Cosmologists are literally over the moon at the prospect of listening to the universe telling its story like never before.
At the heart of this excitement is a small satellite named CosmoCube, which scientists from the Royal Astronomical Society (RAS) plan to send to the far side of the moon, which permanently faces away from the earth.
Expected to be launched before the end of this decade, CosmoCube will orbit the moon and use it as a natural shield from radio interference generated on the earth.
Two-year mission
The compact satellite will have around 40 minutes on the lunar far side during its orbit every two hours, when it will be cut off from all radio noise from the earth. This is when it can capture ultra-faint cosmic signals, particularly one emitted by neutral hydrogen atoms — the most abundant element in space.
“While passing behind the moon, the satellite would listen for an extremely faint radio ‘whisper’ produced by hydrogen in the very young universe, before the first stars and galaxies had fully formed,” Eloy de Lera Acedo, head of the Radio Astronomy and Cosmology research group at the University of Cambridge, who is leading the project, said via email.
A study on the CosmoCube project was published in Nature Astronomy on August 14.
The RAS researchers expect the satellite to gather more than a thousand hours of data during its two-year mission.
“During its scientific observations, CosmoCube would ideally remain radio-silent while behind the moon, so that its own communications did not contaminate the measurement. The recorded data could then be transmitted to the earth during a different part of its orbit,” Dr. De Lera Acedo said.
“The satellite carries a very sensitive and accurately calibrated radio receiver, or radiometer, operating at low frequencies (10-100 MHz) which would separate the incoming radio waves into many frequency channels so that scientists [can] search for the characteristic fingerprint of early hydrogen.”
Dark ages
Current models of the universe suggest that once upon a spacetime, right after being engendered by the Big Bang, the universe must have been a very dark place filled with neutral hydrogen.
This inky black period is called the Cosmic Dark Ages. It stretched from about 380,000 years to around 200 million years after the Big Bang. The first stars and galaxies were yet to ignite their nuclear furnaces and switch on the lights in the universe, ushering in what is known as the Cosmic Dawn.
Today, we can detect blurred pictures of that infant universe in the cosmic microwave background (CMB), the primaeval radiation emitted shortly after the Big Bang.
But no one quite understands what happened during the subsequent Dark Ages as there is nothing for even the state-of-the-art instruments of today to ‘see’ of that mysterious era.
In that sense, the story of the universe would have been left untold at that point but for a Dutch astronomer, Hendrik van de Hulst. In 1944, Van de Hulst predicted a rare quantum mechanical phenomenon called a spin-flip transition that could have prompted the neutral hydrogen filling the cosmos to emit a feeble light.
He reckoned that this light could be detected at a specific wavelength of 21 cm. Unlike visible light, this ancient radiation, whose corresponding frequency is 1,420 MHz, penetrates interstellar dust clouds to bring us snapshots from the very beginning of space and time.
(Of course, as the universe expands, this radiation is stretched to wavelengths of many metres by the time it reaches us.)
First lights
In 1951, the U.S. physicists Harold Ewen and Edward Purcell at Harvard University observed the 21-cm radiation for the first time, heralding the age of spectral-line astronomy.
It meant cosmologists could pick up the story of the universe again because they had a means to study the Dark Ages, one of the few periods in cosmic history that has never been directly observed.
Around 150 million to one billion years after the Big Bang, light from the first stars and galaxies split the ubiquitous neutral hydrogen in the cosmos into free electrons and protons. This ‘Era of Reionisation’ lifted the dark cosmic fog from the universe and made it transparent, traces of which we now see as the CMB.
A timeline of the early universe.
| Photo Credit:
NASA
CosmoCube will also help investigate the Hubble tension: the difference in results when we measure the expansion of the universe by studying nearby celestial systems and the CMB of the early universe.
“CosmoCube would not simply make another direct measurement of today’s Hubble constant,” Dr. De Lera Acedo said. “Instead, it would examine a largely unexplored period between the CMB and the formation of the first stars.”
This will help cosmologists test some of the new-physics explanations proposed for the Hubble tension, including dark matter (which does not emit or reflect light but accounts for more than 80% of the universe’s mass).
‘Extraordinary promise’
As Dr. De Lera Acedo put it, “If a model changes the early expansion history, introduces an additional radio background, or allows new interactions between dark matter and ordinary matter, it may leave a measurable signature in the 21-centimetre signal. CosmoCube could provide an independent test of such ideas.”
The 21-cm signal from neutral hydrogen is like the proverbial needle in a haystack as it is buried beneath foreground radio emissions probably tens of thousands of times stronger.
To isolate it and reveal how the very first stars and galaxies formed is a formidable challenge even for advanced platforms such as CosmoCube and India’s PRATUSH — a proposed radio telescope and radiometer in lunar orbit (its name is short for ‘Probing ReionisATion of the Universe using Signal from Hydrogen’).
As Dr. De Lera Acedo said, “That combination, extraordinary scientific promise coupled with extraordinary experimental difficulty, is precisely why the radio-quiet environment behind the moon is so valuable.”
Prakash Chandra is a science writer.
Published – September 09, 2026 09:00 am IST
