Résumé

Thierry Fouchet et Imke de Pater sont PI du projet ERS 1373 (https://www.stsci.edu/jwst/science-execution/approved-programs/dd-ers/program-1373) qui vise à démontrer les performances du télescope JWST pour des observation-type. Ce programme ERS est le seul dédié au système solaire, et visera le système de Jupiter qui présente un certains nombres de défis pour JWST, en terme de brillance des objets, de leur taille angulaire, de leur dynamique photométrique (aussi bien spectrale que angulaire), de leur suivi non-sidéral, etc...

Notre programme utilisera tous les instruments de JWST (NIRCam, NIRSpec, MIRI, NIRISS) et observera Jupiter, ses anneaux et les deux satellites Io et Ganymède. Nous avons réuni une équipe de 15 coI et d’une cinquantaine de scientifiques (incluant doctorants et post-doctorants) répartis en Europe et aux Etats-Unis.

Les observations seront conduites entre fin juin et début août 2022.

L’atelier aura pour but de réunir l’ensemble de l’équipe travaillant sur le programme pour :
1) Analyser scientifiquement les données qui seront publiques immédiatement
2) Tester et valider les livrables que nous nous sommes engagés à délivrer au STScI dans le cadre de ce projet (outil de réduction des données saturées, outils de navigation des images et de création de cube hyperspectraux d’objets en rotation, etc...)

Justification scientifique

Despite numerous spacecraft flybys, orbiters, Hubble Space Telescope and ground-based observations of the jovian system, there remain numerous unresolved questions that our JWST-ERS proposal is addressing. We can investigate these questions with JWST thanks to its high spatial resolution, superb sensitivity, stable point spread function (PSF), absolute photometry in the mid-IR, and broad wavelength coverage, specifically within spectral windows typically hidden by telluric absorption. Our data will enable us to obtain new scientific insights into satellite volcanic activity and surface composition, ring sources and evolution, auroral emissions, atmospheric dynamics and chemical composition.

We focus on the following topics and Science Goals (SG)

1. Jupiter’s atmosphere (SG1 and SG2) : We will address two particularly outstanding questions with regard to Jupiter’s atmosphere via spatially-resolved spectroscopy
SG1. to understand the connection between auroral precipitation and upper atmospheric heating in the South Polar and Auroral Region (50°S–90°S), and the transition between the organized banded structure (Jupiter’s zones and belts) seen at lower latitudes and the chaotic turbulence of the polar region.
SG2. to understand the physics and dynamics in Jupiter’s Great Red Spot (GRS), which, as the most famous meteorological feature in the solar system, serves as an archetype to provide fundamental insights into the chemistry, clouds, and dynamics of planetary vortices.
The key advantage of the JWST measurements that enable us to get a deeper understanding of these processes are the broad spectral coverage offered by combining NIRSpec and MIRI data, enabling derivation of the temperature, composition, and aerosol structure from a few nanobars down to the cloud layers (near 0.8 bar). Mapping several disequilibrium species (e.g., PH3, GeH3, CO) will constrain vertical transport in the South Polar and Auroral Region (and its transition to the banded structure at lower latitudes) and the GRS.

2. Jovian rings (SG3) : The primary outstanding questions with regard to Jupiter’s rings relates to the identification of its sources, sinks and morphological evolution. We intend to address these with JWST’s NIRCam imaging system, taking advantage of its superb spatial resolution, sensitivity, and stable PSF.
Jupiter’s rings are mainly composed of dust ; however dust has a limited lifetime, possibly no longer than a few years. We will search for the population of embedded source bodies (JWST can detect bodies of sizes as small as 100 meters, which is 5 times smaller than have hitherto been detected) to explain the existence of the rings and its structure. The structure also includes “ripple” patterns, which are evolving structures attributed to impacts by comets and asteroids. These can be detected with JWST, and enable us to determine the number, size and approximate date of potentially recent comet impacts (the 1994 impact of comet Shoemaker-Levy 9 was detected this way, about a decade after the impact).
Jupiter’s rings may also provide information on the planet’s interior and tesseral field.

3. Volcanically active Io (SG4 and SG5) : The composition and temperature of the magma leading to volcanic eruptions on Io are poorly constrained. Although volcanic eruptions are ultimately the source of Io’s SO2-dominated atmosphere, there is much debate on how much volcanic plumes contribute to Io’s atmosphere, both with regard to its composition and its dynamics. The atmospheric temperature structure is also not known, as different observations have revealed temperatures varying from 110 K up to a few 100 K.
We will address these topics (SG4 : Surface ; SG5 : atmosphere) through observations with NIRSpec, MIRI and NIRISS/AMI (Aperture Masking Interferometry) while Io is in sunlight and in eclipse. Multi-wavelength observations of the surface, and separation/resolving of hot spots, will aid in constraining surface properties and magma temperature. MIRI spectra of SO2’s ν1 and ν3 bands at 8.6 and 7.3 μm (hard to observe from the ground) will help determine the temperature structure. Finally, observing SO while Io is in eclipse may elucidate its source, perhaps “stealth volcanism”, which are high-temperature eruptions without dust or condensates so that such plumes escaped detection by spacecraft.

4. Icy satellite Ganymede (SG6) : Ganymede, the largest satellite in our Solar System, comprises a molten core, a silicate mantle, and a complex ice-rich crust overlying a liquid water layer, making it an archetype of water worlds. Most intriguing, Ganymede has an intrinsic magnetic field. H2O and O2 have been detected in Ganymede’s diffuse atmosphere (exosphere), and O in polar auroral regions. Although a complex interaction with magnetospheric plasma and Ganymede’s surface is expected, there are no observations elucidating such processes.
The combination of spatially resolved NIRSpec and MIRI spectra of Ganymede both in sunlight and eclipse will provide complementary constraints on the nature of organic and inorganic surface materials, on gases trapped in the ice (e.g., O2 and O3), and on interactions between Ganymede’s surface, atmosphere, and plasma through, e.g., sputtering on the surface by magnetospheric plasma.
These four scientific goals showcase the breadth of potential scientific discoveries enabled by the JWST dataset, bringing together expertise in atmospheres, magnetospheres, surfaces, rings, and the space environment in a collaborative endeavour.

The Need for a Workshop at the Jules Janssen Center

The observing window for our JWST-ERS observations is between 22 June and 15 August, 2022 ; the data will be available within a few hours after they are downloaded to the Space Telescope Science Institute (STScI), and hence we expect them before the end of August 2022. As mentioned in the introduction, we will have to face many challenges as these data will be one of the first JWST datasets available. Moreover, these data are far from standard : the planet and satellites move with respect to the background stars, and rotate around their axes at time scales much shorter than a typical observation. Since STScI expects our deliverables (see point 3.3 below) within months after the data have been taken, we only have a short time to organize our team to reduce and analyze these data, building software specific for planetary applications, and obtain the best scientific outcomes. The Jules Janssen workshop will allow us to gather the world experts on JWST data reduction and analysis as applied to planets, together in Leiden, to build our team, train young scientists and organize the deliverables. A Jules Janssen workshop will be a unique opportunity for us to achieve these goals, as our ERS project does not support such meetings financially.
Although we started with a core team at the time we wrote the proposal, due to endless delays of JWST’s launch we need to (re)build our team, i.e., re-populate our team with a large number of scientists at an earlier point in their career, whom we expect to carry out an important part of the research and become future experts in JWST data reduction and analysis. JWST being in its first months of its activity, and having a lifetime that may be well over 10 years, such expertise will be invaluable for years to come. Also, the proposed workshop will reinforce the position and visibility of the Netherlands in planetary sciences by training young scientists working in the Netherlands, and by increasing the international collaborations in planetary sciences. Hence a Jules Janssen workshop will facilitate :

3.1. Data reduction : We will use the same instruments and observing modes to observe a large variety of phenomena : for example, NIRCam is used on Jupiter and the rings, NIRSpec and MIRI, using the same IFU (Integral Field Unit) mode, on Jupiter and the satellites. Jupiter affects almost all observations through its scattered light, in particular the rings and satellites in eclipse. Reducing data from each instrument requires intimate knowledge of that instrument as applied to planetary observations ; i.e., bodies that move and rotate. All bright objects will tend to saturate the very sensitive JWST detectors and will require non-standard data reduction schemes.
Training in data reduction will be organised initially by instrument subgroups, each subgroup focusing on one instrument (Instrument Groups, IGs). This will foster interaction between people from different science subgroups (SGs) to learn from each other how best to reduce the data, i.e., which software is available, and how to adapt such software for our specific (planetary) needs. Members from different SGs can help and educate each other. A few members of our team are experts and will have been working with both synthetic data and (hopefully) the real observations prior to the workshop, and will help train others.

3.2. Data analysis : Interpretation of the data requires scientists with experience in radiative transfer calculations to model spectra (both thermal and in reflected sunlight) of Jupiter’s atmosphere, and of the atmospheres and surfaces of Io and Ganymede. We therefore started to build a diverse team : scientists with observational and/or modeling expertise in near-infrared and in mid-infrared spectroscopy of Jupiter, and others with such expertise for the satellites Io and icy Ganymede. Interpretations of data from Ganymede’s surface will involve experimentalists with experience in measuring spectra of icy and rocky analogs in the laboratory. A different expertise is needed to map Jupiter with NIRCam, and be able to extract wind profiles from such data. Extracting information on Jupiter’s rings and small moonlets requires scientists with experience in data reduction, as well as interpretation, such as, e.g., extracting the size distribution of particles from observations.
This phase is organised by science subgroups (SGs), each of them focusing on an object or a topic. Each data analysis subgroup will be using data from a combination of JWST instruments, and may also fold in external expertise (e.g., supporting ground-based observations and observations from the ongoing Juno mission). A Jules Janssen workshop will facilitate and encourage interaction between people within a subgroup and between subgroups how best to interpret the data. Examples include : an intercomparison between results obtained from different radiative transfer programs for atmospheres (such as SUNBEAR, NEMESIS, and others), and how best to interpret spectral features seen in tenuous atmospheres (Io, Ganymede), and on surfaces.

Work on our “deliverables”, i.e., science-enabling products to help the community in future JWST planetary science endeavors. These tasks are much facilitated via our proposed in-person meeting. In a nutshell these products are :
3.3.1. Characterize Jupiter’s scattered light (glare) pattern (NIRCam, NIRSpec IFU)
3.3.2. Navigation, mosaicking and derotation software (NIRCam, NIRSpec IFU, MIRI IFU)
3.3.3. Calibration intercomparison between NIRSpec/MIRI/NIRCam, and with other space missions and ground-based datasets.
3.3.4. Persistence performance after saturation, and MSA leakage on images (NIRCam, NIRSpec).
3.3.5. Resolve point sources on extended backgrounds, and develop AMI photometry in such fields. (NIRISS/AMI)
3.3.6. Dynamic range : Assess weak absorption/emission lines on a strong continuum (NIRSpec IFU, MIRI IFU), near a very bright source (Jupiter)
In addition, the Jovian system is the target of two flagship missions, both on the European side (JUICE, ESA) and American side (Europa Clipper, NASA), which are bound to reach the planet by 2030s and provide data for several years to the community. The workshop will help to provide the training of a new generation of planetary scientists that will engage with these missions.
Finally, the recently-announced extended mission for NASA’s Juno spacecraft until 2025 offers a unique opportunity for overlap between our JWST observations and those of an in situ spacecraft. The ERS team features a number of individuals with roles in the Juno project, enabling a direct intercomparison of results from both facilities during the Jules Janssen workshop.

As shown in Section 3.2, our JWST-ERS proposal consists of a variety of scientific topics, all related through being a part of the jovian system. Although they may appear uncorrelated at first glance, these individual “pieces” need to be understood before an integrated picture of the jovian system can emerge. All bodies affect each other through e.g., their gravity, and all are embedded in Jupiter’s strong magnetic field. Io’s volcanic activity is the main source for the plasma torus surrounding Jupiter, and hence one might expect material from Io to pollute the surfaces of other moons and the jovian rings (our data may show if this actually happens). Plasma sputtering may produce and shape other satellites’ atmospheres.

The immediate goals of the Workshop are :
● To build a team to handle the JWST-ERS jovian system data and look ahead to
future Solar System observations.
● To gather world experts in planetary research on JWST data reduction in Leiden to adapt the necessary software and to train our team in its use.
● To initiate new collaborations, and train early-career researchers to become future experts in JWST data reduction and analysis of planetary data.
● To develop the deliverables required for STScI and the wider astronomical community to benefit from this ERS program.
● To explore the first observations of the jovian system with JWST and discuss drafts of a first high-level summary paper describing the main results of our endeavor
● To identify future publications that will be obtained from these JWST data, as well as the people who will lead each of these publications.
● To develop preliminary plans for Cycles 2 and 3 Solar System observations, based on lessons learned from this ERS program.
Programme scientifique préliminaire

We envision a 5-day workshop, Monday through Friday. We expect guests to arrive Sunday, and leave on Saturday. Each morning starts with a small social gathering with coffee, tea and food. The workshop is planned such as :
i) to give early-career researchers the scientific background that led to the JWST-ERS proposal,
ii) to train people in sub-groups in data reduction specific to our JWST-ERS proposal. These subgroups will be organised by instrument (IGs : MIRI/NIRSpec/NIRCam/NIRISS) and experts will lead the training sessions (Fletcher/Fry/Hueso/Conrad, or their delegates),
iii) to train people in sub-groups in the analysis of the data. In this case, the subgroup will be organised by topic (SGs ; atmosphere/rings/satellites)
The deliverables to STScI (Section 3.3) are naturally intertwined with the reduction and analysis of the data.

Day 1 : Presentation, data reduction in IGs. On the morning of the first day, we will have a general presentation on our ERS proposal and deliverables, and set the goals of the workshop. This is followed by a specific presentation of how to retrieve the data from the STScI MAST Archive. The rest of the day is dedicated to data reduction in instrument-specific sub-groups (IGs), where the leaders of the IGs, with their delegates, will provide guidance on how best to reduce the data. This will require interactive data processing, via Python, IDL, and other software tools, whilst ensuring that all members of the IG follow the steps and have the opportunity to ask questions. With the setup of the Jules Janssen Center the division in groups can remain very fluid, so knowledge can easily be shared between subgroups. At the end of the day the entire team will reconvene to discuss progress, and any issues that came up during the breakout sessions. In addition to produce reduced datasets, the goal is to obtain the deliverables outlined in Section 3.3.

Day 2 : Finish data reduction in IGs, with Tools and Deliverables ; science presentations.
On Day 2 we plan to finish the data reduction, software data reduction tools and most of the deliverables.
In the afternoon we start with progress reports from each sub-group on the deliverables (which include tools). We proceed with a few science presentations focused on the ultimate scientific product from our data, and how this ties in with recent developments in the field. These sessions are primarily meant for the benefit of the early career scientists, as well as cross-fertilization between scientific subdisciplines.
At the end of the day, several hours are dedicated to finish the data reduction, tools and deliverables.

Day 3 : Science presentations, and data analysis. Day 3 starts with quick progress reports by the IGs, followed by science presentations as on Day 2.
The rest of the day is dedicated to the analysis of the data in small sub-groups by topic (SGs) and instrument. Leaders of the subgroups will introduce the analysis tools specific to their group ; there may be more than one tool (such as more radiative transfer packages, i.e., NEMESIS, SUNBEAR) to be discussed and used in any subgroup.
Such scientific divisions were also done in 2017 when the ERS proposal was written, and was very efficient. From our experience during that previous workshop, these divisions are very natural and very fluid, and team members are sometimes needed in several teams and can be asked to join a different team when needed. Based upon our JWST proposal, we will focus on the following topics with subgroups. These subgroups and how they relate to the scientific contents of the JWST ERS proposal is illustrated in Fig. 1. The subgroups are : SG1, SG2 : Jupiter’s atmosphere and ionosphere, split into 4 subgroups : structure/composition, winds, GRS, ionosphere/aurora ; SG3 : Rings and ring moons : Structure and moonlets ; SG4 : Io’s surface & hot spots (with a separate NIRISS/AMI breakout group) ; SG5 : Io’s atmosphere (divided between MIRI and NIRSpec) ; SG6 : Ganymede : split between its icy surface, and its exosphere and aurora.

Day 4 : Data analysis. After short progress reports by each sub-team, the day proceeds as the afternoon of Day 3. The aim will be to make progress in both deliverables and to draw preliminary scientific conclusions from the data, and identify potential improvements needed in the data reduction processes.

Day 5 : This last day of the workshop starts with a synthesis of the workshop with conclusions per subgroup ; this will be used for a draft outline of our summary paper. The various groups will then reconvene, tie up loose ends, summarize their deliverables, and discuss which papers will be written, and who will lead those. The PIs (de Pater and Fouchet) will work on the outline of the summary paper, and visit the various sub-groups to gather any relevant information for this paper, the deliverables, and future steps.

Monday
08:30 – 09:00 Social Coffee&tea
09:00 – 10:00 Presentation Welcome, Logistics, Summary of ERS proposal and deliverables ; Goal of workshop. | De Pater/Fouchet

10:00 – 10:45 Presentation Review of data, and download the data from MAST | Wong
10:45 – 11:15 Social Coffee&tea
11:15 – 12:30 Breakout groups : 1. MIRI 2. NIRSpec 3. NIRCam 4. NIRISS Hands-on data reduction and training by instrument : 1. Fletcher 2. Fry 3. Hueso & Showalter 4. Conrad with delegates and JWST/STScI experts
12:30 – 13:30 Lunch
13:30 - 17:00 Breakout groups : 1 MIRI : Jupiter, Io, Ganymede 2 NIRSpec : Jupiter, Io, Ganymede 3 NIRCam : Jupiter, Rings, 4 NIRISS : Io Continue data reduction and training by instrument and topic | Fletcher Fry Hueso, Showalter Conrad with delegates and JWST/STScI experts
17:00 – 17:30 Discussion Overall discussion, questions. | Fouchet/de Pater
17:30 - Free evening

Tuesday
08:30 - 9:00 Social+Discussion Coffee&Tea, setting goals for today | Fouchet/de Pater
09:00 - 12:30 Breakout groups : 1 MIRI : Jupiter, Io, Ganymede 2 NIRSpec : Jupiter, Io, Ganymede 3 NIRCam : Jupiter, Rings, 4 NIRISS : Io Continue data reduction and training by instrument and topic ; focus on deliverables. | Fletcher, Fry, Hueso, Showalter, Conrad, with delegates and JWST/STScI experts
12:30 – 13:30 Lunch
13:30 - 14:30 Discussion Progress reports by each subgroup, with status of tools and deliverables | de Pater/Fouchet
14:30 - 14:50 Presentation Jupiter : Temperature/composition, aerosol structure | Irwin and Fletcher
14:50 - 15:10 Presentation Jupiter : winds in the visible & near-IR | Hueso & Antunano
15:10 - 15:30 Social Coffee&Tea
15:30 – 17:30 Breakout groups : 5. MIRI : Jupiter, Io, Ganymede 6. NIRSpec : Jupiter, Io, Ganymede
7. NIRCam : Jupiter, Rings, 8. NIRISS : Io. Finish data reduction, tools, deliverables. | Fletcher Fry, Hueso, Showalter Conrad with delegates and JWST/STScI experts
17:30 - Free evening

Wednesday

8:30 - 9:00 Social+Discussion Coffee&Tea
09:00 - 10:00 Discussion Progress reports by each subgroup, with status of tools and deliverables | Fouchet/de Pater
10:00 - 10:10 Presentation Io’s atmosphere | Lellouch
10:10 - 10:30 Presentation Io’s surface | De Kleer
10:30 – 11:00 social Coffee&tea
11:00 - 11:20 Presentation Ganymede | Bockelee-Morvan
11:20 - 11:40 Presentation Jupiter : Aurora and upper stratosphere structure, comp. | Melin
11:40 - 12:00 Presentation Jovian rings | Showalter
12:00 - 12:30 Discussions Goals for afternoon, +general questions regarding presentations | De Pater/Fouchet
12:30 - 13:30 lunch
13:30 – 17:30 Discussions and work in breakout groups, per instrument and topic : 1-3 : Jupiter atmosphere (MIRI, NIRSpec, NIRCam), 4 : jupiter Ionosphere 5,6 : Io atmosphere (MIRI, NIRSpec) 7 : Io NIRISS 8 : Io Surface
9 : Jovian rings 10 : Ganymede surface 11 : Ganymede exosphere Analysis, deliverables 1 Fletcher 2 Fry 3 Hueso 4 Melin 5 Lellouch 6 de Pater 7 Conrad 8 de Kleer 9 Showalter 10 Cazaux 11 Bockelee-Morvan
19:30 – 22:00 Social Conference Dinner

Thursday
08:30 – 09:00 Social Coffee&Tea
09:00 – 09:30 Discussion Progress reports subgroups
09:30 – 12:30 Discussions and work in breakout groups, per instrument and topic as on Day 3, afternoon
Analysis, deliverables | 1 Fletcher 2 Fry 3 Hueso 4 Melin 5 Lellouch 6 de Pater 7 Conrad 8 de Kleer 9 Showalter 10 Cazaux 11 Bockelee
12:30 – 13:30 Lunch
13:30 – 17:30 Discussions and work in breakout groups, per instrument and topic, as in the morning Analysis, deliverables 1 Fletcher 2 Fry 3 Hueso 4 Melin 5 Lellouch 6 de Pater 7 Conrad 8 de Kleer 9 Showalter 10 Cazaux 11 Bockelee
17:30 - Free evening

Friday
08:30 - 09:00 Social Coffee&Tea
09:00 – 10:30 Discussion Synthesis workshop with conclusions on deliverables and scientific results per subgroup Fouchet/de Pater
10:30 – 11:00 Social Coffee&tea
11:00 – 12:30 Discussions and work in breakout groups Deliverables ; Lead-authors for subsequent papers 1 Fletcher 2 Fry 3 Hueso 4 Melin 5 Lellouch 6 de Pater 7 Conrad 8 de Kleer 9 Showalter 10 Cazaux 11 Bockelee
12:30 – 13:30 Lunch
13:30 - 14:30 Discussions, continued from the morning Summary paper outline, deliverables and analysis
De Pater/Fouchet
14:30 – 17:30 Discussions and work in breakout groups Finish loose ends, work on deliverables, analysis, summary paper.
17:30 – 18:30 Social Goodbye Pot