The nearest star system to the Sun, α Centauri, has been all the rage after the discovery of an Earth-sized world in the habitable zone around the smallest of its three stars, Proxima Centauri. Scientists, however, are equally eager to learn more about the planetary systems around α Centauri's two larger Sun-like stars, α Centauri A and B. Those systems might offer an environment still more conducive for an Earth-like planet.

Although NASA has plans to eventually develop optical telescopes that might be able to image planets around these stars, some scientists say we should not wait that long. Moreover, these scientists say that, with a modestly sized telescope, we could start looking for Earth-like worlds around Centauri A and B by the end of the decade. To that end, several organizations plan to announce a privately led, non-profit effort to do just that. The project, titled “Project Blue,” will be announced on Tuesday.

Project Blue takes its name from the famous Pale Blue Dot image taken by Voyager in 1990, when the probe was about 6 billion km from Earth. Our planet filled just a single blue pixel against the vast, black, seemingly endless heavens. Project Blue aims to capture such an image of one or more Earth-sized planets in the habitable zone around α Centauri A or B.

“We feel that the moment is right [when] there is this confluence of scientific impact and technology maturing rapidly,” said John Morse, chief executive of the BoldlyGo Institute, which is co-sponsoring the initiative along with Mission Centaur. “We won’t resolve planetary features, but we believe we have a really good chance of seeing something like a pale blue dot.”

Finding a firefly next to a lighthouse

In an interview with Ars, Morse said he believes Project Blue can be accomplished for comfortably less than $50 million. His goal is to slice the overall cost to less than half of that. This price includes building both the telescope and launching it by the end of the decade. He intends to launch his telescope either as a “ride share” on a larger rocket or on one of the smaller, dedicated microsatellite launchers under development.

Morse said Project Blue will employ an “all of the above” fundraising strategy, beginning with crowdfunding to initiate meaningful technical work on the telescope’s design. In addition, the organization will also seek larger-sized donations, beginning with the donor network that has supported the Boldly Go Institute. The organization will also pursue in-kind contributions from partners to keep costs down.

Based upon a number of technical studies, such as this one, Project Blue believes it can obtain a sufficient resolution to image a planet around one of the α Centauri stars with a telescope 50cm or smaller in size (the primary mirror of the Hubble Space Telescope is 2.4 meters).

Unlike the Kepler Space Telescope—which monitored 100,000 stars and looked for slight dimming to determine when planets passed in front of their parent stars—Project Blue will use high-contrast imaging. Technical studies have shown that, with an advanced coronagraph to block light from the stars and data processing techniques, such a telescope could reject light from the two stars at a rate of 10 billion to one. This is sufficient to allow direct imaging of a planet with observations made over the course of several years. Put another way, such an observation system is akin to detecting a firefly next to a lighthouse 10 miles away.

A bit of a gamble

Unfortunately, the telescope will not have the power to resolve the Earth-sized planet found around the red dwarf star Proxima Centauri, which is much cooler than the other two stars in the system. The world, Proxima b, orbits its star every 11.2 days at a distance of approximately 7.5 million km, about 5 percent of the distance that Earth lies from the Sun.

Because that world is so close to its star, there is no way a telescope with a coronagraph, at the scale being contemplated, would be able to separate the light of the planet from its star. However, Morse said he believes the discovery of Proxima b has increased public attention toward the α Centauri system, which should help Project Blue gain attention.

This is a bit of a gamble, of course. The planetary scientists do not actually know whether any Earth-size worlds lurk about α Centauri A and B in the habitable zones of the two stars. Using a different technique, in which a planet induces a subtle “wobble” on its parent star, astronomers identified an Earth-size world around α Centauri B in 2012. But the planet is so close to its star that it’s thought to be a charred, rocky world.

Nevertheless, Morse said the odds favor the existence of an Earth-like world. The proposed telescope should be able to resolve a world that is 0.5 to 1.5 times of the size of Earth and orbiting within the host star’s “habitable zone,” where water theoretically could exist on the surface. Based on Kepler’s data, with two Sun-like stars to search around, Morse said, statistically, the odds of at least one terrestrial planet in the habitable zone is about 80 percent. With enough water on its surface, the planet would appear blue in any visible light image taken. And what a sight that would be.