Transits of extrasolar moons around luminous giant planets

Abstract

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 ( 10 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 β Pic b would have a transit depth of 1.5 × 10 −3 , in reach of near-future technology.

Exploring exomoon atmospheres with an idealized general circulation model

“…On the one hand, the habitability of some exomoon systems may therefore be precluded based upon the presence of a luminous host planet, although planetary illumination itself does not necessarily limit an exomoon's habitability (Heller 2016). On the other hand, we expect polar amplification of warming in all cases, which may suggest that exomoons in orbit around a luminous host planet may be less likely to develop polar ice caps.…”

“…In terms of the odds of an actual detection of the climatic effects described in this paper, this could in principle be possible if the moon's electromagnetic spectrum (either reflection or emission) could be separated from that of the planet. This might be possible in very fortunate cases where a large moon is transiting its luminous giant planet (Heller & Albrecht 2014;Heller 2016) or where both the planet and its moon transit their common low-mass host star (Kaltenegger 2010). Alternatively, if the moon is subject to extreme tidal heating, it could even outshine its host planet in the infrared and therefore directly present its emission spectrum (Peters & Turner 2013) while the planet would still dominate the visible part of the spectrum, where it reflects much more light than the moon.…”

“…At the transitional mass regime to giant planets, models of moon formation have shown that Marssized moons should commonly form around the most massive super-Jovian gas giant planets (Heller & Pudritz 2015b,a). Photometric accuracies of 10 −2 have now been achieved on BDs using the Hubble Space Telescope (Zhou et al 2016), and an improvement of about one order of magnitude should allow the detection of moons transiting luminous giant planets that can be directly imaged around their host star (Cabrera & Schneider 2007;Heller & Albrecht 2014;Heller 2016).…”

Detecting and Characterizing Exomoons and Exorings

“…One could either try and detect the shadows and transits of the moons across their host planet in the integrated (i.e. unresolved) infrared light curve of the planet-moon system (Cabrera and Schneider 2007;Heller 2016), or one could search for variations in the position of the planet-moon photocenter with respect to some reference object, e.g. another star or nearby exoplanet in the same system (Cabrera and Schneider 2007;Agol et al 2015).…”

The effect of multiple heat sources on exomoon habitable zones

“…This implies relatively small orbital separations from the star, typically < 1 AU (Szabó et al 2006). It might, however, be possible to image exomoons with extreme tidal heating (Peters and Turner 2013) or to observe the transits of moons around luminous giant planets (Heller and Albrecht 2014;Heller 2016;Sengupta and Marley 2016) at several AU from their host stars.…”