Why ISRO’s Aditya spacecraft is at ‘L1’, what it means

Why ISRO’s Aditya spacecraft is at ‘L1’, what it means

Context- ISRO initiated the Aditya-L1 mission on September 2, 2023, with the objective of studying and enhancing our comprehension of the Sun. It reached its target, the first Sun-Earth Lagrangian point, also known as L1, on January 6.

But first, why study the Sun?

• The Sun generates energy via nuclear fusion within its core and releases it from its outer layers. The photosphere, a layer with a temperature of 6,000 degrees Celsius, emits all visible and infrared light, which is vital for life. Above this layer is the chromosphere, and even further above is the corona, which has a temperature of a million degrees Celsius.
• Interestingly, the corona’s temperature is significantly higher than the Sun’s inner layers, indicating an unknown energy source. The processes contributing to this heat are not fully understood.
• The corona also emits lethal ultraviolet and X-ray radiation, which would be harmful to Earth’s life forms if not for our atmosphere that absorbs most of this harmful radiation.
• The Sun constantly emits a stream of electrically charged particles known as the Solar wind. These particles create the stunning Northern and Southern Lights, visible near Earth’s poles.
• Additionally, the Sun occasionally ejects charged particles into space in events known as Solar flares and coronal mass ejections. These events can affect space weather, disrupt technologies dependent on space (like satellite communication networks), and cause power outages in Earth’s higher latitudes. Predicting these events can be challenging.

What will Aditya-L1 do?

• Aditya-L1, positioned outside Earth’s atmosphere, is equipped to observe the Sun’s corona’s ultraviolet radiation, thereby enhancing our understanding of its operations. It’s crucial to continuously monitor the Solar atmosphere and corona to track Solar eruptions and study the Solar wind’s charged particles.
• This monitoring must be done outside Earth’s atmosphere and as close to the Sun as feasible. This proximity allows for early detection of Solar eruptions, enabling us to take measures to mitigate any potential disruptions.
• Aditya-L1 is equipped with seven instruments designed to observe all radiation and charged particles. Its location, 1.5 million km from Earth towards the Sun, facilitates uninterrupted observations.

What is L1, the location of Aditya?

• L1 refers to the first Lagrangian point, one of five points (L1 to L5) associated with the movement of two celestial bodies, in this case, Earth and the Sun.
• These points were theoretically identified by mathematicians Leonhard Euler and Joseph-Louis Lagrange in the 19th century. L1 and L2 are of particular interest due to their relevance to space missions.
• A spacecraft in Earth’s orbit is influenced by the planet’s gravitational force. However, it doesn’t fall to Earth’s surface because the gravitational pull is counterbalanced by a centrifugal force resulting from the spacecraft’s motion around Earth.
• As a spacecraft moves further from Earth, the planet’s gravitational pull weakens. At a certain point, Earth’s gravitational force becomes comparable to that of the Sun. If the spacecraft moves beyond this point, it will be pulled into the Sun’s orbit or even crash into the Sun, depending on its speed.
• L1 is the optimal point between Earth and the Sun where the gravitational forces from both bodies and the centrifugal force cancel each other out. Consequently, once Aditya is precisely positioned at L1, it will remain there without using any energy.

Does this mean that Aditya is at a stationary point in space?

• Contrary to what one might assume, L1 is not a fixed point in space. It lies on the line connecting the Sun and Earth. As the Earth orbits the Sun, L1 also orbits the Sun, maintaining its position on the same line. Therefore, Aditya doesn’t stay at a fixed point in space but maintains a constant position relative to the Sun and Earth.
• The L1 point is inherently unstable. A slight disturbance can cause the spacecraft to veer off in a different direction. To prevent this, Aditya is placed in an orbit around L1.
• This orbit, which is nearly perpendicular to the line connecting the Sun and Earth, is complex. It takes the spacecraft approximately 178 days to complete one full orbit.

Why L1?

• While positioning Aditya in Earth’s orbit would have simplified the mission, it would also have resulted in Earth obstructing Aditya’s view of the Sun for considerable periods.
• Although the duration of such eclipses can be minimized by selecting an appropriate orbit, they cannot be completely avoided. As Aditya is designed to serve as an early warning system for solar flares and coronal mass ejections, it is essential to maintain an uninterrupted view of the Sun.
• When Aditya is at the L1 point, Earth is always on one side, and the Sun on the other, allowing the spacecraft’s instruments to have a continuous view of the Sun. Despite the complexity of placing the spacecraft in an orbit around L1, the advantages of an uninterrupted view of the Sun justify the effort, risk, and cost.
• Several space missions, including the LISA Pathfinder and the Solar and Heliospheric Observatory (SOHO), joint ventures of NASA and the European Space Agency, are already stationed around the L1 point.

And what about L2?

• While the L1 point is ideal for observing the Sun, the L2 point, located on the opposite side of Earth about 1.5 million kilometers away, serves as a valuable staging area for spacecraft observing the distant Universe.
• A spacecraft in a halo orbit around L2 can point its instruments away from Earth for an uninterrupted view of deep space.
• Notable astronomical probes currently in orbit around L2 include the James Webb Space Telescope (JWST), Gaia, and Euclid. The Planck mission, which made groundbreaking observations of cosmic microwave background radiation, was also positioned at L2.

Conclusion- The Aditya-L1 mission, stationed at L1, provides an uninterrupted view of the Sun, enabling continuous monitoring of solar activities and serving as an early warning system for solar flares and coronal mass ejections. On the other hand, the L2 point serves as a valuable staging area for spacecraft observing the distant Universe, offering an uninterrupted view of deep space.

These missions, despite their complexity and cost, have proven invaluable in expanding our knowledge of the cosmos. As technology advances, we can expect even more groundbreaking discoveries from these and future missions stationed at these strategic points in space.