Brave New Worlds

For now, NEAR is the only coronagraph on Earth with a realistic chance of imaging Alpha Centauri’s hidden worlds. But other instruments and facilities are already waiting in the wings to apply their own scrutiny to the system. Fischer’s high-precision EXPRES radial velocity spectrograph—and an even more advanced European counterpart, ESPRESSO—are both already operational. They could help indirectly confirm the planet candidate and others, and could estimate their masses, by watching for periodic wobbles each world’s orbital tugging induces upon its host star. A related technique, astrometry, could do much the same thing, pinpointing planetary masses by measuring how each world’s gravitational influence slightly shifts its star’s position in the plane of the sky. Such observations using the Atacama Large Millimeter Array in Chile, or even a modest, Breakthrough-funded dedicated space mission, could occur later this decade.

NASA’s James Webb Space Telescope, slated to launch in late October, would also be capable of directly imaging the candidate planet given one full day of observing time, according to a recent study led by one of Webb’s foremost scientists, Charles Beichman of the California Institute of Technology. “Because Alpha Centauri A is a twin of our own sun and less than five light-years away, it really is our closest solar neighbor,” Beichman says. “That makes it first among equals, of all the stars in the sky. No other system will lend itself to more detailed possible studies over the next several decades.”

The space agency’s follow-up mission to Webb, the Nancy Grace Roman Space Telescope, will also carry a coronagraph as a technology demonstration that could (with certain tweaks now being actively considered) potentially snap pictures of the candidate.

And, around the same time Roman may launch, a new generation of sophisticated coronagraphs mated to gargantuan ground-based observatories should begin operations that could in mere minutes produce images of Centauri planets that would currently require hours upon hours of NEAR’s time on the VLT. Armed with starlight-gathering mirrors 30 meters or more across, ESO’s European Extremely Large Telescope and its American counterpart, the Giant Magellan Telescope, could both in theory gather enough light from a habitable-zone Neptune around Alpha Centauri A to study its atmosphere, sniffing out what familiar or alien chemistry occurs there. (A third behemoth, the U.S.’s Thirty Meter Telescope, is presently planned for a site in the Northern Hemisphere from which Alpha Centauri would not be visible.) Finally, NASA and other space agencies are now studying concepts for multibillion-dollar space telescopes for the 2030s and beyond. Some of these could image and search for signs of life on small rocky planets around Alpha Centauri as well as many other nearby stars.

All of which means that, even if this latest candidate from Alpha Centauri proves spurious, it still signals something quite real: a looming sea change, in which planet-hunting astronomers shift from safe, statistical surveys to the more daring in-depth study of individual worlds, some of which might harbor life.

“Whether this thing is real is, to me, almost secondary,” says study co-author Olivier Guyon, an innovator in direct imaging and chair of Breakthrough Watch. “Because either way it shows we’re clearly opening a new era in the history of astronomy where, finally, after more than 20 years of hard work, we can at last perform direct imaging of another star’s habitable zone. This is the ‘game on’ moment for the field.”