17 Apr. (EUROPE PRESS) –
The ESA/NASA Solar Orbiter mission may have taken another step toward solving the eighty-year-old mystery of why the outer atmosphere of the Sun is so hot.
On March 3, 2022, just a few months after Solar Orbiter’s nominal mission, the spacecraft’s Extreme Ultraviolet Imager (EUI) returned data showing for the first time that a magnetic phenomenon called reconnection was persistently occurring on minute scales.
At that time, the spacecraft was halfway between the Earth and the sun. This enabled coordinated observations with NASA’s Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS) missions. The data from the three missions was then combined during the analysis.
Magnetic reconnection occurs when a magnetic field changes to a more stable configuration. It is a fundamental mechanism for the release of energy in superheated gases known as plasmas and is believed to be the main mechanism for driving large-scale solar flares. This makes it the direct cause of space weather. and a leading candidate for the mysterious heating of the sun’s outer atmosphere.
It has been known since the 1940s that the sun’s outer atmosphere, called the corona, is much hotter than the sun’s surface. While the surface glows at around 5,500 °C, the corona is a rarefied gas at around 2 million °C. How the sun injects energy into its atmosphere to heat it to this tremendous temperature has been a great puzzle ever since. ESA reports.
In the past, magnetic reconnection has generally been seen during large-scale explosive events. However, the new result presents ultra-high-resolution observations of small-scale persistent reconnection (about 390 km in diameter) in the corona. These are revealed to be a full-length ‘soft’ sequence compared to the sudden explosive releases of energy that reconnection is usually associated with.
The event on March 3, 2022 took place over the period of one hour. Temperatures around the point in the magnetic field where the magnetic field strength drops to zero, known as the null point, hovered around 10 million degrees Celsius and generated an outflow of material that came in the form of discrete “spots.” moving away from the null point with a speed of about 80 km/s.
In addition to this continuous output, there was also an explosive episode around this null point, which lasted four minutes.
The Solar Orbiter results suggest that magnetic reconnection, at scales previously too small to resolve, proceeds continuously in a smooth and explosive manner. This is important because it means that the reconnection can therefore persistently transfer mass and energy to the overlying corona, contributing to its heating. These results are published in Nature Communications.
These observations also suggest that even smaller and more frequent magnetic reconnections are waiting to be discovered. The goal now is to observe them with EUI at even higher spatiotemporal resolution in the future around the closest approaches of Solar Orbiter. to estimate what fraction of the corona’s heat can be transferred in this way.
Solar Orbiter’s most recent closest pass to the sun took place on April 10, 2023. At that time, the spacecraft was only 29% of the distance from Earth to the sun.
Solar Orbiter is an international collaborative space mission between ESA and NASA, operated by ESA.
