On 7 January 1610, Galileo raised a telescope to the night sky, and turned the world upside down.
By revealing the moons of Jupiter, he showed that all things did not revolve around the Earth, as the prevailing dogma maintained. His discovery opened a new perspective on the Universe, in which Earth was just one planet among perhaps innumerable others.
It is only in this century that this insight has been confirmed. Thanks to the discoveries of the Kepler Mission and other teams, it now seems likely that most stars have planets; and that tens of billions, in the Milky Way alone, are “exo-Earths”: rocky, roughly Earth-sized planets basking the habitable zone of their stars, where liquid water – and so perhaps life – could potentially exist.
And in August 2016, the Pale Red Dot team at the ESO discovered an Earth-like planet in our own cosmic back yard: Proxima b, which orbits Proxima Centauri, the closest star to the Sun.
If habitable planets are common, does that mean life is common? This is still the great unknown. To find out, we need to locate these planets and analyze their composition. Much can be learnt from their color alone: just as Earth appeared to Voyager I’s camera, six billion kilometers away, as a “Pale Blue Dot,” so a planet that appeared blue in our telescopes would be a prime candidate for an oxygen atmosphere – and therefore primitive life.
Telescopes have come a long way since Galileo’s crude refractor. But so have the challenges. Spotting a pale blue dot against the intense glow of a nearby star, and analyzing it for signs of life, is a significant technical challenge for ground-based telescopes. And it has not proved attractive to space agencies to invest in the space-based instruments that could study these systems with precision.
Breakthrough Watch aims to identify and characterize Earth-sized, rocky planets around Alpha Centauri and other stars within 20 light years of Earth, in search of oxygen and other “biosignatures.” Half a millennium after Galileo, the discovery of life would once again revolutionize our perspective on the Universe.
With this remit, Watch is also a bridge between the Listen and Starshot initiatives: if such planets are habitable, they are targets for Starshot; if they are inhabited, they are of prime interest to Listen.