CosmoCube design Credit: Surrey Space Technology Ltd.
A tiny UK-developed satellite, roughly the size of a small carry-on suitcase, could help answer one of the biggest questions in cosmology: what happened in the roughly 150 million years of cosmic dark ages, before the universe's first stars appeared?
An international team, led by the University of Cambridge and including scientists from the University of Portsmouth, will use the dark side of the Moon as a 'shield' so that the satellite - called CosmoCube - can block out all the noise from Earth and listen for a faint whisper from the very early universe.
This whisper, known as the 21-centimetre line, is a signal emitted by hydrogen atoms in the period in between the afterglow of the Big Bang and Cosmic Dawn, when nuclear fusion lit up the first stars. No one has directly observed this era before.
Detecting this signal from more than 13.5 billion years ago is extremely difficult with Earth-based telescopes, since the Earth's ionosphere blocks the right frequencies, and interference from FM radio, satellites and telecommunications drowns it out.
However, the Moon provides a natural shield. As CosmoCube orbits the far side of the Moon, it will be shielded from all the noise of Earth for roughly 40 minutes of each two-hour orbit. Over an expected two-year mission, it will build up 1000 hours of data on one of the last unexplored periods of the universe, helping us understand how the universe transitioned from dark and nearly empty to the complexity we see today.
The mission has received funding for mission design from the UK Space Agency, and the researchers hope CosmoCube can be launched within the next five years. Details are published in the journal Nature Astronomy .
In addition to exploring the universe in the period before the first stars, CosmoCube will also explore the role of dark matter - the mysterious force that holds galaxies together.
"This emission from hydrogen after the Big Bang, but before the first stars, will hopefully allow us to understand the role of dark matter in the early universe, how it worked to pull together hydrogen into the first stars and galaxies," said lead author Professor Eloy de Lera Acedo from Cambridge's Cavendish Laboratory.
To study this period, CosmoCube will operate at extremely low frequencies - between 10 and 50 MHz - far outside the range of ground-based telescopes, which is why the Moon will be used as CosmoCube's 'fortress of solitude'.
"There's no other place where you can get the sort of shielding you need to detect such a faint signal, while at the same time looking at the whole of space," said de Lera Acedo, who is also affiliated with the Kavli Institute for Cosmology. "The far side of the Moon is really the only option: it solves multiple problems at once, opening a clear window to the very early universe."
Fellow CosmoCube researcher Professor David Bacon , Director of the University of Portsmouth's Institute of Cosmology and Gravitation which is participating in the mission, added: "How extraordinary it will be to observe the era before the stars started to shine - and to have the Moon as our ally in this effort!"
Once in orbit around the Moon, CosmoCube will unfold a long and lightweight radio antenna, sensitive enough to detect the 21-centimetre signal from hydrogen atoms in the early universe when the satellite is on the Moon's far-side.
While in lunar orbit, CosmoCube will constantly check and correct its own electronics using a 'Dicke switched' calibrator, which will flip between the sky and several built‑in reference sources. This will help cancel out tiny drifts and noise inside the satellite that could otherwise masquerade as cosmic signals.
Once CosmoCube's data is back on Earth, the team will use advanced Bayesian statistical methods to remove foreground noise - mainly radio emissions from our own galaxy. They will also reconstruct how the antenna responds to different parts of the sky using computer simulations and in-flight measurements, allowing them to subtract any remaining distortions.
"Aside from the science, what makes our mission unique is its size: we're probing the earliest, deepest parts of the dark ages that others don't reach, but with a compact, relatively low-cost platform," explained de Lera Acedo.
However, the far side of the Moon may not stay quiet for long: other missions are being planned by the US, India and other countries to take advantage of the Moon's silence.
CosmoCube features a state-of-the-art fully integrated miniature radiometer, using the latest on analogue and digital technology, the so-called RF-Systems-on-Chip (RFSoCs). The CosmoCube space platform ('SSTL-21') is being developed in the UK by Surrey Space Technology Limited (SSTL), which specialises in the manufacturing of small satellites. Instrument development is well underway, with functioning lab prototypes and environmental testing taking place and key collaboration with industry partners. In the UK, academic partners include Portsmouth University and STFC RAL Space, and participation from EU countries such as Malta. The CosmoCube team recently participated in the ESA mini-Fast missions Call for Ideas, targeting a mission cost under 50 million Euros.
"This could be a real UK success story: the hardware, the software, the implementation and the technology is all being developed here, and it could help us answer one of the most profound questions in the universe," said de Lera Acedo.
CosmoCube is supported under the UK Space Agency's Science Bilateral Programme, the Kavli Foundation, and is being developed by a UK-led international consortium with researchers based at the University of Portsmouth, University of Cambridge and the Science and Technology Facilities Council (STFC) RAL Space, part of UK Research and Innovation (UKRI).
As a recognised international centre of research excellence, Portsmouth's Institute of Cosmology and Gravitation (ICG) brings together more than 70 researchers - faculty, postdoctoral fellows and PhD students - tackling some of the Universe's most profound mysteries, from the earliest moments after the Big Bang to the large-scale structure of galaxies, dark energy and gravitational waves.
Its world-class impact was confirmed in REF 2021, where 100 per cent of ICG research was rated world-leading or internationally excellent.
The institute's contributions include roles in major international projects such as Euclid , LISA (Laser Interferometer Space Antenna) , the LIGO gravitational wave detectors , and the Dark Energy Spectroscopic Instrument (DESI).
