Sun, the heart of the solar system, and a fireball of burning gases. The gravitational force of the sun is the basis for the existence of the solar system. The smallest objects to the largest planets continue to traverse in their orbits only due to the force of the sun. Almost 99.8% of the size of the solar system is of the sun. Our earth, other planets, and members of the solar system form only 0.2% of the solar system. Though the sun is considered a giant star by us due to its proximity, it is indeed not that big compared to other stars. Though the sun is a hero for us with eight planets orbiting around it, there are billions of similar stars in the Milky Way galaxy of which our solar system is a part.
According to NASA’s official website, the average distance from earth to sun is about 93 million miles. Even at such a distance, the earth's seasons, ocean currents, climate, atmospheric conditions, radiation fields, and halos result from the relationship and interactions between the sun and the earth. We can live well only as long as the sun remains like this.
There is another face to the sun; the source of energy supporting all life forms on earth. As we go near the sun, we can see its extreme form, perpetually burning with flames and its corona emitting charged particles and solar gases. For science, it is essential to understand all the behaviours of the sun, and with that goal, many solar missions were carried out in the world. India is also in the last stages of preparing for a solar mission. India had to delay the mission, which was scheduled for 2020, due to the Covid 19 pandemic. The first Indian solar mission is named Aditya - L1.
Before delving into the details about Aditya- L1, Let us take a look at the layers of the sun.
Photosphere - The innermost layer of the solar atmosphere, including the solar surface. This is the area that we can see directly. According to Space.com, it stretches from the solar surface to 400 km above. Here, the temperature is 6500 Kelvin in the lowest region and 4000 Kelvin in the highest region.
Chromosphere - It is the layer above the photosphere, stretching from 400 to 2100 kilometres. Here the temperature varies from 4000 Kelvin in its lower parts to 8000 Kelvin in the upper parts. The temperature in the chromosphere rises as the distance from the sun increases.
Corona - It is the outermost part of the sun’s atmosphere. It is 2100 kilometres from the sun’s surface, extending up to thousands of kilometres. The temperature is highest here. It ranges from 500,000 Kelvin to millions of Kelvin. Corona cannot be watched with the naked eye except at the time of the Solar eclipse. Or else we have to use the coronagraph.
Aditya - L1 towards the sun
The Director of the Human Space Flight Center under ISRO, Dr Unnikrishnan Nair, has made it clear that the plan is to launch the Aditya - L1 by the end of this year. Aditya - L1 is predicted to be able to give us more insights into the origin and unravel many yet unknown secrets of the universe.
India’s first solar mission was initially named Aditya - 1, but later it was changed to Aditya - L1. What changes could have happened to Aditya - 1 with the addition of an ‘L’ to its name?
Aditya is a term for the sun in Sanskrit. India had planned to study the solar corona through the Aditya -1 mission. Corona ,the outermost ring or layers of the solar atmosphere, like mentioned before. The temperature there is unimaginable and is in the range of 2 million Kelvin. This is much more than the temperature of the photosphere ( around 6000 Kelvin), the lowest layer of the sun’s atmosphere, including its surface. There is no answer yet to why the corona attains such high temperatures. It was the aim of Aditya - 1 to observe and study the corona. And then the ‘L’ made its entry.
What does the ‘L’ in Aditya - L1 stand for?
L1 is one of the Lagrange points in space. An object sent there tends to stay put. The gravitational pull or centripetal forces of other planets do not tend to affect the object at those points. Let us now see how that happens. At Lagrange points, the gravitational pull of two large masses (for example, the sun and the earth) precisely equals the centripetal force required for a small object (the satellite) to move with them. That is why an object placed at these points tends not to change its position. These points in space can be used by spacecrafts to reduce their fuel consumption, which is needed to remain in the same position in space.
There are five Lagrange points in space where a small mass can orbit in a consistent pattern with two larger masses. L1 is one of them. Situated between the sun and earth, we can observe the sun continuously without any obstacles from point L1. Thus Aditya - L1 will be stationed in the halo orbit around the L1 point in order to study the sun. Another satellite SOHO (Solar & Heliospheric Observatory Satellite), will keep Aditya-L1 company in observing the sun. SOHO was jointly launched into the orbit in 1995 by European Space Agency and NASA to study the sun.
The prime aim of Aditya - L1 is to understand more about the outer rings of the sun, the corona. But along with the modified name, Aditya - L1 has extended its aims with the requisite arrangements. Apart from studying the corona, Aditya - L1 has plans to explore the other two outer layers of the sun.
Instruments aboard Aditya - L1
According to ISRO’s official website, Aditya - 1 weighing 400kg, was planned to have only a single payload of Visible Emission Line Coronagraph. However, six more payloads were added with its modification to Aditya - L1. Still, the coronagraph will be the primary payload to observe the sun’s corona minutely. Let us now examine all the payloads of Aditya - L1 and their purpose in detail.
· Visible Emission Line Coronagraph (VELC)-The aims of the principal payload VELC was to gather data regarding the detectable characteristics of the sun’s outer layer corona, to learn about the origin of the coronal plasma explosion with magnetic properties (Coronal Mass Ejection, CME), and measure the magnetic fields of the corona. This payload was developed indigenously by the Indian Institute of Astrophysics.
· Solar Ultraviolet Imaging Telescope (SUIT)- Capturing images of the photosphere and chromosphere are the goals of this telescope. This was developed by the Inter-University Centre for Astronomy and Astrophysics.
· Aditya Solarwind Particle Experiment (ASPEX)- It aims to study the differences in characteristics of the solar gases, their distribution, and special features at the spectral level. It was developed by the Physical Research Laboratories.
· Plasma Analyzer Package for Aditya (PAPA)-Studying the composition of solar wind and its resultant energy distribution is the purpose of this package. It was developed by the Space Physics Laboratory of VSSC.
· Solar Low Energy X-ray Spectrometer (SoLEXS)-Its job is to observe the x-rays to help study the heating processes of the sun’s corona. ISRO Satellite Centre developed this.
· High Energy L1 Orbiting X-ray Spectrometer (HEL1OS)- The expected goals of HEL1OS are to observe the events happening in the corona and calculate the approximate energy expended during explosions in the corona to disperse the particles. This was jointly developed by the ISRO Satellite Centre, Udaipur Solar Observatory, and Physical Research Laboratory.
· Magnetometer- Finding out the extent and features of interplanetary magnetic fields is its aim. It was jointly developed by the Laboratory for Electro-Optics System (LEOS) and the ISRO Satellite Center.
With the addition of other payloads along with VELC to Aditya- L1, ISRO hopes that these authoritative findings derived from them can help scientists studying the sun in different parts of the country to make new discoveries. ISRO, one of the world’s foremost space research centres, believes that the mission can help understand many events and phenomena of the sun. It can also help answer some important questions in the field of solar astrophysics.
Now put on your thinking hats and think about the following questions for a couple of minutes.
Can you think of how Aditya L1 will influence the field of solar astrophysics?
Can you think of the characteristics of the three layers of the sun?
Write down your thoughts and discuss them with your students, children and your colleagues. Listen to their views and compare them with your own. As you listen to others, note how similar or different your views are to others’.
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Happy Teaching!
Aditya L1: India’s first solar mission