  At 30-50 K, the temperatures typical for surfaces in the Kuiper Belt (e.g.
Stern & Trafton 2008), only seven species have sublimation pressures higher
than 1 nbar (Fray & Schmitt 2009): Ne, N$_2$, CO, Ar, O$_2$, CH$_4$, and Kr. Of
these, N$_2$, CO, and CH$_4$ have been detected or inferred on the surfaces of
Trans-Neptunian Objects (TNOs). The presence of tenuous atmospheres above these
volatile ices depends on the sublimation pressures, which are very sensitive to
the composition, temperatures, and mixing states of the volatile ices.
Therefore, the retention of volatiles on a TNO is related to its formation
environment and thermal history. The surface volatiles may be transported via
seasonally varying atmospheres and their condensation might be responsible for
the high surface albedos of some of these bodies. The most sensitive searches
for tenuous atmospheres are made by the method of stellar occultation, which
have been vital for the study of the atmospheres of Triton and Pluto, and has
to-date placed upper limits on the atmospheres of 11 other bodies. The recent
release of the Gaia astrometric catalog has led to a "golden age" in the
ability to predict TNO occultations in order to increase the observational data
base.
