The Indian Space Research Organisation (ISRO) has announced that the Aditya-L1 mission, the first space-based Indian observatory to study the Sun, will be launched on September 2 from Sriharikota. According to an ISRO release, “The spacecraft will 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 This will provide a greater advantage of observing the solar activities and its effect on space weather in real time.” 🚀PSLV-C57/🛰️Aditya-L1 Mission: The launch of Aditya-L1, the first space-based Indian observatory to study the Sun ☀️, is scheduled for 🗓️September 2, 2023, at 🕛11:50 Hrs. IST from Sriharikota. Citizens are invited to witness the launch from the Launch View Gallery at… pic.twitter.com/bjhM5mZNrx — ISRO (@isro) August 28, 2023 What is the Lagrange point 1? What exactly will the Aditya-L1 mission study near the Sun? Why is observing and understanding solar phenomena important? Where is the Aditya-L1 mission going? As the ISRO release says, the spacecraft will be put in orbit around the L1 point, from where it will be able to observe the Sun without obstructions. A Lagrange point, as defined by NASA, is a position in space where “the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them. These points in space can be used by spacecraft to reduce fuel consumption needed to remain in position.” Basically, this means that at that point, the gravitational attraction and repulsion between two heavenly bodies is such that an object placed between them will effectively stay in the same relative position while moving with them. The Lagrange points are named in honor of Italian-French mathematician Josephy-Louis Lagrange, and there are five of them: L1, L2, L3, L4, and L5. According to NASA, “The L1 point of the Earth-Sun system affords an uninterrupted view of the Sun and is currently home to the Solar and Heliospheric Observatory Satellite SOHO.” NASA's James Webb Space Telescope is at L2. "What is special about this orbit is that it lets the telescope stay in line with the Earth as it moves around the Sun. This allows the satellite's large sunshield to protect the telescope from the light and heat of the Sun and Earth (and Moon)," NASA's website says. What will the Aditya-L1 mission study? The spacecraft carries seven payloads to observe the photosphere [the deepest layer of the sun we can directly observe], chromosphere [the layer about 400 km and 2,100 km above the photosphere], and the outermost layers of the Sun (the corona), using electromagnetic and particle and magnetic field detectors. Of the seven playloads, four will directly study the Sun, and the remaining three will in situ study particles and fields at the Lagrange point L1, “thus providing important scientific studies of the propagatory effect of solar dynamics in the interplanetary medium,” ISRO says. “The suits of Aditya L1 payloads are expected to provide most crucial informations 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 ISRO release says. Why is it important to study the Sun? Every planet, including Earth and the exoplanets beyond the Solar System, evolves — and this evolution is governed by its parent star. The solar weather and environment affect the weather of the entire system. Variations in this weather can change the orbits of satellites or shorten their lives, interfere with or damage onboard electronics, and cause power blackouts and other disturbances on Earth. Knowledge of solar events is key to understanding space weather. To learn about and track Earth-directed storms, and to predict their impact, continuous solar observations are needed. Every storm that emerges from the Sun and heads towards Earth passes through L1. What are the payloads Aditya-L1 mission will carry? According to ISRO, the Remote Sensing Payloads, which will study the Sun, include: Visible Emission Line Coronagraph (VELC) for corona/imaging and spectroscopy; Solar Ultraviolet Imaging Telescope (SUIT) for photosphere and chromosphere imaging; Solar Low Energy X-ray Spectrometer (SoLEXS), which is a soft X-ray spectrometer for Sun-as-a-star observation; and High Energy L1 Orbiting X-ray Spectrometer (HEL1OS), which is a Hard X-ray spectrometer for Sun-as-a-star observation. The payloads to study the L1 in situ (meaning at their place, or position) are: Aditya Solar wind Particle Experiment (ASPEX), for solar wind/particle analyzer protons and heavier ions with directions; Plasma Analyser Package For Aditya (PAPA), for solar wind/particle analyzer electrons and heavier ions with directions; and Advanced Tri-axial High Resolution Digital Magnetometers for in situ magnetic field study.
