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

“Dogged” Search of Fresh Nakhla Surfaces Reveals New Alteration Textures

Special Issue: 74th Annual Meeting of the Meteoritical Society, August 8-12, 2011, London, U.K.International audienceCarbonaceous chondrites are considered as amongst the most primitive Solar System samples available. One of their primitive characteristics is their enrichment in volatile elements.This includes hydrogen, which is present in hydrated and hydroxylated minerals. More precisely, the mineralogy is expected to be dominated by phyllosilicates in the case of CM chondrites, and by Montmorillonite type clays in the case of CI. Here, in order to characterize and quantify the abundance of lowtemperature minerals in carbonaceous chondrites, we performed thermogravimetric analysis of matrix fragments of Tagish Lake, Murchison and Orgueil

Synergies between interstellar dust and heliospheric science with an Interstellar Probe

We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavors and programmatic aspects that are important to maintain or develop in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an Interstellar Probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute-through measuring dust - to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it `rolls' into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions.Comment: 18 pages, 7 Figures, 5 Tables. Originally submitted as white paper for the National Academies Decadal Survey for Solar and Space Physics 2024-203

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

Abstract 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

A Dedicated Small Lunar Exploration Orbiter and a Mobile Surface Element

The Moon is an integral part of the Earth-Moon system, it is a witness to more than 4.5 b. y. of solar system history, and it is the only planetary body except Earth for which we have samples from known locations. The Moon is thus a key object to understand our Solar System. The Moon is our closest companion and can easily be reached from Earth at any time, even with a relatively modest financial budget. Consequently, the Moon was the first logical step in the exploration of our solar system before we pursued more distant targets such as Mars and beyond. The vast amount of knowledge gained from the Apollo and other lunar missions of the late 1960's and early 1970's demonstrates how valuable the Moon is for the understanding of our planetary system (e.g. [1], [2]). Even today, the Moon remains an extremely interesting target scientifically and technologically. New data have helped to address some of our questions about the Earth-Moon system, but many remain and new questions arose. In particular, the discovery of water at the lunar poles, and water and hydroxyl bearing surface materials and volatiles, as well as the discovery of young volcanism have changed our view of the Moon. Therefore, returning to the Moon is the critical stepping-stone to further exploring our immediate planetary neighborhood. Here, we present scientific and technological arguments for a Small Lunar Explorations Orbiter (S-LEO) dedicated to investigate so far unsolved questions and processes. Numerous space-faring nations have realized and identified the unique opportunities related to lunar exploration and have planned missions to the Moon within the next few years. Among these missions, S-LEO will be unique, because of its unprecedented spatial and spectral resolutions. S-LEO will significantly improve our understanding of the lunar environment in terms of composition, surface ages, mineralogy, physical properties, and volatile and regolith processes. S-LEO will carry an entire suite of innovative, complementary technologies, including high-resolution camera systems, several spectrometers that cover previously unexplored parts of the electromagnetic spectrum over a broad range of wavelengths, and a communication system to interact with landed equipment on the farside. The Small Lunar Explorations Orbiter concept is technologically challenging but feasible, and will gather unique, integrated, interdisciplinary data sets that are of high scientific interest and will provide an unprecedented new context for all other international lunar missions. The most visible mission goal of S-LEO will be the identification and mapping of lunar volatiles and investigating their origin and evolution with high spatial as well as spectral resolution. Therefore, in addition to mapping the geological context in the sub-meter range, a screening of the electromagnetic spectrum within a very broad range will be performed. In particular, spectral mapping in the ultraviolet and mid-infrared will provide insight into mineralogical and thermal properties so far unexplored in these wavelength ranges. The determination of the dust distribution in the lunar orbit will provide information about processes between the lunar surface and exosphere supported by direct observations of lunar flashes. Measuring of the radiation environment will finally complete the exosphere investigations. Combined observations based on simultaneous instrument adjustment and correlated data processing will provide an integrated geological, geochemical and geophysical database that enables: • the exploration and utilization of the Moon in the 21st century; • the solution of fundamental problems of planetology concerning the origin and evolution of terrestrial bodies; • understanding the uniqueness of the Earth-Moon System and its formation and evolution; • the absolute calibration of the impact chronology for the dating of solar system processes; • deciphering the lunar regolith as record for space environmental conditions; • mapping lunar resources. S-LEO is featuring a set of unique scientific capabilities w.r.t. other planned missions including: (1) dedicated observation of volatiles (mainly H2O and OH), their formation and evolution in direct context with the geological and mineralogical surface with high spectral and spatial resolution (< 1m/px); (2) besides the VIS-NIR spectral range so far uncovered wavelengths in the ultraviolet (0.2 – 0.4 µm) and mid-infrared (7 - 14 µm) will be mapped to provide mineralogical context for volatile processes (e.g. sources of oxygen); (3) detection of rock-forming elements by means of x-ray fluorescence in the spectral range of .5-10 keV in order to constrain the composition of key elements of lunar surface materials; (4) monitoring of dust and radiation in the lunar environment and its interaction with the surface; and (5) monitoring of present-day meteoroitic impacts. In 2009 ESA commissioned a Mobile Payload Element (MPE) to assist the ESA Lunar Lander mission. The MPE, currently under study in Germany, is designed to be a small, autonomous, innovative vehicle of roughly 10 12 kg for scouting the environment in the vicinity of the lunar landing site. The novel capability of the MPE will be to acquire samples of lunar soil in an area of >100m around the lander and to bring them back to the spacecraft for analysis by on-board instruments. This will enable access to soils that are less contaminated by the descent propulsion system plumes to increase the chances of detection of any indigenous lunar volatiles. The MPE shall acquire samples of regolith with landing-induced contamination being below the detection limit of the associated volatile-seeking instruments. Subsurface regolith sampling is preferable to understand the concentration of volatiles as a function of depth. Additional benefits for the overall science accomplished by a Lunar Lander mission could be obtained if the MPE were to conduct ‘field geology’ type observations and measurements along its traverses, such as geochemical and mineralogical in situ investigations with dedicated instruments on rocks, boulders and regolith. This would dramatically expand the effective area studied by the ESA Lunar Lander mission. Based on technology trades the baseline concept for the MPE system is composed by a 4-wheel active chassis with wheels, a power supply with fixed solar generators plus a secondary battery, a thermal system with active heating and passive insulation, a sensor package for autonomous operations and a VHF/UHF communication system between MPE and the Lander. One unique scientific aspect of the MPE could be the in situ study of rocks, boulders and lithic (rock) fragments which otherwise would only be amenable to measurements using any instrument heads mounted on the lander robotic arm (provided any rocks were within reach of the arm). To fulfill the science objectives, the MPE will be equipped with a stereo camera, the PLUTO mole subsurface regolith sampling system (as flown on Beagle 2) as well as a close-up imager. This instrument package allows acquisition of regolith samples from both illuminated and locally shaded terrain, sampling from the subsurface and from underneath large boulders and documentation of the samples acquired by close-up imaging of the sample site, ideally before and after sample acquisition. A suite of terrain temperature sensors is implicitly included to provide context for the samples acquired from permanently shadowed locations or below the surface, but also to contribute to landing site general science. As an option for the in-situ characterization of the sample material with respect to mineralogy and possibly volatile content, spectrometer experiments or a color capability of the camera could be added. Further, a laboratory environment is currently being established at Freie Universität Berlin in order to allow sample-based geochemical measurements of key rock-forming elements in the soft X-Ray domain (.5-10 keV). The laboratory is used for the hardware development of X-Ray spectrometer experiments to be employed on lunar orbiter and on lunar lander missions. References: [1] H. Hiesinger, J.W. Head, New Views of Lunar Geoscience: An Introduction and Overview, In: Ne Views of the Moon (B.L. Jolliff et al. eds.) Rev. Min. Geochem., 60, 1-81 (2006). [2] R. Jaumann, The Moon, In: Encyclopedia of Astrobiology, M. Gargaud et al. (eds.), Vol. 2, Springer, 280-282 (2011)

Dust measurements during Galileo's approach to Jupiter and Io encounter

About a hundred dust impacts per day were detected during the first week in December 1995 by Galileo during its approach to Jupiter, These impacts were caused by submicrometer-sized particles that were just above the detection limit. After the closest approach to Io on 7 December, impacts of these small particles ceased, This effect is expected for dust grains emitted from Io that exit the field of view of the instrument after the flyby. The impact rate of bigger micrometer-sized dust grains continued to increase toward Jupiter. These dust particles are in orbit about Jupiter or are interplanetary grains that are gravitationally concentrated near Jupiter

Three years of Galileo dust data: II. 1993-1995

Between January 1993-December 1995, the Galileo spacecraft traversed interplanetary space between Earth and Jupiter and arrived at Jupiter on 7 December 1995. The dust instrument onboard the spacecraft was operating during most of the time and data from the instrument were obtained via memory readouts which occurred at rates between twice per day and once per week. All events were classified by an onboard program into 24 categories. Noise events were usually restricted to the lowest categories (class 0). During Galileo's passage through Jupiter's radiation belts on 7 December 1995, several of the higher categories (classes 1 and 2) also show evidence for contamination by noise. The highest categories (class 3) were noise-free all the time. A relatively constant impact rate of interplanetary and interstellar (big) particles of 0.4 impacts per day was detected over the whole three-year time span. In the outer solar system (outside about 2.6 AU) they are mostly of interstellar origin, whereas in the inner solar system they are mostly interplanetary particles. Within about 1.7 AU from Jupiter intense streams of small dust particles were detected with impact rates of up to 20,000 per day whose impact directions are compatible with a Jovian origin. Two different populations of dust particles were detected in Jovian magnetosphere: small stream particles during Galileo's approach to the planet and big particles concentrated closer to Jupiter between the Galilean satellites. There is strong evidence that the dust stream particles are orders of magnitude smaller in mass and faster than the instrument's calibration, whereas the calibration is valid for the big particles. Because the data transmission rate was very low, the complete data set for only a small fraction (2525) of all detected particles could be transmitted to Earth; the other particles were only counted. Together with the 358 particles published earlier, information about 2883 particles detected by the dust instrument during Galileo's six years' journey to Jupiter is now available

Detection of phosphates originating from Enceladus’s ocean

Abstract Saturn’s moon Enceladus harbours a global ice-covered water ocean. The Cassini spacecraft investigated the composition of the ocean by analysis of material ejected into space by the moon’s cryovolcanic plume. The analysis of salt-rich ice grains by Cassini’s Cosmic Dust Analyzer10 enabled inference of major solutes in the ocean water (Na+, K+, Cl-, HCO3-, CO32-) and its alkaline pH. Phosphorus, the least abundant of the bio-essential elements, has not yet been detected in an ocean beyond Earth. Earlier geochemical modelling studies suggest that phosphate might be scarce in the ocean of Enceladus and other icy ocean worlds. However, more recent modelling of mineral solubilities in Enceladus’s ocean indicates that phosphate could be relatively abundant. Here we present Cassini’s Cosmic Dust Analyzer mass spectra of ice grains emitted by Enceladus that show the presence of sodium phosphates. Our observational results, together with laboratory analogue experiments, suggest that phosphorus is readily available in Enceladus’s ocean in the form of orthophosphates, with phosphorus concentrations at least 100-fold higher in the moon’s plume-forming ocean waters than in Earth’s oceans. Furthermore, geochemical experiments and modelling demonstrate that such high phosphate abundances could be achieved in Enceladus and possibly in other icy ocean worlds beyond the primordial CO2 snowline, either at the cold seafloor or in hydrothermal environments with moderate temperatures. In both cases the main driver is probably the higher solubility of calcium phosphate minerals compared with calcium carbonate in moderately alkaline solutions rich in carbonate or bicarbonate ions

Poster 14: Explorer of Enceladus and Titan (E2T)

International audienceThe NASA-ESA Cassini-Huygens mission has revealed Titan and Enceladus to be two of the most enigmatic worlds in the Solar System. Titan, with its organically rich and dynamic atmosphere and geology, and Enceladus, with its active plume, both harboring subsurface oceans, are prime environments in which to investigate the conditions for the emergence of life and the habitability of Ocean Worlds. Explorer of Enceladus and Titan (E2T) is dedicated to investigating the evolution and habitability of these Saturnian satellites and will be proposed as a medium-class mission led by ESA in collaboration with NASA in response to ESA's M5 Call. E2T has a focused payload that will provide in-situ sampling and high-resolution imaging during multiple flybys of Enceladus and Titan using a solar-electric powered spacecraft in orbit around Saturn. The E2T mission will provide high-resolution mass spectroscopy of the plume emanating from Enceladus' south polar terrain (SPT) and of Titan's upper atmosphere as well as high-resolution IR imaging of the plume and the source fractures on Enceladus' SPT, and it will detail Titan's geomorphology at 50-100 m resolution. The E2T mission has three scientific goals: 1) Investigate the origin and evolution of volatile-rich icy worlds by examining both Enceladus and Titan, 2) Investigate the habitability and potential for life in ocean worlds on both Enceladus and Titan and 3) Investigate Titan as an Earth-like world with an evolving climate and landscape. These investigations will be accomplished by measuring the nature, abundance and isotopic properties of solid- and vapor-phase species in Enceladus' plume and Titan's upper atmosphere. E2T's high-resolution time-of-flight mass spectrometers will enable us to untangle the ambiguities left by Cassini regarding the identification of low-mass organic species, identify high-mass organic species for the first time, further constrain trace species such as the noble gases, and clarify the evolution of solid and volatile species. High-resolution IR imaging will reveal Titan's surface and Enceladus's fractured SPT and plume in detail unattainable by the Cassini mission, allowing us to investigate the processes that are transporting and transforming organic materials on the surface of Titan, and constrain the mechanisms controlling, and the energy dissipated by, Enceladus' plume. The proposed mission will address key scientific questions regarding extraterrestrial habitability, abiotic/prebiotic chemistry and emergence of life, which are among the highest priorities of ESA's Cosmic Vision program

Poster 14: Explorer of Enceladus and Titan (E2T)

International audienceThe NASA-ESA Cassini-Huygens mission has revealed Titan and Enceladus to be two of the most enigmatic worlds in the Solar System. Titan, with its organically rich and dynamic atmosphere and geology, and Enceladus, with its active plume, both harboring subsurface oceans, are prime environments in which to investigate the conditions for the emergence of life and the habitability of Ocean Worlds. Explorer of Enceladus and Titan (E2T) is dedicated to investigating the evolution and habitability of these Saturnian satellites and will be proposed as a medium-class mission led by ESA in collaboration with NASA in response to ESA's M5 Call. E2T has a focused payload that will provide in-situ sampling and high-resolution imaging during multiple flybys of Enceladus and Titan using a solar-electric powered spacecraft in orbit around Saturn. The E2T mission will provide high-resolution mass spectroscopy of the plume emanating from Enceladus' south polar terrain (SPT) and of Titan's upper atmosphere as well as high-resolution IR imaging of the plume and the source fractures on Enceladus' SPT, and it will detail Titan's geomorphology at 50-100 m resolution. The E2T mission has three scientific goals: 1) Investigate the origin and evolution of volatile-rich icy worlds by examining both Enceladus and Titan, 2) Investigate the habitability and potential for life in ocean worlds on both Enceladus and Titan and 3) Investigate Titan as an Earth-like world with an evolving climate and landscape. These investigations will be accomplished by measuring the nature, abundance and isotopic properties of solid- and vapor-phase species in Enceladus' plume and Titan's upper atmosphere. E2T's high-resolution time-of-flight mass spectrometers will enable us to untangle the ambiguities left by Cassini regarding the identification of low-mass organic species, identify high-mass organic species for the first time, further constrain trace species such as the noble gases, and clarify the evolution of solid and volatile species. High-resolution IR imaging will reveal Titan's surface and Enceladus's fractured SPT and plume in detail unattainable by the Cassini mission, allowing us to investigate the processes that are transporting and transforming organic materials on the surface of Titan, and constrain the mechanisms controlling, and the energy dissipated by, Enceladus' plume. The proposed mission will address key scientific questions regarding extraterrestrial habitability, abiotic/prebiotic chemistry and emergence of life, which are among the highest priorities of ESA's Cosmic Vision program