Astrobiology publishes LTT 1445A b method

Nicholas Wogan and four co-authors posted a new method paper on May 14 that aims to turn James Webb Space Telescope eclipse data from rocky exoplanets into quantitative limits on whether those worlds still have atmospheres. (arxiv.org) The study, posted on arXiv and described by Astrobiology.com, uses LTT 1445A b as its worked example. The target is a 1.34-Earth-radius rocky planet orbiting an M dwarf every 5.36 days in the nearby LTT 1445 system, according to the NASA Exoplanet Archive. The authors say the broader goal is to determine whether temperate rocky planets around M stars can retain atmospheres at all. ### Why did the authors build a new retrieval method instead of using a standard spectrum fit? (arxiv.org) The paper says standard atmospheric retrievals often use parameterized pressure-temperature profiles, while this framework fits spectra generated from self-consistent radiative-convective climate profiles. (arxiv.org) Wogan, Natasha Batalha, Jegug Ih, Jacob Lustig-Yaeger and Kevin Stevenson write that the method is designed to include planetary, stellar and model uncertainties in one Bayesian inference framework. JWST has begun searching for atmospheres on rocky planets with MIRI secondary-eclipse spectroscopy and photometry, the authors wrote, and that creates a need for methods tuned to sparse, low-signal data. Their case study focuses on eclipse measurements, which isolate the planet’s thermal emission by comparing the system’s light before and during the planet’s passage behind its star. (arxiv.org) That is the same observing approach highlighted in earlier JWST work on LTT 1445A b. ### Why was LTT 1445A b a useful test case? NASA’s Exoplanet Archive lists LTT 1445A b as a confirmed transiting planet discovered in 2019 with a radius of 1.34 Earth radii and an orbital period of 5.36 days. The new paper gives its equilibrium temperature as about 431 kelvin, placing it cooler than many previously studied hot rocky worlds. (arxiv.org) CU Boulder researchers said in a 2025 university release that earlier observations had already ruled out a light hydrogen-helium envelope for the planet but had not separated a cloudy heavy atmosphere from a bare-rock surface. (arxiv.org) That made LTT 1445A b a useful target for a method intended to decide how much atmosphere, if any, the data still permit. (exoplanetarchive.ipac.caltech.edu) ### What did the new analysis actually find for this planet? The clearest result is negative: the authors say an atmosphere does not need to be invoked to explain the existing MIRI low-resolution eclipse spectrum. (arxiv.org) In their fit, a bare-rock model is adequate. The same analysis also sets upper limits if an atmosphere is present. (colorado.edu) The paper reports 2-sigma limits of about 1 bar or less for optically thin gases such as oxygen, nitrogen or carbon monoxide, about 0.1 bar or less for carbon dioxide, about 10^-3 bar for water vapor and about 10^-4 bar for sulfur dioxide. (arxiv.org) ### How does this connect to earlier JWST results on LTT 1445A b? Pat Wachiraphan and collaborators reported in 2025 that JWST observations of three eclipses could rule out a thick carbon-dioxide atmosphere like Venus’s, according to a University of Colorado Boulder summary of that work. (arxiv.org) The new Wogan-led paper does not replace that result so much as recast the interpretation inside a climate-constrained Bayesian framework that yields pressure limits across several candidate gases. The NASA Exoplanet Archive bibliography for the system lists both the 2025 thermal-emission study and the earlier transit-based work on LTT 1445A b, showing how the target has become part of a wider effort to characterize nearby rocky planets around M dwarfs. (colorado.edu) ### What observations come next? The paper points to scheduled JWST MIRI F1500W observations as the next direct test. The authors write that those measurements could detect some of the thicker atmospheres still allowed by current data — including a 1-bar O2 atmosphere or a 0.01-bar CO2 atmosphere — if the observations reach precision of 20 parts per million or better. (arxiv.org) STScI said in a September 4, 2025 update that LTT 1445A b is one of the rocky exoplanets in the JWST Rocky Worlds Director’s Discretionary Time sample, a program built to search for atmospheres on rocky planets orbiting M dwarfs using 15-micron MIRI photometry. (exoplanetarchive.ipac.caltech.edu) The preprint is available on arXiv as 2605.14997 while the journal submission proceeds. (arxiv.org) (stsci.edu)