnetic and kinetic energy from larger scales to smaller scales is the essence of turbulence. At the smallest scales, the fluctuations can eventually interact with individual particles, primarily protons, and heat them.
Conclusion and implications
More research is needed before the problem of solar heating can be said to be solved, but thanks to Daniele’s work, solar physicists have measured this process for the first time.
“This is a scientific first. This study represents an important step forward in solving the coronal heating problem,” said project scientist Daniel Müller.
Solar Orbiter is an international space mission between ESA and ESA. NASAoperated by ESA.