A new initiative called “Project Blue” aims to spy on our interstellar neighbor, Alpha Centauri, to capture an unprecedented visible-light image of any Earth-like planets that might orbit there.
The project, which hopes to launch a lightweight telescope into Earth orbit by 2019, was announced today (Oct. 11).
The two stars of Alpha Centauri, along with the associated red dwarf star Proxima Centauri, are the closest stars outside our solar system — and the Alpha Centauri stars are by far the closest sun-like stars to Earth’s system. While the dual system makes imaging a challenge, the stars’ extraordinary closeness means that a relatively small and inexpensive space telescope could potentially view them directly
These six narrow-angle color images were made from the first ever “portrait” of the solar system taken by NASA’s Voyager 1 spacecraft on Feb. 14, 1990, when the probe was about 4 billion miles (6.4 billion kilometers) from Earth. Clockwise from top left: Venus, Earth, Jupiter, Neptune, Uranus and Saturn. Credit: NASA/JPL-Caltech
Alpha Centauri is a tantalizing target because of its sheer closeness to Earth. The binary system is just 4.3 light-years away, which is 270,000 times the distance from the Earth to the sun. (The next nearest sun-like star is more than twice as far away.)
When it comes to Alpha Centauri, “We don’t need a big giant telescope that’s at least a meter [3.3 feet] in size or larger-type project that NASA’s currently doing, like the WFIRST mission — we’re able to keep this telescope to roughly half a meter, and we can still explore that habitable zone,” Morse said, referring to the Wide Field Infrared Survey Telescope, a mission that NASA aims to begin in the mid-2020s.
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.
Rendering of the telescope Project Blue aims to put in space to search for planets around the nearby star system Alpha Centauri.
Credit: Project Blue
Morse said he hopes to use similar methods — described in Belikov’s and other studies — to use deformable mirrors and star shades to cancel out the stars’ glare.
And the rest of the technology, like that required to hold the telescope steady enough in space to image the star system, has made rapid strides lately, Chakrabarti said. Such advances should make Project Blue possible on a smaller budget than ever — and it’s a project that would be extremely difficult to do on more general-purpose telescopes, like Hubble, team members said.
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.
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.
Several mission concepts are being studied to directly image planets around nearby stars. It is commonly thought that directly imaging a potentially habitable exoplanet around a Sun-like star requires space telescopes with apertures of at least 1m. A notable exception to this is Alpha Centauri (A and B), which is an extreme outlier among FGKM stars in terms of apparent habitable zone size: the habitable zones are ~3x wider in apparent size than around any other FGKM star. This enables a ~30-45cm visible light space telescope equipped with a modern high performance coronagraph or starshade to resolve the habitable zone at high contrast and directly image any potentially habitable planet that may exist in the system. We presents a brief analysis of the astrophysical and technical challenges involved with direct imaging of Alpha Centauri with a small telescope and describe two new technologies that address some of the key technical challenges. In particular, the raw contrast requirements for such an instrument can be relaxed to 1e-8 if the mission spends 2 years collecting tens of thousands of images on the same target, enabling a factor of 500-1000 speckle suppression in post processing using a new technique called Orbital Difference Imaging (ODI). The raw light leak from both stars is controllable with a special wavefront control algorithm known as Multi-Star Wavefront Control (MSWC), which independently suppresses diffraction and aberrations from both stars using independent modes on the deformable mirror. We also show an example of a small coronagraphic mission concept to take advantage of this opportunity.
SOURCES- Space.com, Arxiv, NASA, Project Blue, Ars Technica