Abstract

subNeptunes are low-density planets that are generally somewhat larger in radius than Earth but still considerably smaller than Uranus or Neptune. Their low densities mean that they cannot be composed primarily of rock an Iron (like Earth or Venus) but must instead have a very extensive low molecular weight volatile envelope. There are nonetheless many possible compositions and structures that can fit into the characteristics of a subNeptune. subNeptunes are very common in the catalogue of known exoplanets, and they may well be the most common kind of planet in the Universe. Temperate subNeptunes are subNeptunes that have an installation that, for a rocky planet, would put them in the nominal habitable zone, and they have attracted attention in part because of the hypothetical possibility of life in water clouds; water vapour condensation also makes them interesting from a basic dynamical standpoint. In this talk, I will discuss the radial structure of subNeptunes, the meaning of the concept of “runaway greenhouse” as applied to subNeptunes, and the general circulation of temperate subNeptune atmospheres.