Aditya L-1, India’s eye in the sky to observe the Sun, turned two this month. What exactly have Indian scientists learnt about the centre of our solar system in the last couple of years?
The launch carried with it few instruments to help observe the Sun at historically close quarters. Key among these are the Solar Ultraviolet Imaging Telescope (SUIT) and the Vision Emission Line Coronagraph (VELC) – both made in India.
The SUIT device takes pictures of the Sun in different ‘colours’ of ultraviolet light to study phenomena such as solar flares. In an article published in The Astrophysical Journal of Letters in February this year, co-author Soumya Roy notes that for the first time, we were able to capture detailed images of a powerful solar flare (called the X6.3) as it erupted on the Sun’s visible surface. The authors also published another letter following the observation of a plasma blob from another flare.
These images were taken in specific ultraviolet ‘colours’.
Why is this significant?
Seeing flares in these particular light bands helps scientists understand the different layers of the Sun’s atmosphere and how flares develop. Over time, amassing data from hundreds of thousands of flares enhances human understanding of flares and their impact on space weather as well as on instruments on Earth.
Dr Roy, now post-doctoral research fellow at the Manipal Centre for Natural Sciences, and his team observed that the brightest moments of the flare in certain narrowband UV colours (NB01, NB03, NB04, NB08) happened at the same time as bursts of high-energy X-rays (hard X-rays) and when the plasma reached its hottest temperature. This, he says, tells us that the UV light is coming from superheated gas, which gets hot as energetic particles in the flare slow down and dump their energy.
In the case of the gas blob, this is the first time such a plasma blob has been seen in this specific near-ultraviolet light. Analysed data showed that the gas blob was actually cooler and denser than the gas it was moving through.
Dr Roy, who specalises in solar flares, was also part of the team that developed the SUIT device.
Scientists were also able to observe that the blob’s sudden burst of speed happened at the same time as quick bursts of high-energy X-rays and specific radio signals were emitted. This likely points to a process called ‘magnetic reconnection’ – where tangled magnetic field lines suddenly snap and reconnect, releasing huge amounts of energy. This could have been the cause for the blob’s acceleration.
To give you an idea of the SUIT’s capability, it was able to follow this blob (at speeds over 1,500 km per second!) to a much greater height (about 1,78,000 km) above the Sun’s surface than previous observations in near-ultraviolet light. Such tracking helps scientists understand the full journey and behaviour of these ejections.
While recording the flares, SUIT also observed a very bright, small spot, called a kernel, within a flare. This bright spot is a sign of intense, concentrated heat and energy release in that part of the flare.
The SUIT device is designed in such a way that it captures most flares irrespective of which side of the Sun it appears. “Because SUIT has on-board intelligence that can detect when a flare is taking place and where, it prioritises to read that first. The algorithm works that way, without human intervention.”
When recording the flare in February this year, SUIT also observed two bright kernels in the narrowband 2 and narrowband 5 which had never been observed before.
“Those are possibly some new flare lines that we don’t know of, or some kind of nuclear emission mechanism that has never been observed before, specifically narrowband 2.” He is expecting some results after analysis of simulations to predict the kernel.
Scientists like Dr Roy are also studying the energy release from these flares. Explains Dr Roy, “Solar flares are magnetic explosions. The Sun is a bowl of, or a sphere of, boiling plasma that is held together by its own gravity and the magnetic field. Magnetic field lines in the solar atmosphere often rearrange and that releases the energy that you see in solar flares.”
And when this rearrangement – the explosion happens – it dumps a lot of energy into the surrounding medium that accelerates a lot of electrons and ions down towards the Sun’s surface.
“The kinetic energy that moves away creates the coronal mass ejection which gets the energy from the explosion, but a part of that explosion energy is also injected towards the Earth.”
This creates the hard X-ray and UV-like lights we see from the Sun.
“It’s definitely some emission line, some new flare lines. To understand these better, we have to do simulations of solar flares and then develop models to see what kind of lines actually can come into emission in those wavelength bands,” explains Dr Roy. That is something he and his research mates are working on currently.
Ozone layer
The SUIT could also help provide data that would eventually throw more light on how the ozone layer works. This holds promise to address concerns around global warming. Dr Roy points to three broadband filters in the device that look at three UV channels, which influence the photochemistry in the Earth’s stratosphere, and specifically in the ozone layer.
These three bands provide direct inputs for atmospheric modelling. Atmospheric scientists, who model the photochemistry of the upper stratosphere, use simulations to predict changes in the ozone density on the Earth’s surface. Earlier, there were no direct way to measure the Sun’s irradiation in these specific wavelengths.
As to how SUIT can actually help solar science advance, Dr Roy says, “The goal for me as a solar scientist, in studying solar flares, is when we see a flare, if we can predict what kind of changes in the solar atmosphere you will see over the next three to five days, because that is usually how long it takes for the disturbance from the Sun to come to Earth.”
Observing the Sun from historically close quarters will help mankind find ways to quickly respond to how solar flares impact the functioning of our satellites or even power grids on the ground, or, to the effect of flares on space weather, points out Dr Roy.
The other instrument on the spacecrat, the VELC, is designed to study the Sun’s outer atmosphere (the corona) by looking at specific “colours” of visible light. According to a paper by Jagdev Singh and others published earlier this year in the Solar Physics journal, “the VELC was able to offer direct proof of a phenomenon called ‘coronal dimming’.”
During a coronal mass ejection, parts of the Sun’s corona actually got darker. This is a direct observation of how the corona reacts to these massive explosions. This type of observation is critical for understanding the origin of mass ejections, their nature, and how they are propagated.
‘Sit and stare’ observations that the VELC has enabled the study of periodic oscillations in coronal structures, which help in investigating the existence of waves, flows, and the dynamics of the corona — a primary step towards understanding the ‘coronal heating problem’.
The coronal heating problem has for long left scientists puzzled – the corona, which is the outermost layer of the Sun, is much hotter than the photosphere below it, and it is not clear why. Hopefully, observations from Aditya L-1 will help unravel this mystery, too.
Published on September 22, 2025
