New Method to Estimate Helium Abundance in the Sun

Background

• Helium is the second most abundant element in the Sun, but direct detection in the Sun’s photosphere is extremely difficult due to the absence of Helium spectral lines in the visible range.
• Traditionally, Helium abundance was estimated indirectly using:
  • Solar wind or corona data,
  • Extrapolation from hotter stars,
  • Helioseismology (solar interior vibrations).
• These methods were not based on direct photospheric observations, and hence lacked precision.

What is the New Method?

• Scientists used spectral lines of neutral Magnesium (Mg I) and neutral Carbon (C I), along with molecular lines of MgH, CH, and C₂, observed in the Sun’s photosphere.
• This method is based on the principle that the relative abundance of Helium affects the availability of Hydrogen, which in turn influences the formation and strength of molecular lines (e.g., CH and MgH).
• The researchers matched the atomic and molecular abundances of Magnesium and Carbon for different Helium-to-Hydrogen (He/H) ratios.
• The technique confirmed that only at a He/H ratio of ~0.1 do the atomic and molecular line abundances agree, validating the assumed solar value.

About Helium

• Helium (He) is a noble gas with a closed-shell electronic configuration, making it stable and chemically inert.
• Discovered in 1868 by Jules Janssen and Norman Lockyer via a yellow spectral line during a solar eclipse.
• Named after the Greek word ‘Helios’, meaning Sun.
• Largest global reserves: United States, Algeria, and Russia.
• India’s Rajmahal Volcanic Basin (Jharkhand) is a significant helium reservoir trapped for billions of years.