Giants through Time: Towards a Comprehensive Giant Planet Climatology

Project Information

GIANTCLIMES

Grant agreement ID: 723890

DOI

10.3030/723890

Project closed

EC signature date 13 January 2017

Start date 1 April 2017

End date 31 March 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 999 815,00

EU contribution

€ 1 999 815,00

Coordinated by

UNIVERSITY OF LEICESTER
United Kingdom

Periodic Reporting for period 5 - GIANTCLIMES (Giants through Time: Towards a Comprehensive Giant Planet Climatology)

Reporting period: 2023-04-01 to 2024-03-31

Summary of the context and overall objectives of the project

Planetary science stands at a unique threshold – the discovery of thousands of new worlds beyond our own Solar System is bringing a fascinating new perspective on the forces shaping both the architecture of our planetary system and the fragile climate of our home planet. Our solar system offers an extreme test of our understanding of how planetary climate, dynamics and chemistry differ from world to world, and whets our appetite for the myriad possibilities that remain to be discovered. The past seven years have transformational in our understanding of outer solar system environments, with the Juno mission at Jupiter and the Cassini mission at Saturn, along with new exploration of Uranus and Neptune by the James Webb Space Telescope (JWST).

But these missions offer only fleeting glimpses of these dynamic, ever-changing worlds when compared to their long orbital periods (10 years for Jupiter, 165 years for Neptune). How does the climate, circulation and chemistry of these atmospheres evolve over these large spans of time? What are the natural cycles of climate variability, and how do they differ from world to world? What can the giant planets reveal about the governing forces shaping planetary atmospheres in all their guises?

The aim of GIANTCLIMES was to assemble the first comprehensive climatology of all four giant planets by combining an unprecedented multi-decade archive of ground-based infrared imaging with new spectroscopic observations from space telescopes and visiting spacecraft. This wealth of observational data was studied via a sophisticated suite of spectral analysis software to understand the spatial and temporal variability in the redistribution of energy and material on the four giants. The GIANTCLIMES programme at the University of Leicester consisted of three objectives that hoped to provide something that no single space mission has ever done before: the ability to explore the giants over large spans of time.

1. Climate Cycles on Jupiter: What drives the spectacular transformations of Jupiter’s banded structure and triggers storms? Can these events be predicted? We discovered quasi-regular cycles of activity within Jupiter’s bands and interconnections between the hemispheres that were unexpected, potentially driven by waves emanating from the deep interior, and occasionally disrupted by gargantuan storm eruptions. We constructed a comprehensive climate record (temperature, composition, clouds) over three Jovian years to set the environmental context for Juno’s exploration and JWST’s new observations in 2022-23.

2. Seasons of Saturn: How does the circulation and chemistry of planetary stratospheres change with time as a result of the different conditions on each world? We explored the changing stratosphere of seasonal Saturn using Cassini and JWST observations, combined with four decades of ground-based monitoring to develop a new paradigm for the seasons on giant planets.

3. Ice Giants: How do circulation patterns and climate cycles differ between the Ice and Gas Giants? We combined state-of-the-art observations from space observatories (Spitzer, Herschel, and JWST) with ground-based observations and simulations of their dynamics and chemistry to reveal the climate of these distant worlds like never before, providing the first 3D maps of temperature, composition and circulation within an ice giant atmosphere.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The GIANTCLIMES programme spanned seven years (2017-2024), bridging the gap between the end of Cassini’s exploration of Saturn, and the world-leading new observations of all four giant planet systems from JWST. GIANTCLIMES allowed us to fully exploit the wealth of ground-based records of natural climate variability on all four giant planets before JWST, producing long-term records of temperature, clouds, and composition on all four worlds. Notable results for the three work packages are as follows:

• WP1: Jupiter's Climate: WP1 explored the atmospheric variability of Jupiter over long spans of time, combining data from Earth-based observatories with new observations from NASA’s Juno spacecraft. Using more than three decades of ground-based observations, we identified periodic cycles of atmospheric variability, both in the deep clouds, in the stratosphere, and in tropospheric temperatures. Patterns at widely-separated latitudes appear to be interconnected (suggesting deep origins), and prone to teleconnections by extreme storm events and belt/zone variability. These studies were used as context for Juno’s close-in studies in microwave and infrared light, and for JWST spectroscopic observations of regions of interest in 2022-23. Ultimately, the developing understanding of jovian climate cycles, meteorology, and chemistry have supported our role in the science planning for ESA’s Jupiter Icy Moons Explorer, which launched in 2023.

• WP2: Saturn's Seasonal Stratosphere: Cassini completed its unprecedented exploration of Saturn in 2017, allowing the GIANTCLIMES team to publish new insights into the long-term seasonal variations in Saturn's atmosphere. We supplemented this work using our long-term ground-based infrared campaign, which extends both before and after Cassini's mission, allowing us to track a full seasonal cycle of the giant planet for the first time, and revealing hints of inter-annual variability in Saturn’s seasonal response. These projects culminated with the publication of the first JWST maps of Saturn's northern summer hemisphere in 2022, showing how large-scale circulation patterns completely switch direction over the course of a Saturnian year.

• WP3: Ice Giants: Uranus and Neptune remain the least explored planets in our solar system. GIANTCLIMES enabled the first maps of Uranus' stratosphere and a comprehensive assessment of Neptune's stratosphere over two decades, revealing surprising sub-seasonal variability for the first time. These long-term studies paved the way for the first global maps of the Ice Giant atmospheres from JWST in 2022-23, the most significant new dataset since Voyager.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Seven years of GIANTCLIMES funding allowed the team to fully exploit enormous long-term databases of atmospheric variability on four different worlds. These data were from a variety of different space-based and ground-based facilities, each with their own challenges and peculiarities, and each had to be explored in a fully self-consistent framework. This was achieved, and the codes required for data processing and spectral retrieval/analysis have all been made publicly available for the benefit of the community. Our general-purpose spectral retrieval model was extended to model ultraviolet data (from Cassini and Juno) for the first time, adapted for the novel instrumentation of JWST, and combined with new ab initio calculations of hydrogen-helium opacity to create world-leading simulations of giant planet spectra. The personnel afforded by this grant has allowed the ERC team to expand in new directions. Most significantly, GIANTCLIMES allowed us to have a team of experts in place ready to lead and exploit the unprecedented new observations from JWST. Despite the 3-year delay to JWST’s launch, GIANTCLIMES allowed us to capitalise on our leadership of guaranteed-time programmes, publishing new discoveries on all four giant planets (and their satellite and ring systems) in the final years of the project.

The giant planets in infrared light, as observed by the Very Large Telescope in Chile.