Moonraker: Enceladus Multiple Flyby Mission

Enceladus, an icy moon of Saturn, possesses an internal water ocean and jets expelling ocean material into space. Cassini investigations indicated that the subsurface ocean could be a habitable environment having a complex interaction with the rocky core. Further investigation of the composition of the plume formed by the jets is necessary to fully understand the ocean, its potential habitability, and what it tells us about Enceladus's origin. Moonraker has been proposed as an ESA M-class mission designed to orbit Saturn and perform multiple flybys of Enceladus, focusing on traversals of the plume. The proposed Moonraker mission consists of an ESA-provided platform with strong heritage from JUICE and Mars Sample Return and carrying a suite of instruments dedicated to plume and surface analysis. The nominal Moonraker mission has a duration of &sim;13.5 yr. It includes a 23-flyby segment with 189 days allocated for the science phase and can be expanded with additional segments if resources allow. The mission concept consists of investigating (i) the habitability conditions of present-day Enceladus and its internal ocean, (ii) the mechanisms at play for the communication between the internal ocean and the surface of the South Polar Terrain, and (iii) the formation conditions of the moon. Moonraker, thanks to state-of-the-art instruments representing a significant improvement over Cassini's payload, would quantify the abundance of key species in the plume, isotopic ratios, and the physical parameters of the plume and the surface. Such a mission would pave the way for a possible future landed mission. &nbsp;</p

Mapping the surface composition of Europa with SUDA

To assess the potential habitability of Jupiter's moon Europa, it is important to understand its chemical composition (Hand et al., 2007). Young terrain features on Europa's surface likely consist of material up-welled from the liquid water source below (Wilson et al., 1997; Pappalardo et al., 1998; McCord et al., 1999; Figueredo and Greeley, 2004; Mével and Mercier, 2007), encoding relevant compositional information. A major science objective of NASA's Europa Clipper mission is to characterize the composition of young terrain features using data acquired on close flybys. The Surface Dust Analyzer (SUDA) is an in situ instrument that collects and analyzes the composition of individual grains (Kempf et al., 2012), which are ejected from Europa's surface by a continuous bombardment of interplanetary impactors (Krüger et al., 1999, 2003; Goode et al., 2021). By applying a dynamical model of these particles, we compute the probability of SUDA's detections originating from a given feature along the flyby trajectory based on Monte Carlo (MC) simulations. The time-of-flight (TOF) mass spectra that characterize the chemical composition of individual grains, results in a time series of various compositional types along the flyby. We present here a method to analyze a time series of compositional spectra recorded by SUDA that provides a robust estimate for the abundance of compositional types on the surface, spatially resolved for features along the ground track of the flyby. By demonstrating the association of compositional detections with geological sites of origin, data collected by SUDA can be used to infer the compositional ground truth for terrain features on Europa

Simulation of grid morphology's effect on ion optics and the local electric field

Electric field ion optics are employed by many scientific instruments for investigating ions, e.g., using time-of-flight mass spectrometers. A common design feature of such instruments is the grounded grid that provides boundaries between regions that need to have different electric fields. In order to save computer memory, these grids are often modeled by indefinitely thin conducting sheets. This approximation does not include the effects of the grid morphology on the electric field. This paper investigates these grid morphology effects on both the electric field and the trajectories of ions passing through the grids using finite element analysis. The simulations in this paper indicate that a significant amount of the electric potential will leak through a grid&rsquo;s empty space. The leakage of this field through the grid slows an ion down relative to the speed that it would be assumed to have based on the indefinitely thin sheet model. The ions are then eventually accelerated back to the energy that they would have if the grid were a thin sheet. However, this deceleration and acceleration result in the lengthening of the ion time of flight, independent of the size of the drift region. The deflection of the ions passing through the grid increases with the ion&rsquo;s proximity to the grid struts, the size of the acceleration region, and the shape of the grid cell. This deflection also results in a small but potentially significant loss of focus and changes in the path length. &nbsp;</p

Micrometeoroid infall onto Saturn’s rings constrains their age to no more than a few hundred million years

There is ongoing debate as to whether Saturn’s main rings are relatively young or ancient— having been formed shortly after Saturn or during the Late Heavy Bombardment. The rings are mostly water-ice but are polluted by non-icy material with a volume fraction ranging from ∼0.1 to 2%. Continuous bombardment by micrometeoroids exogenic to the Saturnian system is a source of this non-icy material. Knowledge of the incoming mass flux of these pollutants allows estimation of the rings’ exposure time, providing a limit on their age. Here we report the final measurements by Cassini’s Cosmic Dust Analyzer of the micrometeoroid flux into the Saturnian system. Several populations are present, but the flux is dominated by low-relative velocity objects such as from the Kuiper belt. We find a mass flux between 6.9 · 10−17 and 2.7 · 10−16 kg m−2s−1 from which we infer a ring exposure time ≲100 to 400 million years in support of recent ring formation scenarios

How to identify cell material in a single ice grain emitted from Enceladus or Europa

Icy moons like Enceladus, and perhaps Europa, emit material sourced from their subsurface oceans into space via plumes of ice grains and gas. Both moons are prime targets for astrobiology investigations. Cassini measurements revealed a large compositional diversity of emitted ice grains with only 1 to 4% of Enceladus's plume ice grains containing organic material in high concentrations. Here, we report experiments simulating mass spectra of ice grains containing one bacterial cell, or fractions thereof, as encountered by advanced instruments on board future space missions to Enceladus or Europa, such as the SUrface Dust Analyzer onboard NASA's upcoming Europa Clipper mission at flyby speeds of 4 to 6 kilometers per second. Mass spectral signals characteristic of the bacteria are shown to be clearly identifiable by future missions, even if an ice grain contains much less than one cell. Our results demonstrate the advantage of analyses of individual ice grains compared to a diluted bulk sample in a heterogeneous plume

Sample return of interstellar matter (SARIM)

n/

Observation of saturnian stream particles in the interplanetary space

In January 2004 the dust instrument on the Cassini spacecraft detected the first high-velocity grain expelled from Saturn - a so-called stream particle. Prior to Cassini's arrival at Saturn in July 2004 the instrument registered 801 faint impacts, whose impact signals showed the characteristic features of a high-velocity impact by a tiny grain. The impact rates as well as the directionality of the stream particles clearly correlate with the sector structure of the interplanetary magnetic field (IMF). The Cosmic Dust Analyser (CDA) registered stream particles dominantly during periods when the IMF direction was tangential to the solar wind flow and in the prograde direction. This finding provides clear evidence for a continuous outflow of tiny dust grains with similar properties from the saturnian system. Within the compressed part of co-rotating interaction regions (CIRs) of the IMF, characterized by enhanced magnetic field strength and compressed solar wind plasma, CDA observed impact bursts of faster stream particles. We find that the bursts result from the stream particles being sped up inside the compressed CIR regions. Our analysis of the stream-particle dynamics inside rarefaction regions of the IMF implies that saturnian stream particles have sizes between 2 and 9 nm and exit the saturnian systems closely aligned with the planet's ring plane with speeds in excess of 70 km s-1.</p

Mapping the surface composition of Europa with SUDA

Abstract To assess the potential habitability of Jupiter’s moon Europa, it is important to understand its chemical composition (Hand et al., 2007). Young terrain features on Europa’s surface likely consist of material up-welled from the liquid water source below (Wilson et al., 1997; Pappalardo et al., 1998; McCord et al., 1999; Figueredo and Greeley, 2004; Mével and Mercier, 2007), encoding relevant compositional information. A major science objective of NASA’s Europa Clipper mission is to characterize the composition of young terrain features using data acquired on close flybys. The Surface Dust Analyzer (SUDA) is an in situ instrument that collects and analyzes the composition of individual grains (Kempf et al., 2012), which are ejected from Europa’s surface by a continuous bombardment of interplanetary impactors (Krüger et al., 1999, 2003; Goode et al., 2021). By applying a dynamical model of these particles, we compute the probability of SUDA’s detections originating from a given feature along the flyby trajectory based on Monte Carlo (MC) simulations. The time-of-flight (TOF) mass spectra that characterize the chemical composition of individual grains, results in a time series of various compositional types along the flyby. We present here a method to analyze a time series of compositional spectra recorded by SUDA that provides a robust estimate for the abundance of compositional types on the surface, spatially resolved for features along the ground track of the flyby. By demonstrating the association of compositional detections with geological sites of origin, data collected by SUDA can be used to infer the compositional ground truth for terrain features on Europa

Detecting the surface composition of geological features on Europa and Ganymede using a surface dust analyzer

Abstract Europa and Ganymede are both likely to have subsurface oceans (Carr et al., 1998; Khurana et al., 1998; Kivelson et al., 2000). Young surface features may provide an opportunity to sample material from either a subsurface ocean or bodies of liquid water near the surface (McCord et al., 1999, 2001). Detailed compositional information is of large interest for understanding the evolution, oceanic chemistry, and habitability of these moons. To develop an altitude-dependent model for the detectability of ejecta particle composition originating from surface features of a given size, we simulate detections by a dust analyzer with the capability of measuring compositional makeup on board a spacecraft performing close flybys of Europa and Ganymede (Postberg et al., 2011). We determine the origin of simulated detections of ejecta by backtracking their trajectories to the surface using velocity distributions given in the ejecta cloud model by Krivov et al. (2003). Our model is useful for designing flybys with typical closest approach altitudes, such as the ones planned for NASA’s Europa Clipper mission, where we wish to accurately identify the composition of surface features using a dust analyzer