Zoom on the Sun

Solar Orbiter captured unique data from a distance of only 48 million kilometers from our star

New data from ESA's Solar Orbiter spacecraft show the Sun's outer hot atmosphere, the corona, in unprecedented detail. The images reveal high-resolution coronal loops as well as a curious structure surrounded by ray-like plasma flows and offer unique views of our star's polar region. About a month and a half after the spacecraft passed the closest point in its orbit around the Sun, the teams of all ten science instruments today are releasing the first results and images from this phase of the mission. The images and movies highlight the probe’s special strength: the simultaneous view into different layers of our star. In the days around the flyby, the spacecraft witnessed several coronal mass ejections and solar flares in this way. The Max Planck Institute for Solar System Research (MPS) in Germany is involved in four of Solar Orbiter’s instruments as well as in the analysis of the data.

On March 26, Solar Orbiter’s trajectory brought the space probe within a distance of approximately 48 million kilometers from the Sun. This corresponds to less than one third of the distance between Earth and Sun - and marks a preliminary high point of the mission. Only three spacecraft have ever come closer to the Sun - none of them, however, with imaging instruments looking at our star. Solar Orbiter, however, uses six scientific instruments to look at the Sun's surface, atmosphere and surroundings; four more, called in situ instruments, measure the particles and electromagnetic fields that flow around the spacecraft.

In the days surrounding the recent flyby, all instruments were operating. However, because of the current large distance between the spacecraft and Earth, the data transmission rate is rather low. Therefore, only a part of the recorded data has reached Earth so far and could be reviewed by the scientific teams in the past weeks. Further data are still expected.

Some of the most exciting images show the Sun's corona, where hot plasma flows trapped by strong magnetic fields. Violent bursts of particles and radiation occur there again and again. Three of Solar Orbiter’s instruments image these and other processes in the corona. The coronagraph Metis blocks out the solar disk, making the outer region of the corona visible. The instrument SPICE (Spectral Imaging of the Coronal Environment) splits the light from the corona into its wavelengths and can thus determine, for example, which elements are present in which region of the corona. The MPS has contributed essential components to both instruments.

The same applies to the EUI (Extreme Ultraviolet Imager) instrument, which images the corona in extremely short-wave ultraviolet light using three reflecting telescopes. At such close distances from the Sun as during the flyby, the instrument provides meaningful data not only from the low corona on the disk, but up to a distance that overlaps with Metis' field of view. This provides a unique opportunity to observe the processes in the corona from the surface up to a distance up to three solar radii in high resolution and without loss of continuity. This is the region where most of the solar activity originates.

EUI's images obtained around the time of the flyby show the corona in the highest-resolution ever. "Solar Orbiter's images of the corona exceed all previous ones in detail and will help to better understand the structures and processes in this part of the Sun," says Prof. Dr. Sami K. Solanki, director at MPS. 

In images from March 30, for example, there is a curious structure from which hot plasma flows in all directions in a ray-like fashion. It measures about 25,000 kilometers in diameter. "We have never seen a phenomenon like this before. It is unclear what exactly is going on there and how this structure is formed," says Prof. Dr. Hardi Peter of MPS, a member of the EUI team. In addition, images of the solar south pole region were obtained. From Earth, the poles of the Sun can hardly be seen. To shed light on this region, Solar Orbiter has already left the plane within which the Earth orbits the Sun by four degrees. By the end of the mission, this will have risen to 33 degrees.

Coronal loops are also found in the EUI and SPICE images. Their footpoints, the areas on the surface of the Sun where they originate, can be seen in simultaneous measurements by the Solar Orbiter’s instrument PHI (Polarimetric and Helioseismic Imager). The instrument was developed and built under the lead of MPS and is operated by the PHI team at MPS. Among other things, it can visualize the polarity of the magnetic fields at the solar surface. "PHI allows us to understand the physical origin of coronal loops," MPS scientist and PHI project manager Dr. Joachim Woch explains

The scientists are also taking a close look at the fireworks of radiation and particles that the Sun provided during the time around the flyby. The in-situ instruments caught evidence of one burst of energetic particles and three solar flares. Scientists classified the flare of March 31, 2022 as one of the highest category, called X. Flares of this strength occur only rarely, even during periods of high solar activity. The data from imaging instruments can help track down where these eruptions originated on the Sun and what processes triggered them. For example, EUI images show early signs of the observed particle eruption.

Solar Orbiter is expected to come even closer to the Sun as early as October of this year. Then only 42 million kilometers will separate the spacecraft and our star.