It’s a much more convincing signal than a previous putative planet at this star system. In 2012, a Swiss team announced a blockbuster finding of a planet orbiting the smaller sunlike star, Alpha Centauri B. But during follow-up observations, the signal evaporated, and with it astronomers’ hopes of a nearby world.
This time, the planet-hunters knew they’d found the real deal after only two weeks of HARPS time, says team member Cristina Rodríguez-López of the Institute of Astrophysics of Andalusia in Spain.
“Guillem sent us what was coming out, and I wrote him and said ‘I would like to print this and put it as a poster in my office,’” she says. “You could see it so clearly.”
That clarity is despite a lot of noise from the host star. Though Proxima is dim, it’s constantly firing off X-rays and stellar flares, activity that can easily be mistaken for a wobble, says Mike Endl, an astronomer at the University of Texas at Austin. He started studying Proxima in 2000, and his data set was one of the keys to proving the planet exists.
“When we started observing Proxima, there were only a few exoplanets known. We live in a completely different time now,” he says. I asked Endl if he ever thought it would be possible, when he completed his Ph.D two decades ago, that we would have not only a bumper crop of exoplanets, but a realistic chance of sending probes to one around the nearest star.
“No. No. No. No, I never thought that would be possible in my lifetime,” he said. Now, he thinks Proxima has a few planets that might be worth visiting.
The team noticed a second signal, deep within the data, but they can’t tell yet whether it’s a planet. Its wobble is somewhere between 60 and 500 days, so further observations will help pin it down, says Jenkins, the Scottish astronomer.
“Small planets seem to come along with more brothers and sisters,” he says. “Small stars come quite packed with planets, so that motivates us to really pin down this signal.”
As the Pale Red Dot team members sift through more data, astronomers around the world will race to double-check their findings, and examine the star with different telescopes and spectrographs. The community is collectively holding its breath for a transit, a view of the planet crossing in front of the star. There’s only a 1.5 percent chance the Proxima Centauri system’s geometry is arranged in such a way that we could see this. But if so, we might be able to look at its atmosphere.
“That’s where the game becomes really exciting,” Butler says. “That’s when we go from ‘potentially habitable’ to something that has life.”
For centuries, if not millennia, thinkers of various stripes have wondered whether other stars played host to planets. But it took us until 1995 to find one, and another 20 years to find more than a handful. In one sense, this is a discovery that spans centuries, and as such it’s a fitting preface to our actual exploration of these worlds, which may take just as long.
Visiting the Proxima planet, with a probe or in person, would be a multi-generational effort. Decades from now, stargazers might consider the discovery of Proxima Centauri b a turning point that transformed the way we look at the stars. No longer an anonymous collection of glitterings in the night sky, the stars were now a destination, beckoning us to a future we’d only dreamt about.