Chinese astronomers aim to peer for the first time into the cosmic “dark ages,” an unexplored era about 200 million years after the Big Bang, by using the Moon as a shield to block out noisy radio signals caused by human activity on Earth, reports the South China Morning Post.
The Discovering the Sky at the Longest Wavelength (DSL) mission envisions sending a fleet of satellites to the Moon that could capture ultralong radio waves made by hydrogen atoms in the darkness before cosmic dawn, when the first stars were born bursting with radiant light.
These ancient radio signals contain juicy secrets about the early universe, but they are challenging to pick up from Earth because our planet is bustling with natural and artificial radio interference. For this reason, many scientists have proposed building telescopes or arrays on the far side of the Moon, where this earthly noise can be tuned out.
The mission, which is nicknamed Hongmeng after the primordial mist of Chinese mythology, offers a riff on this idea that sidesteps the headaches of landing and constructing an observatory on the Moon’s surface.
Instead, Hongmeng would consist of six to nine “daughter” satellites in a circular orbit around the Moon, along with a “mother” satellite tasked with communicating to ground teams, which would together create a mobile array capable of picking up radio signals from the dark days before starlight existed. This approach allows “the Moon to shield the radio frequency interferences (RFIs) from the Earth,” according to an outline of the mission published in a 2020 issue of Philosophical Transactions of the Royal Society A.
Chen Xuelei, a professor at the National Astronomical Observatory at the Chinese Academy of Sciences who serves as the project scientist for DSL, said the mission could provide “a first peek of the cosmic dawn and dark age” as well as “potential for great discoveries” across a host of other fields such as Sun science, planets and exoplanets, and radio signals from other galaxies.
“It is time to consider a new space mission to explore and reveal the mysteries of this wave band,” the team said in the study. “As a first explorer mission, the main science objectives of the DSL are (1) to open up a new window of observation by mapping the sky and cataloging the major sources at this wavelength, to reveal new astrophysical phenomena at this wavelength, and to discover the unknown unknowns; (2) to explore the dark ages and cosmic dawn by making high precision global spectrum measurements.”
Chen and his colleagues first started assessing the feasibility of this mission in 2015, and they now await an official greenlight from China’s space program, which may come within the next few weeks. If the mission gets the go-ahead, it could be ready for launch by the mid-2020s and would require just one rocket launch to deploy the fleet of satellites. That means that humanity might be able to pull back the veil on one of the most elusive and important eras in the universe’s history—either with DSL or similar observational efforts—within the decade.
“The ultra-long wavelength radio signals have great potential for scientific breakthroughs, especially for the study of the cosmic dawn and dark ages,” Chen and his colleagues concluded in the study. “This first step can be made in the coming decade with a lunar orbit array such as the DSL.”