India's first dedicated solar observatory, Aditya-L1, has completed a successful first year of observations with its Solar Ultraviolet Imaging Telescope, offering scientists a closer and more detailed look at the Sun's lower atmosphere and its explosive activity.
A research paper describing the instrument's performance during its first year of operation has been accepted for publication in the Journal of Astrophysics and Astronomy, marking a scientific milestone for a mission that has quietly become one of the Indian Space Research Organisation's most productive ventures.
The study, titled "Unraveling the Secrets of the Lower Solar Atmosphere: One Year of Operation of the Solar Ultraviolet Imaging Telescope (SUIT) on board Aditya-L1", was led by Rahul Gopalakrishnan and a team of researchers. It describes how the telescope, known as SUIT, was operated, calibrated and maintained while capturing important features of the Sun, including solar flares, prominences and other violent events that shape space weather around the Earth.
Aditya-L1 was launched by the Indian Space Research Organisation on 2 September 2023 aboard the Polar Satellite Launch Vehicle, PSLV-C57. It travelled for 127 days before reaching its destination, the Sun-Earth Lagrange Point 1, on 6 January 2024, becoming the first Indian spacecraft to reach that vantage point.
Positioned about 1.5 million kilometres from the Earth, in a halo orbit around L1, the observatory can watch the Sun continuously, without the interruptions caused by the Earth's shadow or the day-night cycle that limit ground-based telescopes.
The SUIT instrument was switched on on 20 November 2023 and captured its first scientific images on 6 December, while the spacecraft was still travelling towards L1. It is designed to image the Sun in the ultraviolet band between 200 and 400 nanometres, using eight narrowband and three broadband filters, and a 4096 by 4096 pixel detector that can record full-disk images of the Sun at a cadence of 16 seconds.
That combination of sharpness and speed allows scientists to follow the rapid evolution of solar flares and eruptions as they unfold.
The lower solar atmosphere, the region SUIT is built to study, holds some of the most stubborn puzzles in solar physics. It includes the photosphere, the visible surface of the Sun, and the chromosphere, the layer immediately above it, where temperatures rise sharply and magnetic energy builds up before being released in flares and coronal mass ejections.
Understanding how energy moves through these layers, and how it heats the corona to millions of degrees, is central to predicting space weather, the stream of charged particles and radiation that can disrupt satellites, navigation systems, power grids and communication networks on Earth.
During its first year of observations, SUIT recorded a series of remarkable events. Even before reaching its final orbit, it captured an X-class solar flare and a coronal mass ejection on 31 December 2023, demonstrating its capabilities while still in the cruise phase.
The research paper documents the many program sequences orchestrated to meet the instrument's science requirements, including detailed observations of a prominence eruption and the flaring loops that followed it on 27 May 2024. In all, the SUIT team now has 26 program sequences stored on board, allowing the telescope to switch between full-disk imaging and close-up views of regions of interest on the Sun.
The mission carries seven scientific instruments in total, each designed to observe a different aspect of the Sun. Together, they study the dynamics of the corona, the plasma environment around the Sun, the temperature, velocity and density of different regions of the corona, the sequence of solar activities, and the initiation and development of coronal mass ejections and flares.
The observatory was designed for a planned mission life of five years, and with its instruments performing well, scientists expect it to keep working well beyond that.
Aditya-L1's position at L1 is what makes it so valuable. The Lagrange Point 1 is a gravitationally stable location between the Sun and the Earth where the pull of the two bodies balances out, allowing a spacecraft to hover in a halo orbit and stare at the Sun without interruption. Each halo orbit takes about 178 Earth days to complete.
Aditya-L1 completed its first halo orbit on 2 July 2024, and it has been collecting data ever since, building up an archive that now runs to tens of terabytes.
The data from the mission is released to the Indian and global scientific community through ISRO's science data portal, PRADAN, and by April this year more than 27 terabytes of information had been received from the spacecraft.
On the second anniversary of the mission's arrival at L1 in January this year, ISRO issued an announcement of opportunity inviting research proposals based on the data from its first cycle of observations, opening the mission's findings to universities and research institutions across the country and abroad.
The timing of the SUIT paper is significant because the Sun is currently passing through the most active phase of its roughly 11-year cycle. The years between 2025 and 2028 are expected to be a crucial window for solar research, with frequent flares and eruptions offering scientists a wealth of events to study.
Aditya-L1, with its uninterrupted view and its suite of instruments, is positioned to capture these events in unprecedented detail, and the lessons learned could improve forecasts of space weather that protect satellites and infrastructure worth billions of dollars.
For India, the mission represents a leap in space science. Before Aditya-L1, the country had no dedicated solar observatory in space, and Indian solar physicists relied on data from foreign missions and ground-based telescopes.
The spacecraft, whose project director is Nigar Shaji, was designed and developed by ISRO together with various Indian research institutes, and its success has demonstrated the country's ability to build and operate complex scientific payloads far from Earth.
The SUIT instrument itself is a product of that collaboration, and its first year in space has validated years of design and testing on the ground. Operating a sensitive ultraviolet telescope in space requires constant calibration, careful management of its detector and optics, and the ability to respond quickly when the Sun produces an event worth capturing.
The paper accepted for publication describes how the instrument's team met those challenges, and how the data it returned is already reshaping understanding of the lower solar atmosphere.
As Aditya-L1 enters its fourth year in space, the mission's work is far from over. With its instruments healthy and its data flowing, the observatory will continue to watch the Sun through the peak of the solar cycle, recording flares, tracking coronal mass ejections and helping scientists build a more complete picture of the star that governs life on Earth.
The first year of SUIT observations, now documented in the scientific literature, is only the beginning of what the mission promises to reveal.
(Reporting based on India Today and arXiv.)