The ocean worlds science case for the Pollux spectropolarimeter

Abstract

Pollux is a candidate European instrument contribution to the Habitable Worlds Observatory (HWO), designed to advance our understanding of the formation and evolution of cosmic structures in the universe, and specifically search signs of life on extrasolar planets. This high-resolution spectrograph (R\,$>$\,40,000) with polarimetric capabilities offers nearly continuous and simultaneous coverage from the FUV ($\sim$100\,nm) to the NIR ($\sim$1.9\,$\micron$), making it a versatile tool for a wide range of scientific investigations from solar system studies to cosmology. Several Solar System ocean worlds have been the focal point of the scientific community to understand the conditions of their internal saline oceans, as well as the possible emergence of life beyond Earth. The ocean world science case will leverage Pollux's UV spectropolarimetric capabilities to investigate surface reflectance and composition, characterize airglow emissions in the environments of giant-planet moons, as well as constrain the microphysical properties of atmospheric aerosols.

Figures (5)

• Figure 1: Summary of the current properties of the Pollux instrument. The spectral resolution is defined as $\lambda$/$\Delta \lambda$. Point-source spectroscopy traditionally involves injecting the light into a narrow aperture, while slit spectroscopy is optimized for spatially-extended sources.
• Figure 2: Pollux instrument concept schematic diagram.
• Figure 3: Polarization curves measured at eight wavelengths (from 327 nm to 1.05 $\micron$m) for Mare Tranquillitatis on the lunar surface. From Dollfus1971.
• Figure 4: Comparison of polarization–phase curves for a range of Solar System bodies, including the Moon, Deimos, Europa, Callisto, Enceladus, Rhea, Iapetus, and the Uranian moons Ariel, Titania, Oberon, and Umbriel. For reference, E- and S-type asteroids, Centaurs (Chiron, Pholus), and trans-Neptunian objects (Ixion, Varuna) are also shown. The corresponding geometric albedos (A$_g$) are listed. The letters L and T corresponds to the leading and trailing hemisphere of given moons. From Rosenbush2015, and references therein.
• Figure 5: Spatial resolution of an 8-m diameter HWO telescope at the distance of Jupiter (5.2 AU) as a function of wavelength (Personal communication from K. France). The solid black curve shows the linear footprint on the surface. Colored shaded regions indicate the wavelength bands relevant for ultraviolet, visible, and near-infrared observations: FUV (100–123 nm), FMUV (101–236 nm), NUV (234–472 nm), visible (472–944 nm), and NIR (944–1888 nm).