Dr. Megan Mansfield (University of Arizona)

One of the most exciting opportunities enabled by JWST is the characterization of atmospheres on terrestrial planets orbiting M Dwarfs (M-Earths). However, transmission spectroscopy of M-Earths with JWST has been ambiguous due to challenges such as stellar contamination. I will describe the technique of using thermal emission to search for atmospheres on M-Earths and present several new observations of M-Earths in thermal emission with JWST/MIRI+LRS. These observations overall show hot daysides which firmly rule out the presence of thick, Venus-like atmospheres. However, when combined with other JWST M-Earth results, they show a tentative trend in measured brightness temperature as a function of instellation, with less irradiated planets generally less consistent with dark and bare rocks. I will discuss potential hypotheses that could explain this trend and the prospects for using the ongoing Rocky Worlds DDT program to differentiate between them.