ESA and NASA team up on solving solar atmosphere mystery

14 Sep 2023

Image: ESA/ATG medialab/NASA/Johns Hopkins APL

The sun’s atmosphere is more than 150 times hotter than its surface, and now two solar spacecrafts have worked together to figure out why.

Two spacecrafts created by NASA and the European Space Agency (ESA) respectively have worked in tandem to help scientists come closer to understanding one of the solar system’s biggest mysteries: why the sun’s atmosphere is hotter than its core.

Known as the corona, the sun’s atmosphere consists of an electrically charged gas known as plasma and has a temperature of around 1m degrees Celsius. In comparison, the sun’s surface is only 6,000 degrees Celsius – a phenomenon considered unusual by astrophysicists.

This means that the sun’s atmosphere is more 150 times hotter than its surface, even though the general understanding in astrophysics is that the temperature gets cooler the further away you get from a celestial object’s core, as is true for the Earth.

While scientists have long suspected that turbulence in the solar atmosphere could result in significant heating of the plasma in the corona, the theory has been hard to confirm practically using only one spacecraft.

“There are two ways to investigate the sun: remote sensing and in-situ measurements. In remote sensing, the spacecraft is positioned a certain distance away and uses cameras to look at the Sun and its atmosphere in different wavelengths,” a statement from the ESA reads.

“For in-situ measurements, the spacecraft flies through the region it wants to investigate and takes measurements of the particles and magnetic fields in that part of space.”

This is where a transatlantic space collaboration came in handy. By aligning the ESA-led Solar Orbiter and NASA’s Parker Solar Probe, scientists were able to make the two spacecrafts work together to make simultaneous measurements like never before.

“This is a scientific first,” said Daniel Müller, project scientist. “This work represents a significant step forward in solving the coronal heating problem.”

The idea behind the manoeuvre to align the two spacecraft came from Daniele Telloni, a researcher at the Italian National Institute for Astrophysics who is part of the team behind Solar Orbiter’s Metis instrument.

Metis, a coronagraph that blocks out light from the sun’s surface and takes pictures of the corona, is the perfect instrument to use for the large-scale measurements. Telloni found that the two spacecraft would almost be in the correct orbital configuration on 1 June 2022.

Telloni realised that a 45 degree roll from the Solar Orbiter and a slight change in the direction it points at would bring the Parker Solar Probe into view.

Once the manoeuvre was authorised and the feat was achieved, the two spacecrafts produced the first ever simultaneous measurements of the large-scale configuration of the solar corona and the microphysical properties of the plasma.

“This work is the result of contributions from many, many people,” says Telloni, who led the analysis of the datasets. Working together, they were able to make 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,” added Gary Zank of the University of Alabama and co-author of the resulting paper published in the Astrophysical Journal Letters today (14 September).

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Vish Gain is a journalist with Silicon Republic