When astronomers confirmed the discovery of Proxima Centauri b back in 2016, it felt like the kind of headline you’d expect from a movie trailer, not a real research paper. An Earth-sized planet, sitting in the habitable zone, orbiting the single closest star to our own Sun. For a while, it looked like the best shot we had at finding life just next door in cosmic terms. Nearly a decade later, the picture has gotten a lot more complicated, and honestly, a lot more interesting.
A Planet Right Next Door
Proxima Centauri b orbits Proxima Centauri, a small, dim red dwarf star that happens to be the closest star to our own Sun, sitting just 4.24 light-years away. Discovered using the radial velocity method, watching for the tiny gravitational wobble a planet causes in its host star, Proxima b turned out to be roughly Earth-sized, with a mass somewhere between 1.07 and 1.3 times our own planet’s, depending on which study you check.
What got everyone excited from the start was its orbit. Proxima b completes a full trip around its star in just 11.2 days, sitting extremely close, but because Proxima Centauri is such a small, cool star, that tight orbit still lands the planet inside the habitable zone, the region where temperatures could theoretically allow liquid water to exist on the surface.
The Catch: A Genuinely Bad-Tempered Star
Heres where the story gets messy. Proxima Centauri isn’t just small and dim, its also a flare star, meaning it erupts in sudden, violent bursts of radiation far more often and far more intensely than our own comparatively well behaved Sun. Because Proxima b sits so close to its star to stay warm enough for liquid water, it’s directly in the blast radius of every one of these outbursts.
Research using NASA’s Chandra X-ray Observatory found that planets in Proxima Centauri’s habitable zone receive an average dose of X-rays roughly 500 times greater than what Earth gets from our Sun, and during a major flare, that number can spike to 50,000 times the normal dose. In 2019, astronomer Meredith MacGregor and her team coordinated observations from nine different telescopes and caught Proxima Centauri producing a flare so powerful it briefly made the star 14,000 times brighter than normal in ultraviolet light. Giant flares, it turns out, aren’t rare exceptions for this star, they’re closer to a daily occurrence.
What That Means for Habitability
This kind of relentless radiation raises a serious problem, atmospheric erosion. Over billions of years, repeated blasts of high energy particles can gradually strip away a planet’s atmosphere entirely, and without an atmosphere, there’s no way to hold onto surface water or shield the ground from lethal levels of radiation. One particularly large flare detected in 2017 alone hit Proxima b with an estimated 4,000 times more radiation than Earth typically receives from a comparable solar flare. Researchers involved in that study noted plainly that flares like this could have evaporated any early ocean or atmosphere the planet once had, and effectively sterilized its surface over time.
Its also worth mentioning that Proxima b is very likely tidally locked, meaning the same side of the planet always faces its star, similar to how the same side of our Moon always faces Earth. That would leave one hemisphere in permanent daylight and the other in permanent darkness, with only a narrow twilight band in between offering anything close to moderate conditions.
None of this rules out life outright. Some models suggest a strong planetary magnetic field, similar to Earth’s own, could help deflect a meaningful portion of that charged radiation, and a sufficiently thick atmosphere might partially absorb the rest, the same way Venus’s dense atmosphere shields its surface today. Laboratory experiments testing UV radiation on hardy microorganisms have even found some simple life forms could plausibly survive exposure levels similar to what Proxima b experiences during a flare, though surviving one flare is a very different question from surviving billions of years of them.
So, Is It Still the Most Promising Candidate?
Its complicated, honestly. Proxima b still holds a genuinely unique advantage that no other habitable zone exoplanet can claim, sheer proximity. At just over four light-years away, it’s the closest known exoplanet to Earth by a wide margin, making it one of the only realistic targets for future direct imaging missions and, eventually, any theoretical interstellar probe. Privately funded initiatives exploring fast interstellar travel concepts have specifically cited Proxima b as a motivating destination for exactly this reason.
But “most promising” depends heavily on what you’re measuring. If the question is which known exoplanet is easiest to actually study in detail, Proxima b’s proximity makes it a clear frontrunner. If the question is which exoplanet is most likely to actually host life, the picture looks a lot less certain than it did back in 2016, given how hostile its stellar environment appears to be. Other systems, like the seven rocky planets orbiting the ultra-cool dwarf TRAPPIST-1, present a similar trade-off, tightly packed habitable zone worlds around a star that’s also prone to dangerous flaring. If comparing nearby stellar neighborhoods interests you, our full rundown of the closest star systems to Earth covers several other nearby candidates worth knowing about.
What Happens Next
Directly studying Proxima b’s atmosphere, if it has one at all, remains extremely difficult with current technology, largely because the planet hasn’t been observed transiting in front of its star from our vantage point, which is the method astronomers normally rely on to sample a planet’s atmospheric makeup. For now, scientists are mostly working from computer models, simulating how Earth’s own atmosphere and magnetic field would hold up if transplanted into Proxima b’s orbit.
Future instruments, including NASA’s proposed Habitable Worlds Observatory, are being designed specifically with nearby targets like this one in mind, aiming to directly image rocky exoplanets and search their atmospheres for genuine biosignatures rather than relying purely on indirect modeling. If you’re curious how astronomers detect planets like Proxima b in the first place, our breakdown of what an exoplanet actually is covers the detection methods behind discoveries just like this one.
The Bottom Line
Proxima Centauri b remains a genuinely fascinating world, the closest known exoplanet to Earth, sitting right in its star’s habitable zone, and still one of the very few realistic targets for detailed future study given the sheer scale of everything else out there. Whether it’s actually habitable is still an open question, and honestly, the more we learn about Proxima Centauri’s temper, the less certain the answer looks. But being close enough to actually investigate properly still counts for a lot, and that alone keeps Proxima b near the top of the list every time this conversation comes up.
For more detailed research on Proxima b’s habitability and its host star’s flare activity, check out the full coverage from NASA Science and the atmospheric modeling study from NASA’s exoplanet research team.
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