In 2009, NASA launched the Kepler space observatory into an orbit around the sun with the express purpose of using the satellite to discover Earth-like planets orbiting other stars. The only instrument on board Kepler is a photometer, which measures the brightness of nearly 150,000 stars in the Milky Way. When the brightness of these stars dims slightly due to a planet passing in front of the star, scientists on Earth are able to determine quite a bit about that planet, such as its size and distance from the sun.
Photometry is a great way of quickly covering a lot of ground when searching for exoplanets, but it is still an indirect way of observing exoplanets. The ultimate goal is direct observation, which can give planetary scientists still more information about the planet being observed, such as its atmospheric composition.
This is why a handful of space institutions have come together to create Project Blue, a satellite mission that aims to directly image the exoplanets around our solar system's closest stellar neighbor—Alpha Centauri—in hopes of directly imaging an Earth-like planet.
Project Blue is being carried out by the non-profit organization Mission Centaur, which was founded to facilitate the project. It will bring together top scientists from a range of non-profit space institutions such as the Boldly Go Institute and the SETI Institute, including Jon Morse, NASA's former director of astrophysics and the director of Boldly Go.
"For every mission that NASA selects, there are two or three they don't select that could fly and be outstanding," Jon Morse, NASA's former director of astrophysics and current director of Boldly Go, told Motherboard. "Our goal is to augment and enhance the national portfolio of space science missions so that NASA doesn't have to pay for this. We think it's entirely plausible to do find backers to do this privately because we can leverage all the technology investments they've made."
The goal of Project Blue is to put a telescope the size of a small washing machine in Low Earth Orbit by 2020. That telescope will be training its sights on Alpha Centauri, a star system that is a mere 4.7 light years away, making it our closest stellar neighbor by a longshot. The two stars making up the main Alpha Centauri solar system (fittingly named 'A' and 'B') are similar enough to our own sun that the scientists at Project Blue think there is a roughly 85 percent chance that one of them will host an Earth-like planet.
Ultimately, the scientists at Project Blue hope to photograph another "pale blue dot" in the Alpha Centauri system, which would suggest that that planet harbored liquid water.
"Project Blue hopes to image in blue light in order to get a sense of the color of any planet we see," said Morse. "It's a nice indication that the planet has liquid water on its surface."
At this point, however, imaging anything around Alpha Centauri would be a step forward. So far, only one planet has been discovered in the solar system, but it is orbiting the small red dwarf star Proxima Centauri, not one of the main binary stars.
To directly image exoplanets orbiting the main Alpha Centauri stars, the Project Blue telescope would make use of a device called a coronagraph which essentially blocks out the majority of the light coming from a star. This allows the telescope to observe light being reflected off of planets in orbit, which are over a billion times dimmer than their host star—Morse compares it to trying to observe a firefly that is in front of a bright light house from ten miles away.
Although there are ground-based telescopes that have recently become capable of directly imaging exoplanets using coronagraphs, according to Morse, these instruments wouldn't suffice for Project Blue's mission.
"We're not going to do direct, ground-based imaging of Earth-size exoplanets anytime soon," Morse said. "The technology used by ground-based observatories is very similar to what we'll use, but they do imaging in the infrared, not visible light [like Project Blue]. We're going to space because that's the environment that would allow us to make this very precise measurement with a modest telescope."
The coronagraph that would be used by the Project Blue telescope is specialized for its target stars. Alpha Centauri is mainly a binary solar system (with a small red dwarf nearby called Proxima Centauri), so it needs to block the light from two stars at once, so the project's scientists are leveraging published work that was done at NASA Ames Research Center for this exact purpose.
Perhaps the most remarkable aspect of Project Blue is that it hopes to accomplish this mission with just a $50-million budget—just a fraction of the $600-million that went into Kepler. The first million is being crowd-sourced on Kickstarter and will go toward planning the mission details and creating a mission simulation. Roughly $30 million will go toward developing the telescope, and the rest will be used to hitch a ride to space. According to Morse, the vast majority of this funding will be supplied by "high net-worth individuals and institutions."
"We feel the citizen participation is important so even if we don't make our goal, we still have a community of over 1200 backers that care about this kind of discovery," said Morse. "[Project Blue] will shape the technology and resources developed in the future, especially if we know there's something [in Alpha Centauri] to study."