International Space Agencies – Missions and Discoveries

Magnetoseismology of Sun’s Corona

Note4Students

From UPSC perspective, the following things are important :

Prelims level : MHG, CoMP, Corona

Mains level : Study of solar atmosphere

A group of researchers has measured the global magnetic field of the Sun’s corona for the very first time.

Try this PYQ:

The terms ‘Event Horizon’, ‘Singularity’, `String Theory’ and ‘Standard Model’ are sometimes seen in the news in the context of (CSP 2017)-

(a) Observation and understanding of the Universe

(b) Study of the solar and the lunar eclipses

(c) Placing satellites in the orbit of the Earth

(d) Origin and evolution of living organisms on the Earth

Basis of the research

  • The properties of waves depend on the medium in which they travel.
  • By measuring certain wave properties and doing a reverse calculation, some of the properties of the medium through which they have travelled can be obtained.
  • Waves can be longitudinal waves (for example, sound waves) or transverse waves (for example, ripples on a lake surface).
  • The waves that propagate through magnetic plasma are called magnetohydrodynamic (MHD) waves.
  • From the theoretical calculation, it can be shown that the properties of the transverse MHD wave are directly related to the strength of magnetic fields and the density of the corona.

How was the Magnetic Field measured?

  • The team used a technique known as coronal seismology or magnetoseismology to measure the coronal magnetic field which has been known for a few decades.
  • This method requires the measurement of the properties of magnetohydrodynamic (MHD) waves and the density of the corona simultaneously.
  • In the past, these techniques were occasionally used in small regions of the corona, or some coronal loops due to limitations of our instruments/and proper data analysis techniques.

The CoMP instrument

  • The team used the improved measurements of the Coronal Multi-channel Polarimeter (CoMP) and advanced data analysis to measure the coronal magnetic field.
  • CoMP is an instrument operated by High Altitude Observatory, of the U.S.
  • It is located at Mauna Loa Solar Observatory, near the summit of that volcano on the big island of Hawaii.

Why measure the solar magnetic field?

  • It is very important to measure the corneal magnetic fields regularly since the solar corona is highly dynamic and varies within seconds to a minute time scale. There are two main puzzles about the Sun which this advancement will help address:

(1) Coronal heating problem

  • Though the core of the Sun is at a temperature of about 15 million degrees, its outer layer, the photosphere is a mere 5700 degrees hot.
  • However, its corona or outer atmosphere, which stretches up to several million kilometres beyond its surface, is much, much hotter than the surface.
  • It is at a temperature of one million degrees or more.
  • What causes the atmosphere of the Sun (corona) to heat up again, though the surface (photosphere) is cooler than the interior? That is the question which has baffled solar physicists.
  • Popular attempts to explain this puzzle invoke the magnetic field of the corona. Hence the present work will help understand and verify these theories better.

(2) Mechanisms of eruptions of the Sun

  • The eruptions on the Sun include solar flares and coronal mass ejections.
  • These are driven by magnetic reconnections happening in the Sun’s corona.
  • Magnetic reconnection is a process where oppositely polarity magnetic field lines connect and some of the magnetic energy is converted to heat energy and also kinetic energy which leads to the generation of heating, solar flares, solar jets, etc.
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