Astronomers today reported finding one of the most intriguing exoplanets yet: a world about the size of Earth, with a decent chance of surface water, orbiting the star closest to our sun.
In a paper published in Nature, scientists working for the Pale Red Dot consortium show convincing evidence for a rocky planet about 1.3 times as massive as Earth, orbiting Proxima Centauri, which is only 4.2 light years away. Even better, the planet circles the star in a “temperate zone” where liquid water—thought to be essential for life—could exist on its surface. The scientists, led by Guillem Anglada-Escudé of Queen Mary University of London, used a precision spectrometer at the La Silla Observatory in Chile and other instruments in an intensive campaign to follow up and confirm earlier observations of the planet, which they’ve named Proxima b.
As to whether there actually is water on the surface—here’s where the speculation begins. It would depend, in part, on whether the planet formed in its current orbit, or migrated in from farther out in the Proxima Centauri system, where icy comets could have seeded it with water. Right now, scientists can’t tell if Proxima b is dry and dead like Venus or wet like Earth, or even whether it has an atmosphere.
Proxima Centauri is a red dwarf star—by far the most common variety in the galaxy. Because these stars are smaller and less luminous than our sun, astronomers once thought that planets around them would be inhospitable to life. In recent years, though, that opinion has changed, and red dwarf planets have become of significant interest to astrobiologists.
Unfortunately, without more data—including “transit” data where the planet appears to cross the disk of the star as seen from Earth—there isn’t much more scientists can say right now about Proxima b. And transits are a rare accident of viewing geometry, with only about a 1.5 percent chance that this particular world will line up in the right way.
The most significant thing about the new planet is its closeness to Earth. It’s near enough that telescopes already on the drawing board should be able—just barely—to take pictures of Proxima b that show it separate from its host star.
It’s also near enough that we can think about sending a spacecraft there. At a press conference today to announce the new planet, Pete Worden of the Breakthrough Starshot initiative sketched out plans to use laser beams to propel a fleet of tiny “nanoprobes” at up to 20 percent of the speed of light, which could get them to Proxima Centauri within 20 years or so. Such a launch could be done “within a generation,” Worden said.