Why In News?

Researchers from the Aryabhatta Research Institute of Observational Sciences (ARIES) discovered that the Sun's upper atmosphere rotates faster than its visible surface.

About the Sun  

  • The Sun is a G2V (Yellow Dwarf) main-sequence star located at the centre of the Solar System.

  • It formed about 4.6 billion years ago through the gravitational collapse of a giant molecular cloud.  

  • It accounts for 99.86% of the total mass of the Solar System and consists of approximately 73% Hydrogen, 25% Helium, and 2% heavier elements by mass. 

Internal Structure of the Sun

Core

  • It extends to about 25% of the Sun's radius.

  • Temperature reaches nearly 15 million K, where nuclear fusion converts hydrogen into helium and powers the Sun.

  • Produces enormous energy through the proton-proton chain reaction. 

Radiative Zone

  • Extends from about 0.25–0.70 solar radius.

  • Energy moves outward through radiative diffusion.

  • A photon may take thousands to hundreds of thousands of years to escape this region.

Convective Zone

  • Extends from 0.70 solar radius to the visible surface.

  • Hot plasma rises while cooler plasma sinks, transporting energy through convection.

  • Produces granulation observed on the solar surface. 

Sun's Upper Atmosphere

  • The Sun is a ball of ionized plasma, not a solid body, composed mainly of hydrogen and helium.

  • Its atmosphere extends millions of kilometres into space, gradually merging with the solar wind.

  • The upper atmosphere is dominated by magnetic fields, hot plasma and highly dynamic solar activity responsible for flares and coronal mass ejections (CMEs). (Source: NASA; ARIES)

What Does the New Discovery Reveal?

Faster Atmospheric Rotation

  • The chromosphere rotates faster than the photosphere, indicating that atmospheric plasma gains rotational speed with altitude.

Rotation Speed Increases with Height

  • Radio observations show a progressive increase in rotation speed from the visible surface to higher atmospheric layers.

Solar Activity Connection

  • Rotation slows slightly during periods of high sunspot activity, suggesting a close relationship between magnetic fields and atmospheric dynamics.

New Observational Technique

  • Researchers used observations from the Nobeyama Radioheliograph (Japan) to probe atmospheric rotation at multiple heights, providing unprecedented insights into solar plasma behaviour.

What is Differential Rotation?

  • Differential rotation occurs when different parts of a gaseous or fluid body rotate at different angular velocities.

On the Sun

  • Equator: completes one rotation in about 25.05 days.

  • Mid-latitudes: rotate more slowly.

  • Poles: require about 34.3 days for one rotation. 

Cause

  • Because the Sun is made of plasma rather than a solid body, its different latitudes and atmospheric layers rotate independently under the influence of convection and magnetic fields.

Importance

  • Differential rotation stretches and twists magnetic field lines, powering the solar dynamo, generating sunspots, solar flares, and Coronal Mass Ejections (CMEs) that drive space weather. 

Source: PIB

PRACTICE QUESTION

Consider the following statements regarding the rotation of the Sun:

  1. The Sun exhibits differential rotation, where its polar regions rotate faster than its equatorial regions.

  2. Recent findings by Indian researchers reveal that the Sun's upper atmosphere rotates faster than its visible surface.

Which of the statements given above is/are correct?

A) 1 only

B) 2 only

C) Both 1 and 2

D) Neither 1 nor 2

Answer: B

Explanation:

Statement 1 is incorrect: The Sun exhibits differential rotation, but its equatorial regions rotate faster than its polar regions. Because the Sun is composed of plasma rather than a solid structure, its equator takes roughly 24 to 25 days to complete one full rotation, whereas the high-latitude polar regions take upwards of 30 to 35 days.  

Statement 2 is correct: Recent scientific research by Indian astronomers has established that the Sun's upper atmosphere (chromosphere) rotates significantly faster than its visible surface (photosphere). This investigation revealed that the rotation speed actually increases progressively with height above the surface.