Aditya-L1's Indian-Built Coronagraph Showed a Solar Eruption of 5 August 2024 Expanding Unevenly, With Plasma Moving Both Towards and Away From the Spacecraft

On 3 November 2026 ISRO and the Ministry of Science and Technology announced that India’s Aditya-L1 solar observatory had helped scientists reconstruct how a coronal mass ejection (CME, a huge burst of hot, magnetised gas thrown off the Sun) grew on 5 August 2024. It did not swell like a symmetric bubble. Scientists at the Indian Institute of Astrophysics (IIA) in Bengaluru read the eruption’s motion towards and away from the spacecraft in the colour shifts of the light recorded by Aditya-L1’s Visible Emission Line Coronagraph (VELC), then combined that with images from NASA and a three-dimensional model.

The paper is by Saurabh Tripathi, Tanmoy Samanta and Jayant Joshi, and it appeared in The Astrophysical Journal Letters (volume 1009, article L24). The journal lists it as published on 25 September 2026, open access, so anyone can read the data behind the announcement.

The eruption of 5 August 2024

The CME followed an X1.7 flare, a burst of X-rays, from just beyond the Sun’s western edge. NOAA’s Space Weather Prediction Center recorded the flare at 13:40 UTC and judged an Earth-directed CME unlikely because of where it started. The IIA paper puts the start of the eruption at about 13:27 UT.

Using extreme ultraviolet images from the Atmospheric Imaging Assembly (AIA) on NASA’s Solar Dynamics Observatory, the authors tracked the front of the CME leaving the Sun. They measured a projected radial speed of 1,134.9 kilometres a second, give or take 33.4. “Projected” means the part of the motion that shows up across the sky as seen from the spacecraft.

What a spectrograph sees that a camera cannot

A coronagraph blocks the Sun’s bright disc so that the faint corona, the Sun’s outer atmosphere, can be seen. Most coronagraph images, ISRO’s release explains, show how a CME moves across the sky but cannot say how fast the gas is moving towards or away from the observer.

VELC records spectra as well. It watches the green line of the corona at 530.3 nanometres (5303 angstroms), light given off by highly ionised iron atoms at about 1.8 million kelvin, between 1.05 and 1.5 solar radii from the Sun’s centre. A solar radius is the Sun’s own radius, so 1.05 is a point about 5 per cent of the Sun’s radius above its edge. When the gas moves, the line shifts in wavelength, the same principle ISRO compares to a traffic speed gun: gas rushing towards the observer shifts to bluer light, gas rushing away shifts to redder light.

According to its design paper, VELC has four parallel slits that each sample a strip of the corona at once. In this event one slit, near the western edge of the Sun, recorded the iron line every 51 seconds as the eruption crossed it.

VELC was designed and built by IIA with substantial support from ISRO, according to ISRO’s release; ETV Bharat and the PIB text name the MGK Menon Laboratory for Space Sciences on IIA’s CREST campus at Hosakote as the place. IIA itself was founded in 1977 by M K Vainu Bappu, who had directed the Kodaikanal Solar Observatory since 1960. Aditya-L1, which carries seven instruments, was launched on 2 September 2023.

Two branches in the spectrum

Around 13:27:57 UT the emission from the CME front split into two branches on opposite sides of the iron line’s normal wavelength, one shifted to blue and one to red. The redshifted emission appeared at lower heights and the blueshifted emission at greater heights. The paper reports one position along the slit where the extra component was blueshifted by 81.0 kilometres a second, and another where it was redshifted by 217.9 kilometres a second. The authors say 217.9 is likely a lower limit, because that component ran to the edge of the wavelength range VELC records.

The sideways front of the CME, tracked in the AIA images along the same slit, moved across the sky at a projected 691.5 kilometres a second, give or take 30.7. That is well below the 1,134.9 kilometres a second measured for the radial front, and the paper reads the difference as expansion that is not the same in every direction.

A symmetric bubble did not match

To explain the two branches, the IIA team built a simplified three-dimensional model of an expanding shell of gas and calculated the spectra it would produce. They tried four set-ups. A shell seen edge-on and expanding evenly gave a symmetric pattern of blue and red. Adding the tilt and orientation taken from a separate three-dimensional reconstruction, which puts the eruption about 7 degrees behind the Sun’s edge, changed the pattern but matched less closely. The match came from the fourth set-up, which combined that orientation with sideways expansion that differs between two perpendicular directions. The paper says that case closely resembles the VELC observations in both shape and time evolution, while the symmetric set-ups matched less well.

ISRO’s release states the finding in plain terms: the eruption did not expand outward like a simple symmetric bubble, and the combination of imaging, VELC spectroscopy and modelling is evidence that it did not expand uniformly close to the Sun. Samanta, the corresponding author, told ETV Bharat the team found that “it does not expand uniformly in all directions.”

How the shape can change an arrival time

NOAA’s Space Weather Prediction Center says CMEs travel from slower than 250 kilometres a second to nearly 3,000, and that the fastest Earth-directed ones can arrive in 15 to 18 hours while slower ones take several days. Forecasters work out size, speed and direction from coronagraph images, and the centre notes that NOAA’s DSCOVR satellite at the Sun-Earth L1 point can often give 15 to 60 minutes of warning that the shock ahead of a CME is arriving.

Joshi said the asymmetric shape of an early CME can affect how it interacts with the solar wind and how much drag it feels, which can influence its speed and, in the end, its arrival time at Earth, according to the IANS report. ISRO’s release adds that different shapes may feel different drag, which could make arrival-time predictions more challenging.

What the result claims and what it leaves open

The PIB release text, as reproduced by idrw.org, says the study showed “for the first time” that the CME did not expand like a simple symmetric bubble. Earlier work had already found uneven expansion using several spacecraft: Cremades and colleagues reconstructed a dozen CMEs with images from NASA’s STEREO and SDO spacecraft and reported in Astronomy and Astrophysics in 2020 that their expansion below about three solar radii was considerably asymmetric. The IIA paper cites that line of work and says its own result agrees with it. What VELC adds, according to ISRO, is the line-of-sight motion from a single vantage point.

The paper is careful about its limits. It calls the model qualitative, says its parameters are representative and not a unique reconstruction of the eruption, and says the lower of the two branches is faint and cannot be followed through the whole event. It offers one possible reason for the lopsided growth, an uneven magnetic environment around the eruption, and adds that the observations do not provide enough constraints to establish that link. ETV Bharat notes that the study does not directly establish whether asymmetric expansion changes how severe a geomagnetic disturbance is, and ThePrint adds that it examined one event and does not suggest a major storm is imminent. The eruption itself started just beyond the Sun’s limb, and NOAA judged at the time that an Earth-directed CME was unlikely.

What comes next

The researchers plan to apply the technique to other CMEs, ISRO’s release says, to establish how reliably VELC spectroscopy can recover an eruption’s direction, speed and expansion, and to reconstruct motion without relying entirely on images from several spacecraft. ETV Bharat reports that the next targets are eruptions near the Sun’s edge, where line-of-sight motion is hardest to get from images. Samanta told the outlet that VELC is at present the only operational space-based coronagraph that regularly provides spectroscopic observations of the corona beyond the Sun’s visible edge.

The result came less than three weeks after IIA’s joint analysis of VELC and Europe’s Proba-3 coronagraph, announced on 15 October 2026. ISRO says the halo orbit that Aditya-L1 entered on 6 January 2024, around the L1 point about 1.5 million kilometres from Earth, was chosen to give a mission life of five years.