New Delhi: A solar eruption does not necessarily travel through space like a perfectly expanding bubble. It can stretch and spread unevenly, changing shape as it moves away from the Sun. That detail matters because the way an eruption expands can influence how fast it travels and when it reaches Earth.
India’s Aditya-L1 mission has now offered scientists a closer look at this process. In a study published in The Astrophysical Journal Letters on 3 November, researchers from the Indian Institute of Astrophysics used observations from the spacecraft to examine a solar eruption recorded on 5 August 2024. They found that it expanded asymmetrically, rather than uniformly in all directions.
The finding could help improve our understanding of space weather, which can affect satellites, communication systems and other technology on which people depend.
What exactly did Aditya-L1 observe?
The event studied was a coronal mass ejection, or CME. These are enormous bursts of hot, electrically charged gas, known as plasma, released from the Sun’s outer atmosphere. They often carry magnetic fields with them and can travel through space at very high speeds.
Not every CME is directed towards Earth. But when one is, it can disturb the space environment around our planet. Depending on its strength and direction, it can interfere with satellites, radio communication and navigation systems. Powerful events can also induce currents in electricity networks.
To understand the threat, scientists need to know more than simply whether an eruption has occurred. They need to estimate its direction, speed and likely arrival time.
This is where the new observations become important. The team combined data from Aditya-L1’s Visible Emission Line Coronagraph, or VELC, with images from NASA’s Solar Dynamics Observatory and a three-dimensional model of the eruption.
How did the spacecraft see what was previously difficult to measure?
A coronagraph allows scientists to observe the Sun’s faint outer atmosphere by blocking out the much brighter solar disc. Images from such instruments can show how an eruption moves across the sky, but they do not necessarily reveal how quickly material is moving towards or away from the observer.
VELC adds another layer of information. It studies changes in the light emitted by hot gas. When that gas moves, the light’s wavelength shifts slightly. This is similar to how the pitch of an ambulance siren appears to change as it approaches and then moves away.
By studying these shifts, researchers could detect material moving both towards and away from the spacecraft’s line of sight. When combined with images and modelling, this helped them reconstruct the eruption’s shape and movement in three dimensions.
The researchers found that a model in which the eruption expanded evenly could not explain the observations. A model involving uneven sideways expansion and a tilted structure provided a much closer match.
Why should this matter for Earth?
The shape of a CME can affect how it interacts with the solar wind, the continuous stream of charged particles flowing out from the Sun. Different shapes can experience different levels of resistance as they travel through space, potentially changing their speed.
That, in turn, can make it harder to predict when a CME will reach Earth. Arrival-time estimates are important because they give satellite operators, power-grid managers and other agencies time to prepare for possible disturbances.
A more accurate understanding of how eruptions develop close to the Sun could therefore improve the models used to forecast space weather.
It is important, however, not to overstate what this particular observation means. The study does not establish that the eruption posed a threat to Earth, nor does it suggest that a major solar storm is imminent. It examined one event and demonstrated how its expansion could be reconstructed using Aditya-L1’s observations.
What comes next for Aditya-L1?
The researchers plan to apply the technique to other solar eruptions. Studying more events will help establish how reliably VELC can reveal their three-dimensional structure and movement.
Aditya-L1, launched in September 2023, is positioned around the Sun-Earth L1 point, roughly 1.5 million kilometres from Earth. Its position allows it to observe the Sun continuously, without the interruptions caused by Earth’s rotation.
The latest finding shows why that continuous view matters. Understanding a solar storm begins long before it reaches Earth. The more accurately scientists can follow its early stages, the better they can estimate what it might do on the way here.