Solar Orbiter: Progress Towards Solving a Long-Standing Solar Enigma

Scientists have made a groundbreaking discovery that may finally explain why the Sun’s atmosphere, known as the corona, is so much hotter than its surface. The corona has a temperature of around one million degrees Celsius, while the surface temperature is only 6000 degrees. This stark difference has puzzled researchers for over 65 years.

The prevailing theory suggests that turbulence in the solar atmosphere could be responsible for heating the plasma in the corona. However, investigating this phenomenon has been challenging due to the limitations of using a single spacecraft. To overcome this obstacle, scientists have utilized two spacecraft: the Solar Orbiter, led by the European Space Agency (ESA), and NASA’s Parker Solar Probe.

The Solar Orbiter is designed to perform remote sensing operations and in-situ measurements, while the Parker Solar Probe focuses solely on in-situ measurements. By combining the data from these two spacecraft, scientists can gain a comprehensive understanding of both the large-scale and small-scale processes happening in the plasma.

Daniele Telloni, a researcher at the Italian National Institute for Astrophysics, played a key role in coordinating joint observations between the Solar Orbiter and Parker Solar Probe. By carefully maneuvering the Solar Orbiter, Telloni was able to bring the Parker Solar Probe into the field of view of the Solar Orbiter’s instrument, called Metis. This alignment allowed for simultaneous measurements of the solar corona’s large-scale configuration and the microphysical properties of the plasma.

The analysis of these combined measurements provided scientists with the first-ever estimate of the coronal heating rate. By comparing this measurement with theoretical predictions, Telloni and his team found strong evidence to support turbulence as a mechanism for transferring energy in the corona. Turbulence stimulates random movements of the magnetized fluid in the corona, converting energy into heat at ever smaller scales. This process ultimately heats up individual particles, such as protons.

While more research is needed to fully solve the coronal heating problem, this breakthrough represents a significant step forward. Scientists now have the first measurement of the process responsible for heating the Sun’s corona. Daniel Müller, the Project Scientist for Solar Orbiter, describes this work as a “scientific first” and highlights its importance in addressing the long-standing mystery of the corona’s extreme temperatures.

The findings from this study were published in the Astrophysical Journal Letters and mark an exciting milestone in solar physics. The collaboration between ESA and NASA, through the Solar Orbiter mission, has opened up new avenues for exploration and deepened our understanding of the Sun. As researchers continue to unravel the secrets of our star, we can expect further breakthroughs that will reshape our knowledge of the cosmos.