  Beyond Earth-like planets, moons can be habitable, too. No exomoons have been
securely detected, but they could be extremely abundant. Young Jovian planets
can be as hot as late M stars, with effective temperatures of up to 2000 K.
Transits of their moons might be detectable in their infrared photometric light
curves if the planets are sufficiently separated ($\gtrsim10$ AU) from the
stars to be directly imaged. The moons will be heated by radiation from their
young planets and potentially by tidal friction. Although stellar illumination
will be weak beyond 5 AU, these alternative energy sources could liquify
surface water on exomoons for hundreds of Myr. A Mars-mass H$_2$O-rich moon
around $\beta$ Pic b would have a transit depth of $1.5\times10^{-3}$, in reach
of near-future technology.
