  X-ray observations of star-planet systems are important to grow our
understanding of exoplanets; these observation allow for studies of
photoevaporation of the exoplanetary atmosphere, and in some cases even
estimations of the size of the outer planetary atmosphere. The German-Russian
eROSITA instrument onboard the SRG (Spectrum Roentgen Gamma) mission is
performing the first all-sky X-ray survey since the 1990s, and provides X-ray
fluxes and spectra of exoplanet host stars over a much larger volume than was
accessible before. Using new eROSITA data as well as archival data from
XMM-Newton, Chandra and ROSAT we estimate mass loss rates of exoplanets under
an energy-limited escape scenario, and identify several exoplanets with strong
X-ray irradiation and expected mass-loss that are amenable to follow-up
observations at other wavelengths. We model sample spectra using a toy model of
an exoplanetary atmosphere to predict what exoplanet transit observations with
future X-ray missions such as Athena will look like, and estimate the
observable X-ray transmission spectrum for a typical Hot Jupiter-type
exoplanet.
