Aditya (Sanskrit: आदित्य, lit: Sun, pronunciation (help·info)) or Aditya-L1 is a spacecraft whose mission is to study the Sun. It was conceptualised by the Advisory Committee for Space Research in January 2008. It has been designed and will be built in collaboration between Indian Space Research Organisation (ISRO) and various Indian research organizations and will be launched by ISRO around 2019 or 2020. This will be the first Indian space mission to study the Sun, and also the first Indian mission to be placed at Lagrangian point L1 -- far away from the Earth from where continuous solar observations are possible. Only NASA and ESA have successfully placed satellites at the L1 point as of date. An experimental budget of 3 Crore INR has been allocated it for the financial year 2016-17.
Aditya-L1 is a solar mission. It was initially envisaged as a small 400 kg, Low-Earth Orbiting Satellite with a coronagraph to study the million-degree solar outer atmosphere known as the solar corona and got approved by Government of India in 2008-09. Subsequently, the scope of the mission has been enhanced and it is now planned to be a comprehensive solar and space environment observatory to be placed at the Lagrangian point L1. This enhanced mission named Aditya-L1 has recently been accepted by the Government of India.
A Satellite placed in the halo orbit around the Lagrangian point L1 of the Sun-Earth system has the major advantage of continuously viewing the Sun without any occultation or eclipses. The Aditya-L1 mission will be inserted in a halo orbit around the L1, which is about 1.5 million km from the Earth. The 1,500 kg class satellite carries a total of seven payloads with diverse objectives, including but not limited to, the coronal heating problem, solar wind acceleration, coronal magnetometry, origin and monitoring of near-UV solar radiation (which drives Earth's upper atmospheric dynamics and global climate), coupling of the solar photosphere to chromosphere and corona, in-situ characterizations of the space environment around Earth by measuring energetic particle fluxes and magnetic fields of the solar wind and solar magnetic storms that have adverse effects on space and ground-based technologies.
The outer layers of the Sun, extending to thousands of kilometers above the disc (photosphere) is termed as the corona. It has a temperature of more than a million kelvins, which is much higher than the solar disc temperature of around 6000 K. How the corona gets heated to such high temperatures is still an unanswered question in solar physics with far-reaching implications for the heating of stellar atmospheres and magnetic reconnection or wave-induced plasma phenomena across the Universe. Aditya-L1 with additional experiments can now provide observations of Sun's photosphere, chromosphere and corona. In addition, particle payloads will study the particle flux emanating from the Sun and reaching the L1 orbit, and the magnetometer payload will measure the variation in magnetic field strength at the halo orbit around L1. These payloads have to be placed at a location with minimal influence from the Earth’s magnetic field, which could not have been achieved at the low Earth orbit.
One of the major unsolved issues in the field of astrophysics is that the upper atmosphere of the Sun is a million degrees hot whereas the lower atmosphere is just 6000 degrees. In addition, we have not comprehended that how exactly the Sun’s radiation effects the dynamics of the Earth’s atmosphere on shorter as well as on longer time scale. There are multi-fold advantages of observing the Sun in this wavelength range. On one hand, we shall obtain near simultaneous images of the different layers of the Sun’s atmosphere, which shall let us study the ways in which the energy may be channeled and transferred from one layer to other. Using SUIT observations, we shall also be able to shed lights on the origin of energetic events occurring on the Sun’s surface such as flares and coronal mass ejections. On the other hand, the radiation from the Sun in this wavelength range governs the dynamics of the Earth’s atmosphere, for example, formation and dissociation of ozone layers. The ozone layer is of particular important as it blocks the UV radiation coming to the Earth and saving us from having skin cancer. Although solar radiation in this range is a very small fraction (~8%) of the total solar radiation, it varies by about 60% over a solar cycle. The SUIT observations will help us unravel the mystery of the cause of these variations.
Thus the enhanced Aditya-L1 project will enable a comprehensive understanding of the dynamical processes of the sun and address some of the outstanding problems in solar physics.