Montreal Space Symposium 2019

ÉPPÉ (Extrasolar Planet Polarimetry Explorer / Explorateur polarimétrique des planètes extrasolaires) is a proposed concept for a microsatellite mission that would use time-resolved differential polarimetry to characterize known exoplanets (hot Jupiters, Neptunes, super Earths) and serve as a pathfinder for spectropolarimetric exoplanet biomarker detection. Exoplanet characterization is a top astrophysical science priority as enunciated by the NASA Exoplanet Exploration Program, the CASCA (Canadian Astronomical Society) 2011–2020 Long Range Plan, the Space Astronomy Origins and Planetary Systems Astrobiology topical team reports of the CSEW (Canadian Space Exploration Workshop), and ESA Cosmic Vision 2015-2025.

One of the limitations of current and future precision transit photometry and spectroscopy is that clouds and hazes prohibit spectroscopic feature detection. Vetting of a prospective exoplanet target prior to investing observation resources for detailed spectroscopy is therefore critical. The differential polarimetry capabilities of ÉPPÉ would be uniquely sensitive to polarized scattered light (dust, clouds, haze). So far, ground-based polarimeters have struggled to reach the 1 part-per-million level of precision required to detect scattered light from an exoplanet. By going to a dawn-dusk, Sun-synchronous orbit, we nearly eliminate the two major suspects for uncalibrated instrumental noise in ground-based measurements: the thermal stability of the optical setup and flexure of the optics at different telescope orientations.

The notional ÉPPÉ concept consists of a polarimetry instrumentation payload with a 30 cm aperture operating in the 300-800 nm band from a 180 kg class spacecraft in low-Earth orbit. ÉPPÉ is currently being advanced under a concept study funded by the Canadian Space Agency (CSA). In addition to defining the science requirements and developing technical concepts for the mission, spacecraft, and payload, planning for education and public outreach is also an integral component of the study.