First Radio Signal from Moon’s Far Side

Why in News?

Scientists are preparing to deploy miniature space observatories, primarily the UK-led CosmoCube mission along with India's proposed PRATUSH project into lunar orbit.

Target Signal

• Origin - Emitted by neutral atomic hydrogen, the most abundant element in the early universe.
• Hyperfine Transition - Originates from a "spin-flip" transition in ground-state neutral hydrogen atoms.
• Cosmological Redshift - Originally emitted at a wavelength of 21 cm (1420 MHz), the expansion of the universe over ∼13.5 billion years has stretched these signals into ultra-low radio frequencies (10 to 100 MHz).
• Scientific Benchmark - Serves as a cosmic "thermometer" and timeline to map:
• Cosmic Dark Ages - The period (∼380,000 to 150 million years post-Big Bang) before the first stars ignited.
• Cosmic Dawn - When the first stars and galaxies formed and reionized neutral hydrogen gas.
• Hubble Tension & Dark Matter - Provides observational data to resolve discrepancies in the universe's expansion rate and test dark matter-baryon interactions.

Far Side of the Moon

• Radio-Quiet Zone - The far side of the Moon is the most pristine, radio-quiet environment in the inner Solar System.
• Earth Noise Shielding- The Moon acts as a physical shield against human-made Radio-Frequency Interference (RFI), such as FM radio, satellite networks, and aircraft communications.
• Ionospheric Bypass - Ground-based radio telescopes struggle to detect these low-frequency signals because Earth's ionosphere refracts and blocks radio waves below 30 MHz.
• Observation Window - During a typical 2-hour lunar orbit, a satellite gets approximately 40 minutes of absolute radio silence while positioned behind the lunar far side.

Reference

The Hindu | A satellite to look for the first radio signal