Solar Probe Aditya-L1: Explosive Debut in Space

Just a few months after its launch, the space probe observed a large solar flare - and looked into a barely explored layer of our star.

When the Sun hurled enormous amounts of radiation into space in an explosive eruption on February 22 of last year, the Indian space probe Aditya-L1, launched a few months earlier, was watching closely – and thus captured the first images of such a flare in the lowermost solar atmosphere. Today, a team of researchers led by the Inter-University Centre for Astronomy and Astrophysics (India) presents the analysis of the observational data in the journal The Astrophysical Journal Letters. The Max Planck Institute for Solar System Research (MPS) in Germany is also involved in the publication. The observed category X6.3 flare was one of the most powerful of the past year; a few months later, similarly strong flares were accompanied by spectacular auroras visible even in southern Europe. The new observations help to understand how flares originate and propagate in the different layers of the solar atmosphere.

Among the solar probes in space, the Aidyta-L1 spacecraft is a newcomer. The solar observatory was only launched into space in September 2023 and took up its observation post at the near-Earth equilibrium point L1 between Earth and the Sun shortly after. After the initial commissioning of the seven telescopes and scientific instruments on board, the probe did not have to wait long for rewarding work: on February 22, 2024, there was a huge burst of radiation on the side of the Sun facing the Earth. Researchers classify the flare as category X6.3 ranking it among the most energetic radiation bursts. On Earth, eruptions of this kind can affect the operation of satellites, power grids, and radio communications. Other space observatories, such as NASA's Solar Dynamics Observatory (SDO) and ESA's Solar Orbiter, as well as Earth-based telescopes, also turned their attention to the spectacular event.

Unlike its solar-observing siblings, Aditya-L1 takes images of the Sun in the long-wavelength ultraviolet light with wavelengths between 200 and 400 nanometers. This light is mainly produced directly above the visible surface of the Sun, the photosphere, and in the adjacent lower atmosphere, the chromosphere. To more precisely identify a specific layer, the Aditya’s Solar Ultraviolet Imaging Telescope (SUIT) is equipped with eleven filters. Until now, the processes that take place in the lower chromosphere during a violent flare were not accessible to researchers with this level of detail.

“It is a great stroke of luck that Aditya-L1 was able to witness such a strong flare right at the beginning of its research career,” says Sami Solanki, director at MPS and co-author of the current publication. “Together with observations from other probes and telescopes, this for the first time provides a complete picture of the processes that occur in different layers of the solar atmosphere during a flare,” he adds.
The flare on February 22, 2024 originated in a region in the Sun’s northern hemisphere of the among a group of sunspots. It lasted about 35 minutes and reached its peak at around 22:34 (UTC). In the SUIT images, during this period a bright flashes can be seen at two closely adjacent locations.

For the current publication, the team also analyzed data from Aditya’s spectrometer Solar Low Energy X-ray Spectrometer (SoLEXS) as well as data from other space probes and ground-based solar observatories. In this way, the team was able to track how the released energy propagates through the different layers of the solar atmosphere. For example, the analysis shows that the flare in the lower solar atmosphere is directly accompanied by a temperature increase in the outer atmosphere, the corona.

About the mission and the instrument

The Aditya-L1 spacecraft is a project of the Indian Space Research Organization (ISRO). The concept of the Solar Ultraviolet Imaging Telescope (SUIT) was originally envisaged by the MPS; the instrument was designed, developed and built by the Inter-University Centre for Astronomy and Astrophysics in Pune, India.The current publication was led by the same research institution. Three MPS scientists are members of the SUIT team.