Aditya-L1: All about Indian Space Research Organisation's first mission to study the Sun

Photo Credit: ISRO Website

Indian Space Research Organisation (ISRO) plans to study the Sun through its Aditya-L1 satellite which will be inserted in a halo orbit, which is 1.5 million km from the Earth during 2019-2020. Aditya-L1 will be launched by PSLV-XL from Sriharikota in Andhra Pradesh. The satellite will carry six payloads with enhanced science scope and objectives to ensure a detailed study of the Sun.

According to the ISRO, the Aditya-1 mission was conceived as a 400kg class satellite carrying one payload, the Visible Emission Line Coronagraph (VELC) and was planned to be launch in a 800 km low earth orbit. Scientists say that any satellite in the halo orbit around the Lagrangian point 1 (L1) of the Sun-Earth system can view the Sun without any occultation/ eclipses. Now, the Aditya-1 mission has now been revised to "Aditya-L1 mission".

ISRO had planned to use Aditya-1 to observe only the solar corona, which is the outer layer of the Sun and extends to thousands of km above the disc (photosphere). The corona has a temperature of more than a million degree Kelvin which is much higher than the solar disc temperature of around 6000K. Scientists are still trying to find out how the corona gets heated to such high temperatures.

Aditya-L1 with additional experiments can now provide observations of Sun's Photosphere (soft and hard X-ray), Chromosphere (UV) and corona (Visible and NIR). 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 outside the interference from the Earth’s magnetic field and could not have been useful in the low earth orbit.

The main payload continues to be the coronagraph with improved capabilities.  The main optics for this experiment remains the same.  The complete list of payloads, their science objective and lead institute for developing the payload is provided below:

• Visible Emission Line Coronagraph (VELC): To study the diagnostic parameters of solar corona and dynamics and origin of Coronal Mass Ejections (3 visible and 1 Infra-Red channels); magnetic field measurement of solar corona down to tens of Gauss – Indian Institute of Astrophysics (IIA)
• Solar Ultraviolet Imaging Telescope (SUIT): To image the spatially resolved Solar Photosphere and Chromosphere in near Ultraviolet (200-400 nm) and measure solar irradiance variations - Inter-University Centre for Astronomy & Astrophysics (IUCAA)  
• Aditya Solar wind Particle Experiment (ASPEX) : To study the variation of solar wind properties as well as its distribution and spectral characteristics – Physical Research Laboratory (PRL)        
• Plasma Analyser Package for Aditya (PAPA) : To understand the composition of solar wind and its energy distribution – Space Physics Laboratory (SPL), VSSC        
• Solar Low Energy X-ray Spectrometer (SoLEXS) : To monitor the X-ray flares for studying the heating mechanism of the solar corona – ISRO Satellite Centre (ISAC)
• High Energy L1 Orbiting X-ray Spectrometer (HEL1OS): To observe the dynamic events in the solar corona and provide an estimate of the energy used to accelerate the particles during the eruptive events - ISRO Satellite Centre (ISAC)and Udaipur Solar Observatory (USO), PRL
• Magnetometer: To measure the magnitude and nature of the Interplanetary Magnetic Field – Laboratory for Electro-optic Systems (LEOS) and ISAC.

With the inclusion of multiple payloads, the Aditya-L1 mission will ensure that solar scientists from several Indian institutions are able to participate in space-based instrumentation and observations. 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.