Aditya-L1's VSEIL reveals unbalanced expansion of solar explosion

According to reports from PIB Delhi and PIB Ahmedabad, scientists have made a major revelation about the unbalanced expansion of a solar explosion or Coronal Mass Ejection (CME) through India's first space-based solar observatory, Aditya-L1. This important discovery could have serious impacts on space weather, satellites, and communication networks.

As stated in the PIB reports, Aditya-L1 was launched in September 2023 and is currently operating actively at the L1 point between the Sun and the Earth. The spacecraft carries a total of 7 payloads, with the Visible Emission Line Coronagraph (VELC) being its primary payload. VELC is an internally occulted coronagraph specially designed to simultaneously observe the solar corona in various modes.

For this study, scientists from the 'Indian Institute of Astrophysics' (IIA), an autonomous institute of the Department of Science and Technology, used data obtained by VELC along with observations from NASA's SDO spacecraft and relied on 3-D modeling to reconstruct the complete 3-D geometric structure and dynamics of solar explosions. This study has been published in 'The Astrophysical Journal Letters'.

According to sources, this study has shown for the first time that the CME did not expand outward like a normal symmetrical bubble, but instead exhibited non-uniform expansion and its shape became unbalanced. This difference in the expansion of the CME can influence its speed towards the Earth and cause disturbances in space weather.

VELC studies the emerging CME via spectroscopy at the 530.3 nanometer wavelength green emission line due to highly ionized iron atoms present in the corona. This line emission captures the hot coronal plasma at a temperature of approximately 18 lakh Kelvin. In addition, the Doppler shift provides information about the velocity of the plasma along the line of sight and close to the solar disk.

According to PIB reports, the design and fabrication of VELC was carried out by IIA at the MGK Menon Lab for Space Sciences located at the Hoskote campus, with abundant support from ISRO. Saurabh Tripathi, a PhD student at IIA and the lead author of the study, explained that they observed the CME that occurred on 5 August 2024 using data from the Atmospheric Imaging Assembly (AIA) of NASA's Solar Dynamics Observatory (SDO) and VELC.

This CME was launched from an active region near the western limb of the sun. The spectroscopic data of VELC shows an unusual yet clear Doppler pattern of blue-ward and red-ward shifted emissions originating from the plasma moving towards and away from us. Tanmay Samanta, a solar astronomer and co-author at IIA, stated that AIA images captured the propagation of the CME in the sky, while VELC showed the motion of the CME bubble expanding towards and away from us.

Jayant Joshi, co-author from IIA, stated that to understand the unusual spectral patterns observed by VELC, they developed a 3-D geometric-kinematic model of the expanding CME. A model with symmetrical expansion could not reproduce the observed pattern, whereas a model with a tilted CME axis and unbalanced lateral expansion produced the exact same spectral patterns and temporal evolution observed by VELC.

Researchers are planning to apply this technique to other CMEs to reconstruct their kinematics without relying entirely on multi-viewpoint imaging from space telescopes. This is especially valuable in the lower corona where CMEs evolve rapidly. Jayant Joshi noted that the unbalanced shape of the initial CME can influence its interaction with the solar wind, stretching during heliospheric propagation, speed, and arrival time at Earth.