The closest images ever taken of the Sun reveal the existence of 'bonfires'

"They are only the first images and we can already see new phenomena of interest," he says. Daniel Müller, a scientist with ESA's Solar Orbiter project. “We did not expect such good results at the beginning. We can also see how the ten scientific instruments complement each other, offering a comprehensive image of the Sun and its environment. "

Solar Orbiter includes six remote sensing instruments (telescopes), who will observe the Sun and its surroundings, and four instruments in situ to probe the environment around the ship. By comparing the data from both classes of instruments, information will be obtained on how the solar wind is generated, the rain of charged particles from the Sun that affects the entire solar system.

What makes Solar Orbiter unique is that, until now, no other mission has been able to take pictures from this close to the solar surface.

One of the results is the 'bonfires' that appear in the photographs captured by the Extreme Ultraviolet Imaging Camera (EUI) during Solar Orbiter's first perihelion, the point on its elliptical orbit closest to the Sun. At that time, the spacecraft was just 77 million kilometers from the Sun, about half the distance between Earth and our star.

"These bonfires are like minor relatives of the solar flares observed from Earth, but between millions and billions of times smaller," he points out. David Berghmans, from the Royal Observatory of Belgium (ROB) and principal investigator of the EUI instrument, which takes high-resolution images of the lower layers of the solar atmosphere, or corona. "At first glance, the Sun may appear motionless, but as you look closely we can see these small eruptions everywhere."

The mysterious warming of the crown

The researchers still don't know if these are tiny versions of great flares or if they are due to different mechanisms. In any case, there are already theories that these small eruptions could contribute to one of the most enigmatic phenomena of the Sun: the heating of the corona.

"Each of these bonfires is insignificant by itself, but if we add their effect across the entire surface, they could contribute significantly to the heating of the solar corona," he explains. Frédéric Auchère, from the French Institute for Space Astrophysics (IAS) and EUI's main co-researcher.

The solar corona is the outermost layer of the Sun's atmosphere, stretching millions of kilometers into outer space. Their temperature exceeds a million degrees Celsius, several orders of magnitude warmer than the Sun's surface, which is "just" at 5,500 ° C. After decades of studies, the physical mechanisms that heat the corona are still not fully understood, but identifying them is considered the 'holy grail' of solar physics.

"Logically, it is too early to know, but we trust that, by linking these observations with the measurements of the rest of the instruments that study the solar wind that passes next to the ship, we can solve some of these mysteries," he points out. Yannis Zouganelis, Associate Scientist for ESA's Solar Orbiter Project.

For its part, the Polarimetric and Helioseismic Imaging Camera (PHI) It is another advanced instrument on board Solar Orbiter. Make high-resolution measurements of the magnetic field lines on the solar surface. It is designed to monitor active regions of the Sun, areas with especially strong magnetic fields that could lead to flares.

During these flares, the Sun releases bursts of energetic particles that strengthen the solar wind that the star constantly releases into space. When these particles interact with the Earth's magnetosphere, they can cause magnetic storms capable of disrupting telecommunications networks and electrical ground infrastructure.

"Right now we are in a part of the eleven-year solar cycle in which the Sun is very calm," he clarifies. Sami Solanki, director of the Max Planck Institute for Solar System Research in Göttingen (Germany) and principal investigator of PHI. "But since Solar Orbiter is at a different angle from the Sun than Earth, we could see an unobservable active region from our planet. That is something totally new; until now we have never been able to measure the magnetic field of the hidden face of the Sun ”.

The magnetograms, which show how the intensity of the magnetic field varies along the solar surface, could then be compared with the measurements of the instruments in situ. At the moment, the ship has already provided the first magnetic map of the Sun, which is also the first obtained autonomously, that is, from space and without human intervention.

"The PHI instrument measures the magnetic field on the surface, while with EUI we see structures in the solar corona, but we also try to infer the lines of the magnetic field that extend to the interplanetary medium, where Solar Orbiter is located," he clarifies. José Carlos del Toro Iniesta, from the Andalusian Institute of Astrophysics and main co-researcher of PHI.

Capturing the solar wind

Furthermore, the four instruments in situ Solar Orbiter characterize the lines of the magnetic field and the solar wind that passes by the spacecraft.

Christopher Owen, from the University College London Mullard Space Science Laboratory and principal investigator of the Solar Wind Analyzer in situ (SWA), adds: "With this information we can calculate from where the specific portion of the solar wind was emitted from the Sun, and then use the mission's set of instruments to reveal and understand the physical processes that operate in the different regions of the Sun and that give rise to the formation of the solar wind ”.

"We are very excited about these first images, but they are only the beginning," adds Müller. "Solar Orbiter has started a long journey through the inner solar system, and in less than two years it will get much closer to the Sun. In the end, will approach just 42 million km, which is almost a quarter of the distance from Earth to the Sun ”.

Solar Orbiter is a space mission resulting from the international collaboration between ESA and NASA. Twelve ESA Member States (Germany, Austria, Belgium, Spain, France, Italy, Norway, Poland, the United Kingdom, the Czech Republic, Sweden and Switzerland), as well as NASA, have contributed to the scientific payload. The satellite has been built by the prime contractor, Airbus Defense and Space, in the United Kingdom.

Spanish researchers have a prominent role in two of the ten instruments on board the ship: the energy particle detector (EPD), led by the University of Alcalá and the University of Kiel (Germany); and the PHI magnetographer led by the IAA and the Max Planck Institute for Solar System Research (Göttingen, Germany).