Traces of exomoons in computed flux and polarization phase curves of starlight reflected by exoplanets

Abstract

Context. Detecting moons around exoplanets is a major goal of current and future observatories. Moons are suspected to influence rocky exoplanet habitability, and gaseous exoplanets in stellar habitable zones could harbor abundant and diverse moons to target in the search for extraterrestrial habitats. Exomoons contribute to exoplanetary signals but are virtually undetectable with current methods. Aims. We identify and analyze traces of exomoons in the temporal variation of total and polarized fluxes of starlight reflected by an Earth-like exoplanet and its spatially unresolved moon across all phase angles, with both orbits viewed in an edge-on geometry. Methods. We compute the total and linearly polarized fluxes, and the degree of linear polarization P of starlight that is reflected by the exoplanet with its moon along their orbits, accounting for the temporal variation of the visibility of the planetary and lunar disks, and including the effects of mutual transits and mutual eclipses. Our computations pertain to a wavelength of 450 nm. Results. Total flux F shows regular dips due to planetary and lunar transits and eclipses. Polarization P shows regular peaks due to planetary transits and lunar eclipses, and P can increase and/or slightly decrease during lunar transits and planetary eclipses. Changes in F and P will depend on the radii of the planet and moon, on their reflective properties, and their orbits, and are about one magnitude smaller than the smooth background signals. The typical duration of a transit or an eclipse is a few hours. Conclusions. Traces of an exomoon due to planetary and lunar transits and eclipses show up in the F and P of sunlight reflected by planet–moon systems and could be searched for in exoplanet flux and/or polarization phase functions.

Collisional formation of massive exomoons of superterrestrial exoplanets

“…Observationally, several different ways have been proposed for the search of exomoons (Kipping et al 2009;Simon et al 2009;Liebig & Wambsganss 2010;Peters & Turner 2013;Heller 2014;Agol et al 2015;Noyola et al 2016;Sengupta & Marley 2016;Forgan 2017;Lukić 2017;Berzosa Molina et al 2018;Vanderburg et al 2018). Transitbased techniques are the most promising methods given current observational capabilities, e.g.…”

Explicit relations and criteria for eclipses, transits, and occultations

“…Ford et al 2011;Agol & Fabrycky 2017), for which analytic work (Agol et al 2005;Nesvorný & Morbidelli 2008;Nesvorný 2009;Lithwick et al 2012;Deck & Agol 2015;Agol & Deck 2016;Hadden & Lithwick 2016) has also yielded fruitful results. Although exoplanetary literature rarely distinguishes umbral, penumbral, and antumbral cases from one another, recently Berzosa Molina et al (2018) have analysed these different cases in flux and polarization phase curves of exoplanets with orbiting exomoons.…”

Exomoons in the Habitable Zones of M Dwarfs

“…For the majority of exoplanet-exomoon phase curves, the lunar component is undetectable to the current technology of transits observations, and future surveys would require a photometric precision of a few parts per million (Forgan 2017, but see again . Nevertheless, the detectability of exomoons has been proposed feasible with current or near-future technology and a variety of methods: microlensing (Han & Han 2002), photocentric transit timing variation (Simon et al 2007(Simon et al , 2015, modulation of planetary radio emissions (Noyola et al 2014), spectroastrometry (Agol et al 2015), polarization of transits (Berzosa Molina et al 2018), radial velocity (Vanderburg et al 2018, and transits of the plasma torus produced by a satellite (Ben-Jaffel & Ballester 2014; see the reviews by Cabrera & Schneider 2007, Perryman 2018, and Heller 2018. In particular, the European Space Agency (ESA) mission CHaraterising ExOPlanet Satellite (CHEOPS) could detect Earth-sized exomoons with the transit method (Simon et al 2015).…”