Cosmic Alignment and Spacecraft Gymnastics Help Solve Sun’s Hot Atmosphere Mystery
The Sun’s atmosphere, known as the corona, has long puzzled scientists with its extremely high temperature of around one million degrees Celsius. This is surprising because the surface of the Sun is only about 6,000 degrees Celsius. A recent breakthrough measurement has shed light on this 65-year-old cosmic mystery.
The corona’s temperature is an enigma because objects naturally cool down the further they are from a heat source. So, the corona should be cooler than the Sun’s surface. However, it is more than 150 times hotter. This has led scientists to suspect that there must be another process driving the heating of the corona.
To investigate this phenomenon, scientists face a challenge. They require both remote sensing, which provides large-scale results, and in-situ measurements, which offer specific information about small-scale processes. To address this, solar physicists have two spacecraft at their disposal – the ESA-led Solar Orbiter and NASA’s Parker Solar Probe.
The Solar Orbiter is designed to perform remote sensing operations from as close to the Sun as possible, while the Parker Solar Probe focuses on in-situ measurements by flying through specific regions of space. However, to maximize their capabilities, the two spacecraft needed to align in a way that allowed Solar Orbiter to capture large-scale consequences of what Parker Solar Probe was measuring in situ.
Enter Daniele Telloni, a researcher at the Italian National Institute for Astrophysics. He discovered a potential alignment between the two spacecraft on June 1, 2022. It would require a 45-degree roll and a slight adjustment in pointing for Solar Orbiter to bring Parker Solar Probe into view.
Although such deviations from planned spacecraft operations are uncommon, the scientific potential outweighed the risks. The spacecraft operations team approved the maneuver, and the roll and pointing went ahead. The result was the first-ever simultaneous measurements of the large-scale configuration of the solar corona and the microphysical properties of the plasma.
Daniele, who led the analysis of the data sets, emphasized the importance of collaboration and teamwork in this breakthrough work. Gary Zank, a co-author and researcher at the University of Alabama in Huntsville, praised the combined usage of both spacecraft, which opened up new dimensions in research.
By comparing the newly measured coronal heating rate with theoretical predictions, Daniele confirmed that solar physicists were on the right track with their identification of turbulence as a key factor in transferring energy. Turbulence, similar to stirring a cup of coffee, stimulates random movements in the fluid and converts energy into heat. In the case of the solar corona, the fluid is magnetized, allowing for the conversion of stored magnetic energy into heat.
While more work is needed to fully solve the coronal heating problem, this breakthrough measurement provides a significant step forward in unraveling the mysteries of the Sun’s hot atmosphere. Daniel Müller, Project Scientist, hailed the work as a scientific first and a milestone in understanding the coronal heating problem.
Solar Orbiter, an international collaboration between ESA and NASA, continues to provide valuable insights into our nearest star, the Sun.