2490

Antonija Oklopcic

Atmospheric escape in exoplanet atmospheres

Atmospheric escape can have a profound influence on the extent, composition, and
evolution of planetary atmospheres, particularly those at short distances from
their host stars. These planets are exposed to intense stellar radiation that
can cause significant mass loss of their atmospheres and leave signatures of
this process imprinted in the demographics of planetary systems. For example,
the observed lack of Neptune-size planets at short periods (the 'hot Neptune
desert') and the under-abundance of planets with radii between 1.5 and 2 Earth
radii (the 'radius valley') have both been predicted by models of planetary
evolution dominated by atmospheric escape. By investigating its effects on the
overall exoplanet population, the driving mechanism behind atmospheric escape
could be revealed. However, at present, it seems that the demographic properties
can be equally well explained by the photoevaporation model, in which
atmospheric mass loss is caused by the high-energy radiation of the host star,
and the core-powered escape model, in which the energy driving atmospheric
escape is a combination of the energy leftover from the planet's formation and
the stellar bolometric luminosity. Atmospheric escape can also be studied 'in
action', as it happens in individual planets. Transmission spectroscopy of
close-in exoplanets at wavelengths corresponding to strong atomic transitions,
such as the hydrogen Lyman-alpha line or the helium 1083 nm triplet, can be used
to probe the upper atmospheres of exoplanets and measure the properties and the
dynamics of planetary outflows. This talk will review the recent and upcoming
observational and modeling efforts aimed at improving our understanding of the
atmospheric-escape physics and its effect on the evolution of exoplanet
atmospheres.