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COBRA – A compact, next-generation radiometer for determining atmospheric structure and radiative balance of ice giants, and thermophysical properties of ice giant satellites

Presentation #201.06 in the session Future Missions, Instrumentations and Facilities - Part 1 (Oral Presentation)

Published onOct 23, 2023
COBRA – A compact, next-generation radiometer for determining atmospheric structure and radiative balance of ice giants, and thermophysical properties of ice giant satellites

We present the next-generation Cold OBject RAdiometer (COBRA) concept, which is optimized for measurements at ice giants and their satellites at far infrared wavelengths. COBRA would address key scientific questions about ice giant radiative balance, ice giant atmospheric structure, and surface thermophysics of ice giant satellites. Its measurements would be an essential contribution to a Flagship mission to Uranus, identified as a high priority by the recent decadal survey. Specifically, COBRA would fulfill the following science objectives:

• Determine the radiative balance of ice giants,

• Characterize the thermal structure and understand the large-scale circulation in the upper troposphere/lower stratosphere of ice giants,

• Quantify thermal inertias and identify possible thermal anomalies on ice giant satellites.

COBRA would use passive radiometry from an ice giant orbiter at wavelengths from 0.3 to >200 µm to fulfill its science objectives. It would operate in a pushbroom scan mode, where channels with different band passes are oriented perpendicular to the direction of spacecraft motion. Atmospheric temperature profiling of an ice giant’s upper troposphere and lower stratosphere would be enabled by measuring the collision-induced H2/He continuum absorption at 26 - 43 µm in nadir geometry. Temperature information would be supplemented by measurements of ortho- to para-hydrogen ratio, which is indicative of vertical motions, and of C2H2, which acts as a chemical tracer in the stratosphere. Determination of ice giant radiative balance would be enabled by measurements of thermal emission in the mid- and far IR (8 - >200 µm) and reflected sunlight in the UV/vis./near-IR (0.3 - 5 µm) using broadband channels in nadir and off-nadir geometries that cover a wide range of emission and phase angles. Ice giant satellite science would be enabled by far IR measurements near the peak of the Planck function. Measurements at multiple wavelengths and multiple times of day would allow the derivation of thermal inertia, providing information on surface structure and porosity, and possibly reveal thermal anomalies if the moons are geologically active.

The enabling key technology for COBRA is thermopile detector arrays, which provide high sensitivity at cold temperatures without requiring cooling. COBRA has strong heritage from MCS on MRO and Diviner on LRO, which use this technology. COBRA would have ~100x more pixels with ~2x higher sensitivity per pixel compared to MCS and Diviner but with an instrument mass of only ~4.5 kg. A prototype is being developed under the MaTISSE program and is expected to reach TRL 6 in 2024.

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