At a mere 4.24 light-years from Earth, Proxima Centauri holds the distinction of being our closest stellar neighbor. Nestled within the Alpha Centauri star system, this small but mighty red dwarf has long fascinated astronomers—not just because of its proximity, but also because it harbors at least one Earth-sized planet within its habitable zone. The possibility of life on Proxima Centauri b has tantalized scientists for years. However, recent observations using the Atacama Large Millimeter/submillimeter Array (ALMA) have unveiled a stark reality: Proxima Centauri is an extremely active star, bombarding its planetary system with powerful stellar flares and streams of energetic particles that may render its planets uninhabitable.
This research, led by Kiana Burton (University of Colorado) and Meredith MacGregor (Johns Hopkins University), offers an unprecedented glimpse into Proxima Centauri’s violent nature—especially in radio and millimeter wavelengths. Their findings, published in The Astrophysical Journal, provide critical insights into how stellar activity impacts planetary atmospheres and, ultimately, the potential for life beyond Earth.
A Star Unlike Our Sun
Though Proxima Centauri is much smaller than our Sun—roughly one-seventh the Sun’s diameter and about 12% of its mass—it is vastly more active. Unlike our Sun, which has a stable outer layer and separate convective zones, Proxima Centauri is fully convective. This means that its interior is constantly churning, allowing magnetic fields to twist, accumulate stress, and eventually snap, unleashing massive flares into space.
These flares release energy across the entire electromagnetic spectrum, from visible light to high-energy X-rays and millimeter radio waves. While the Sun produces solar flares as well, Earth’s thick atmosphere and strong magnetic field act as shields, preventing these bursts from stripping away essential atmospheric components.
However, the question MacGregor and her team seek to answer is far more pressing for exoplanet habitability:
“What are these flares doing to their atmospheres? Is there such a large flux of radiation and particles that the atmosphere is getting chemically modified, or perhaps completely eroded?”
If Proxima Centauri’s planets lack strong magnetic fields or thick atmospheres, their habitability could be seriously compromised.
A Torrent of Flares: ALMA’s Breakthrough Observations
Until now, astronomers have mostly studied Proxima Centauri’s flares in visible and ultraviolet wavelengths. But Burton, MacGregor, and their colleagues took a different approach, analyzing archival data and new millimeter-wave observations from ALMA—a powerful observatory in Chile known for its ability to detect faint radio emissions from distant objects.
By sifting through 50 hours of ALMA observations, the team identified a staggering 463 individual flare events, with energies ranging from 10²⁴ to 10²⁷ ergs. For comparison, a typical solar flare on our Sun releases around 10²⁶ ergs—meaning some of Proxima Centauri’s flares are on par with, or even more powerful than, our Sun’s strongest outbursts.
What’s even more fascinating is how these flares behave. Unlike many stellar eruptions that peak and fade symmetrically, Proxima Centauri’s strongest flares exhibit an asymmetrical decay phase, meaning they linger for much longer than their initial burst. This slow decay could have profound implications for planetary atmospheres, exposing them to sustained radiation bombardment.
The Hidden Power of Millimeter-Wavelength Flares
One of the most groundbreaking aspects of this research is the realization that millimeter-wavelength flares are more frequent than optical flares, following a different power law distribution.
Traditionally, scientists have assumed that stellar flares behave in a predictable manner: smaller, less energetic flares are more common, while larger, more energetic ones are rare. However, ALMA’s data suggests that at millimeter wavelengths, these flares don’t quite follow the expected pattern—there are more frequent high-energy flares than previously believed.
MacGregor highlights why this is significant:
“If we only look in optical wavelengths, we’re missing critical information. ALMA is the only millimeter interferometer sensitive enough for these measurements.”
This means that past studies may have underestimated the total amount of energy being released by Proxima Centauri’s flare activity. It also suggests that energetic particles from these flares are much more abundant than previously thought.
The Impact on Proxima Centauri b and Other Planets
The big question remains: Can Proxima Centauri b sustain an atmosphere in the face of such extreme stellar activity?
This Earth-sized planet orbits its host star at a distance of 0.05 AU (just 5% of the distance between Earth and the Sun), placing it firmly within the habitable zone, where liquid water could exist. However, this proximity also means it is subjected to intense radiation and stellar winds.
If Proxima Centauri’s flares are frequent and energetic enough, they could strip away the planet’s atmosphere, preventing it from retaining crucial elements like ozone and water vapor. This would make it difficult—if not impossible—for life as we know it to survive on the surface.
However, there’s still hope. Some exoplanet models suggest that if Proxima Centauri b has a strong magnetic field, similar to Earth’s, it might be able to deflect some of these charged particles, reducing the damage to its atmosphere. Alternatively, if the planet has a thick enough atmosphere, it could partially absorb the impact, much like how Venus’s dense atmosphere shields it from solar radiation.
Future Observations and the Hunt for Habitability
Understanding the full impact of Proxima Centauri’s extreme flares is crucial—not just for assessing its own planets, but for studying exoplanets around other M dwarf stars. Red dwarfs are the most common type of star in the galaxy, and many of the potentially habitable exoplanets discovered by missions like Kepler and TESS orbit stars just like Proxima Centauri.
If flare activity turns out to be a universal feature of M dwarfs, habitability around these stars may be far more challenging than previously assumed.
Future missions, such as the James Webb Space Telescope (JWST) and upcoming radio observatories, will provide even more detailed observations of these exoplanetary atmospheres, helping scientists determine whether planets like Proxima Centauri b have retained their atmospheres—or if they are barren, radiation-scorched wastelands.
Conclusion: A Chaotic Star with Deep Implications
Proxima Centauri’s newly revealed millimeter-wavelength flares have reshaped our understanding of stellar activity and the potential habitability of exoplanets. Thanks to ALMA’s unprecedented sensitivity, astronomers can now probe the energetic particle emissions from stars like never before, opening new avenues for research into how stellar environments shape planetary evolution.
While Proxima Centauri remains an exciting candidate for future exploration, this study reminds us of a harsh truth: life beyond Earth may not just depend on finding the right planet—but also on finding the right star.
Reference: Kiana Burton et al, The Proxima Centauri Campaign—First Constraints on Millimeter Flare Rates from ALMA, The Astrophysical Journal (2025). DOI: 10.3847/1538-4357/ada5f2