The KELT-11b Opportunity: Measuring the Atmospheric Water Abundance for a Sub-Saturn-Mass Planet around a Metal-Rich Star
Abstract
Measurements of exoplanet atmosphere composition provide an unparalleled window into planetary nature and origins. Water in particular is an important tracer of the planet formation process because it is a dominant component by mass of icy planetesimals. Exoplanets provide the opportunity to measure water abundance over a wide range of planet masses and thereby test predictions of planet population synthesis models. So far, however, precise constraints on water abundance have been limited to Jupiter-mass objects. Here we propose to measure the transmission spectrum of the recently discovered low density sub-Saturn KELT-11b with HST/WFC3. We will use this measurement to determine the planet's atmospheric water abundance. KELT-11b is one of the few Saturn-mass planets for which we can obtain constraints on the water abundance with a modest amount of telescope time. Our results will enable meaningful comparison with both objects in the Solar System and with the other few planets in the sub-Saturn population. This program will also be the first investigation of the metal enhancement of a planet with a metal-rich host star. Even if the atmosphere is cloudy, our data will be sufficiently precise to detect water above a 1 mbar cloud-deck, and will constrain cloud physics in a new regime of surface gravity. These measurements will set the stage for comparative planetology that will be possible with JWST.
- Publication:
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HST Proposal
- Pub Date:
- August 2017
- Bibcode:
- 2017hst..prop15255C