To peer back to the universe’s earliest years will need sensitive telescopes in a place where Earth’s ionosphere and radio chatter cannot interfere
FORTY years after NASA ditched the idea of landing Apollo 17 on the far side of the moon, the forbidden fruit is being sought once again. Not by astronauts this time, but by astronomers seeking a quiet spot from which to observe the universe’s “dark ages”.
This was an epoch in the development of the cosmos, which lasted for a few hundred million years after the big bang, before stars and galaxies began to form. The only way to observe the dark ages is to look for faint radio signals from neutral hydrogen – single protons orbited by single electrons – which filled the early universe.
Telescopes on Earth, such as the Murchison Widefield Array in Western Australia, are searching for such signals, at frequencies above 100 megahertz. This can probe the universe back to 400 million years after the big bang.
To explore even earlier times, telescopes need to receive radio waves at frequencies below 100 megahertz. Interference from radio sources on Earth such as FM radio and the planet’s ionosphere can mess up these signals. “You get to the point where the ionosphere is just a hopeless barrier,” says Dayton Jones of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “You have got to go to space, and the most promising location by far is the far side of the moon.”
This is why astronomers were discussing it at an American Astronomical Society meeting in Anchorage, Alaska, this month. Telescopes behind the moon would not have to contend with Earth’s ionosphere, and they would also be shielded from our planet’s radio chatter. “It is a very pristine environment for low-frequency observation,” says Jones.