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Sun’s atmospheric mystery solved

Date: 17 November 2019 Tags: Space


An international team of researchers including one at Indian Institute of Astrophysics, Bengaluru, have made observations that may answer why the Sun’s atmosphere is hotter than its surface.



The Sun is one of the most familiar celestial objects on the sky and it harbours many a puzzle for the solar physicist. One of the puzzles concerns its surface and atmospheric temperature.



  • The temperature at the core of the Sun is nearly 15 million degrees Celsius, while that at its surface layer, known as the photosphere, is merely 5,700 degrees C.

  • The natural expectation is that still further outwards, in its atmosphere, known as the corona, the temperatures would be comparable to that at the surface (photosphere).

  • However, the temperature of the corona is much higher. It starts increasing outside the photosphere, reaching a value of about one million degrees or more in the corona.

  • With respect to the Sun, after dropping to a low, the temperature again rises to one million degrees in the corona which stretches over several million kilometres from the surface of the Sun. This implies there should be a source heating the corona. 

  • The key to the puzzle lies in geyser-like jets known as solar spicules that emanate from the interface of the corona and the photosphere.

  • Eventhough they look like tiny hairlike projections, they are in fact 200-500 kilometres wide and shoot up to heights of about 5,000 km above the solar surface.

  • It has been suspected that these spicules act as conduits through which mass and energy from the lower atmosphere bypass the photosphere and reach the corona.

  • The research involved taking many high-spatial-resolution images of the same region of the Sun within a short time, since spicules have a very short lifetime of about 10 to 100 seconds.

  • The key findings are that bursts of spicules originate from the boundaries of web like networks of magnetic structures in the surface.

  • Near their footpoints, there emerge magnetic elements that have opposite polarity to the existing magnetic network.


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