Project Blue will attempt to build a space telescope to be pointed at Alpha Centauri, hoping to glimpse planets where life may have gained a foothold

Astronomers have launched an ambitious project to capture the first picture of an Earth-like planet that could be home to life beyond the solar system.

The privately-led mission aims to build a space telescope the size of a washing machine and point it at Alpha Centauri, the closest star system to Earth, in the hope of glimpsing a rocky world or two where life may have gained a foothold.



If the project is successful - and there is no guarantee - it could produce an image to rival the iconic “pale blue dot” photograph taken in 1990 when Nasa’s Voyager 1 probe looked back at Earth as it barrelled out of the solar system.

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The pale blue dot picture was taken from a distance of 6bn km at the request of the astronomer Carl Sagan, who saw profound meaning in the image. “Every saint and sinner in the history of our species lived there: on a mote of dust suspended in a sunbeam,” he said in a lecture at Cornell University in 1994. “To me, it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot, the only home we’ve ever known,” he added.



Since the 1980s, astronomers have confirmed the presence of more than 3,000 “exoplanets”, or worlds beyond the solar system. But all are known only from indirect measurements: the wobble they induce in their parent star, and the minuscule dip in light as they cross the face of the star. No has yet captured a direct image of a planet that is comparable to Earth



Voyager’s “pale blue dot” image of Earth. “Every saint and sinner in the history of our species lived there: on a mote of dust suspended in a sunbeam,” said Carl Sagan of the picture. Photograph: Nasa/JPL

The new mission, named Project Blue, builds on the work of Nasa’s Kepler space telescope and other instruments which have spotted a string of faraway planets that appear to be rocky and within their star’s “habitable zone” - the region of space where the temperature is just right for water to flow freely. Astronomers suspect they are the best candidates to harbour life elsewhere.



“The past ten years of exoplanet research has shown us that small planets are very abundant. Now we’re trying to determine whether life is common or rare,” said Jon Morse, former director of astrophysics at Nasa, and CEO of the BoldyGo Institute which is co-leading Project Blue. “We’re setting the context for understanding ourselves and our place in the universe.”



No one pretends the mission will be easy. Alpha Centauri may be the closest star system to Earth, but at 4.4 light years or 40 trillion kilometres away, it is hardly next door. And rather than hosting a single star, Alpha Centauri has two that swing around each other. The light from both must be blocked before any orbiting planets, one billion times dimmer, can be seen.

Supriya Chakrabarti, professor of physics at the University of Massachusetts, Lowell, said the success of the mission rests on at least three crucial technologies. The first keeps the telescope pointing in the precise direction of Alpha Centauri. The second separates unwanted starlight from the light reflected off any orbiting planets. The third replaces a single telescope mirror with a thousand tiny ones, each adjustable to bring images into focus.



“It’s a very challenging measurement, but the challenge makes it exciting,” Chakrabarti said.



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While the project is led by the BoldlyGo Institute and another private organisation, Mission Centaur, which has drawn up plans for the half-metre-wide space telescope, Morse hopes to bring in other partners from academia and national space agencies. The mission is expected to cost less than $50m (£40m).



If Project Blue gets off the launchpad, the telescope will spend two years gazing at Alpha Centauri in the hope of spotting planets around either one of the system’s stars. The telescope can only hope to capture a lonely dot in the darkness, but even that would be groundbreaking, astronomers believe.



“For me, finding an Earth-like planet around the closest sun-like star, the first place we could get to, would be phenomenal, ”Chakrabarti said.



Hopes to take a snapshot of an Earth-like planet are not new. In the past two years, Ruslan Belikov and Eduardo Bendek at Nasa’s Ames Research Center in California developed similar mission proposals. Their Acesat (Alpha Centauri Exoplanet Satellite) telescope was considered too risky for the US space agency to take on, but work continues on the technology. “It is a really difficult challenge to meet,” Bendek said.



Even a pale dot of an image would have scientific value, according to Belikov. Astronomers could deduce the planet’s orbit, its rough size and colour. If the alien world turned out to be blue, and it lay in the habitable zone, it would be hard not to conclude it had watery oceans and an atmosphere, he said. “It would be hugely exciting if we could find another pale blue dot,” Belikov said. “I think such an image has the power to be one of the most iconic and transformative images of our time.”

Chris Lintott, an astrophysicist at Oxford University, said the first image of an exoplanet would be a landmark moment, but was sceptical that Project Blue could manage the feat. “If such an image could be obtained, I think it would be hugely exciting,” he said. “The pale blue dot was not scientifically useful, but it’s inspired generations of astronomers and the public.”

• This article was amended on 12 October 2016 to clarify a statement that no one has yet captured a direct image of such distant worlds. That has been amended to say no one has yet captured a direct image of planet that is comparable to Earth.