Aditya-L1, India's first solar observatory to study sun’s photosphere, chromosphere, and corona

After the successful launch of Chandrayaan-3 on August 23, 2023 by Indian Space Research Organisation (ISRO), on September 2, 2023 India's first solar observatory began its journey to the destination of Sun-Earth L1 point. The vehicle has placed the satellite precisely into its intended orbit. The launch of Aditya-L1 by PSLV-C57 has been accomplished. 

Aditya L1 is going to be the first space based Indian mission to study the Sun. The spacecraft shall be placed in a halo orbit around the Lagrange point 1 (L1) of the Sun-Earth system, which is about 1.5 million km from the Earth. A satellite placed in the halo orbit around the L1 point has the major advantage of continuously viewing the Sun without any occultation/eclipses. This will provide a greater advantage of observing the solar activities and its effect on space weather in real time. The spacecraft carries seven payloads to observe the photosphere, chromosphere and the outermost layers of the Sun (the corona) using electromagnetic and particle and magnetic field detectors. 

Using the special vantage point L1, four payloads directly view the Sun and the remaining three payloads carry out in-situ studies of particles and fields at the Lagrange point L1, thus providing important scientific studies of the propagatory effect of solar dynamics in the interplanetary medium.

The suits of Aditya L1 payloads are expected to provide most crucial information to understand the problem of coronal heating, coronal mass ejection, pre-flare and flare activities and their characteristics, dynamics of space weather, propagation of particle and fields etc.

The major science objectives of Aditya-L1 mission are:

• Study of Solar upper atmospheric (chromosphere and corona) dynamics.
• Study of chromospheric and coronal heating, physics of the partially ionized plasma, initiation of the coronal mass ejections, and flares
• Observe the in-situ particle and plasma environment providing data for the study of particle dynamics from the Sun.
• Physics of solar corona and its heating mechanism.
• Diagnostics of the coronal and coronal loops plasma: Temperature, velocity and density.
• Development, dynamics and origin of CMEs.
• Identify the sequence of processes that occur at multiple layers (chromosphere, base and extended corona) which eventually leads to solar eruptive events.
• Magnetic field topology and magnetic field measurements in the solar corona .
• Drivers for space weather (origin, composition and dynamics of solar wind .

The instruments of Aditya-L1 are tuned to observe the solar atmosphere mainly the chromosphere and corona. In-situ instruments will observe the local environment at L1. There are total seven payloads on-board with four of them carrying out remote sensing of the Sun and three of them carrying in-situ observation. 

The four payloads will study the star’s photosphere, its layer visible to us; the chromosphere, a thin layer of plasma on top of the photosphere; and the corona, the outermost layer of the sun that starts about 1,300 miles above the photosphere. 

The photosphere is the source of solar flares: tongues of fire that extend hundreds of thousands of miles above the sun's surface. Solar flares produce bursts of X-rays, ultraviolet radiation, electromagnetic radiation and radio waves.

The chromosphere emits a reddish glow as super-heated hydrogen burns off. But the red rim can only be seen during a total solar eclipse. At other times, light from the chromosphere is usually too weak to be seen against the brighter photosphere.

The sun's corona can only be seen during a total solar eclipse (or with NASA's Solar Dynamics Observatory). It appears as white streamers or plumes of ionized gas that flow outward into space. Temperatures in the sun's corona can get as high as 2 million degrees C. As the gases cool, they become the solar wind.

Why the corona is up to 300 times hotter than the photosphere, despite being farther from the solar core, has remained a long-term mystery.

Out of five scheduled Earth-bound maneuvres before picking the speed for journey to orbit around L1, the first Earth-bound maneuvre has been performed successfully from ISTRAC, Bengaluru. The new orbit attained is 245 km x 22459 km on September 3. The satellite is healthy and operating nominally. The second Earth-bound maneuvre was performed successfully on September 5. The new orbit attained is 282 km x 40225 km.

ISRO is the space agency of India. The organisation is involved in science, engineering and technology to harvest the benefits of outer space for India and the mankind. ISRO was previously the Indian National Committee for Space Research (INCOSPAR), set up by the Government of India in 1962, as envisioned by Dr. VikramA Sarabhai. ISRO was formed on August 15, 1969 and superseded INCOSPAR with an expanded role to harness space technology.