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Searching Alpha Centauri for Earth-Like Planets

By David Reneke

Breakthrough Watch has announced “first light” on a newly built instrument idesigned to hunt for exoplanets in our neighbouring star system, Alpha Centauri.

Breakthrough Watch, the global astronomy program looking for Earth-like planets around nearby stars, has announced “first light” on a newly built planet-finding instrument at the European Southern Observatory’s (ESO) Very Large Telescope in the Atacama Desert, Chile. The instrument, called NEAR (Near Earths in the AlphaCen Region), is designed to hunt for exoplanets in our neighbouring star system, Alpha Centauri, within the habitable zones of its two Sun-like stars, where water could potentially exist in liquid form.

Astronomers have been conducting observing runs to establish the presence or absence of one or more planets in the star system. Planets twice the size of Earth or bigger are detectable, with the upgraded instrumentation operating in the near- to thermal-infrared range picking up the heat emitted by a candidate planet.

Alpha Centauri is the closest star system to our own at 4.37 light-years away. It consists of two Sun-like stars, Alpha Centauri A and B, plus the red dwarf star Proxima Centauri. Current knowledge of Alpha Centauri’s planetary systems is sparse indeed!

Imaging such planets is a major technical challenge since the starlight that reflects off them is generally billions of times dimmer than the light coming to us directly from their host stars. Resolving a small planet close to its star at a distance of several light years has been compared to spotting a moth circling a street lamp dozens of kilometres away.

To solve this problem, in 2016 Breakthrough Watch and ESO launched a collaboration to build a special instrument called a thermal infrared coronagraph, which is designed to block out most of the light coming from the star and optimised to capture the infrared light emitted by the warm surface of an orbiting planet rather than the small amount of starlight it reflects.

Just as objects near to the Sun (normally hidden by its glare) can be seen during a total eclipse, so the coronagraph creates a kind of artificial eclipse of its target star, blocking its light and allowing much dimmer objects in its vicinity to be detected. This marks a significant advance in observational capabilities. The system also uses a technique called adaptive optics to strategically deform the telescope’s secondary mirror, compensating for the blur produced by the Earth’s atmosphere

“Human beings are natural explorers,” said Yuri Milner, founder of the Breakthrough Initiatives. “It is time we found out what lies beyond the next valley. This telescope will let us gaze across it.”

David Reneke is an astronomy lecturer, writer and broadcaster (