Observations from India's Aditya-L1 solar mission have yielded critical new insights into one of astrophysics' most enduring puzzles: why the Sun's outer atmosphere, or corona, remains millions of degrees hotter than its visible surface — and how it sustains that heat despite continuously losing vast energy through solar eruptions. The findings, published in the Astrophysical Journal Letters, were led by Professor R. Ramesh of the Indian Institute of Astrophysics (IIA), and were announced on 14 August from New Delhi.

The Corona Heating Mystery

The temperature structure of the Sun has baffled solar physicists for decades. The Sun's core burns at nearly 15 million degrees Celsius, while its visible surface — the photosphere — is a comparatively cool 5,500 degrees Celsius. Yet the corona, located far above the surface, routinely reaches around 2 million degrees Celsius and can spike to as high as 40 million degrees Celsius during active periods.

This counterintuitive temperature inversion — where the atmosphere grows hotter as it moves farther from the heat source — defies conventional thermodynamic expectations and has remained one of the most contested open questions in solar science.

What Aditya-L1 Data Reveals

India's Aditya-L1, the country's first dedicated solar observation mission, has provided a fresh observational vantage point to study coronal dynamics. According to the research team, the mission's data sheds new light on the mechanisms that both heat the corona and replenish energy lost during powerful solar eruptions such as solar flares and coronal mass ejections (CMEs).

The study, according to the researchers, addresses not just the heating question but also the related problem of energy replenishment — how the corona maintains its extreme temperatures despite the constant drain of eruptions.

Solar Eruptions and Their Scale

The corona is the origin point of extreme space weather events. During a CME, the Sun ejects enormous quantities of energy and charged particles into space. According to Prof. Ramesh, the Sun typically generates two to three CMEs per day during periods of low solar activity. At the peak of its 11-year solar cycle, that rate can climb to ten or more eruptions daily.

These events carry significant consequences for Earth. While they can produce spectacular auroras, they also pose serious risks to power grids, communication networks, satellite systems, and navigation infrastructure through geomagnetic storms.

Why Energy Replenishment Matters

Scientists have long questioned how the corona sustains its extreme temperatures in the face of such frequent and massive energy losses. If the energy expelled through CMEs and flares were not continuously replenished, the corona would gradually cool — an outcome that would have cascading effects across the solar system. The Aditya-L1 findings, according to the IIA team, bring researchers meaningfully closer to understanding the replenishment mechanism.

Notably, this is among the first major peer-reviewed outputs from the Aditya-L1 mission, signalling that the spacecraft's instruments are delivering scientifically significant data. As the mission continues its observations from the Sun-Earth Lagrange Point 1, further findings are expected to refine the current models of coronal heating.