Science Implicaons of ICEMAG Descope: OPAG Update Robert Pappalardo, Europa Clipper Project Scienst1 Haje Korth, Europa Clipper APL Deputy Project Scienst2 Carol Raymond, ICEMAG Principal Invesgator1 1Jet Propulsion Laboratory, California Instute of Technology; 2Johns Hopkins University Applied Physics Laboratory April 23, 2019 08/20-24/2018 Copyright 2019 California Institute of Technology. Government sponsorship acknowledged 0-1 . Summary: Science Impact of Descoping the SVH Sensors

• Descope of the ICEMAG scalar-vector helium (SVH) sensors means there will be no absolute measurement of the magnec field, liming reliable retrieval of the inducon signal at Europa’s orbital period (85 hr), which is central to characterizing Europa’s ocean properes (salinity and thickness) • Puts at risk the current Level 1 requirement: – Constrain the average thickness of the ice shell, and the average thickness and salinity of the ocean, each to ±50% • Other Baseline Level 1 requirements are not affected; Threshold Level 1 requirements are not affected; and Mission Success Criteria can sll be achieved • Diminished informaon on ocean thickness and salinity will limit our understanding of Europa’s ocean habitability, interior structure, composional fraconaon, and plume provenance – Ocean salinity is especially relevant to ocean habitability (specifically: water acvity, available energy for metabolism, and long-term history of water-rock reacons), important to the mission goal of understanding Europa’s habitability • Other instruments cannot reliably recover the lost science: – Data from other Europa Clipper composional instruments provide limited informaon on ocean salinity, given possible fraconaon within Europa, and we cannot be assured of flying through a putave plume sourced from the ocean

– Combined radar (ice shell) and Gravity Science (total H2O layer) are not expected to be definive for ocean thickness

– Ice shell thickness could potenally be constrained from radar ranging (h2) plus gravity science (k2), but how precisely is work in progress, and these are currently not required measurements of the mission

Presentaon to OPAG: April 23, 2019 2 Europa’s Ocean Thickness and Conducvity Can be Derived from Induced Magnec Field Measurement at Mulple Frequencies

Simulaon of Europa’s Dipole Field Induced at 11-hr Synodic Period Induced Magnec Field at Europa (nT)

Simulaon by Corey Cochrane

• Europa’s inducon response at mulple frequencies probes of the depth and salinity of the conducve ocean – Jupiter–Europa synodic period = 11.2 h; Europa orbital period = 85.2 h • Inducon efficiency at the synodic period (11.2 h) provides ice shell thickness, if conducvity is known • Measurement of Europa’s induced magnec field at Europa’s 85.2 h orbital period requires high precision (~0.1 nT) over flyby me scales, and high absolute accuracy sustained over the course of the mission (~1 nT over 2+ yr) [Khurana, 2002] Presentaon to OPAG: April 23, 2019 3 Spacecra Magnec Field Removal

• Europa Clipper’s challenge is magnetic mapping by a flyby mission in a dynamic ambient field, with variable magnetic noise and offsets • ICEMAG employed 2 fluxgate (FG) and 2 scalar- The Europa Clipper spacecraft has a complex and strong vector helium (SVH) magnetometers to measure magnetic field that cannot be Z (m) the complex spacecraft field, to allow the modeled as a simple dipolar field. Each circle here is a spacecraft field to be removed from the data magnetic moment, scaled to • Intended to enable the long-term stability needed its magnitude. to connect flybys into a single measurement set

• Multiple sensors permit correction at a cadence Y (m) fast enough to separate transient spacecraft noise from the induction field, and permit identification and removal of higher-order spacecraft fields • ICEMAG’s approach enabled a relaxed magnetic cleanliness of 10 nT field at end of a 5 m boom For comparison, this diagram • A 2-fluxgate system would need a >15-m boom represents a dipolar space- and a more stringent magnetic cleanliness program craft field. to allow spacecraft field removal at sub-nT levels Presentaon to OPAG: April 23, 2019 4 Magnetometer Comparison

• Fluxgate magnetometers: – Sense the imbalance of the voltage induced in a coil surrounding a ferromagnec material oscillang between saturated states of opposite magnezaon direcon, as created in presence of an ambient magnec field – Fluxgate offsets change due to temperature variaons and thermal gradients and can dri over me, so require periodic calibraon in flight inducon – Fluxgate magnetometers have high precision (<0.1 nT), but coil offset uncertainty and difficulty removing the spacecra field smulaon coil result in errors ~3 nT on long-term retrieved inducon accuracy [Drljača et al., 2004] Image credit: sensorland.com • Helium magnetometers: Fiber – Sense a magnec resonance, with the resonance frequency Opc proporonal to the magnec field Cable RF coil – He magnetometer measurements are absolute because the constant of proporonality is an atomic constant – Fiber opc cable guiding circularly polarized laser light from the electronics to the sensors is sensive to radiaon and temperature, so was quite challenging to accommodate – Absolute measurement such as provided by a He magnetometer would have ensured an order of magnitude improvement of [Rutkowski et al., 2014] flyby-to-flyby accuracy over the Europa Clipper mission duraon 5 Presentaon to OPAG: April 23, 2019 Impact of Descoping SVH Sensors: Ocean Properes

• Without correcon, driing zero-level offsets of the fluxgate sensors can result in errors that significantly 4 FG (±3 nT) 225nT degrade the accuracy of the inducon retrieval ICEMAG Req (±1.5 nT) 2 SVH & 2 FG (±0.2 nT) – Errors for a 4-FG system include contribuons from residual low-frequency dynamic spacecra fields and 228nT ± 0.2 nT uncalibrated offsets and gains • Example of the impact of this error on determinaon of ocean parameters is illustrated by plong expected 231nT uncertainty in the thickness-conducvity soluon* (for an example case of a 60-km thick ocean with 11nT conducvity of 1.0 S/m) – Including absolute reference data would yield ght 8nT ± 0.2 nT bounds on ocean thickness and conducvity – Nominal 4-FG case yields a large error on ocean thickness 5nT and conducvity, unable to confidently disnguish freshwater from seawater Putative Earth * Errors determined by an inducon simulaon that ulizes a realisc error spectrum lower limit seawater SVH sensor descope increases uncertaines in esmates of ocean thickness and conducvity, liming our understanding of Europa’s ocean habitability, interior structure, composional fraconaon, and plume provenance

Presentaon to OPAG: April 23, 2019 6 Impact of Descoping SVH Sensors: Ocean Conducvity

Low Conductivity Case: Medium Conductivity Case: High Conductivity Case:

Conductivity: 0.5 S/m Conductivity: 1.0 S/m Conductivity: 3.0 S/m Ocean Thickness: 120 km Ocean Thickness: 60 km Ocean Thickness: 25 km Fixed Ice Thickness: 10 km Fixed Ice Thickness: 20 km Fixed Ice Thickness: 30 km

9.1nT

228nT

230nT

8nT

4FG (±3 nT) ICEMAG Req (±1.5 nT) 2FG + 2SVH (±0.2 nT) Conducvity is only weakly constrained for oceans with conducvity > ~2 S/m; errors in conducvity (salinity) rise non-linearly as conducvity increases

Presentaon to OPAG: April 23, 2019 7 Impact of Descoping SVH Sensors: Ice Shell Thickness

4FG (±3 nT) ICEMAG Req (± 1.5 nT) 2FG + 2SVH (± 0.2 nT) This plot illustrates the induced magnec field at Conductivity uncertainty broadens the error bounds the 11.2 hr period (nT) vs ice shell thickness (km), on ice thickness determination for ocean conducvies of 1 and 10 S/m

• Intrinsic error doubles between the conservave ICEMAG requirement (±1.5 nT) and the 4-FG esmate (±3 nT) • For the 1 S/m example shown, the ±50% Level-1 10 S/m requirement is met for ice shell thickness >15 km

• However, ice shell thickness determinaon is 1 S/m conducvity dependent, such that error in conducvity increases error in ice shell thickness, especially for high conducvity oceans

Ice shell thickness measurement accuracy depends on conducvity, which in turn depends on long-term accuracy of the inducon at the 85-h period

Presentaon to OPAG: April 23, 2019 8 Paral Recovery of Measurement Accuracy

• Facility magnetometer with 4 fluxgates is less capable than original payload with SVH sensors, but lost measurement accuracy may be parally recovered • Regular spacecra rolls and other maneuvers may permit determinaon of zero levels – Although the large spacecra maneuvers slowly, and extended maneuver me could impact mission resources, addional work is underway to understand how currently planned spacecra maneuvers can aid calibraon of offsets, what addional maneuvers would be most beneficial to this calibraon, and whether zero levels determined near apoapse represent the spacecra environment during flybys • Longer boom would allow sensor mounng farther from spacecra source fields, more closely approximang the spacecra field as dipolar – NASA has directed to implement the facility magnetometers on the exisng 5-m boom, and boom changes could impact the propulsion module design, but the potenal impacts will be examined and assessed • More stringent magnec cleanliness would reduce spacecra contribuons to the measured magnec field – We wish to avoid spacecra and payload design changes or material choices that would increase cost and complexity but will look to idenfy any simple improvements • The new Team Leader and reconstuted Mag science team is tasked with fully characterizing the measurement accuracy and potenal science return [Pudney, 2014] of the facility Europa Clipper Magnetometer Presentaon to OPAG: April 23, 2019 9 Adopted Science Teaming Structure

• Project Scienst received detailed input from across the full Europa Clipper Science Team – Telecon and WebEx meengs, wrien communicaons, private phone conversaons, and in-person discussions • Team Leader – Given immediate need, Team Leader for development (Phases C/D) was chosen from among the exisng Europa Clipper Science Team members, with established magnetometry experse – Open compeon to the planetary science community for the post-launch operaons (Phase E) Team Leader – Will have budget and managerial authority over the Magnetometer Science Team members – May nominate their own Deputy Team Leader, from inside or outside the Europa Clipper science team – Diversity should be considered in selecon of the Team Leader and Deputy Team Leader – During development: Provide oversight of science instrument operaons and science data processing definion – During operaons: Oversee instrument operaons and data processing, calibraon, analysis, and archiving • Science Team Members as Co-Invesgators – Team members are designated as Co-Invesgators, mirroring the science management organizaon of a PI-led team – Designang as Co-Invesgators assures future ability to promote early career members onto the science team – Team Leader should assess whether any addional team experse is currently needed, given new mag configuraon • Science Interface Lead – A member of the Europa Clipper Project Science Team knowledgeable of the magnetometer hardware serves as the informaon interface between engineering team and the Magnetometer Science Team during development – Aends relevant project engineering meengs and facilitates conversaons, to ensure science requirements are met – Instrument Scienst liaison and a role parallel to the Instrument Engineer (IE) funcon are also being included

Presentaon to OPAG: April 23, 2019 10 Backup Post-PDR NASA Charges regarding Europa Clipper Requirements from NASA to the Project Manager and Project Scienst

HQ • The project is directed to Level 1 Baseline & Threshold recommend changes to Level 1 requirements as appropriate to PS PS Level 2 reduce complexity and cost risk. P-STAF Guiding Science Themes Science Requirements

• The project is directed to scrub the IS Level 2 requirements that exceed SM Level 2 M-STAFs Level 1 requirements, and to reduce Measurement Requirements environmental requirements as Level 3 appropriate to reduce complexity Requirements

Flight and cost risk. Mission System Science System System

Spacecraft Payload

Presentaon to OPAG: April 23, 2019 12 Proposed Edits to Baseline Level 1 Science Requirements: Ice Shell & Ocean

Baseline Level 1 Recommended Level 1 (tracked) Recommended Level 1 (accepted) Raonale for Change Map the vercal subsurface Map the vercal subsurface structure Map the vercal subsurface structure in Clarifies the intent of the L1, structure beneath ≥50 globally beneath ≥50 globally distributed regions of potenal surface-ice-ocean provides significant relief on mission distributed landforms to ≥3 km landforms in regions of potenal exchange to >3 km depth along globally design and provides margin on depth[, to understand the surface-ice-ocean exchange to ≥3 >3 km distributed ground tracks achieving a downlink and data storage. Baseline distribuon of subsurface depth along globally distributed ground total cumulave length ≥30,000 km. is achievable in ≈20 flybys, so water and processes of surface- tracks achieving a total cumulave reduces cost risk by perming ice-ocean exchange]. length ≥30,000 km[, to understand the instruments to collect data non- distribuon of subsurface water and simultaneously if EMI becomes a processes of surface-ice-ocean significant technical problem. exchange]. Ice Shell & Ocean Constrain the average Constrain the average thickness of the Constrain the average thickness of the No recommended changes: N/A. thickness of the ice shell, and ice shell, and the average thickness and ice shell, and the average thickness and the average thickness and salinity of the ocean, each to ±50%. salinity of the ocean, each to ±50%. salinity of the ocean, each to ±50%.

Presentaon to OPAG: April 23, 2019 13 Proposed Edits to Baseline Level 1 Science Requirements: Composion Recommended Level 1 Baseline Level 1 Recommended Level 1 (accepted) Raonale for Change (tracked) Create a composional map at ≤10 km Create a composional map at ≤10 Create a composional map at ≤10 km Clarifies intent of the spaal scale, covering ≥70% of the km spaal scale, covering ≥70% of the spaal scale, covering ≥70% of the requirement, specifying the surface[, to idenfy the composion surface, sufficient to idenfy non-ice surface, sufficient to idenfy non-ice relevance of organic and distribuon of surface materials]. materials especially organic materials especially organic compounds. compounds. compounds [, to idenfy the composion and distribuon of surface materials]. Characterize the composion of ≥50 Characterize the composion of ≥50 Characterize the composion of ≥0.3% Significant reducon in the globally distributed landforms, at 0.3% of the surface, globally of the surface, globally distributed at required total areal coverage, ≤300 m spaal scale[, to idenfy non- distributed landforms, at ≤300 m ≤300 m spaal scale, sufficient to accomplishable in ≈30 flybys. ice surface constuents including any spaal scale, sufficient [,to idenfy idenfy non-ice materials, especially Wording change to clarify the carbon-containing compounds]. non-ice surface constuents including organic compounds. requirement, aiding mission any carbon-containing materials, design and requirements

Composion especially organic compounds]. validaon. Eliminaon of explanatory brackets. Characterize the composion and Characterize the composion and Characterize the composion and Clarifies intent of the sources of volales, parculates, and sources of volales, parculates, and sources of volales, parculates, and requirement, specifying the plasma, with sensivity sufficient to plasma, with sensivity sufficient to plasma, sufficient to idenfy the relevance of organic idenfy the signatures of non-ice idenfy the signatures of non-ice signatures of non-ice materials, compounds. materials including any carbon- materials including any carbon- especially organic compounds, in containing compounds, in globally containing compounds, especially globally distributed regions of the distributed regions of the atmosphere organic compounds, in globally atmosphere and local space and local space environment. distributed regions of the atmosphere environment. and local space environment. Presentaon to OPAG: April 23, 2019 14 Proposed Edits to Baseline Level 1 Science Requirements: Geology, Current Acvity

Baseline Level 1 Recommended Level 1 (tracked) Recommended Level 1 (accepted) Raonale for Change Produce a controlled photomosaic Produce a controlled photomosaic Produce a controlled photomosaic map Simplificaon of requirement map of ≥80% of the surface at ≤100- map of ≥80% of the surface at ≤100-m of ≥80% of the surface at ≤100-m spaal language to eliminate m spaal scale[, to map the global spaal scale[, to map the global scale. explanatory brackets. distribuon and relaonships of distribuon and relaonships of geologic landforms]. geologic landforms].

‑ Characterize the surface at ≤25‑m Characterize the surface at ≤25‑m Simplificaon of requirement Characterize the surface at ≤25 m spaal scale, and measure spaal scale across ≥5% of the surface spaal scale across ≥5% of the surface language, aiding mission design topography at ≤15-m vercal with global distribuon, and measure with global distribuon, including and requirements validaon, precision, across ≥50 globally including measurements of measurements of topography at ≤15-m and eliminaon of explanatory Geology distributed landforms[, to idenfy topography at ≤15-m vercal vercal precision within at least one brackets. their morphology and diversity]. precision, across within at least one third of that surface area. third of that surface area 50 globally distributed landforms[, to idenfy their morphology and diversity]. Characterize the surface at ~1-m Characterize the surface at ~1-m Characterize the surface at ~1-m spaal Relaxes and simplifies scale to determine surface spaal scale to determine surface scale to determine surface properes, requirement. Permits increasing properes, for ≥40 sites each ≥2 km x properes, for ≥40 18 globally for ≥18 globally distributed sites. flyby velocity, enabling 4 km. distributed sites each ≥2 km x 4 km. Clipper:Europa 6:1 resonance. Search for and characterize any Search for and characterize any Search for and characterize any current No changes: N/A. current acvity, notably plumes and current acvity, notably plumes and acvity, notably plumes and thermal thermal anomalies, in regions that thermal anomalies, in regions that are anomalies, in regions that are globally Acvity Current are globally distributed. globally distributed. distributed.

Presentaon to OPAG: April 23, 2019 15 ICEMAG Contribuon to Europa Clipper Level-1 Requirements on Ice Shell and Ocean ICEMAG ICEMAG, Fluxgates only L1 RQ Science Science Theme B/T L1 Requirements Approach Magnetic Waves Magnetic Waves Number Themes Definitions

Thickness and Ice Shell thermophysical properties Induction Properties Constrain the average thickness of the of the ice shell. P I Baseline RQ106.317 ice shell, and the average thickness and salinity of the ocean, each to +/-50%. Existence, thickness, and Ocean Properties Induction salinity of the ocean. P E?

Thickness and Confirm the presence of a subsurface Ice Shell thermophysical properties Induction ocean, and constrain whether the ice Properties Threshold RQ106.325 of the ice shell. shell is in a “thin” (several km) or P P “thick” (10s km) regime. Ocean Properties Existence of the ocean. Induction P P

Can provide, most robustly and Can enable a given approach to Expected to further enhance with greatest probability, be achieved, though potenally overall science return beyond science data necessary to fully less robustly than from Primary that of Primary or Independent Primary achieve a given approach. Independent instrument’s data. Enhancing instrument.

Without the absolute calibraon provided by the SVH sensors, ice shell thickness measurements would be degraded, while ocean properes (thickness and salinity) could not be reliably aained.

Presentaon to OPAG: April 23, 2019 16 The Prospects and Limitaons of Other Techniques (PSTAF) Pre-ICEMAG Descope

Approach Coding: 0 is not required of the mission

Presentaon to OPAG: April 23, 2019 17 The Prospects and Limitaons of Other Techniques (PSTAF) Post-ICEMAG Descope

X X

? ?

X X

Approach Coding: 0 is not required of the mission

Presentaon to OPAG: April 23, 2019 18 The Prospects and Limitaons of Other Techniques Ice Shell Properes Ocean Properes • Radio Frequency Probing (Radar Sounding): • Shape & Gravity: – Prospects: Possibility to penetrate the ice shell to sub-ice ocean. – – Limitaons: Prospects for radar penetraon to an ocean are Prospects: Shape and stac gravity can best for a thin (~kilometers) and clean ice shell, as the radar constrain H2O-layer thickness. signal is aenuated in the (more plausible) occurrence of warm – Limitaons: Lile measurement improvement convecng ice and/or chloride or brine impuries. is expected over exisng Galileo results, and • Tidal Amplitude & Gravity: composion uncertainty dominates the uncertainty in layer thicknesses. – Prospects: Gravitaonal (k2) and dal (h2) Love numbers, in combinaon, will constrain ice shell elasc thickness. • – Limitaons: Requires high-precision radar ranging at cross-over Composion: points measured from <1000 km, topographic characterizaon – Prospects: Surface composion and ejected of cross-over regions, improved true anomaly coverage by the parculates can indicate major salt species; trajectory, and small radial orbit error necessitang 70-m- composion of plume parculates and gases antenna equivalent tracking, and may not enable the current L1 can directly indicate ocean salinity and other precision; elasc thickness may be less than total ice thickness. geochemical properes. • Libraon & Shape: – Limitaons: Fraconaon between ocean and – Prospects: Libraon can constrain ice shell thickness, and limb- surface may limit conclusions regarding ocean derived topography and shape can constrain ice shell thickness. – Limitaons: Libraon is large only for a thin-shell case, may be salinity and other properes; plumes (if real) below detecon limits, and may not be diagnosc depending on may tap subsurface lakes rather than the internal structure; ice shell thickness can be derived from limb ocean. topography only in the unlikely case of a conducve ice shell.

Presentaon to OPAG: April 23, 2019 19 Europa Clipper Themac Working Group Summary Findings

• Habitability Working Group: Co-Chairs Jonathan Lunine (Cornell), Britney Schmidt (Georgia Tech) – Descope of the ICEMAG SVH sensors would jeopardize primary constraints on ocean thickness and salinity that are essenal to understanding the chemical condions in Europa’s ocean, including water acvity, available energy for metabolism, pressure at the water-rock interface, and long-term history of water-rock reacons that might support a global biosphere. • Interior Working Group: Co-Chairs Carol Paty (Univ. Oregon), James Roberts (JHU/APL) – The proposed descope of the ICEMAG SVH sensors will preclude direct measurement of the ocean thickness and salinity, and will degrade measurement of the ice shell thickness; other Europa Clipper measurements will not be sufficient to replace the science loss. • Composion Working Group: Co-Chairs Jason Soderblom (MIT), Murthy Gudipa (JPL/Caltech) – Descoping the ICEMAG SVH sensors would result in very significant science loss: the ability to characterize the composion of Europa’s ocean and the exchange of material between its interior and surface, and observaons by other instruments via plumes and/or surface observaons are not an effecve replacement. • Geology Working Group: Co-Chairs Geoff Collins (Wheaton College), Julie Rathbun (PSI) – Increased uncertainty in average global ice shell thickness and loss of ocean salinity informaon risks ambiguous interpretaons of several key aspects of Europa geology, which could degrade our scienfic confidence in linking observed surface features to the ocean.

Presentaon to OPAG: April 23, 2019 20 Habitability Working Group Findings

• The Habitability Themac Working Group for the Europa Clipper affirms the crical importance of ICEMAG measurements of the induced magnec field at Europa at mulple frequencies, and strongly suggests that the instrument not be descoped. • The determinaon of Europa’s ice thickness is a key factor for determining the nature and rates of chemical exchange between Europa’s acve surface and its underlying ocean to which ICEMAG contributes unique informaon. • Most important, ICEMAG is the primary instrument to provide constraints on ocean thickness and salinity that are essenal to understanding the chemical condions in Europa’s ocean, including the acvity of water, available energy for metabolism, and pressure at the water-rock interface, as well as the long-term history of water-rock reacons that could support a putave biosphere. • Addionally, knowledge of the ocean depth and salinity would improve inferences of Europa’s deeper interior structure. • All of this informaon will be needed to properly interpret Europa Clipper data on habitability and to prepare for future missions, such as a Europa lander and a deep drilling mission to probe the ocean directly.

Presentaon to OPAG: April 23, 2019 21 Interior Working Group Findings

• Detecon of a potenal subsurface ocean on Europa by the magnetometer on Galileo was a key movaon for proposed future exploraon of Europa by a flight system which includes a magnetometer with sufficient absolute accuracy to allow more detailed characterizaon of Europa’s subsurface ocean, namely independent determinaon of ocean layer thickness and conducvity. • ICEMAG is the only instrument on the payload capable of making observaons which would enable determinaon of the ocean thickness and salinity. Ocean thickness could be inferred from a combinaon of radar and gravity measurements of the ice shell thickness and moment of inera, respecvely. While the precision of these esmates may be an improvement over Galileo, in absence of constraints on the oceanic composion/salinity, they would not be definive. • The approach of measuring the ice shell properes using mulple instruments is powerful, as each technique is sensive to different ice shell characteriscs (e.g., rheology, total thickness, thickness of the cold elasc layer). In combinaon these measurements can provide insight into the ice shell that would elude a single instrument measurement, and provide robustness to ice shell characterizaon. • Planned measurements of the dal Love numbers with Gravity Science and REASON will enable confirmaon of the presence of an ocean, but will not constrain the ocean thickness and would provide only constraints on the depth of the ice-ocean interface, with ambiguity due to uncertaines on ice shell rheology and oceanic composion (density). The proposed descope of the SVH sensors would remove our ability to resolve these ambiguies. • The proposed descope of the SVH sensors would reduce the accuracy of ICEMAG’s measurements because of the loss of absolute calibraon, would jeopardize independent determinaon of the ocean thickness and salinity, and would degrade the accuracy of the determinaon of the ice shell thickness.

Presentaon to OPAG: April 23, 2019 22 Composion Working Group Findings

• Descoping the ICEMAG SVH sensors would result in very significant science loss: the ability to characterize the composion of Europa’s ocean and of the exchange of material between its interior and surface, both of which are fundamental to the Europa Clipper level 1 science requirements. • Understanding Europa’s ice-shell thickness, ocean depth, and ocean conducvity (and thus salinity), are crically important to fully understanding Europa’s geochemistry and interior structure, and to modeling its physical and chemical evoluon, as captured by the relevant level 1 science requirement. • While constraints can be placed on the composion and salinity of Europa’s plumes and exosphere from SUDA dust observaons, the composion of gases in its plumes and exosphere from MASPEX gas observaons, and the composion of surface materials believed to be sourced from the interior from MISE spectroscopy observaons, relang these constraints to ocean salinity requires major assumpons and significant modeling that will be poorly constrained and therefore cannot sasfy the level 1 requirement. • This informaon is also fundamental to modeling the dynamical transport of material from the ocean to the surface, which is a key component of understanding Europa’s geochemistry. REASON radar observaons can only constrain ice-shell thickness under very specific condions and are not a replacement for ICEMAG SVH- based observaons.

Presentaon to OPAG: April 23, 2019 23 Geology Working Group Findings

• Under some combinaons of ice shell thickness, salinity, and radar results, there may be a large uncertainty in the average global ice shell thickness, which translates into several other geological uncertaines outlined below. • Geophysical models for the formaon of several common types of terrain features (e.g. chaos, ridges) depend on the distance between the surface and water derived from the ocean, and without a reliable ice shell thickness it will be more difficult to disnguish among plausible models. • Lack of independent knowledge of ice shell thickness may affect the interpretability of shallow radar reflectors associated with geological features, making it uncertain what role the ocean plays in forming such features, and the degree of connecvity between geological features and the ocean. • Constraints on ocean salinity are necessary for understanding ice shell rheology, fluid fraconaon processes within the ice shell, and how much radar aenuaon is due to temperature or salinity effects. All of these factors are important for interpreng the formaon of surface features, disnguishing among formaon models, and understanding the extent to which material can be exchanged between the surface and ocean. • Because future landing site reconnaissance is within the purview of our working group, we also point out that lower confidence in landform formaon models directly affects our confidence in selecng a landing site where material sourced from the ocean could be sampled. The uncertainty in ocean connecvity may also increase the level of cauon necessary for planetary protecon in lander operaons.

Presentaon to OPAG: April 23, 2019 24