Proxima b Is Real: Our Nearest Neighboring Planet Gets Confirmed
ESPRESSO data from ESO's VLT confirms Proxima b, an Earth-sized planet orbiting the closest star to the Sun.
Proxima Centauri is the closest star to the Sun – about 4.2 light-years away, which still sounds close only in the way “next town over” sounds close when the town is on another continent. Back in 2016 astronomers announced a candidate planet there, Proxima b, using radial velocity measurements: the tiny wobble a star exhibits as an orbiting planet tugs on it gravitationally. Candidate detections like that are notoriously fragile. Stellar activity, instrument noise, and just plain bad luck have killed off plenty of “planets” before they could be confirmed.
This week that changed. Using ESPRESSO, the spectrograph installed on ESO’s Very Large Telescope in Chile, researchers reported they’ve confirmed Proxima b is real, and it’s roughly Earth-sized. ESPRESSO is a serious upgrade over the instruments used in the original 2016 detection – it was built specifically to measure the kind of minuscule stellar wobbles that a small, rocky planet induces, the sort of precision that previous spectrographs could only approximate.
Why this one keeps mattering
Proxima b already had a reputation before today. It’s Earth-sized, it orbits in what’s roughly considered the habitable zone of its star (the zone where liquid water could theoretically exist on a surface), and it’s next door in cosmic terms. Every one of those facts individually is unremarkable – there are other roughly Earth-sized planets, other habitable-zone candidates, other planets around red dwarfs. What makes Proxima b interesting is having all three at once, around the single nearest star we have.
Proxima Centauri is a red dwarf, which comes with real caveats. Red dwarfs are prone to flares and high-energy radiation that could strip a close-in planet’s atmosphere over time, and Proxima b orbits tight enough that tidal locking (one side permanently facing the star) is a plausible outcome. None of that is settled by today’s confirmation – confirming the planet’s existence and mass doesn’t tell you what its atmosphere looks like, or whether it has one at all.
But confirmation is the prerequisite for everything more ambitious. You can’t justify pointing a next-generation instrument at a target for weeks of exposure time if there’s lingering doubt about whether the target actually exists. Now there isn’t. That’s the real headline here – less “here’s the planet” and more “here’s a confirmed, worthwhile target.”
What comes next
The obvious follow-up is direct imaging: actually capturing a photon of light reflected or emitted by the planet itself, separate from its star’s glare, rather than inferring its presence from stellar wobble. That’s an enormously harder technical problem – Proxima Centauri is faint as stars go, which helps a little with contrast, but the angular separation between star and planet as seen from Earth is still tiny. There’s been talk for years of dedicated instruments and even interstellar probe concepts (Breakthrough Starshot has had half an eye on this system) aimed at this exact target. A confirmed planet is a much easier thing to build a mission case around than a candidate.
I don’t think anyone’s expecting biosignatures or anything close to that in the near term. But having a confirmed, Earth-sized, close-by exoplanet to point instruments at for the next decade is genuinely exciting, if only because it turns “is there a planet there” into “what is that planet actually like” – a much better question to be stuck on.