JWST confirms GJ 1132 b lacks an environment. This challenges the habitability of planets round M-dwarfs.
Astronomers usually encounter conflicting outcomes when investigating cosmic questions. It is a regular facet of the scientific methodology, because it highlights the necessity for extra information to substantiate or reject a speculation.
A distinguished instance in exoplanet research involves GJ 1132 b, where different observations alternately suggested the planet had an atmosphere or none at all. Using extended observation time with the James Webb Space Telescope (JWST), researchers now report that GJ 1132 b almost certainly lacks an atmosphere, a conclusion that carries broader consequences for the study of exoplanets.
A rocky world under scrutiny
GJ 1132 b orbits a nearby M-dwarf star about 41 light-years away. The planet has drawn significant attention because it is both similar to Earth in some respects and entirely alien in others. It is rocky, with a radius and mass only slightly greater than Earth’s. Yet it lies just 0.0153 AU from its host star and completes an orbit in only 1.6 days. Given its close proximity, it seems unlikely that the planet could retain an atmosphere, although some theoretical models suggest that even worlds so near to M-dwarfs might be able to hold on to one.
The question matters because M-dwarfs are highly active stars, emitting strong radiation and frequent flares that can strip atmospheres away. To address this, astronomers have developed the concept of a “cosmic shoreline,” which describes the threshold of stellar irradiation and planetary size beyond which a planet can no longer maintain an atmosphere.
Artist’s impression of GJ 1132 b – which now ought to be up to date given its definitive lack of environment. Credit score: NASA/JPL-Caltech/Robert Hurt
This new study directly engages with that debate and builds on earlier work. Previous JWST observations of two planetary transits produced conflicting results: one indicated a water-rich atmosphere, while the other suggested no atmosphere at all. By analyzing two additional transits, the researchers found that the evidence overwhelmingly supports the conclusion that GJ 1132 b is most likely airless.
Considering a thin steam layer
There is still room in the data for the possibility of a very low pressure (around 1 mbar) “steam” atmosphere, but most astronomers think that is not possible for this particular planet, given the proximity to its star and its seeming lack of water, which was noted in previous JWST studies. Importantly, even that possibility goes away almost completely if the first data set (i.e. the one pointing to a water atmosphere) isn’t used in the analysis – meaning three other data sets agree that GJ 1132 b doesn’t have an atmosphere.
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As soon as they realized that, the authors went again to take a look at what might need made the primary information set so out of line with the opposite three. When trying on the star itself, it turned clear that there have been extra “cool spots” on the star’s floor than throughout the different three transits, which influenced the information collected in regards to the planet itself. The authors consider that may have been what made it appear like the planet had an environment in a single dataset, when it actually didn’t. As a part of this discovering, the authors counsel utilizing a “leave-one-out” strategy for exoplanet datasets when a couple of is obtainable, particularly if the star is very variable.
Strategies and JWST instrumentation
One other vital characteristic of this paper is the strategies used to gather the information. It used two completely different viewing modes of the NIRSpec instrument onboard JWST – G395H and G395M. G395H is increased decision, whereas the G395M viewing mode is “medium” decision. The trade-off is that the G395H mode has a “hole” in its information between 3.75um and three.82 um, which may affect the information. Nonetheless, the authors discovered this wasn’t an issue, with the noise comparable between the 2 modes. Their suggestion is to make use of the medium decision mode if solely capturing one exoplanet transit, but it surely’s most likely secure to simply use the excessive decision mode if allotted time for a couple of.
Finally, this paper fairly clearly places to relaxation the concept GJ 1132 b has an environment – particularly any type of thick one. It additionally affords options for ensuring the type of confusion that occurred for this explicit planet doesn’t occur once more in different research of exoplanet atmospheres. However maybe most significantly, it’s one other information level within the ongoing debate about whether or not planets round M-dwarf stars can maintain on to their atmospheres – and it seems to firmly assist the concept they’ll’t.
Reference: “Further JWST/NIRSpec Transits of the Rocky M Dwarf Exoplanet GJ 1132 b Reveal a Featureless Spectrum” by Katherine A. Bennett, Ryan J. MacDonald, Sarah Peacock, Junellie Perez, E. M. Might, Sarah E. Moran, Lili Alderson, Jacob Lustig-Yaeger, Hannah R. Wakeford, David Ok. Sing, Kevin B. Stevenson, Natasha E. Batalha, Mercedes López-Morales, Munazza Ok. Alam, Joshua D. Lothringer, Guangwei Fu, James Kirk, Jeff A. Valenti, L. C. Mayorga and Kristin S. Sotzen, 9 September 2025, The Astronomical Journal.
DOI: 10.3847/1538-3881/adf198
Tailored from an article initially printed on Universe Immediately.
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