  Characterizing habitable exoplanets and/or their moons is of paramount
importance. Here we show the results of our magnetic field topological modeling
which demonstrate that terrestrial exoplanet-exomoon coupled magnetospheres
work together to protect the early atmospheres of both the exoplanet and the
exomoon. When exomoon magnetospheres are within the exoplanet's magnetospheric
cavity, the exomoon magnetosphere acts like a protective magnetic bubble
providing an additional magnetopause confronting the stellar winds when the
moon is on the dayside. In addition, magnetic reconnection would create a
critical pathway for the atmosphere exchange between the early exoplanet and
exomoon. When the exomoon's magnetosphere is outside of the exoplanet's
magnetosphere it then becomes the first line of defense against strong stellar
winds, reducing the exoplanet's atmospheric loss to space. A brief discussion
is given on how this type of exomoon would modify radio emissions from
magnetized exoplanets.
