The Solar Ultraviolet Imaging Telescope, SUIT, is India’s first solar space observatory onboard Aditya-L1. Aditya-L1 travels around in a halo orbit, a large, three-dimensional loop along L1, the Sun–Earth Lagrange point 1, the region between the Sun and the Earth where the gravitational effects of the two bodies are in balance. So the spacecraft requires minimum energy expenditure and SUIT gets an almost uninterrupted, round-the-clock view of the sun, free from interference caused by the earth’s atmosphere and orbital eclipses.
The Sun-Center Finder Toolkit in SUIT uses full-disk telescope pictures to calculate the exact middle of the Sun and sends location coordinates back to mission controllers so that they can determine whether the satellite is drifting or off-target. This data tracks the spacecraft’s drift over time, revealing a minor periodic variation of about two hours. This helps the mission team during manoeuvres to ensure accurate pointing.
The focus of the SUIT telescope is on the Sun’s lower atmosphere, the photosphere and chromosphere. The Charge-Coupled Device, CCD camera on the SUIT telescope captures each single pixel. Each pixel represents a 502 × 502 kilometers area on the Sun’s surface. A single frame of 4096 × 4096 pixel resolution can capture the entire disk of the Sun with extra room around the edges to observe solar prominences, flares, and plasma explosions. To provide clues about the kind of ions in the ionosphere and chromosphere, the camera records in the near-ultraviolet and mid-ultraviolet wavelengths in the range between 200 to 400 nanometres using 11 bands of filters.
Though image capture can be done every sixteen seconds, the daily data allowance is limited to a hundred gigabytes. So, it is programmed to capture the full disc at full resolution every 2.4 hours and capture slightly lower resolution images every minute with only one filter. If a flare is detected, then it focuses on the region of interest, and captures images every minute, with all eleven filters.
When X-rays from a flare hit the spacecraft, SUIT receives automated alert signals from two companion X-ray spectrometers on Aditya-L1. Even if external instruments don’t trigger it, SUIT can detect flares on its own. And once an alert is confirmed, SUIT automatically interrupts its standard routine. It runs a quick algorithm that pinpoints the exact coordinates of the flare and switches to observing the region of the flare. Rather than receiving new instructions from Earth for every single picture, SUIT can quickly load one of 26 pre-configured routines to achieve specific scientific goals.
How has SUIT, onboard Aditya-L1, fared in the first year of its operations?
To report a summary of findings so far, researchers from the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune collaborated with others who were involved so far. They started analysing the data sent by SUIT from December 2023 even before Aditya L1 settled down to its predetermined orbit to ensure that the engineering skills they had put in were working.
Scattered light can reduce the quality of the images. So the researchers instituted a system of closing the door of the telescope periodically and used the LED lights within the system to estimate the scattered light to correct the errors in the images due to scattering.
The images were slowly degrading over time. The researchers diagnosed the problem quickly. SUIT’s camera sensor, the CCD, is kept continuously chilled at -50 ℃. As it is the coldest component inside the telescope, trace chemical vapors released by spacecraft materials gradually drift toward it and freeze onto the cold sensor surface, forming a thin microscopic layer of chemical grime over the detector chip. To clean off the grime by evaporating the chemical contaminants, the engineers temporarily stopped solar observations and turned on internal heaters to warm the camera assembly up to 30 ℃. To do this automated heating every 3 to 4 months, SUIT was programmed to keep its ultraviolet images sharp and clear.
Having overcome the minor problems, the researchers started focussing on the data sent by the SUIT from Aditya-L1.
The first was an observation of a solar ‘tornado’ – a huge, rotating structure of hot, magnetised plasma near the eastern edge of the Sun, on December 6, 2023.
The next was an X5 flare – an extraordinarily intense blast of X-rays erupting from a magnetic active region on the eastern edge of the Sun, on December 31, 2023. This confirmed that magnetic reconnection – the sudden snapping and reconnecting of twisted magnetic fields – was actively powering and accelerating this massive gas blob as it shot into space.
Another interesting observation was a more intense X6.3 flare – an even more powerful solar explosion on February 22, 2024. This was the first time that the solar physicists were able to get clear, high-resolution images of flare brightening at specific ultraviolet wavelengths, giving them a detailed look at where flare energy hits the lower solar atmosphere.
On May 27, 2024, a large prominence erupted from the Sun, followed by bright loops of hot plasma rising above the solar surface. Using specialised filters, SUIT captured sharp, high-contrast images of both the cool exploding gas and the warm, rising magnetic arches in a layer of the Sun that is normally very difficult to see.
The researchers confirm that the SUIT’s automatic system detected most moderate solar flares and almost all of the stronger flares during its first year of operations. It could also automatically identify the location and track more than half of the stronger flares.
Now that the capabilities of the mission are tested and confirmed, the researchers and engineers are ready for more.
There are 26 programme sequences already loaded on SUIT. More can be uploaded as per the requirements of the scientific community interested in specific research objectives, say the researchers.
The mission also provides opportunities for scientists and researchers around the world to use its data for further research. The Quick Look Display Software converts raw binary signals downloaded from the satellite into standard scientific image files, and displays the most recent solar pictures taken across all 11 filters in full-disk. A modified version of this tool powers the Latest Observations page on the public SUIT website, allowing anyone to view recent images of the Sun. Thus, the solar images from the mission give anyone on Earth direct web access to view current images of the Sun across 11 UV filters.
Scientists can submit proposals through the Aditya-L1 Proposal Processing System to request observations of specific targets. These observations can help space weather centres monitor powerful solar eruptions that could disrupt satellites, radio communications and power grids, thus directly benefiting everyday life on Earth in several practical ways.
Journal of Astrophysics and Astronomy, 47: 57 (2026) ;
DOI: 10.1007/s12036-026-10160-5
Reported by Sanghamitra Deobhanj
Freelance science writer, Cuttack
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