Daniele Telloni, researcher at the Italian National Institute for Astrophysics (INAF) at the Astrophysical Observatory of Torino, is part of the team behind Solar Orbiter’s Metis instrument. Metis is a coronagraph that blocks out the light from the Sun’s surface and takes pictures of the corona. It is the perfect instrument to use for the large-scale measurements and so Daniele began looking for times when Parker Solar Probe would line up.
He found that on 1 June 2022, the two spacecraft would almost be in the correct orbital configuration. Essentially, Solar Orbiter would be looking at the Sun and Parker Solar Probe would be just off to the side, tantalisingly close but just out of the field of view of the Metis instrument.
As Daniele looked at the problem, he realised all it would take to bring Parker Solar Probe into view was a little bit of gymnastics with Solar Orbiter: a 45 degree roll and then pointing it slightly away from the Sun.
But when every manoeuvre of a space mission is carefully planned in advance, and spacecraft are themselves designed to point only in very specific directions, especially when coping with the fearsome heat of the Sun, it was not clear that the spacecraft operations team would authorise such a deviation. However, once everyone was clear on the potential scientific return, the decision was a clear ‘yes’.
The roll and the offset pointing went ahead; Parker Solar Probe came into the field of view, and together the spacecraft produced the first ever simultaneous measurements of the large scale configuration of the solar corona and the microphysical properties of the plasma.
Artist impression of Solar Orbiter and Parker Solar Probe
“This work is the result of contributions from many, many people,” says Daniele, who led the analysis of the data sets. They made the first combined observational and in-situ estimate of the coronal heating rate.
“The ability to use both Solar Orbiter and Parker Solar Probe has really opened up an entirely new dimension in this research,” says Gary Zank, University of Alabama in Huntsville, USA, and a co-author on the resulting paper.
By comparing the newly measured rate to the theoretical predictions made by solar physicists over the years, Daniele has shown that solar physicists were almost certainly right in identifying turbulence as a way of transferring energy.
The specific way turbulence does this is not dissimilar to when you stir your morning cup of coffee. By stimulating random movements of a fluid, either a gas or a liquid, energy is transferred to ever smaller scales, which culminates in energy transformation into heat. In the case of the solar corona, the fluid is also magnetized, so stored magnetic energy is also available to be converted into heat.
Such a transfer of magnetic and movement energy from larger to smaller scales is the very essence of turbulence. At the smallest scales, it allows the fluctuations to finally interact with individual particles, mostly protons, and heat them up.
More work is needed before we can say that the solar heating problem is solved but now, thanks to Daniele’s work, solar physicists have their first measurement of this process.
“This is a scientific first. This work represents a significant step forward in solving the coronal heating problem,” says Daniel Müller, Project Scientist.
Source: European Space Agency
