The Why, What, When, Where and How of India's Aditya-L1 Sun Mission explained

At 12:10 pm on September 1, the 24-hour countdown timer began ticking at the Satish Dhawan Space Centre spaceport in Sriharikota.

At the end of this countdown, Saturday at 11:50am, India's PSLV rocket in its XL configuration lifted-off carrying the world's most populous nation's maiden mission to study the sun. Named Aditya-L1, the craft will cover a distance of 1.5 million kilometres in space, during a span of approximately 120 days. The craft will be travelling to Lagrange Point 1 or L1, a vantage point from where it would have an unobstructed view of the sun.

To understand the science and applications of Aditya-L1, WION spoke to Prof Ramesh from the Indian Institute of Astrophysics (IIA). Notably, the IIA has contributed the Visible Emission Line Coronagraph payload for this mission and Prof Ramesh is the Principal Investigator of the same.

While this is a mission to study the sun, it would be travelling only 1 per cent if the Earth-Sun distance, unlike NASA's Parker Solar Probe that has flown a few million miles in the vicinity of the Sun. The Earth-Sun distance is approximately 150 million kilometres.

The launch of Aditya-L1 comes barely 10 days after India soft-landed its Chandrayaan-3 craft (comprising a lander and rover) on the moon.

"Studies related to the Sun can be carried out from ground-based observatories, but they are limited by the day-night cycle. So, an agency would require multiple stations across the earth to study the sun continuously, but each of these observatories would offer their own data (based on the unique characteristics of the equipment). Also, the earth's atmosphere and dust particles scatter the radiation coming in from the sun and affect the quality of the data" Prof Ramesh from the Indian Institute of Astrophysics told WION.

Explaining the exterior layers of the sun, he said that the sun's Photosphere emitted the strongest light, the photosphere is then covered by the Chromosphere (which extends 1000s of kms) and finally there is the Corona (Sun's outermost layer).

"The Corona emits light, but it is million times less intense than that of the Photosphere. Therefore, it is only during a solar eclipse(when moon covers the sun's Photosphere by coming in the path between earth and Sun) that we are able to study the faint light from the Corona" he added.

However, eclipses happen only one or twice a year and the data from eclipses which last a few minutes would be insufficient to study transient changes.

On the Aditya-L1 craft, we have a device known as Visible Emission Line Coronagraph (VELC), which is capable of artificially blocking the light of the Photosphere and studying the light from the Corona.

"We are interested in studying the Corona owing to its dynamic nature and regular eruptions from the Corona(Coronal Mass Ejections), where charged particles from the sun travel at 3000km/sec speeds. At this speed, it can reach the earth in around 15hours, he explained.

Such phenomena can affect the electronics and solar panels of satellites orbiting the earth, it can also cause geomagnetic storms that can temporarily swell up earth's atmosphere and drag satellites that are flying as low as 200km orbit. Such incidents can even known out high-tension power lines (as it happened in Quebec City Canada and In Zurich Airport).

From the L1 vantage point, around which the spacecraft will be circling, the VELC payload will be able to image the sun's corona every single minute and help researchers understand the fast changes in Solar atmosphere.

Using a Polarimeter, we can also measure and predict which sun spots(dark regions with strong magnetic fields, where even light cannot enter) can erupt and lead to Coronal Mass ejections. in future, this could help us predict any danger to satellites around earth, assess which CMEs will reach earth and which won't.

Notably, when such high-speed particles from the Sun reach the earth's atmosphere, the upper layers of the atmosphere act as a barrier and divert the charged particles to earth's poles, thereby causing the Northern Lights (Aurora Borealis) and Southern Lights (Aurora Australis), a dazzling display of light blue-green-yellow-red lights in the winter night skies near the earths north polar and south polar regions.