The Mapping Imaging Spectrometer for Europa (MISE)

Abstract

The Mapping Imaging Spectrometer for Europa (MISE) is an infrared compositional instrument that will fly on NASA's Europa Clipper mission to the Jupiter system. MISE is designed to meet the Level-1 science requirements related to the mission's composition science objective to "understand the habitability of Europa's ocean through composition and chemistry" and to contribute to the geology science and ice shell and ocean objectives, thereby helping Europa Clipper achieve its mission goal to "explore Europa to investigate its habitability." MISE has a mass of 65 kg and uses an energy per flyby of 75.2 W-h. MISE will detect illumination from 0.8 to 5 μm with 10 nm spectral resolution, a spatial sampling of 25 m per pixel at 100 km altitude, and 300 cross-track pixels, enabling discrimination among the two principal states of water ice on Europa, identification of the main non-ice components of interest: salts, acids, and organics, and detection of trace materials as well as some thermal signatures. Furthermore, the spatial resolution and global coverage that MISE will achieve will be complemented by the higher spectral resolution of some Earth-based assets. MISE, combined with observations collected by the rest of the Europa Clipper payload, will enable significant advances in our understanding of how the large-scale structure of Europa's surface is shaped by geological processes and inform our understanding of the surface at microscale. This paper describes the planned MISE science investigations, instrument design, concept of operations, and data products.

Keywords: Composition; Europa; Europa Clipper; Mapping; Spectrometer.

Fig. 1

(a) The MISE instrument in a clean room at JPL in May 2023. The Entrance Baffle and Radiator have temporary protective covers. (b) A view of MISE showing the Scan Mirror Assembly. (c) The main components of MISE. The Optical Bench Assembly (OBA) consists of the OBA bipods, telescope, spectrometer detector (Teledyne) and the Scan Mirror Assembly (APL). The Radiator and Cryocooler Mount (RCM) consists of a cryocooler (which is radiation-shielded), radiator, and a Thermal Strap. The OBA and RCM are mounted on the MISE Base Frame. Figure 1a shows the RCM sheathed in mylar for electronic noise protection. The Base Frame is mounted on the Europa Clipper vault nadir wall. The MISE Data Processing Unit (DPU) and Cryocooler Electronics Unit (CEU) are in the spacecraft vault. The Focal Plane Integrated Electronics (FPIE) are mounted on the outside of the vault. Photos by Ryan Lannom

Fig. 2

The distribution of amorphous water ices (top) and crystalline water ices (bottom) on Europa’s surface, as derived from ground-based telescope data (from Ligier et al. 2016). By summing the fraction (see color bar) of both states of ice from the two panels, it is possible to estimate the amount of total water ice in the top layer of Europa’s surface. Most notably, the trailing apex, which faces into the plasma ram, is relatively depleted of water ice. See also Brown and Hand (2013). MISE will extensively map the type and state of ice across Europa

Fig. 3

Simplified view from Dalton et al. (2013) of the predicted sulfur bombardment pattern (the color bar is sulfur ions per cm²/s) into Europa’s surface, using a model by Cassidy et al. (2013). Also drawn in this figure are other agents relevant to surface weathering. As shown, the leading and trailing hemispheres will experience substantially different fluxes and there will be latitudinal controls on the amount of processing of the surface. G1ENNHILAT01, 14ENSUCOMP03, 14ENSUCOMP01 and 17ENSUCOMP02 refer to Galileo NIMS observations

Fig. 4

A map highlighting the main regions (in pink) on Europa’s surface where deep processing by energetic electrons takes place, one type of moon–magnetosphere interaction on Europa. 20 MeV (and higher) electrons move retrograde to Europa’s orbital motion and preferentially hit the leading hemisphere when their drift paths guide them over the moon. Figure from Nordheim et al. (2018)

Fig. 5

Galileo Solid State Imager (SSI) images of Europa at (a) 25 m/pixel, (b) 300 m/pixel, and (c) 7 km/pixel, which correspond roughly to MISE local, regional, and global spatial sampling performance. Note that albedo variations associated with different ice and non-ice components (salts, organics) are seen at all scales and reflect different processes that can be measured by MISE

Fig. 6

Many endogenic and exogenic processes detectable by MISE have the capacity to alter Europa’s surface chemistry and structure. (a) Sketch of macroscale geological and tectonic processes (described in detail in Daubar et al. , this collection) that can transport organics and other molecules to the surface. On a microscale (b), radiation (colored downward arrows), particle bombardment, and endogenic heat flow (red upward arrows) can alter ice structure and chemistry through damage of exposed ice grains (c), changing their observed spectra

Fig. 7

Two theoretical MISE spectra of a Europan plume, computed assuming that the plume particles are composed of pure water ice and that the particles’ size and launch velocity distributions are similar to those of Enceladus’ plume. The spectrum of the plume’s upper reaches is bluer than that of the plume’s base because larger particles are launched at lower speeds (Schmidt et al. ; Postberg et al. 2011)

Fig. 8

Detection of thermal anomalies by MISE. The solid lines represent a pixel-filling thermal anomaly. The dashed lines represent a 10% pixel fill fraction. The acceptable SNR is 10. Co-adding of bands further increases instrument sensitivity

Fig. 9

The MISE optical design (Bender et al. 2019). Figure 9a shows the MISE optical ray trace. The enlargement in Fig. 9b shows the MISE Dyson spectrometer ray trace in detail

Fig. 10

A schematic of the MISE thermal architecture with thermal control zones, temperature ranges, and heat loads

Fig. 11

The scan system: (a) a computer-aided design (CAD) model of the scanner, (b) a cross-section view to highlight the mechanical approach of the cantilever design and lightweight AlBeMET mirror; (c) photos of MISE double-sided mirror in its shipping container; large image shows diffuse reflectance of a green laser at approximate operational calibration angles. Acronyms in the labels in (b) are explained in the text

Fig. 12

On-board processing steps for the MISE scanning control system

Fig. 13

BRDFs of diffuse surface at 70° incidence angle; approximate operational range is depicted by the green box. AOI is the angle of incidence in degrees

Fig. 14

Example calibration of spectral observations based on laboratory-derived parameters, shown via the M3 imaging spectrometer at the Apollo 15 landing site on Earth’s moon (from Green et al. 2011) – representative of what will be done with MISE observations at Europa. (A) Raw signal in digital numbers (DN) per spectral channel. (B) Spectrally, spatially, and radiometrically calibrated spectra in units of spectral radiance. The calibration enables quantitative analysis of the measured spectra, which is crucial for scientific applications. (C) Fully calibrated M3 image cube delivered for science analysis

Fig. 15

Wavelength calibration and spectral sampling curve, with masked rows (beyond row 435) and spectral requirements boundaries (800 nm and 5000 nm) indicated

Fig. 16

Spatial response function centroid errors and Gaussian FWHM. (a) Cross-Track Response Function (CRF) and (b) Along-Track Response Function (ARF) centroid errors both exhibit Spectrometer Uniformity Variations (SUVs). The vertical axis represents the magnitude of deviation from perfect uniformity. The bonded gap between the order sorting filter (OSF) and linear variable filter (LVF) at 2600 nm has low signal, and thus data in this region is not displayed

Fig. 17

Spectral response function centroid errors for select laser wavelengths and spectral Gaussian FWHM across the spatial field. The vertical axis represents the magnitude of deviation from perfect uniformity. Spectral nonuniformity is low in the wavelengths above 2.1 μm, with low peak-to-peak centroid nonuniformity across spatial columns. Spectral nonuniformity is higher in the short wavelengths (below 2.1 μm), another example of Spectrometer Uniformity Variations (SUVs)

Fig. 18

An example MISE dark frame

Fig. 19

Initial a) linearity correction mapping, b) radiometric calibration coefficients, and c) radiometric flatfield results from recent instrument testing

Fig. 20

This synthetic Europa image cube illustrates how MISE cubes contain several types of compositional information that will aid the assessment of habitability. (a) 1 μm albedo map of the surface with the full spectrum and compositional information at each pixel extending backwards. (b) Map of ice phases: red = acid hydrate, green = crystalline ice, blue = amorphous ice. (c) Distribution of epsomite, a salt, (d) Map of thermal anomalies, and (e) Map of epsomite (red) and two organics: benzene (green) and octane (blue). Yellow areas have both epsomite and benzene. MISE shows this area contains multiple spectral tracers of habitability: salts, temperatures indicative of recent activity, and organics associated with bands, a landform hypothesized to reflect transport of material from within the ice shell

Fig. 21

A schematic representation of the MISE activities that will occur during each Europa flyby. An encounter (E_n) is defined as starting 2 days before closest approach (C/A) h (i.e., at about the five-day (5d) marker, where days are counted from apoapsis). In addition to the observation acquisition strategy explained in 4.1 (and during the green curve) and data validation/downlink plan explained in 4.2 (see receipt of one processed cube on right and green triangle near apoapsis), key events include (1) around the start of the E_n, the spacecraft team will generate the last orbital determination (OD) predicts and MISE then generate and uplink their scan mirror profiles and command sequence for E_n. The MISE cooldown will also start, bringing the instrument to its operational temperatures for data acquisition. The spacecraft’s Bulk Data Storage BDS filters (red boxes) are part of the spacecraft sorting of data for downlink; as MISE collects its data on-instrument for processing before sending to the spacecraft (explained in Sect. 5.1), a BDS filter will run about two days after C/A so that all MISE data from E_n can be processed and readied for downlink

Fig. 22

The global-scale coverage achieved with the notional observation plan for tour Rnd7_T1; this map is representative of the observations that MISE would collect. During flight, targeting may be a little different as that would include consideration of interesting geologic units or features, maximizing unique coverage with higher resolution observations, and other science priorities of the Europa Clipper science team. (a) This map shows the coverage that would be used for generation of a near-global map better than 10 km/pixel in resolution; in this simulation the achieved coverage is 87.2%. Also shown are the regional-scale images (small, dark blue boxes), which could also be integrated into this map. (b) This map shows the resolutions that would be achieved at better than 30 km/pixel in resolution (i.e., the areas 10–30 km/pixel would be imaged with the observations shown in (a) and useable by the science team, but not counted towards the Europa Clipper Level-1 science requirements); in this simulation the achieved coverage is 95.6%. These lower-resolution observations are of science value; for example, even lower-resolution imaging of the polar regions is of interest for a search for cold-trapped volatiles. These two maps were generated with CADMUS using SIMPLEX with a simple algorithm for scheduling, as outlined in Sect. 4.2

Fig. 23

The regional-scale coverage achieved with the notional observation plan for tour Rnd7_T1; this map is representative of the observations that MISE would collect. Coverage shown is 0.61%. During flight, targeting may be a little different as there would be consideration of interesting geologic units or features, maximizing unique coverage with higher resolution observations, and other science priorities of the Europa Clipper science team. The map was generated with CADMUS using SIMPLEX with a simple algorithm for scheduling, as outlined in Sect. 4.2

Fig. 24

The local-scale coverage achieved with the notional observation plan for tour Rnd7_T1; this map is representative of the observations that MISE would collect. During flight, targeting may be a little different as there would be consideration of interesting geologic units or features, maximizing unique coverage with higher resolution observations, and other science priorities of the Europa Clipper science team. The map was generated with CADMUS using SIMPLEX with a simple algorithm for scheduling, as outlined in Sect. 4.2

Fig. 25

The number of nightside cubes collected via the notional observation plan for tour Rnd7_T1; this map is representative of the observations that MISE would collect. During flight, targeting may be a little different as there would be consideration of interesting geologic units or features, maximizing unique coverage with higher resolution observations, and other science priorities of the Europa Clipper science team. The map was generated with CADMUS using SIMPLEX with a simple algorithm for scheduling, as outlined in Sect. 4.2

Fig. 26

A schematic of the MISE reference Europa encounter data acquisition scenario. Each global-scale [G] and joint scan [J] cube (40,000–1200 km altitude) is bracketed by dark frame stacks [D]. Since observing time surrounding closest approach (C/A) is limited, dark frame stacks bracket rather than interleave with the regional [R] and local [L] observation set (<1200 km altitude)

Fig. 27

The sequence of processing steps within the MISE baseline frame aggregation and radiation noise mitigation. Starting with the oversampled observation (a) and related dark calibration observations, the results are dark-corrected (b) and statistics on the noise are generated (c). The final cube (d) would have radiation noise removed