APEx research focuses on exoplanet atmosphere characterization, from the ground and space. Small planets, big planets, transits, direct imaging, theoretical modeling (1D, 3D, interior), instrumentation (esp ground-based high-res) - we love it all!

My money is on bare rock for both planets - this simple explanation fits the data well, no fine-tuning needed. This may disappoint some folks, but I think it's amazing that we can measure this at all!! if atmospheres are rare on rocky planets orbiting M-dwarfs, that is a profound thing to know.

There *are* still some atmospheres that are compatible with the data, but the parameter space is shrinking - can't have too high surface pressure (> 1 bar) or too much CO2 (> 100 ppm or so). These scenarios are a bit finely tuned - a bare rock or thick, Venus-like atmosphere are easier to produce.

Now, we have a joint thermal phase curve for the planets, finding no significant heat redistribution from dayside to nightside. Here are the constraints on dayside and nightside temperature (K) for the planets. Dayside is red, nightside is blue, top row is planet b, and bottom row planet c.

Previous measurements of thermal emission from planet b were consistent with either a bare rock or a thermal inversion in a CO2-rich atmosphere (arxiv.org/abs/2412.11627). Planet c was best fit by a moderately reflective surface or a thin atmosphere with not too much CO2.

you did it!!!! 🙌

Compared to other planets in this temperature range, HD 86226c is surprisingly featureless ... indicative of either very high metallicity (which might have helped it survive in this intense irradiation environment), or high-altitude clouds. Or both!

I had fun writing this with @stevensonanddone.bsky.social! thanks for being a great writing buddy!

Even though no atmospheres have been unequivocally detected, we're optimistic about the future! JWST's performance is excellent: with a larger sample of planets, more precise transmission spectra, and pushing to cooler targets, we are confident that atmospheres can be found (if they are there!).

The emission measurements are consistent with very hot daysides (ave. temp is 95% the maximum expected for a zero albedo bare rock). While some atmosphere scenarios are compatible with individual measurements, the ensemble of data is well fit by a simple picture where all the planets are bare rocks.

The transmission spectra are not (yet) precise enough to definitively detect molecules in many high MMW atmospheres. As a goal for future observations, we suggest a "five scale challenge" - reaching the precision needed to detect a CO2 feature in a nitrogen-rich atmosphere (like Earth's).