By Girish Linganna
Aditya L1, India’s inaugural solar study mission, is set for launch by the Indian Space Research Organisation (ISRO) on September 2, 2023. Previously known as Aditya 1, the mission’s name, ‘Aditya’, has been derived from Sanskrit, meaning the Sun. Its ‘L-1’ designation refers to the Lagrange Point positioned around 1.5 million kilometers from Earth in the Sun-Earth system, where the mission’s halo orbit will be established. The primary scientific goals of the Aditya L-1 mission encompass investigation of the dynamic processes in the solar upper atmosphere, including the chromosphere and corona. The mission is planned for a duration of 5.2 years.
At the heart of the solar system, the Sun reigns as a nearly flawless sphere of scorching plasma, a glow due to nuclear fusion reactions in its core. Emitting energy primarily as light, ultraviolet and infrared radiation, it stands as the vital life force for Earth.
With a colossal radius of approximately 695,000 kilometres (432,000 miles)—about 109 times that of our planet—and a mass that dwarfs Earth’s by 330,000 times, making up 99.86% of the solar system’s total mass, the Sun’s composition is dominated by hydrogen, comprising around 73% of its mass, alongside helium at about 25%, and trace amounts of other elements, such as oxygen, carbon, neon and iron.
The Sun is made up of 7 parts. The inner layers are the Core, the Radiative Zone and the Convection Zone. The outer layers are the Photosphere, the Chromosphere, the Transition Region and the Corona.
The temperature behaviour within the Sun poses a significant scientific puzzle. While the core generates extreme heat surpassing 15° Celsius, the temperature diminishes as one moves outward, reaching around 5,500 degrees Celsius at the photosphere—the Sun’s visible surface. Intriguingly, the temperature surges again up to 2° Celsius within the corona, the outermost layer. Scientists are actively exploring the factors contributing to this intriguing temperature distribution in the Sun.
The Corona is about 2,100 kilometres above the Sun’s surface (photosphere). Investigation of the dynamic processes in the chromosphere and corona involves studying such phenomena as chromospheric and coronal heating, the behaviour of partially ionized plasma, the initiation of coronal mass ejections and solar flares. Additionally, the mission aims to collect data on particle and plasma conditions around the Sun, contributing to the understanding of solar particle dynamics.
Furthermore, the objectives encompass delving into the physics underlying the solar corona and its heating mechanism. This involves diagnosing the plasma properties of the corona and coronal loops, including temperature, velocity and density. The mission also seeks to understand the formation, evolution and triggers of coronal mass ejections (CMEs). It aims to map out the sequence of processes spanning various layers—the chromosphere, base and extended corona—that culminate in solar eruptive events. Another aim is to study the magnetic field topology and measurements in the solar corona, while also investigating the sources, composition and dynamics of the solar wind, which is a driver for space weather.
A Lagrange Point is a spot in space where the gravitational forces of two massive objects—such as the Earth and the Moon, or Earth and the Sun—produce a stable gravitational balance. This allows a spacecraft to essentially ‘hover’ at that point without needing constant propulsion.
Within the Sun-Earth system, there exist five Lagrange Points denoted as L. The L-1 point, positioned about 1.5 million km from Earth, represents one of these points. Aditya L-1 is destined for placement at the L1 point due to the presence of a halo orbit encircling that location. This unique orbit grants spacecraft the valuable capability of uninterrupted solar observations, free from any occultation or eclipses. This positioning offers a distinct advantage for studying real-time solar activities and their impact on space weather. Aditya L-1’s journey to reach the L-1 point spans approximately 125 days.
The L-1 point serves as the designated parking position for the Solar and Heliospheric Observatory Satellite (SoHO), a joint venture between NASA and the European Space Agency.
The Aditya L-1 space vehicle will transport seven payloads designed for the purpose of observing the photosphere, chromosphere, and the outermost layers of the Sun (known as the corona). These payloads encompass a range of detectors, including those sensitive to electromagnetic radiation, particles, and magnetic fields.
Leveraging the strategic advantage of the L-1 vantage point, four of the payloads will directly observe the Sun, while the remaining three payloads will conduct in situ studies of particles and fields at Lagrange Point L-1. The paramount data will originate from the Aditya L-1 payloads’ instrumentation. These payloads are anticipated to furnish insights crucial for comprehending such issues as coronal heating, coronal mass ejections, pre-flare and flare activities, along with their distinctive traits. Additionally, they will aid in unravelling the dynamics of space weather, as well as the propagation behaviours of particles and fields. (IPA Service)
(The author is a Defence, Aerospace & Political analyst based in Bengaluru)