JWST as the New Voyager: A Chemical Inventory of the Giant Planets

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James Webb Space Telescope (JWST) has become a cornerstone in the current phase of planetary exploration. We will use JWST as a “New Voyager,” leveraging its exceptional spectral coverage and sensitivity to construct a comprehensive chemical inventory of the giant planets. JWSTVoyager will build on our early leadership with this world-class facility, alongside Jupiter exploration by NASA’s Juno spacecraft and ESA’s JUICE mission (2031). Our inventory, developed across three interconnected themes, will provide a window onto the hidden depths of giant planet atmospheres, and a mirror for processes shaping their climates:

Time Capsules: Comparative planetology of the elemental and isotopic composition of the giants serves as a window on the past, revealing the chemical makeup of the disc materials available during the era of planet formation, and a benchmark for trends in planetary metallicity around other stars. Joint modelling of infrared and microwave data will sound through the cloud layers, providing an intercomparison of atmospheric composition and robust constraints on models of planetary origins.

Striped Worlds: Combining JWST, Juno, and ultimately JUICE (2031), we will test the canonical picture of giant planet circulation responsible for Jupiter’s colourful bands, and use JWST to assess the ubiquity of these banded circulations across fluid worlds.

Ever-changing Atmospheres: Our chemical inventory will be placed into a wider context, studying how time-variable phenomena shape changing climates. We will use Juno to identify the causes of Jupiter’s natural climate cycles to develop a ‘weather forecast’ ahead of JUICE; and exploit new JWST observations of Saturn, Uranus, and Neptune as templates for variability in seasonal worlds.

No other dataset will offer comparable potential for giant planet discovery for the foreseeable future. Comparative planetology from JWSTVoyager aims to set the paradigm for the characterisation of giants for the decades to come.