On the Io-type plasma source in Hot Jupiters systems

We discuss the possibility of the existence of Io-type plasma source in the exoplanetary systems from the stability point of view. We point out that close-in exoplanets possibly have no or only very small moons because of the small Hill radii defined by their proximity to the host stars. For close-in Hot Jupiters, the Hill radius is of the order of only several planetary radii. Some exoplanets, e.g. WASP-12b, are so inflated, that they are believed to fill their Roche lobes with the expanded atmosphere only. For stability reasons, the orbits of the moons have to be within the Hill sphere of their planets, this makes the very existence of the Earth- and even Io-size moons in such systems questionable, and, thus, probably also the Io-type plasma source. However, one can not exclude plasma producing exomoons orbiting in or near the Lagrange points L4 and L5. We discuss also the outgassing rates of such an exomoon in comparison to Io.