Why in News?

A study published in Nature Astronomy highlighted a proposed lunar satellite mission named CosmoCube, led by scientists from the Royal Astronomical Society (RAS) and the University of Cambridge. The mission aims to orbit the Moon's far side before the end of this decade to detect the elusive 21-cm radio signal from the universe's infancy — a scientific challenge India is also pursuing through its proposed PRATUSH mission.

CosmoCube Mission: Key Features

  • About: A compact satellite designed for a two-year mission in lunar orbit.
  • Strategic Orbit: The satellite will orbit the Moon every two hours, spending approximately 40 minutes on the lunar far side (the side that permanently faces away from Earth) during each orbit.
  • Target Objective: To detect ultra-faint radio signals emitted by neutral hydrogen during the Cosmic Dark Ages — a period before the formation of the first stars and galaxies.
  • Scientific Instruments: A highly sensitive radiometer operating at low frequencies (10–100 MHz), which separates incoming radio waves into multiple frequency channels to search for the characteristic "fingerprint" of early hydrogen.
  • Operational Mechanism: To prevent contamination of data by its own communications, CosmoCube will remain radio-silent while collecting data behind the Moon, transmitting gathered data back to Earth only during the Earth-facing portion of its orbit.

Importance of the Lunar Far Side for Radio Astronomy

  • The far side of the Moon permanently faces away from Earth, providing a pristine, radio-quiet environment.
  • This natural shield protects sensitive radiometers from:
  • Terrestrial radio frequency interference (RFI) — such as FM radio and telecommunications.
  • Earth's ionosphere, which distorts low-frequency radio signals.
  • This enables detection of ultra-faint cosmic signals impossible to observe from Earth.

Significance of the Mission

  • Understanding the Cosmic Dawn: The 21-cm signal acts as a "cosmic thermometer", allowing scientists to trace the exact period when the first stars and galaxies formed and reionised the universe.
  • Investigating Dark Matter: The amplitude and shape of the ancient hydrogen signal are influenced by the distribution and properties of dark matter, offering a new avenue to study this mysterious component.
  • Addressing the Hubble Tension: CosmoCube may help resolve the "Hubble Tension" — the noted discrepancy between the universe's expansion rate measured via the early universe (CMB) and nearby celestial bodies.

Cosmic Dark Ages and the 21-cm Signal

Cosmic Dark Ages (380,000 to ~200 million years post-Big Bang)

  • Following the Big Bang and the emission of the Cosmic Microwave Background (CMB), the universe entered a completely lightless phase.
  • It was dominated by dense, neutral hydrogen gas and entirely devoid of luminous objects.
  • This era preceded the Cosmic Dawn (ignition of the first stars and galaxies), which subsequently triggered the Epoch of Reionisation.

The 21-cm Emission

  • Neutral hydrogen atoms occasionally undergo a rare quantum event known as a "spin-flip transition", emitting electromagnetic radiation at a specific wavelength of 21 centimetres.

Redshifting

  • Due to the expansion of the universe over billions of years, the original 21-cm signal has stretched, shifting it into the lower-frequency radio spectrum (MHz range) observed today.

Observational Challenge

  • The signal is incredibly faint and easily drowned out by foreground radiation from the Milky Way (which can be thousands of times stronger) and human-made radio frequency interference.

India's PRATUSH Mission

  • About: PRATUSH (Probing ReionizATion of the Universe using Signal from Hydrogen) is an indigenous radio astronomy project initiated by the Raman Research Institute (RRI), Bengaluru — an autonomous body under the Department of Science and Technology (DST) — in collaboration with the Indian Space Research Organisation (ISRO).
  • Objective: Like CosmoCube, PRATUSH is designed to operate in lunar orbit to detect the redshifted 21-cm signal from the Cosmic Dawn and the Epoch of Reionisation.
  • Technological Innovation:
  • To meet strict Size, Weight, and Power (SWaP) constraints of space payloads, the PRATUSH team developed a digital receiver system powered by a Single-Board Computer (SBC) roughly the size of a credit card.
  • The SBC acts as the master controller, coordinating the antenna, the analog receiver, and a powerful Field Programmable Gate Array (FPGA) chip.
  • This compact computer efficiently records, stores, and calibrates high-speed streams of cosmic radio data, demonstrating how low-power technology can execute precision astrophysics.
  • Significance: Positions India at the frontier of observational cosmology, leveraging the pristine, radio-quiet conditions of the Moon's far side.

Relevance for UPSC

  • Prelims: Mission names, institutions involved, frequency ranges, orbital details, scientific concepts (21-cm signal, Cosmic Dark Ages, CMB, spin-flip transition).
  • Mains (GS Paper 3): India's achievements in space technology, growing role of research institutions in frontier science, and the strategic importance of lunar exploration.

Previous Year Questions (PYQs)

Prelims (2013): Consider the following phenomena: Size of the sun at dusk; Colour of the sun at dawn; Moon being visible at dawn; Twinkle of stars in the sky; Polestar being visible in the sky. Which of the above are optical illusions? — Ans: (c) 1, 2 and 4 only

Prelims (2025): Consider the following space missions: Axiom-4; SpaDeX; Gaganyaan. How many of the space missions given above encourage and support microgravity research? — Ans: (c) All three