A Featureless Infrared Transmission Spectrum for the Super-puff Planet Kepler-79d

Abstract

Extremely low-density planets (“super-puffs”) are a small but intriguing subset of the transiting planet population. With masses in the super-Earth range (1 - 10 $M\oplus)andradiiakintothoseofgiantplanets(>4R\oplus),theirlargeenvelopesmayhavebeenaccretedbeyondthewatersnowlineandmanyappeartobesusceptibletocatastrophicmassloss.Boththepresenceofwaterandtheimportanceofmasslosscanbeexploredusingtransmissionspectroscopy.Here,wepresentnewHubblespacetelescopeWFC3spectroscopyandupdatedKeplertransitdepthmeasurementsforthesuperpuffKepler79d.Wedonotdetectanymolecularabsorptionfeaturesinthe1.11.7μmWFC3bandpass,andthecombinedKeplerandWFC3dataareconsistentwithaflatlinemodel,indicatingthepresenceofaerosolsintheatmosphere.WecomparetheshapeofKepler79dstransmissionspectrumtopredictionsfromamicrophysicalhazemodelthatincorporatesanoutwardparticlefluxduetoongoingmassloss.WefindthatphotochemicalhazesofferanattractiveexplanationfortheobservedpropertiesofsuperpuffslikeKepler79d,astheysimultaneouslyrenderthenearinfraredspectrumfeaturelessandreducetheinferredenvelopemasslossratebymovingthemeasuredradius(opticaldepthunitysurfaceduringtransit)tolowerpressures.Werevisitthebroaderquestionofmasslossratesforsuperpuffsandfindthattheageestimatesandmasslossratesforthemajorityofsuperpuffscanbereconciledifhazesmovethephotospherefromthetypicallyassumedpressureof10mbarto\sim 10\ \mu $ bar.

Publication
AJ