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Indian scientists from the Indian Institute of Astrophysics (IIA) accurately measure Helium abundance in the Sun's photosphere using a spectral method.

Background

Helium is the second most abundant element in the Sun after hydrogen, but detecting it directly in the photosphere is tough because helium doesn’t produce visible spectral lines (light patterns) in this region. Previously, scientists used indirect methods, which were less accurate.

Unlike other elements, helium’s spectral lines (unique light fingerprints) appear in the ultraviolet range, not the visible range. This makes direct detection in the photosphere nearly impossible with standard telescopes.

Old Methods for Estimating Helium

In the past, scientists estimated helium abundance indirectly because they couldn’t observe it in the photosphere. They used:

• Solar Wind and Corona Data: The solar wind (charged particles from the Sun) and the corona (the Sun’s outer atmosphere, visible during eclipses) contain helium. Scientists analyzed these to guess helium levels, but these regions differ from the photosphere, so results were imprecise.
• Hotter Stars: Scientists studied hotter stars where helium spectral lines are visible and extrapolated (made educated guesses) for the Sun. This method wasn’t specific to the Sun’s unique conditions.
• Helioseismology: This involves studying vibrations inside the Sun, like earthquake waves on Earth. These vibrations hint at helium levels in the Sun’s interior, but they don’t directly measure the photosphere’s helium.

The New Method  

Scientists developed a new way to measure helium in the Sun’s photosphere directly.  

• They observed spectral lines of neutral magnesium (Mg I), neutral carbon (C I), and molecules like magnesium hydride (MgH), methane (CH), and carbon dimer (C₂) in the photosphere.
• These atomic and molecular lines depend on hydrogen availability. Since helium is the second most abundant element, its presence affects how much hydrogen is available to form these molecules.
• They found that a He/H ratio of 0.1 (meaning 1 helium atom for every 10 hydrogen atoms) perfectly aligned the data. This confirmed the Sun’s helium abundance is about 10% of hydrogen, matching earlier assumptions but with greater precision.

About Helium

• Helium (He) is a noble gas, meaning it is chemically inert (doesn’t react easily) due to its stable, closed-shell electron structure.
• It’s the second most abundant element in the universe (after hydrogen) and in the Sun.
• On Earth, helium is rare because it’s light and escapes the atmosphere into space.

Uses of Helium

• Medical: Used in MRI scanners for cooling superconducting magnets.
• Scientific: Essential for cryogenics (ultra-low temperature experiments) and particle accelerators.
• Industrial: Used in welding, semiconductor manufacturing, and as a coolant in nuclear reactors.
• Aerospace: Fills balloons and airships due to its low density.
• Space Exploration: NASA uses helium to pressurize rocket fuel tanks.

Global Helium Reserves

Helium is extracted from natural gas fields, as it forms from the radioactive decay of uranium and thorium in Earth’s crust. Major reserves include:

• United States: The largest producer, with significant reserves in Texas, Oklahoma, and Kansas (e.g., the Federal Helium Reserve).
• Algeria: A key supplier, with helium extracted from natural gas in Hassi R’Mel.
• Russia: Emerging as a major player, with the Amur Gas Processing Plant boosting production.

India’s Helium Resources

• India has limited helium reserves, making it import-dependent (90% of helium is imported, mainly from the US and Qatar).
• A significant discovery was made in the Rajmahal Volcanic Basin in Jharkhand. Helium is trapped in ancient geological formations, dating back billions of years.
  

Source:  PIB