Miniaturized Radiometer for an Ice Giants mission for haze and cloud characterization
Authors: Apéstigue Víctor , Toledo Daniel , Arruego Ignacio , Irwin Patrick , Rannou Pascal , Gonzalo Alejandro , Jiménez Juan José , Martínez-Oter Javier , Yela Margarita , Sorribas Mar , Sebastian Eduardo 
Published: February 2023

Uranus and Neptune, the Ice Giants, are the unique planets in the Solar System that have not received a dedicated mission. However, studying these planets is crucial for understanding the formation and evolution of our planetary system and the outer systems, for which the ice planet systems are very common.Our current knowledge comes from Earth and space telescope limited observations and from the brief encounter with the Voyager 2 spacecraft almost three decades ago. The recent decadal survey [1] has established a flag mission to Uranus as the following strategic priority for the Nasa exploration program (apart from the ongoing missions to Mars and Europa). From ESA&#8217;s perspective, the outcomes from the Voyage 2050 [2] are also in alignment, recommending the agency&#8217;s participation in a future mission in a collaboration framework, as established in previous successful partnerships like Cassini-Huygens.Several reference missions have been proposed during the last decade [3-4], most of them suggesting an orbiter plus a descent probe configuration. For the orbiter, the scientific priorities should be to study the planet's bulk composition and internal structure, magnetic field, atmosphere circulation, rings, and satellite system. In the case of the descent probe, its primary mission should be to obtain the atmospheric noble gas abundances, noble gas isotope ratios, and the thermal structure of the atmosphere using a mass spectrometer and a meteorological package.Understanding the thermal structure and dynamics of Uranus&#8217; atmosphere requires studying the vertically distributed aerosols (hazes and clouds) and their microphysical and scattering properties. Indeed, aerosols affect the absorption and reflection of solar radiation, directly affecting the energy balance that drives the planet. In this work we present a lightweight radiometer, as a part of the descending probe, dedicated to studying Uranus&#8217;s aerosols. The principle of measurement is based on the vertical variation of the solar radiance at different wavelengths and geometries of observations as the probe falls using photodetectors, field-of-view masks, and interferential filters. From these observations, information on the vertical structure of clouds and hazes, particle size, or scattering properties could be derived.The radiometer takes its heritage from previous missions for Mars exploration [7-9] where its technology has demonstrated its endurance for extreme environments of operation, using limited resources in terms of power consumption, mass and volume footprints, and data budget. These characteristics make this instrument a valuable complementary probe&#8217;s payload for studying Uranus&#8217; atmosphere with a high scientific return.&#160;[1] Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032.&#160; [2] Linda J. Tacconi, Christopher S. Arridge, et al, Voyage2050 Final recommendations from the Voyage 2050 Senior Committee. [3] Christopher S. Arridge, et al.. 2012. [4] Sushil K.AtreyaaMark, et al.,2019 [5] Ian J. Cohen et al 2022 P [6] Athul Pradeepkumar Girija.&#160; 2023&#160;[7] I. Arruego et al. 2017. [8] Apestigue, V. et al 2022 [9] P&#233;rez-Izquierdo, J., Sebasti&#225;n et al, 2016.