Suitcase-Sized Satellite Would Hide Behind the Moon to Hear a Signal From Before the First Stars

A satellite no bigger than a small carry-on suitcase could help investigate a period of cosmic history that has never been directly observed. Developed in the UK and led by the University of Cambridge, CosmoCube is designed to search for evidence of what happened during roughly 150 million years of cosmic "dark ages" before the universe's first stars began to shine, using the Moon's far side as a natural shield from radio interference generated on Earth.

The satellite would listen for the 21-centimeter line, an exceptionally faint signal from hydrogen atoms dating to the period between the afterglow of the Big Bang and "Cosmic Dawn," when nuclear fusion ignited the first stars. On Earth, the ionosphere blocks the relevant radio frequencies while FM radio, satellites and telecommunications add further interference; during each two-hour orbit, CosmoCube would spend about 40 minutes behind the Moon, shielded from that noise. Over a planned two-year mission, researchers expect it to gather around 1,000 hours of observations of the 10-50 MHz frequency range, largely inaccessible to ground-based telescopes.

"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 of Cambridge's Cavendish Laboratory. "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."

Once in lunar orbit, CosmoCube would deploy a long, lightweight radio antenna and use a "Dicke switched" calibrator that alternates between the sky and built-in reference sources to correct for instrument noise, before researchers apply statistical techniques on Earth to separate the cosmic signal from radio waves produced within the Milky Way. The mission, detailed in a paper in Nature Astronomy, has received funding from the UK Space Agency, and researchers hope to launch it within five years.