The problem of flares in red dwarf planetary systems is stark. With their habitable zones relatively near to the star, planets that might support life are exposed to huge outbursts of particles and radiation that can strip their atmospheres. We can see that in nearby M-dwarfs like Proxima Centauri, which is extremely active not only in visible light but also in radio and millimeter wavelengths. New work at the Atacama Large Millimeter/submillimeter Array (ALMA) digs into the millimeter-wavelength activity. The results do nothing to ease the concern that systems like this may be barren of life.
Small M-dwarf stars are a problem because they operate through convection as energy from fusion at the core is transferred to the surface. A convective structure is one in which hot material from below moves constantly upward, a process that can be likened to what we see in a boiling cauldron of water. Larger stars like the Sun show a mix of radiative transfer – photons being absorbed and reabsorbed as they make their way to the surface – and convection. That enhances M-dwarf flare activity as their plasma is twisted and rotated, producing magnetic fields that snap open only to reconnect. Powerful flares and outbursts of particles are the result.
For a world in an otherwise habitable region around the star, that spells danger. Meredith MacGregor (Johns Hopkins University), who worked with Kiana Burton on the flaring at Proxima Centauri, explains:
“Our Sun’s activity doesn’t remove Earth’s atmosphere and instead causes beautiful auroras, because we have a thick atmosphere and a strong magnetic field to protect our planet. But Proxima Centauri’s flares are much more powerful, and we know it has rocky planets in the habitable zone. 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?”
Image: Artist’s concept of a stellar flare from Proxima Centauri. Credit: NSF/AUI/NSF NRAO/S. Dagnello.
MacGregor and Burton have been working on what they describe as the first multi-wavelength study using millimeter observations to probe into the physics of these flares. At their disposal are 50 hours of ALMA observations, covering some 463 flare events at energies between 1024 to 1027 erg. Most of these flares end quickly, ranging in duration from 3 to 16 seconds. The operative term in the study is flare frequency distribution (FFD), which maps the number of flares against energy levels. A power law function as at optical wavelengths would mean that lower-energy flares would be expected to occur more frequently than flares of higher energy, but the team found many flares within each energy range because of the high flare activity at Proxima.
Adds MacGregor:
“The millimeter flaring seems to be much more frequent–it’s a different power law than we see at the optical wavelengths. So if we only look in optical wavelengths, we’re missing critical information. ALMA is the only millimeter interferometer sensitive enough for these measurements.”
The point is significant, and I want to dig into the paper on this:
Proxima Cen has been observed frequently at optical wavelengths, with a much shallower FFD power-law index of 1.88 ± 0.06. This significant difference could indicate a disconnect between sources of optical and millimeter emission during flares. Since optical observations of stellar flares are more readily available and often used to infer the flaring flux at other wavelengths, this result underlines the need for further multiwavelength campaigns to constrain scaling relations. In particular, the higher rate of millimeter flares compared to optical flares and the tight correlation between FUV and millimeter emission observed by M. A. MacGregor et al. (2021) may suggest that the extreme-UV radiation environment of Proxima b due to small flares is also higher than predicted from the optical flare rate.
So the flare activity at Proxima Centauri is more complicated and perhaps more dangerous than we thought. As we learn more about flaring at this star, we have to hope that Proxima Centauri b has a strong magnetic field that can mitigate the effects of this incoming stream of energy and particles. The prospect of an atmosphere being stripped of ozone and water, for example, makes modification or erosion of its gases a strong possibility. Instruments like the Square Kilometer Array may one day be capable of detecting the interactions between such a magnetic field and the star’s stellar wind. But for now, we can only wait for further data.
The paper is Burton et al., “The Proxima Centauri Campaign — First Constraints On Millimeter Flare Rates from ALMA,” Astrophysical Journal Vol 982, Number 1 (17 March 2025), 43. Preprint / Abstract.
“we have to hope that Proxima Centauri b has a strong magnetic field that can mitigate the effects of this incoming stream of energy and particles”
I doubt this will help. Our magnetic field mostly slows and redirects the particle stream from solar flares and coronal mass ejections (CME) along magnetic field lines, and still impacts the atmosphere. The interaction is complicated.
In the case of a red dwarf planets in the HZ, they are close to the star and often tidally locked. Due to the latter, the magnetic field is likely to be weak. With a strong magnetic field, the lit hemisphere will still be severely eroded. Since the atmosphere is a fluid, that will deplete the entire atmosphere. Charged particles (protons are the major threat) will follow those field lines and attack the dark side atmosphere directly.
I find it difficult to be optimistic about habitable planets around red dwarfs.
Ron, The loss should approach a limit when the atmosphere and water will freeze out on the dark side, won’t be much is my guess.
We are still speculating beyond the data. While we cannot get atmosphere composition data from Proxima Centauri b as it is not a planet detectable by transits (AFAIK), we should look at comparable stars with transiting planets and develop the technology to detect the presence and composition of their planets in their [C]HZ orbits. This should end the speculation and pave the way for elucidating habitability based on likely atmospheres even for planets around M_dwarfs of varying age that are not directly observable.
Does anyone here have any idea when our telescopes might be able to detect rocky planet atmospheres rather than those of gas giants?
We also don’t know how old the Proxima Centauri system is, but we think it is a little older than our Sun. Consequently, Proxima b may have lost a lot of atmosphere through solar wind stripping and the extra energy from the ultra violet and x rays and photolysis of carbon dioxide into oxygen and carbon and water vapor can cause oxygen gas escape. Google AI
The extremely large telescope won’t be ready until 2028, but it will have a chronograph and even light polarization techniques. Getting some spectral lines of Proxima b will be revealing of it’s atmospheric history.
https://astrobiology.com/2025/08/webb-finds-new-evidence-for-a-large-planet-orbiting-in-the-habitable-zone-of-alpha-centauri-a.html
Webb Finds New Evidence For A Large Planet Orbiting in The Habitable Zone Of Alpha Centauri A
By Keith Cowing
Press Release
ESA
August 7, 2025
Astronomers using the NASA/ESA/CSA James Webb Space Telescope have found strong evidence of a giant planet orbiting a star in the stellar system closest to our own Sun. At just 4 light-years away from Earth, the Alpha Centauri triple star system has long been a compelling target in the search for worlds beyond our solar system.
Visible only from Earth’s Southern hemisphere, it’s made up of the binary Alpha Centauri A and Alpha Centauri B, both Sun-like stars, and the faint red dwarf star Proxima Centauri. Alpha Centauri A is the third brightest star in the night sky. While there are three confirmed planets orbiting Proxima Centauri, the presence of other worlds surrounding Alpha Centauri A and Alpha Centauri B has proved challenging to confirm.
Now, Webb’s observations from its Mid-Infrared Instrument (MIRI) are providing the strongest evidence to date of a gas giant orbiting Alpha Centauri A. The results have been accepted in a series of two papers in The Astrophysical Journal Letters.
If confirmed, the planet would be the closest to Earth that orbits in the habitable zone of a Sun-like star. However, because the planet candidate is a gas giant, scientists say it would not support life as we know it.
“With this system being so close to us, any exoplanets found would offer our best opportunity to collect data on planetary systems other than our own. Yet, these are incredibly challenging observations to make, even with the world’s most powerful space telescope, because these stars are so bright, close, and move across the sky quickly,” said Charles Beichman, NASA’s Jet Propulsion Laboratory and the NASA Exoplanet Science Institute at Caltech’s IPAC astronomy center, co-first author on the new papers.
“Webb was designed and optimized to find the most distant galaxies in the universe. The operations team at the Space Telescope Science Institute had to come up with a custom observing sequence just for this target, and their extra effort paid off spectacularly.”
Several rounds of meticulously planned observations by Webb, careful analysis by the research team, and extensive computer modeling helped determine that the source seen in Webb’s image is likely to be a planet, and not a background object (like a galaxy), foreground object (a passing asteroid), or other detector or image artifact.
The first observations of the system took place in August 2024, using the coronagraphic mask aboard MIRI to block Alpha Centauri A’s light. While extra brightness from the nearby companion star Alpha Centauri B complicated the analysis, the team was able to subtract out the light from both stars to reveal an object over 10,000 times fainter than Alpha Centauri A, separated from the star by about two times the distance between the Sun and Earth.
While the initial detection was exciting, the research team needed more data to come to a firm conclusion. However, additional observations of the system in February 2025 and April 2025 (using Director’s Discretionary Time) did not reveal any objects like the one identified in August 2024.
“We are faced with the case of a disappearing planet! To investigate this mystery, we used computer models to simulate millions of potential orbits, incorporating the knowledge gained when we saw the planet, as well as when we did not,” said PhD student Aniket Sanghi of the California Institute of Technology in Pasadena, California. Sanghi is a co-first author on the two papers covering the team’s research.
In these simulations, the team took into account both the 2019 sighting of a potential exoplanet candidate by the European Southern Observatory’s Very Large Telescope, the new data from Webb, and considered orbits that would be gravitationally stable in the presence of Alpha Centauri B, meaning the planet wouldn’t get flung out of the system.
Researchers say a non-detection in the second and third round of observations with Webb isn’t surprising.
“We found that in half of the possible orbits simulated, the planet moved too close to the star and wouldn’t have been visible to Webb in both February and April 2025,” said Sanghi.
Based on the brightness of the planet in the mid-infrared observations and the orbit simulations, researchers say it could be a gas giant approximately the mass of Saturn orbiting Alpha Centauri A in an elliptical path varying between 1 to 2 times the distance between Sun and Earth.
“These are some of the most demanding observations we’ve done so far with MIRI’s coronagraph,” said Pierre-Olivier Lagage, of CEA, France, who is a co-author on the papers and was the French lead for the development of MIRI. “When we were developing the instrument we were eager to see what we might find around Alpha Centauri, and I’m looking forward to what it will reveal to us next!”
“If confirmed, the potential planet seen in the Webb image of Alpha Centauri A would mark a new milestone for exoplanet imaging efforts,” Sanghi says. “Of all the directly imaged planets, this would be the closest to its star seen so far. It’s also the most similar in temperature and age to the giant planets in our solar system, and nearest to our home, Earth,” he says. “Its very existence in a system of two closely separated stars would challenge our understanding of how planets form, survive, and evolve in chaotic environments.”
If confirmed by additional observations, the team’s results could transform the future of exoplanet science.
“This would become a touchstone object for exoplanet science, with multiple opportunities for detailed characterization by Webb and other observatories,” said Beichman.
This 3-panel image captures the NASA/ESA/CSA James Webb Space Telescope’s observational search for a planet around the nearest Sun-like star, Alpha Centauri A. The initial image shows the bright glare of Alpha Centauri A and Alpha Centauri B, then the middle panel shows the system with a coronagraphic mask placed over Alpha Centauri A to block its bright glare. However, the way the light bends around the edges of the coronagraph creates ripples of light in the surrounding space. The telescope’s optics (its mirrors and support structures) cause some light to interfere with itself, producing circular and spoke-like patterns. These complex light patterns, along with light from the nearby Alpha Centauri B, make it incredibly difficult to spot faint planets. In the panel at the right, astronomers have subtracted the known patterns (using reference images and algorithms) to clean up the image and reveal faint sources like the candidate planet.
[Image description: Three panels, each showing a different view of the binary star system Alpha Centauri from the Webb. The left panel shows a rectangular image tilted at a 45 degree angle outlined in white on a grey background. The image is a blown-out bright source at the center, with 8, double columned reddish white diffraction spikes. The center of this bright source is outlined with a vertical box, tilted slightly to the left, with two diagonal lines leading to the second panel. This shows a view of both Alpha Centauri A at the bottom and Alpha Centauri B at the top, both with orange star icons over each star. The star icons are surrounded by mottled red and white blotches. The bottom star is outlined with a white square with two diagonal lines leading to the third panel. Within a large white circle there is a blurry red-toned field with an orange star icon and central black circle outlined in white marking the location of Alpha Cen A. A bright orange blob at 9 o’clock in relation to the star is labeled “S1” and circled.]
Credit: NASA, ESA, CSA, STScI, A. Sanghi (Caltech), C. Beichman (JPL), D. Mawet (Caltech), J. DePasquale (STScI)
More information
Webb is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope’s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.
Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).
Image Credit: NASA, ESA, CSA, STScI, R. Hurt (Caltech/IPAC)
Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits
https://astrobiology.com/2025/08/worlds-next-door-a-candidate-giant-planet-imaged-in-the-habitable-zone-of-%CE%B1-cen-a-i-observations-orbital-and-physical-properties-and-exozodi-upper-limits.html
Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. II. Binary II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis
https://astrobiology.com/2025/08/worlds-next-door-a-candidate-giant-planet-imaged-in-the-habitable-zone-of-%ce%b1-cen-a-ii-binary-ii-binary-star-modeling-planet-and-exozodi-search-and-sensitivity-analysis.html
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