The Sun has a very important place in the life of every organism on this planet Earth. The Sun is the star at the centre of our solar system. It is a massive, luminous ball of hot, glowing gas primarily composed of hydrogen (92.1%) and helium (7.9%). Trace amounts of other elements (0.1%), such as oxygen, carbon, nitrogen, silicon, magnesium, neon, iron, and sulfur are also present The Sun holds 99.8 percent of our solar system’s mass, and its gravitational force is responsible for retaining all celestial bodies within it, including small Mercury, the gas giants, and the distant Oort Cloud, which is located 186 billion miles away. The Sun’s gravitational pull holds the entire solar system, including planets, asteroids, and comets, in orbit around it.
In most civilizations, it has been revered as divine, because of its potential to sustain life. From photosynthesis which provides food for every living organism to meeting energy needs, we cannot think of a day without the illumination from the Sun. If the Sun were to stop emitting light and heat suddenly, it would have catastrophic consequences for life on Earth. The Sun’s energy generation is based on nuclear fusion processes in its core, primarily converting hydrogen into helium, which is expected to continue for billions of years. This phase has lasted for about 4.6 billion years, and it is expected to continue for several billion more years before eventually evolving into a red giant and then a white dwarf. The uniqueness of the sun in sustaining life on our planet makes scientists focus their attention on studies on this star.
Aditya’s Journey
The kingmakers of the next century will be those who make a presence in other celestial bodies in outer space. The successful launching of Chandrayaan-3 followed by the launch of Aditya-L1 have made India a leading player in space research and exploration. The Aditya-L1 mission conceived in 2008 has undergone significant evolution as we stand in 2023. Initially conceived as a modest 880-pound (400 kilogram) satellite in low-Earth orbit, the mission has witnessed substantial growth over the past 15 years. For instance, the spacecraft was recently launched with a mass of nearly 3,300 pounds, and its revised mission profile now entails venturing well beyond low-Earth orbit. On September 2, 2023 Aditya-L1 lifted off on a PSLV-C57 (Polar Satellite Launch Vehicle) rocket from the launch pad at Sriharikota at 11:50 IST. With this India is on the list of select countries that have made their scientific presence both in the moon and sun explorations.
After a flight duration of 63 minutes and 20 seconds, the Aditya-L1 spacecraft was successfully injected into an elliptical orbit of 235×19500 km around the Earth, according to ISRO (Indian Space Research Organisation). The spacecraft is projected to traverse a distance of 1.5 million kilometres (932,000 miles) from Earth, ultimately arriving at the targeted Lagrange point (L1) after a duration of 135 days, assuming successful execution of the mission. The Aditya-L1 satellite will undergo a 16-day orbital period around the Earth in order to acquire the necessary velocity to successfully complete its mission. During this temporal interval, the satellite will be restricted to orbits that are bound to Earth and will undertake a total of five space manoeuvres. Spacecraft space manoeuvre refers to the alteration of the orbital trajectory by the utilisation of propulsion systems. Since the spacecraft started its journey on September 2, it has undertaken four manoeuvers till 15 September, shifting it to its new orbit at 256 km x 121973 km.
After successfully executing four orbital manoeuvres within the Earth’s orbit, the Aditya-L1 mission will proceed to perform a Trans-Lagrangian insertion manoeuvre. This critical step signifies the commencement of its approximately 110-day journey towards its intended destination, which is the L1 Lagrange point. After reaching the L1 point, a subsequent manoeuvre is performed to establish Aditya-L1 in a stable orbit around L1.
There are five Lagrange points in the Earth-Sun system, among them L1 is close to Earth and allows for an unobstructed view of the Sun without being hindered by eclipses or occultation. This will allow scientists to study solar activities and their impact on space weather in real time. Once the Aditya spacecraft reaches the L1 parking area, it will be able to orbit the Sun at the same rate as the Earth. The Solar and Heliospheric Observatory (SOHO), a joint NASA-European Space Agency mission that launched in December 1995, is already positioned at L1. The Aditya-L1 is equipped with seven payloads, namely the Visible Emission Line Coronagraph, Solar Ultraviolet Imaging Telescope, Solar Low Energy X-ray Spectrometer, High Energy L1 Orbiting X-ray Spectrometer, Aditya Solar wind Particle Experiment, Plasma Analyser Package for Aditya, and Advanced Tri-axial High-Resolution Digital Magnetometers. The seven scientific instruments carried in the orbiter will observe and study the dynamics of the crucial parts of the turbulent star, the photosphere, chromosphere and corona. Four of them will view the Sun directly, while the other three will carry out in-situ measurements to explore the nature of the space weather that the Sun generates in interplanetary space.
ISRO’s ingenuity shines through in the design of Aditya-L1. This cube-shaped spacecraft features a honeycomb sandwich structure, and its compact integrated GPS receiver provides real-time information on position, velocity, and time. When deployed, two solar panels will efficiently recharge Aditya-L1’s lithium-ion battery, ensuring a consistent and reliable power source.
The payloads of Aditya-L1 are anticipated to offer vital data for comprehending the phenomenon of coronal heating, coronal mass ejection, pre-flare and flare activity, as well as their features. The solar flares and coronal mass ejections (CME) can affect our planet Earth. Intense CMEs that hit our planet, for example, trigger geomagnetic storms that can disrupt satellite navigation and power grids. India currently has more than 50 satellites in orbit, which provide a variety of important services to the country, including communication links, weather data, and forecasting pest infestations, droughts, and impending disasters. According to the United Nations Office for Outer Space Affairs (UNOOSA), approximately 10,290 satellites remain in the Earth’s orbit, with nearly 7,800 of them functioning. Space weather has an impact on satellite performance affecting the GPS coordinates and radio transmissions on the Earth. Solar winds or storms can destroy satellite equipment and potentially bring power grids down. However, there are certain gaps in our knowledge of space weather. Knowing about the Sun’s activities, such as solar wind or a solar eruption, a couple of days ahead of time will allow us to relocate our satellites. This will help to extend the life of our space satellites.
Box:Major Science Objectives of Aditya-L1 Mission
- Study of Solar upper atmospheric (chromosphere and corona) dynamics.
- Study of chromospheric and coronal heating, physics of the partially ionized 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 CMEs.
- 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, their characteristics, dynamics of space weather, propagation of particles and fields, etc.).
Solar Research in India
Since times immemorial, Indian astronomers have developed systematic studies on various celestial bodies including the sun. Our first mention of the Sun and its importance in religious rituals was mentioned in Rigveda, which dates back to around 1500 BCE. The rigorous scientific inquiry into the Sun is evident in the contributions of eminent astronomers like Aryabhata, Brahmagupta, and Varahamihira, who thrived between the 5th and 7th centuries CE. They formulated mathematical models and methodologies for determining the positions of celestial bodies, including the Sun. Their treatises, such as Aryabhata’s Aryabhatiya and Brahmagupta’s Brahmasphutasiddhanta, encompassed intricate calculations and theories concerning the Sun’s movement and eclipses. Bhaskara I, who lived around 629-688 CE and Bhaskara II (Bhaskaracharya), who lived around 1114-1185 CE, also made significant contributions to Indian astronomy. Their works such as the Mahabhaskariya, and Siddhanta Shiromani, contained calculations related to the Sun’s position and the concept of time. The strong foundation provided by these early astronomers helped later Indian scientists focus on astronomical research. It is noteworthy to acknowledge that ancient astronomers lacked the advantages of contemporary technology, resulting in observations and calculations that were frequently less precise compared to present-day capabilities.
The first scientific observatory in pre-independent India specifically built to study the Sun was the Jantar Mantar astronomical observatory complex constructed by Maharaja Jai Singh II of Jaipur in the early 18th century. Jai Singh II was a keen astronomer, and he built several observatories in various cities including Delhi, Jaipur, Ujjain, Mathura, and Varanasi, known as Jantar Mantars, to carry out precise astronomical observations and calculations. These observatories were equipped with various instruments and structures designed for measuring the positions of celestial objects, including the Sun, Moon, and stars.
In post-independent India, several state-of-the-art modern observatories and astronomical facilities were established under various organisations like the Tata Institute of Fundamental Research (TIFR), Mumbai; Indian Institute of Astrophysics (IIA), Bengaluru; Indian Space Research Organisation (ISRO), Aryabhatta Research Institute of Observational Sciences (ARIES) at Manora Peak, Uttarakhand, and others, for the study of celestial objects, including the Sun.
But till now, all our observations and research about the Sun were from the Earth using sophisticated telescopes. However, despite the Sun’s immense gravitational influence, travelling to the Sun is an astonishingly challenging endeavour, requiring 55 times more energy than a journey to Mars. Why is it such a formidable task? The reason is rooted in the same principle that prevents Earth from falling into the Sun: Our planet is hurtling through space at an astonishing speed of approximately 67,000 miles per hour, primarily in a sideways direction relative to the Sun. The only means to reach the Sun is to nullify this lateral movement.
Solar Missions
Solar missions, which are spacecraft and observatories specifically designed to study the Sun, have a range of objectives aimed at advancing our understanding of our closest star and its impact on the solar system. To study the sun, it’s better to understand the structure of the sun and its atmosphere. From the inside out, the solar interior consists of:
- the Core: The central region where nuclear reactions consume hydrogen to form helium. These reactions release the energy that ultimately leaves the surface as visible light.
- the Radiative Zone: It extends outward from the outer edge of the core to base of the convection zone, characterised by the method of energy transport, i.e., radiation.
- and the Convection Zone: The outermost layer of the solar interior extending from a depth of about 200,000 km to the visible surface where its motion is seen as granules and supergranules.
The solar atmosphere is made up of:
- the Photosphere: The visible surface of the Sun.
- the Chromosphere: An irregular layer above the photosphere where the temperature rises from 6000°C to about 20,000°C.
- a Transition Region: A thin and very irregular layer of the Sun’s atmosphere that separates the hot corona from the much cooler chromosphere.
- and the Corona: The Sun’s outer atmosphere.
Beyond the corona is the solar wind, which is actually an outward flow of coronal gas. The sun’s magnetic fields rise through the convection zone and erupt through the photosphere into the chromosphere and corona. The eruptions lead to solar activity, which includes such phenomena as sunspots, flares, prominences, and coronal mass ejections. Solar missions aim to study and understand the fundamental physical processes occurring in the Sun. This includes the process of nuclear fusion in the Sun’s core, the generation of the solar magnetic field, and the transport of energy from the core to the surface. Solar missions continuously monitor and record the Sun’s activity, including the appearance of sunspots, solar flares, prominences, and coronal mass ejections (CMEs). Understanding solar activity is crucial for space weather prediction and its impact on Earth and the solar system.
Solar missions do not physically land on or go to the surface of the Sun. Instead, they are designed to orbit the Sun at varying distances or fly closer to it to study the Sun and its surrounding environment. Usually, they study from areas known as Lagrange points, often referred to as L-points. These points were first described by the French mathematician Joseph-Louis Lagrange in the late 18th century and are specific locations in space where the gravitational forces of two massive objects, such as a planet and a moon or a planet and the Sun, create stable points of equilibrium for smaller objects.
Box: Lagrange Points
There are five Lagrange points in the Earth-Sun system, known as L1 through L5. Here’s a brief overview of each Lagrange point:
1. L1 (Lagrange Point 1): Located along the line connecting the centers of the two massive bodies, L1 is closer to the smaller body (in this case, Earth) than to the larger body (the Sun). Objects placed at L1 remain roughly stationary with respect to Earth’s position and maintain a stable equilibrium between the gravitational pull of Earth and the Sun. L1 is commonly used for space observatories, such as the Solar and Heliospheric Observatory (SOHO), that study the Sun.
2. L2 (Lagrange Point 2): L2 is located along the line connecting the centers of the two massive bodies but is on the opposite side of Earth from the Sun. Like L1, objects at L2 maintain a stable position relative to Earth. L2 is used for various astronomical observations and missions, including the James Webb Space Telescope (JWST), which studies the universe in infrared wavelengths.
3. L3 (Lagrange Point 3): L3 is located on the opposite side of the Sun from Earth, forming an equilateral triangle with Earth and the Sun. It is rarely used for missions, and its stability is not as favourable as that of L1, L2, or other Lagrange points.
4. L4 (Lagrange Point 4): L4 is located 60 degrees ahead of Earth in its orbit, forming an equilateral triangle with Earth and the Sun. It is also known as the ‘leading Lagrange point’ and is sometimes called the ‘Trojan point’. L4 is associated with asteroids that share the Earth’s orbit and remain relatively stable there.
5. L5 (Lagrange Point 5): L5 is located 60 degrees behind Earth in its orbit, forming an equilateral triangle with Earth and the Sun. Like L4, it is also referred to as the ‘trailing Lagrange point’ and is associated with groups of asteroids that remain relatively stable in that region.
Both our lunar and solar missions were carried out using indigenous technologies at a highly competitive rate showing our scientific strength in pushing forward space technologies for the benefit of humanity. The emergence of women inside India’s space agency is seen in their significant contributions to interplanetary missions. Notably, Nigar Shaji has assumed the role of Project Director for Aditya-L1, India’s ambitious mission to explore the Sun. Over the course of several years, she made significant contributions to a range of initiatives, assuming leadership of Aditya-L1 approximately eight years ago. As our Prime Minister Narendra Modi remarked, “…..without their contribution, this achievement was just not possible. They will inspire generations to come”.
The expected duration of the Aditya-L1 mission is estimated to be around five years. As per the available information, all parameters of the Aditya-L1 spacecraft are working properly and the spacecraft has captured a selfie with the Earth and the moon from space on its way to its destination, Lagrange Point 1. The images show VELC (Visible Emission Line Coronagraph) and SUIT (Solar Ultraviolet Imager) instruments as seen by the camera on board Aditya-L1 on September 4, 2023.
If everything goes as planned India will join select nations that have successfully conducted solar observatory missions to study the sun. The impetus given to space research in recent years, especially by our honourable Prime Minister Narendra Modi, needs appreciation, as it is the need for the next century. Only a visionary leader can direct our scientific community to work on areas that need attention in the next century. Of course, the government should see that overemphasis on space research should not deter the morale of researchers working in other areas of science. The current success in lunar and solar missions is the result of our exemplary strength in basic science we gained over the ages. Aditya-L1 is the shining face of Bharat that will take us to the zenith of global science.
*The writer is a science communicator and an adjunct faculty at the National Institute of Advanced Studies, Bangalore.
