The first images taken by the spacecraft Solar Orbiter have been released, revealing many miniature solar flares near the surface of the Sun, which have been called ‘campfires’.
An international collaboration between the European Space Agency (ESA) and NASA, Solar Orbiter was launched on 10 February 2020 and in mid-June completed its first close pass of the Sun. Its six remote sensing instruments and four in situ instruments collect data on a range of features, allowing scientists to build up a holistic view of the Sun and its surroundings.
The unprecedented images revealing the campfires, made available to the public on 16 July, were taken by the spacecraft’s Extreme Ultraviolet Imager (EUI). In these high resolution pictures, campfires are as small as a few pixels, with a single pixel representing 400 km. Their size may explain why they have been missed until now – campfires could be up to a billion times smaller than ordinary solar flares. Solar Orbiter took the images at its perihelion (the closest point to the Sun in its elliptical orbit), 77 million km from the Sun’s surface. This is the closest distance to the Sun that pictures have ever been captured.
Although little is known yet about this newly-discovered phenomenon, one possibility is that the campfires observed are nanoflares, hypothesised by physicist Eugene Parker. What they lack in size they make up for in number, and the overall effect of these ubiquitous mini-flares on the Sun could be driving the heating of the Sun’s corona, its outermost layer of atmosphere.
The solar corona is over a million degrees Celsius, around 300 times hotter than the surface of the Sun. The mechanism behind this immense temperature is a major mystery in solar physics which scientists have been studying for decades. However, the identity of the campfires cannot be known for sure with the EUI’s images alone. Scientists are awaiting a data set from the Spectral Imaging of the Coronal Environment (SPICE), which it is hoped can measure the campfires’ temperatures and ascertain whether they are nanoflares.
Among the other instruments that have now made measurements available is the Polarimetric and Helioseismic Imager (PHI). Its aim is to map the magnetic field of the Sun, particularly in active regions such as the poles, and areas where solar flares originate. It will collect its best data later in the mission, when Solar Orbiter’s orbit is gradually tilted to 24 degrees from the plane of the planets’ orbits, achieving a better view of the Sun’s poles. Scientists also hope to see the back of the Sun – an area where the magnetic field has never before been measured.
Aside from the remote sensing instruments, the four in situ instruments on Solar Orbiter monitor the spacecraft’s immediate surroundings. One of these is the Solar Wind Analyser (SWA), which has also recorded its first data. This includes measurements of heavy ions like carbon, oxygen, silicon and iron in the solar wind.
Within the next two years, Solar Orbiter will get as close as 42 million km to the Sun, less than a quarter of the distance between the Sun and Earth, and inside the orbit of Mercury. If the first data from the Solar Orbiter mission is anything to go by, scientists can expect many more exciting discoveries to come.
Written by Catriona Roy and edited by Ailie McWhinnie.
Catriona’s thoughts… It’s an object so close to the Earth (relatively speaking) and so familiar to us in day-to-day life; it feels a bit strange to think that there are things all over the Sun’s surface that we have never seen until now. Thanks to teams around the globe working together in spite of the pandemic (with mission control in Darmstadt, Germany temporarily shutting down at one point), the discoveries keep coming, alongside awe-inspiring images. I look forward to the next installment from this thrilling exploration mission.