Why in the news?
Scientists used Aditya-L1’s VELC payload to generate unique Doppler velocity images of the solar corona, revealing CME direction.
UPSC Relevance
Prelims: Aditya-L1 and its payloads, Lagrange points, solar corona, CMEs, Doppler effect, global solar missions.
Mains: GS3 – Science and Technology (awareness in the field of space; achievements of Indians in science and technology).
Aditya-L1 Mission
| Feature | Details |
|---|---|
| Nature | India’s first space-based observatory to study the Sun (Aditya = Sun in Sanskrit) |
| Agency | ISRO, with payloads from national institutes (IIA, IUCAA, PRL, VSSC, URSC, LEOS) |
| Launch | 2 September 2023, by PSLV-C57 (XL variant) from Satish Dhawan Space Centre, Sriharikota |
| Final orbit | Inserted into a halo orbit around Sun-Earth Lagrange Point 1 (L1) on 6 January 2024 |
| Distance | About 1.5 million km from Earth, roughly 1% of the Earth-Sun distance |
| Payloads | 7 in total – 4 remote sensing and 3 in-situ |
| Mission life | Planned for about 5 years |
| Key advantage | Continuous view of the Sun without any eclipse or occultation |
Lagrange Points – Why L1?
- Meaning: Lagrange points are positions in space where the gravitational pull of two large bodies (here the Sun and Earth) balances the centripetal force needed by a small object to move along with them. A spacecraft placed here needs very little fuel to stay in position.
- Number: There are five such points (L1 to L5) in any two-body system, named after mathematician Joseph-Louis Lagrange.
- Stability: L1, L2 and L3 are unstable (small disturbances push objects away, so regular station-keeping is needed). L4 and L5 are stable, and natural objects like Trojan asteroids collect there.
- Halo orbit: Spacecraft do not sit exactly at L1. They loop around it in a halo orbit, which also keeps the Sun-spacecraft-Earth line clear of radio interference from the Sun.
Understanding Key Solar Terms
- Layers of the Sun: Core – radiative zone – convective zone – photosphere (visible surface) – chromosphere – transition region – corona (outermost layer, best seen during a total solar eclipse).
- Coronagraph: An instrument that blocks the bright solar disc with an occulting disc to create an artificial eclipse, so the faint corona can be observed.
- Solar wind: A continuous stream of charged particles (mainly protons and electrons) flowing out from the corona.
- Sunspots: Darker, cooler areas on the photosphere with intense magnetic activity. Their number rises and falls over an 11-year solar cycle. The current cycle, Solar Cycle 25, peaked around 2024-25.
| Basis | Solar Flare | Coronal Mass Ejection (CME) |
|---|---|---|
| What it is | Sudden burst of electromagnetic radiation from the Sun’s surface | Huge cloud of magnetised plasma thrown out from the corona |
| Speed of arrival | Reaches Earth in about 8 minutes (speed of light) | Takes about 1 to 3 days to reach Earth |
| Main effect | Radio blackouts on the sunlit side of Earth | Geomagnetic storms, auroras, damage to satellites and grids |
| Relation | Often occur together, but one can happen without the other | Bigger long-term threat to infrastructure |
Major Solar Missions of the World
| Mission | Agency | Launch | Key feature |
|---|---|---|---|
| SOHO | NASA-ESA | 1995 | At L1; long-running source of CME data |
| Parker Solar Probe | NASA | 2018 | Closest human-made object to the Sun; ‘touched’ the corona |
| Solar Orbiter | ESA-NASA | 2020 | First images of the Sun’s poles |
| Aditya-L1 | ISRO | 2023 | India’s first solar observatory at L1 |
| Proba-3 | ESA | 2024 (by ISRO’s PSLV-C59) | Two satellites flying in formation to create an artificial eclipse |
Practice MCQ
Q1. Consider the following payloads on board Aditya-L1:
1. Visible Emission Line Coronagraph (VELC)
2. Solar Ultraviolet Imaging Telescope (SUIT)
3. Aditya Solar wind Particle Experiment (ASPEX)
4. Plasma Analyser Package for Aditya (PAPA)
How many of the above are in-situ instruments?
(a) Only one
(b) Only two
(c) Only three
(d) All four
Answer: (b)
Explanation: ASPEX and PAPA measure solar wind particles at L1 itself, so they are in-situ. VELC and SUIT observe the Sun from a distance and are remote sensing payloads.
Q2. Consider the following statements:
Statement-I: Doppler velocity images of the solar corona can help determine whether a coronal mass ejection is moving towards the Earth.
Statement-II: Light from a source moving towards an observer appears shifted towards longer wavelengths.
Which one of the following is correct in respect of the above statements?
(a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
(b) Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
(c) Statement-I is correct, but Statement-II is incorrect
(d) Statement-I is incorrect, but Statement-II is correct
Answer: (c)
Explanation: A source moving towards the observer shows a blueshift, i.e. a shift to shorter wavelengths. Redshift (longer wavelength) indicates motion away from the observer.
Mains Practice Question
Q. Space weather is emerging as a serious threat to both space-based and ground-based infrastructure. In this context, discuss how the Aditya-L1 mission strengthens India’s capacity to understand solar activity and prepare for its impacts. (15 marks, 250 words)
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