By Davide Castelvecchi
China has taken its first major step in a groundbreaking lunar mission. On 21 May, a probe launched from Xichang Satellite Launch Centre to head beyond the Moon, where it will lie ready to act as a communications station for the Chang’e-4 lunar lander. The nation hopes that the lander will, later this year, become the first craft to touch down on the far side of the Moon.
The relay probe, named Queqiao and designed by the Chinese Academy of Sciences, also carries two pioneering radio-astronomy experiments. Both are proof-of-principle missions designed to test technologies for exploring a period in cosmic history known as the dark ages. These first few hundred million years of the Universe’s existence, before galaxies and stars began to form, are all but impossible to study from Earth. But the spectrum of radiation from this age — when matter was distributed nearly uniformly across space as a thin, cold haze — could reveal information about the distribution of ordinary matter compared with dark matter in the Universe.
The first experiment is the Netherlands-China Low-Frequency Explorer (NCLE). It will remain attached to Queqiao, which will linger around ‘Earth-Moon L2’ — a gravitational resting point about 60,000 kilometres beyond the Moon that tracks the Moon’s orbit around Earth (see ‘Far-side satellite’). The Dutch-built NCLE experiment will try to exploit the relative quiet there to measure radio waves with frequencies between about 1 megahertz and 80 megahertz, coming from the Solar System, the Galaxy and beyond. Much of this frequency band is blocked by Earth’s atmosphere, but cosmologists expect it to contain information from the dark ages. Around the upper end of this band also fall the ‘cosmic- dawn’ signals from the first stars, which lit up around 200 million years after the Big Bang and were apparently detected for the first time earlier this year. Other experiments are trying to replicate those results — but the NCLE is testing technologies for identifying lower-frequency signatures from the dark ages.)
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