• Aditya-L1 was launched by ISRO on September 2, 2023, with the mission of observing and helping us better understand the Sun. It arrives at its destination, L1 or the first Sun-Earth Lagrangian point.
  • Here is all you need to know about the mission, from why it is important to why it is placed at the L1 point.
  • The Sun produces energy through nuclear fusion in its interior, and emits it from its outer layers. The photosphere, a 6,000-degree Celsius layer, emits all visible and infrared light, crucial for life. 
  •  Above is the chromosphere, and higher still is the million-degree Celsius hot corona.
  • Interestingly, the corona is much hotter than the inner layers of the Sun — there must be some energy source which provides this heat. However, the processes involved in this are not yet fully understood.
  •  Moreover, it also emits ultraviolet and X-ray radiation which would be lethal to life on Earth, without the presence of the atmosphere which absorbs most harmful radiation.
  • The Sun also continuously streams electrically charged particles — a stream known as the Solar wind. These charged particles produce the spectacular aurorae, known as the Northern and Southern Lights, seen close to the north and south poles of the Earth.
  • There are also sudden bursts and ejections of charged particles from the Sun into interplanetary space, known as Solar flares and coronal mass ejections. 
  • These directly affect space weather, space-reliant technologies like satellite communication networks, and can produce electric power blackouts in Earth’s higher latitudes. Notably, they can be extremely difficult to predict
  • Since Aditya-L1 is located outside the Earth’s atmosphere, its instruments can observe the ultraviolet radiation from the corona, and in the process, better understand its workings. Moreover, we need to monitor the Solar atmosphere and the corona continuously to monitor eruptions on the Sun, and study the properties of charged particles in the Solar wind.
  • Crucially, this task has to be carried out from outside Earth’s atmosphere, and as close to the Sun as possible.
  •  This will then help provide early warning of Solar eruptions, and allow us to initiate actions to minimize the disruption they may cause.
  • Aditya-L1 has seven instruments for the observation of all the radiation and charged particles. Its location, 1.5 million km away from Earth towards the Sun (more on that next), allows uninterrupted observations.
  • Putting Aditya in orbit around the Earth would have made the mission much simpler. However, this would also mean that Earth would cover Aditya’s view of the Sun for significant periods of time. 
  • While the duration of such eclipses can be reduced by choosing the correct orbit, it cannot be fully eliminated. 
  • Given that Aditya is meant to act as an early warning system for solar flares and coronal mass ejections, it is necessary to have an uninterrupted view of the Sun.
  • When Aditya is at L1, the Earth is always on one side of it, and the Sun on the other side. Thus, the spacecraft’s instruments can be pointed towards the Sun for a completely uninterrupted view. Even though placing the spacecraft at an orbit around L1 is complex, the benefits of having an uninterrupted view of the Sun at all times is well worth the effort, risk, and expense.
  • A few space missions are already parked around the L1 point, including the LISA Pathfinder, and Solar and Heliospheric Observatory (SOHO), both collaborative missions of NASA and the European Space Agency.

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