Colours from Earth: preparing for exo-earth characterisation

Having orchestrated and obtained the Voyager 1 spacecraft’s 1990 “Portrait of the Planets”, which looked back some 6.1 billion km towards its launch site, Carl Sagan coined the iconic name the “Pale Blue Dot” for our home planet. Since that time, nearly 2000 extrasolar planets have been discovered and, due to the developing sensitivity of the discovery methods, an increasing fraction of these are classified as ‘terrestrial’ and a few even reside within the habitable zone around their parent star. We can anticipate the time, perhaps with the next generation of telescopes on the ground and in space, that we can find and begin to investigate a planet that resembles Earth: “Earth’s twin”. Until then, we can hone our observational strategies by observing the Earth itself as an exoplanet and, along the way, see our world from a more holistic standpoint. There are ways in which we can exploit our moon as a proxy observer to gain some very practical experience.