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  • If 2019 was all about the Moon for Indian space agency ISRO, year 2020 could well be about the Sun. In his Mann Ki Baat address, Prime Minister Narendra Modi spoke about the ISRO’s plans to launch its first Sun Mission AdityaL1.
  • The 400 KG-Class Aditya L1 will carry six scientific payloads that will be inserted in a halo orbit around the Lagrangian point 1 or L1. Incidentally L1 is 1.5 million kilometres from the Earth.

The Sun – Our Central Star:

  • The Sun is the star nearest to us. It is a huge, luminous ball of gas like other stars in the Universe.

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, characterized by the method of energy transport – radiation.
  • The Convection Zone– The outer-most 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 super-granules.

The Solar Atmosphere is made up of:

  • The Photosphere– The visible surface of the Sun
  • TheChromosphere – An irregular layer above the photosphere where the temperature rises from 6000°C to about 20,000°C
  • TransitionRegion – A thin and very irregular layer of the Sun’s atmosphere that separates the hot corona from the much cooler chromosphere
  • 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, andCoronal Mass Ejections.

Aditya – L1:

    • The Aditya-1 mission was conceived as a 400kg class satellite carrying one payload, the Visible Emission Line Coronagraph (VELC) and was planned to launch in a low earth orbit.
    • The Aditya-1 mission has now been revised to “Aditya-L1 mission” – placed in the halo orbit around the Lagrangian point 1 (L1) of the Sun-Earth system, which is 1.5 million km from the Earth.
    • Lagrangian point 1 (L1) of the Sun-Earth system– has the major advantage of continuously viewing the Sun without any Occultation/Eclipses.
      • A Lagrange point is a location in space where the combined gravitational forces of two large bodies, such as Earth and the sun, equal the centrifugal force felt by a much smaller third body.

  • Aditya-1 was meant to observe only the solar corona – It has a temperature of more than a million-degree Kelvin which is much higher than the solar disc temperature of around 6000K.
    • The complete list of payloads and their science objective for developing the Payloads:
    • Visible Emission Line Coronagraph (VELC):To study the diagnostic parameters of solar corona and dynamics and origin of Coronal Mass Ejections.
    • Solar Ultraviolet Imaging Telescope (SUIT):To image the spatially resolved Solar Photosphere and Chromosphere in near Ultraviolet.
    • Aditya Solar wind Particle Experiment (ASPEX):To study the variation of solar wind properties as well as its distribution and spectral characteristics.
    • Plasma Analyser Package for Aditya (PAPA):To understand the composition of solar wind and its energy distribution.
    • Solar Low Energy X-ray Spectrometer (SoLEXS):To monitor the X-ray flares for studying the heating mechanism of the solar corona.
    • 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.
    • Magnetometer:To measure the magnitude and nature of the Interplanetary Magnetic Field.

Questions about the Corona:

  • The outer layers of the Sun, extending to thousands of km above the disc (photosphere) is termed as the corona.
  • It has a temperature of more than a million-degree Kelvin which is much higher than the solar disc temperature of around 6000K.
  • How the corona gets heated to such high temperatures is still an unanswered question in solar physics.
  • With the inclusion of multiple payloads, this project also provides an opportunity to solar scientists from multiple institutions within the country to participate in space-based instrumentation and observations.
  • 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.
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