Seeing blue © Getty Images

Seeing Blue – the hunt for Earth’s sister

A new space telescope is being developed. Its mission? To take a photograph of an Earth-like planet that could shape our understanding of our place in the Universe.

Christmas, 1968. Three men were in orbit around the Moon, as far away from earth as anyone had ever gone. They thought the magnificent desolation of the lunar landscape was the most stunning thing they were going to see during their mission. But they were wrong.


On their fourth orbit, astronaut Bill Anders saw Earth rise above the Moon’s horizon. He photographed the moment and in doing so gave the world one of the most iconic images of the space age. This picture of the seemingly fragile blue planet Earth subsequently became a symbol to represent both the environmental movement and the wonders of space exploration. Now, a group of privately funded astronomers and engineers want to recreate that act by taking a new picture of another blue planet – one around another star.

Blue sky thinking

Dubbed Project Blue, the mission aims to build and launch a space telescope with a single goal in mind: to image any planets in the habitable zones of the nearest Sun-like stars. If such planets were Earth-sized with oceans and atmospheres, then they could even “see Blue”, Project Blue’s term for finding a potentially habitable planet.

The mission is the brainchild of the BoldlyGo Institute. This not-for-profit organisation was founded by Dr Jon Morse, a former NASA scientist and White House science advisor, to investigate highly compelling scientific questions using private money from donors and crowd-funding initiatives. And there are few questions more compelling than whether there are other Earth-like planets around other stars.

Taken on Christmas Eve by the crew of Apollo 8, Earthrise was the first time a human had seen Earth rise from behind the horizon of the Moon.
Taken on Christmas Eve by the crew of Apollo 8, Earthrise was the first time a human had seen Earth rise from behind the horizon of the Moon.

The quest to find Earth-analogues, as these planets are known, began in earnest in 1995 when a pair of Swiss astronomers discovered 51 Pegasi b – the first extrasolar planet (or exoplanet) to be found around a Sun-like star. It was the size of Jupiter and not at all Earth-like, but it proved that planets were now in reach of our technological abilities.

In the decades since, almost 4,000 other exoplanets have been detected but hardly any have had their picture taken. The trouble is that planets do not generate any of their own light and instead simply reflect their star’s light. This makes them more than a billion times fainter than their parent star. Telescopes to date have been able to catch a few glimpses of large planets, but planets the size of Earth have remained impossible to image. Instead, astronomers have used indirect observations to infer the existence of the exoplanets.

Most of the exoplanets found so far were detected using NASA’s Kepler Space Telescope. Kepler tracked a star’s brightness, looking for the dip caused when a planet crossed in front of it. Its instruments were precise enough that it could see smaller rocky (also called terrestrial) planets but none of them have proved to be a twin to Earth. Although some grabbed headlines around the world for being similar, to date we have not found a true Earth-twin in the sense that it is an Earth-sized world in an orbit the size of Earth’s around a Sun-like…

This is an extract from issue 320 of BBC Focus magazine.
Subscribe and get the full article delivered to your door, or download the BBC Focus app to read it on your smartphone or tablet. Find out more


Follow Science Focus on TwitterFacebook, Instagram and Flipboard