A small temperature difference between the two sides of Proxima b would suggest the presence of an atmosphere or ocean to redistribute heat whereas a large thermal contrast would indicate the planet is a dry, airless rock. (scientificamerican.com)
This suggests the presence of an atmosphere that is opaque to this specific light (making the planet appear larger), but transparent to all the others. (sciencedaily.com)
The presence of an atmosphere dims a star's light more gradually, as can be seen in this image of Pluto with an occultation illustrated for context. (space.com)