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Jupiter as an Exoplanet-Analog: How do Atmospheric Color Changes Affect Unresolved Photometry?

Presentation #223.06 in the session Exoplanet Atmospheres (Poster)

Published onOct 23, 2023
Jupiter as an Exoplanet-Analog: How do Atmospheric Color Changes Affect Unresolved Photometry?

Jupiter-like exoplanets – planets with masses, semi-major axes, and ages similar to those of Jupiter – will be directly imaged in reflected light for the first time by the Coronagraph Instrument (CGI) on board NASA’s upcoming Nancy Grace Roman Space Telescope. CGI will image these exoplanets (previously detected by radial velocity) at a variety of phase angles and planet-star separations, requiring ~1-2 days of observing time for individual observations with the spacing between observations of weeks to months. From these observations, astronomers will use detailed atmospheric models to recover fundamental parameters of the exoplanet, including temperature, composition, and radius. Imaging observations of Jupiter show that gas giant planets have dynamic and colorful atmospheres that can evolve on the same timescales over which CGI will be characterizing these exoplanets. The effects that atmospheric color changes have on the disk-integrated brightness of gas giant planets, and therefore the retrieved planet parameters, is currently unknown. In this work, we treat Jupiter as a test exoplanet and measure its disk-averaged absolute reflectivity in the visible and near-infrared regimes from imaging observations by the Cassini Imaging Science Subsystem (ISS) during the Millennium flyby of Jupiter in late 2000 to early 2001. We find that color variation from rotation and weather during the Cassini flyby only causes variations in the phase curve of less than ~2%. As there were no large scale color variations on Jupiter during the Cassini flyby, such as a South Equatorial Belt fade, we inject synthetic atmospheric color changes into the Cassini ISS images and measure the variations these atmospheric color changes introduce into Jupiter’s phase curve during the flyby. We present our preliminary results on how these atmospheric color changes affect the disk-integrated brightness of Jupiter, which will provide context for how color changes on these timescales in the atmospheres of Jupiter-like exoplanets could bias retrieved exoplanet parameters.

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