Explainer | How ISRO will study the Sun from space?

Aditya-L1, the first space-based Indian observatory to study the Sun, is getting ready for its launch soon. The satellite, realised at U.R.Rao Satellite Centre in Bengaluru, has arrived at the ISRO’s spaceport in Sriharikota in Andhra Pradesh.

The Aditya-L1 mission will be launched by ISRO PSLV rocket from Satish Dhawan Space Centre SHAR (SDSC-SHAR), Sriharikota. 

Initially the spacecraft will be placed in a Low Earth Orbit. Subsequently, the orbit will be made more elliptical and later the spacecraft will be launched towards the Lagrange Point L1 by using on-board propulsion. 

As the spacecraft travels towards L1, it will exit the earth’s gravitational Sphere of Influence (SOI). After exit from SOI, the cruise phase will start and subsequently the spacecraft will be injected into a large halo orbit around L1. The total travel time from launch to L1 would take about four months for Aditya-L1.

What are Lagrange Points?

• For a two body gravitational system, the Lagrange Points are the positions in space where a small object tends to stay, if put there. These points in space for a two body systems such as Sun and Earth can be used by spacecraft to remain at these positions with reduced fuel consumption. 

• At Lagrange Points, 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.

• Lagrange Points are named in honor of Italian-French mathematician Joseph-Louis Lagrange.

What is the significance of solar mission?

• The estimated age of the Sun is about 4.5 billion years. It is a hot glowing ball of hydrogen and helium gases. The distance to the Sun from the Earth is about 150 million kilometres, and is the source of energy for our solar system. 

• Without solar energy, the life on earth, as we know, cannot exist. The gravity of the Sun holds all the objects of the solar system together.

• At the central region of the Sun, known as ‘core’, the temperature can reach as high as 15 million degree Celsius. At this temperature, a process called nuclear fusion takes place in the core which powers the Sun. 

• The visible surface of the sun known as photosphere is relatively cool and has temperature of about 5,500°C.

• The Sun constantly influences the Earth with radiation, heat and constant flow of particles and magnetic fields. The constant flow of particles from the Sun is known as solar wind and are mostly composed of high energy protons.

• The solar wind fills nearly all the space of the known solar system. Along with the solar wind, the solar magnetic field also fills the solar system.

• The solar wind along with other explosive/eruptive solar events like coronal mass ejection (CME) affects the nature of space. During such events, the nature of magnetic field and charge particle environment near the planet change. 

• In the case of Earth, the interaction of Earth’s magnetic field with the field carried by CME can trigger a magnetic disturbance near the Earth. Such events can affect the functioning of space assets.

• By studying the Sun we can learn much more about stars in our Milky Way as well as about stars in various other galaxies. 

• The Sun shows several eruptive phenomena and releases immense amount of energy in the solar system. If such explosive solar phenomena is directed towards the Earth, it could cause various types of disturbances in the near earth space environment.

Why study the Sun from space?

• The Sun emits radiation/light in nearly all wavelengths along with various energetic particles and magnetic field. The atmosphere of the Earth as well as its magnetic field acts as a protective shield and blocks a number of harmful wavelength radiations including particles and fields. 

• As various radiations don’t reach the surface of the Earth, the instruments from the Earth will not be able to detect such radiation and solar studies based on these radiations could not be carried out. 

• However, such studies can be carried out by making observations from outside the Earth atmosphere, that is from space. 

• Similarly, to understand how the solar wind particles and magnetic field from the Sun travel through the interplanetary space, measurements are to be performed from a point which is far away from the influence of the Earth’s magnetic field.

Aditya-L1

• Aditya-L1 is the first space based observatory class Indian solar mission to study the Sun.

• The spacecraft is planned to be placed in a halo orbit around the Lagrangian 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/eclipse. 

• This will provide a greater advantage of observing the solar activities continuously. 

• The spacecraft carries seven payloads to observe the photosphere, chromosphere, and the outermost layers of the Sun (the corona) using electromagnetic and particle detectors.

• Using the special vantage point of L1, four payloads directly view the Sun and the remaining three payloads carry out in-situ studies of particles and fields at the Lagrange point L1.

• The instruments of Aditya-L1 are tuned to observe the solar atmosphere, mainly the chromosphere and corona, while the in-situ instruments will observe the local environment at L1.

• The suit of Aditya-L1 payloads are expected to provide most crucial information to understand the problems of coronal heating, Coronal Mass Ejection, pre-flare and flare activities, and their characteristics, dynamics of space weather, study of the propagation of particles, and fields in the interplanetary medium, etc.

Objectives of the mission:

• Study of solar upper atmospheric (chromosphere and corona) dynamics.

• Study of chromospheric and coronal heating, physics of the partially ionised plasma, initiation of the coronal mass ejections, and flares.

• Observe the in-situ particle and plasma environment providing data for the study of particle dynamics from the Sun.

• Physics of solar corona and its heating mechanism.

• Diagnostics of the coronal and coronal loops plasma: Temperature, velocity and density.

• Development, dynamics and origin of coronal mass ejections.

• Identify the sequence of processes that occur at multiple layers (chromosphere, base and extended corona) which eventually leads to solar eruptive events.

• Magnetic field topology and magnetic field measurements in the solar corona.

• Drivers for space weather (origin, composition and dynamics of solar wind).