There Is Now A Radio Telescope Over The Far Side Of The Moon

The always eerily unfamiliar view of the Moon's far side. NASA/LRO

Beyond the Moon, roughly 65,000 kilometers (40,300 miles) from the surface of the far side, humanity has just tested a new approach to radio astronomy. The Netherlands-China Low-Frequency Explorer (NCLE) is designed to look for an elusive cosmic signal, known as the hydrogen line, which can only be achieved far from Earth’s disruptive ionosphere.

The experiment is part of the Chang’e-4 mission. It’s located on the relay satellite, which, for the last year, has been used exclusively to communicate with the lander. NCLE consists of three antennas that began their life folded up but finally unfolded last week after 18 months in space. 

The unfolding of one of the three antennas. (c) Marc Klein Wolt / Radboud University

“Our contribution to the Chinese Chang’e-4 mission has now increased tremendously," Marc Klein Wolt, managing director of the Radboud Radio Lab and leader of the Dutch team, said in a statement. "We have the opportunity to perform our observations during the 14-day-long night behind the Moon, which is much longer than was originally the idea. The Moon night is ours, now.” 

Unfortunately, the unfurling of the antennas didn’t go smoothly, so they are not fully stretched out at present. The experiment should have started much earlier, but the relay satellite was required to assist the lander for a lot longer than planned. The team suspects that this delay might have caused some damage but they have chosen to begin the observations anyway, and will attempt to force the full extension of the antennas in the future. 

Schematic (and very not to scale) representation of the position of the new radio observatory. Isis/Radboud University

With the antennas at their current length, the team expects to see neutral hydrogen emissions from about 800 million years after the Big Bang. If they were fully extended, the observatory would be able to pick up this emission right from the period before the first stars were born: the Cosmic Dark Ages.

Studying this signal in detail is a holy grail of cosmology. Astronomers expect it to provide insights into how matter was distributed after the Big Bang and how the formation of stars ripped apart neutral hydrogen atoms (known as re-ionization), which led to the universe we know today.

A follow-up instrument made of three satellites is currently being planned for 2021 and a much bigger orbiting radio telescope is being investigated for the next decade. This one would have between 50 and 250 nodes and be an invaluable instrument like nothing else on Earth.  

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