International Space Agencies – Missions and Discoveries

Spicules in the Sun


From UPSC perspective, the following things are important :

Prelims level : Spicules, Photosphere

Mains level : Heating of Sun's photosphere

  • One of the puzzles concerning is the Sun’s surface and atmospheric temperature.
  • A team of researchers has observed the reason why Sun’s atmosphere is hotter than its surface.

Anomaly of the Sun’s 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 thing to expect 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.

Coronal heating

  • One would expect that as there are no extra sources of heat, when you move away from a hot object, the temperature steadily decreases.
  • However, 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 puzzle of coronal heating has been tackled by many theories.
  • Now, in a research paper, the team of solar physicists has made observations and matched it with an analysis that explains this conundrum.

Mystery now solved: Spicules in the Sun

  • 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.
  • While in a photograph these 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.
  • These spicules heat up while propagating upward, reaching the coronal temperature.
  • They are made of plasma – a mixture of positive ions and negatively charged electrons.The coronal plasma emits light in extreme ultraviolet.
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