Sascha Kempf

Salt-rich ice particles, termed Type 3, are a major compositional group within Enceladus’ plume and Saturn’s E ring and are thought to represent frozen micrometer-sized aerosolized droplets of Enceladus’ salty subsurface ocean. Here, we present an analysis on the basis of ≈1000 mass spectra of individual Type 3 E ring ice grains recorded by Cassini’s Cosmic Dust Analyzer (CDA), revealing a large compositional diversity among these grains. We find at least five basic compositional subtypes dominated by either sodium chloride (NaCl), sodium bicarbonate (NaHCO ₃ )/sodium carbonate (Na ₂ CO ₃ ), disodium phosphate (Na ₂ HPO ₄ )/trisodium phosphate (Na ₃ PO ₄ ), sodium hydroxide (NaOH), potassium chloride (KCl), or potassium hydroxide (KOH). By conducting experiments and thermodynamic calculations, we show that salt separation in agreement with CDA observations occurs as a consequence of salt mineral precipitation only within droplet sizes >10 micrometers and freezing rates below 20 kelvins per minute. We suggest that oceanic spray forms with an average size of 100s of micrometers entrained in a slow gas flow, causing slow freezing and separation of salts. Subsequently, they are accelerated to speeds >100 meters per second in narrow ice vents where frequent wall collisions lead to much smaller fragments mostly containing a single type of salt, matching CDA observations. The gradual cooling of ocean droplets in combination with wall collisions determines the final size distribution and provides an efficient chemical separation of both inorganic and organic oceanic constituents into differently composed ice grains ejected into Enceladus’ plume.

The Cosmic Dust Analyzer (CDA) on the Cassini spacecraft has convincingly demonstrated the scientific value of mass spectra of ice particles ejected by the plume on Saturn's ice moon Enceladus. Trace amounts of organic and inorganic molecules embedded in ice particles revealed invaluable insight into the chemical composition of the ocean beneath the moon's icy crust. However, it became quickly obvious that to address open questions about the astrobiological nature of the ocean requires impact ionisation mass spectrometers with a considerably higher mass resolution than that of the CDA instrument of m/Δm ~ 50. Other CDA shortcomings include target cleanliness issues and the low detection cadence of 1 impact per second.The High Ice Flux Instrument (HIFI) is a reflectron-type impact mass spectrometer specifically designed for such applications. It has a mass resolution of 1000 to 2000 and has been optimized for using the electronics of the Surface Dust Analyzer instrument on Europa Clipper for recording the spectra. To ensure a high mass resolution HIFI has a long drift region and uses a set of electrostatic Einzel lenses to prevent the ion beam from diverging before entering the single stage reflectron region. The reflectron optics is composed of 23 precision machined electrostatic electrodes to guarantee a smooth reflecting field. In contrast to previous reflectron impact mass spectrometers such as CIDA enter the impacting particles the spectrometer through the reflectron to strike the target at a right angle. The target itself is a highly polished Titanium carrier coated with 250 nm of high purity Iridium (5 nm surface roughness). The high atomic mass of Iridium ensures that no target lines as well as target cluster lines appear in the mass range ≥ 200 u relevant for the compositional analysis of mineral and ice particles. Impact ionization mass spectrometers characterize the composition of microscopic particles hitting the instrument's metal target by recording Time-Of-Flight (TOF) mass spectra of the plasma created upon impact. The resulting TOF spectra show a strong dependence on the impact velocity. At very low speeds around 1 km/s, the spectra are dominated by lines of elements with very low ionization energy, mainly sodium and potassium. At velocities of a few km/s or more, the spectra are dominated by the mass lines associated with the impactor material and the target material.Because dust impacts in interplanetary space are rare events, previous impact ionization mass spectrometers, such as the Surface Dust Analyzer (SUDA) on the payload of NASA's next flagship mission to the Jovian moon Europa, the Interstellar Dust Experiment (IDEX) on the payload of NASA's IMAP mission, or the Dust Detection System (DDS) on the payload of JAXA's Destiny+ mission to the asteroid Phaethon, have been optimized for a large sensitive area. However, there are dust environments where the dust number density is so high that the TOF mass spectra of successive impacts recorded by large area dust detectors begin to overlap. The Cosmic Dust Detector (CDA) onboard the Cassini spacecraft recorded impact rates exceeding 1000 s-1 in the ice particle plume of the Saturnian moon Enceladus (sensitive area ~36 cm2). Therefore, large area dust instruments are not capable of recording high quality mass spectra in dust-rich environments, such as cryovolcanoes on the Saturnian moon Enceladus or comet trails. To prevent mass spectra from overlapping, instruments optimized for high impact rates must have a very small sensitive area.The ideal ion optics for such an instrument is a classical reflectron optimized for impact plasma analysis. Each TOF spectrometer consists of an accelerator region, which provides all ions with the energy Uacc, and an ion detector at a distance L from the accelerator region - the drift length - to measure the flight times of the ions t = t0 + a m1/2, where t0 is the ion launch time and a is the stretch parameter of the instrument. The initial thermal energy of an ion species of mass m leads to a spread Δt in their flight times, which decreases the resulting mass resolution m/Δm = t/2Δt of the instrument. A reflectron uses a repulsive electric field to reduce Δt. Ions launched with excess energy ΔU > 0 penetrate deeper into the repulsive field region and thus have a longer flight path than ions launched with zero initial energy, which partially compensates for the nonzero excess energy.Cosmic dust particle impacts are a stochastic phenomenon, which means that there is no prior knowledge of either the impact or the ion launch time t0. Therefore, techniques such as the extraction pulse method for reducing the initial energy spread cannot be used in impact ionization mass spectroscopy.Current state-of-the-art impact mass spectrometers have a mass resolution of 100 to 300, which is not sufficient to identify astrobiologically relevant materials such as amino acids embedded in ice grains. For example, in an impact mass spectrum of a shock-frozen ice grain from a 0.1 M NaCl solution containing 100 ppm argenine, which is a realistic assumption for the composition of the Enceladus ocean in the presence of life, argenine appears as the sodiated ion [ArgNa]+ (m ~ 219.08 u), which is close to the salt cluster line [(NaCl)2(NaOH)2Na]+ (m ~ 218.89 u). The separation of the two lines requires a mass resolution of m/Δm \sim 219 u / 0.19 u = 1,153.Here we report on the High Ice Flux Instrument (HIFI), which combines a mass resolution sufficient for the unambiguous identification of astrobiologically relevant traces of organic matter in ice particles with a small sensitive area. The instrument is a Time-Of-Flight (TOF) impact mass spectrometer with a single-stage reflectron ion optics, optimized for the acquisition of high-resolution mass spectra of ice particles during close spacecraft flybys through dust-rich environments.

The Interstellar Dust Experiment (IDEX) is a dust impact ionization Time-of-Flight (ToF) mass spectrometer launched onboard the Interstellar Mapping and Acceleration Probe (IMAP) on September 24, 2025. IMAP is in nominal science operations at the Sun-Earth Lagrange Point L1, with IDEX passively collecting cosmic dust grains at a cadence of roughly one interplanetary particle per week. IDEX will detect and analyze both Interstellar Dust Grains (ISDs) from the Local Interstellar Medium (LISM) as well as Interplanetary Dust grains (IDPs). ISD collection will begin in April 2026 as we enter the interstellar dust focusing season. IDEX will collect a variety of ISDs and IDPs over its lifetime, ranging from pristine to heavily processed particles that are a mixture of mineral and organic material.We investigate how IDEX can be used to determine the degree of processing dust grains have undergone. These studies inform the analysis of IDEX flight data representative of organic and mineralogical cosmic dust grains. Assessments of aromaticity and the presence of functional groups can be used to determine the processing of organic species. Polycyclic aromatic hydrocarbons (PAHs) are the most pristine organic compounds. PAH destruction and processing lead to the production of heterocyclic compounds and decreasing aromaticity in organic species. Minerals can be appraised via the degree of serpentinization and conversion from crystalline to amorphous silicates. IDEX's large effective area combined with high mass resolution (m/dm > 200) and dynamic range make it well suited to assess minute variations in mass spectra pointing to pristine versus processed materials. Various campaigns from the last two years build and support the techniques presented here to analyze IDEX flight data.

Launched in September 2025, NASA’s Interstellar Mapping and Acceleration Probe (IMAP) now operates at the Sun–Earth L1 Lagrange point to investigate the interaction between the heliosphere and its interstellar environment. Among its ten-instrument payload is the Interstellar Dust Experiment (IDEX), which is designed to measure the flux, size distribution, and chemical, elemental, and isotopic composition of dust particles entering the solar system.IDEX directly samples interstellar dust (ISD) originating in the local interstellar medium (LISM), providing unique insight into the composition of contemporary interstellar solid matter. A key scientific objective is to assess whether the present-day LISM dust population is compositionally consistent with the primordial material from which the solar system formed. In addition to ISD, IDEX measures interplanetary dust particles (IDPs) of cometary and asteroidal origin, including grains that may preserve pre-solar molecular cloud material as well as particles altered by solar system processing. These observations enable comparisons between interstellar, cometary, and asteroidal dust and help constrain the origins and evolutionary histories of organic-rich materials.IDEX measurements of the directional and size distributions of ISD provide critical constraints on models of dust transport through the heliosphere, including the filtering effects of heliospheric magnetic fields and solar activity on small, charged grains. These data contribute to improved understanding of the heliospheric boundary and the processes governing the penetration of dust into the inner heliosphere.IDEX is an impact-ionization time-of-flight mass spectrometer that analyzes ions generated by high-velocity dust impacts on a target surface. This presentation provides an overview of IDEX’s scientific objectives and measurement capabilities and reports on early in-flight performance and initial results, demonstrating IDEX’s role in linking interstellar and solar system material populations.

Impact mass spectrometers such as the Cosmic Dust Analyser (CDA) on board the Cassini spacecraft have proven invaluable in determining the composition of the surfaces from which detected particles originate. However, connecting impact mass spectra with the composition of the striking particle is not straightforward and requires laboratory impact spectra of particles of known composition and speed. Such data has so far been acquired for minerals, some organic materials and water ice. In this study, we present cation and anion impact mass spectra of aluminum and iron particles striking ammonia ice, a possible surface component of outer solar system bodies such as Europa, Ariel, and Pluto. To reduce ambiguity in the mass lines appearing in the spectra, we performed impact experiments with 14NH3 and 15NH3 ice.The resulting impact mass spectra demonstrate only a slight dependence on impact speed. The cation impact spectra are dominated by protonated ammonia cluster ions, (NH3)NH4, the abundance of which decreases monotonically with cluster size. Consistent with data obtained from gas-phase mass spectrometry experiments involving ammonia clusters, (NH3)4NH4 clusters are overabundant in impact mass spectra at all impact speeds, suggesting that these clusters possess a particularly stable geometric configuration. This finding implies that cluster formation in hypervelocity experiments is well described by gas-phase chemistry. Unlike water ice, well-formed ammonia cluster impact mass spectra can be obtained at impact speeds as low as 1 km/s. This suggests that ammonia deposits could be detected even by instruments in low orbits around icy moons such as Ganymede.We performed Monte Carlo simulations to verify whether the potential ammonia deposits on Europa, as identified in Galileo IR data by Emran (2026), can be detected by the Surface Dust Analyzer (SUDA) impact mass spectrometer on board the Europa Clipper spacecraft [6]. This spacecraft will conduct 49 low altitude Europa flybys starting in 2030. Our simulations clearly demonstrate that, if present, such deposits will be unambiguously identified.

Introduction: Europa’s surface is a dynamic interface where subsurface materials, radiation-processed surface chemistry, and exogenic inputs converge and are cycled back into the subsurface. Direct sampling of that material is central to assessing Europa’s habitability and evaluating the potential delivery of organic and geochemical species from the interior ocean to the surface1. The Surface Dust Analyzer (SUDA) onboard Europa Clipper provides a uniquely powerful means of accessing this material through the compositional analysis of individual ice grains lofted from Europa’s surface during flyby using time-of-flight mass spectrometry (TOF-MS). Each particle to be analyzed by SUDA will carry a chemical fingerprint of the surface unit from which it originated, offering a window into the chemical composition of surface regions that cannot currently be directly sampled in situ, including evidence for salts, organics, and other chemical indicators of habitability.Methods: Successfully interpreting these measurements requires understanding how each detection maps back to its surface provenance. We employ a dynamical modeling framework developed by Goode et al.2,3 which couples an ejecta cloud model with Monte Carlo simulations of Europa Clipper flybys. For a specified flyby geometry, the local number density of ejecta along the trajectory are computed as a function of time, where SUDA detections are stochastic and are described by a Poisson distribution. At each simulated detection event, particle velocities are drawn from the probability density of the ejecta cloud at the spacecraft location. The resulting vector is then propagated backward under Europa’s gravity to determine the corresponding surface launch point. Repeating this procedure over many Monte Carlo simulations yields a statistical distribution of launch sites for a given flyby, enabling the fraction of detections whose origin lies within a predefined surface region to be computed. Associating features within SUDA’s mass spectra with these launch locations allows chemical compositions determined for individual ice grains to be probabilistically linked to compositionally distinct surface features. This framework provides quantitative measures of both the expected number of detections for a given surface feature as a function of feature size and flyby altitude, and the confidence with which a given chemical composition can be attributed to a particular geological feature.Acknowledgements: This work was supported by NASA through the Europa Clipper project. References: 1. Vance, S. et al. (2023). Space Sci. Rev. 219, 81. 2. Goode, W. et al. (2021). Planet. Space Sci. 208, 105343. 3. Goode, W. et al. (2023). Planet. Space Sci. 227, 105633.

The Interstellar Dust Experiment (IDEX) is an impact-ionization time-of-flight mass spectrometer aboard NASA’s Interstellar Mapping and Acceleration Probe (IMAP), launched in September 2025 and operating at the Sun–Earth L1 Lagrange point. IDEX combines a large sensitive area (>600 cm²), high mass resolution (m/Δm > 200 at m = 100 u), and a wide dynamic range to measure the mass, flux, dynamics, and elemental and chemical composition of interstellar and interplanetary dust particles. The instrument’s performance has been validated through extensive laboratory calibration using iron, platinum-coated olivine, and aluminum particles with masses from approximately 3 × 10⁻¹⁸ to 10⁻¹⁴ kg and impact velocities of 4–50 km s⁻¹. In flight, IDEX operates in the ambient space environment, where it is exposed to interplanetary Lyman-α radiation and galactic cosmic rays. Many of the dust particles detected by IDEX in space are substantially larger than those achievable in laboratory accelerators and therefore generate significantly larger impact charges. This presentation provides an overview of the in-flight performance of IDEX, focusing on key instrument parameters and their comparison with laboratory calibration results.

Impact ionization time-of-flight (TOF) mass spectrometry has been shown to be a powerful in situ technique for analyzing the composition of icy bodies in the outer Solar System, providing information inaccessible to remote sensing alone. Instruments such as the SUrface Dust Analyzer (SUDA) aboard Europa Clipper will sample ice grains in Europa’s exosphere, enabling compositional mapping of Europa's surface. Interpretation of these measurements is complicated by the physics of hypervelocity impacts, as fragmentation pathways, ion clustering, and relative ion yields depend strongly on both impact velocity and target composition. Reliable interpretation of spacecraft data, including measurements from Cassini’s Cosmic Dust Analyzer, therefore requires high-fidelity laboratory analogue experiments.Here we present laboratory TOF mass spectra generated from hypervelocity dust impacts into cryogenic ice targets using the dust accelerator facility at the University of Colorado Boulder. These experiments produce reference spectra from known ice compositions that serve as analogue datasets for spaceborne measurements. The materials investigated include ammonia ices, carbon dioxide ices, and salt-rich water ices, all of which have been proposed as relevant to Europa’s icy shell.A central advancement of this work is the use of isotopically labeled ice compositions to reduce ambiguity in spectral interpretation. By generating spectra from 15NH3 and 13CO2 ices, predictable mass shifts are observed in diagnostic ion and cluster peaks originating from the impacted material. These shifts provide direct confirmation of molecular contributions within complex spectra and significantly improve confidence in peak assignments.The experiments were conducted by accelerating micron-scale dust particles to velocities of 1-50 km s-1 and impacting them into thin ice films grown under ultra-high vacuum on cryogenically cooled substrates. Volatile ices were deposited from high-purity gases. And salt-rich water ices were produced from aerosolized liquid particles using novel operating conditions. Impact-generated plasmas were analyzed using TOF mass spectrometry. Isotopically labeled datasets were used to confirm molecular assignments via predictable mass shifts.These results demonstrate that laboratory analogue measurements can reproducibly capture composition-dependent features in impact ionization spectra across a wide range of relevant velocities. Ammonia-bearing ices provide a useful test case for isotopic validation. Our early results indicate that this approach is broadly applicable to diverse icy-world compositions. Ongoing and future work will expand this reference database to additional salts and isotopically marked water ice, chemical compositions relevant to Europa and other ocean worlds.

Organic compounds are a ubiquitous component of cosmic dust and provide insight into the origin of planetary systems, the availability of carbon for life in the solar system and beyond, and the distribution of potential biosignatures in the universe. Compositional and dynamical analysis of such dust grains can shed insight into their origin. The Destiny Dust Analyzer (DDA) onboard JAXA’s interplanetary space mission DESTINY+ will detect and analyse the composition of (sub-)micron sized dust ejecta during flybys of asteroids Apophis and Phaethon [1,2]. DDA will characterise both interplanetary and interstellar dust grains during the mission’s lifetime [3]. DDA is an impact ionisation time-of-flight mass spectrometer, whereby dust particles incident onto the instrument’s target at hypervelocity (≥ 2 km s-1) vaporise and partially fragment into various constituent ions and neutrals. Here, we investigate the capability of DDA to detect a mixture of complex organic compounds in single cosmic dust particles. An organic cosmic dust analogue is prepared by coating polycyclic aromatic hydrocarbon, perylene (C20H12), microparticles with an ultrathin overlayer of a conductive polymer, polypyrrole H(C4H2NH)nH, to enable acceleration up to hypervelocities with a high-voltage van de Graaff instrument. Time-of-flight mass spectra obtained at impact speeds ~3-20 km/s are recorded in this calibration campaign. The characteristic parent molecular ion for perylene, [C20H12 (+H)]+, is observed at m/z 251 ± 1 in mass spectra arising from impacts between 3 and 8 km s-1. However, between 8 and 18 km s-1, no such parent ion is observed. Instead, impact ionisation mass spectra exhibit a characteristic series of homologous [CnHm]+ fragments originating from both polypyrrole and perylene, alongside some non-sequential ions which may be diagnostic for distinguishing between different organic components in cosmic dust. The contributions of each species to fragmentation patterns in the mass spectra is coupled with the impact velocity. Our results are in agreement with Mikula et al. (2024), who investigated impact ionisation of polypyyrole-coated anthracene particles for the Interstellar Dust EXperiment (IDEX) onboard NASA's Interstellar Mapping and Acceleration Probe (IMAP), and observed a similar relationship between fragmentation pattern and velocity [4].Additional experiments with a range of PAHs, heterocycles, and lower mass organics at various velocities, will yield further insight into the detection and characterisation of heterogeneous dust likely to be encountered by DDA. Similarly, theoretical chemical calculations could assist in deciphering the contribution of different species to mass spectral features via the analysis of dissociation thermodynamics and kinetics.[1] Ozaki et al. (2022) https://doi.org/10.1016/j.actaastro.2022.03.029[2] Simolka et al. (2024) https://doi.org/10.1098/rsta.2023.0199[3] Krüger et al. (2024) https://doi.org/10.1016/j.pss.2024.106010[4] Mikula et al. (2024) https://doi.org/10.1021/acsearthspacechem.3c00353

The Europa Clipper spacecraft is located about 1 au downstream from the interstellar comet 3I/ATLAS around its perihelion. Here we model the propagation of pickup ions and cometary dust originating from 3I/ATLAS to examine their detectability by the Europa Clipper spacecraft. Our results suggest that while pick up detection is possible, the dust tail will not reach the Clipper spacecraft, Mars, nor the Jovian system.