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Far-Infrared Remote Sensing for the Uranus Flagship Orbiter

Presentation #311.09 in the session Future Missions and Instrumentations - Icy Bodies, Exoplanets, Stars (Poster)

Published onOct 23, 2023
Far-Infrared Remote Sensing for the Uranus Flagship Orbiter

Science Rationale: Remote sensing spectroscopy is a powerful tool to investigate physical and chemical processes in planetary environments. Far-infrared (far-IR) measurements enable retrieving temperature, dynamics, and chemical composition in atmospheres, as well as temperatures and thermal inertia of surfaces. At the cold temperatures in the Uranus system, the optimal wavelength region for remote-sensing of thermal emission is in the far-IR. A high spectral resolving power (R>106) heterodyne spectrometer operating in the far-IR at 240 µm wavelength on the Uranus Orbiter will enable mapping temperature and composition in the stratosphere as well as meridional circulation and the decay of zonal winds with height. High spectral resolution enables measuring stratospheric zonal winds by Doppler shift, complementing cloud-tracking that probes deeper levels. The spatial extent, temperature, and time evolution of the polar vortex on Uranus also is measurable. The 240-µm wavelength region includes transitions of CH4, CO, H2O, NH3, H2S, and HCN, with CH4 and CO probing stratospheric temperature. Measurements of stratospheric H2O with latitude will constrain the source of icy micrometeoroids.

The far-IR also can map the spatial variation of surface temperature on the Uranian satellites. Thermal inertia measurements derived from day- and night-side temperatures, combined with imaging and near-IR spectroscopy, can reveal the nature of materials on each satellite. The location of elevated temperatures would inform a search for cryovolcanism-driven plumes from the Uranian satellites, and emission lines of any of the targeted volatiles would help constrain plume composition. Escaping volatiles may form a torus around Uranus, such as the Enceladus-driven water torus around Saturn. A far-IR receiver could also determine the spatial extent of such a torus.

Submillimeter Technology: Recent advances with the development of the Wideband Imaging Submillimeter Heterodyne Spectrometer (WISHeS) indicate a path to integrate imaging receiver front-end, photonic signal processing, and ASIC digital filter banks in a receiver [1] with continuum and wideband spectroscopic capability. A smaller version of WISHeS operating at 240 µm can be developed in a SWAP suitable for use on the Uranus Orbiter with ~10 kg mass and ~10W power. A spatial resolution of ~3 mrad is achievable with a 10-cm diameter antenna dish.

References:

[1] Gambacorta (2023) JSTARS, In press.

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