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Kathleen E. Mandt

Publications and source records attributed to Kathleen E. Mandt.

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Recipes for Forming a Carbon–Rich Giant Planet

The exploration of carbon-to-oxygen ratios has yielded intriguing insights into the composition of close-in giant exoplanets, giving rise to a distinct classification: carbon-rich planets, characterized by a carbon–to–oxygen ratio ≥ 1 in their atmospheres, as opposed to giant planets exhibiting carbon–to–oxygen ratios close to the protosolar value. In contrast, despite numerous space missions dispatched to the outer solar system and the proximity of Jupiter, Saturn, Uranus, and Neptune, our understanding of the carbon-to-oxygen ratio in these giants remains notably deficient. Determining this ratio is crucial as it serves as a marker linking a planet’s volatile composition directly to its formation region within the disk. This article provides an overview of the current understanding of the carbon-to-oxygen ratio in the four gas giants of our solar system and explores why there is yet no definitive dismissal of the possibility that Jupiter, Saturn, Uranus, or Neptune could be considered carbon-rich planets. Additionally, we delve into the three primary formation scenarios proposed in existing literature to account for a bulk carbon-to-oxygen ratio ≥ 1 in a giant planet. A significant challenge lies in accurately inferring the bulk carbon-to-oxygen ratio of our solar system’s gas giants. Retrieval methods involve integrating in situ measurements from entry probes equipped with mass spectrometers and remote sensing observations conducted at microwave wavelengths by orbiters. However, these methods fall short of fully discerning the deep carbon-to-oxygen abundance in the gas giants due to their limited probing depth, typically within the 10–100 bar range. To complement these direct measurements, indirect determinations rely on understanding the vertical distribution of atmospheric carbon monoxide in conjunction with thermochemical models. These models aid in evaluating the deep oxygen abundance in the gas giants, providing valuable insights into their overall composition.

Protosolar nebula↗
NASA NTRS2023

Increasing Diversity on Spacecraft Mission Teams Reduces Risk

Many of the NASA spacecraft sent into Earth orbit and throughout the Solar System are competitively selected and led by principal investigators (PIs). These senior scientists are responsible for directing research activities, managing the use of funds, and reporting to the funding agency. Additionally, the European Space Agency (ESA) has competitively selected missions that are led by ESA-nominated project scientists and include instruments that are overseen by PIs. Usually, the PIs and project scientists form a science working team that provides scientific leadership of the mission. These NASA and ESA PI roles require a deep understanding of the mission’s scientific goals and engineering design aspects. And, importantly, these roles also require skills in team management.

Kathleen E. Mandt↗
NASA NTRS2022

Dual Storage and Release of Molecular Oxygen in Comet 67p/Churyumov–Gerasimenko

One of the biggest surprises of the Rosetta mission was the detection of O2 in the coma of 67P/Churyumov–Gerasimenko in remarkably high abundances. The measured levels of O2 in the coma are generally assumed to reflect the overall abundance and chemical origin of cometary O2 in the nucleus. Along with its strong association with H2O and weak association with CO and CO2, these measurements led to the consensus that the source and release of cometary O2 are linked to H2O. We analysed ROSINA observations and found a previously unrecognized change in the correlations of O2 with H2O, CO2 and CO that contradicts the prevailing notion that the release of O2 is linked to H2O at all times. These findings can be explained by the presence of two distinct reservoirs of O2: a pristine source in the deeper nucleus layers dating back to before nucleus formation, and an H2O-trapped secondary reservoir formed during the thermal evolution of the nucleus. These results imply that O2 must have been incorporated into the nucleus in a solid and distinct phase during accretion in significantly lower abundances than previously assumed.

Adrienn Luspay-kuti↗
NASA NTRS2021

Cold Traps of Hypervolatiles in the Protosolar Nebula at the Origin of the Peculiar Composition of Comet C/2016 R2 (PanSTARRS)

Recent observations of the long-period comet C/2016 R2 (PanSTARRS; hereafter R2) indicate an unusually high N2/CO abundance ratio, typically larger than ∼0.05, and at least 2–3 times higher than the one measured in 67P/Churyumov–Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H2O (H2O/CO ∼ 0.32%), compared to other comets. Here we investigate the formation circumstances of a generic comet whose composition reproduces these two key features. We first envisage the possibility that this comet agglomerated from clathrates, but we find that such a scenario does not explain the observed low water abundance. We then alternatively investigate the possibility that the building blocks of R2 agglomerated from grains and pebbles made of pure condensates via the use of a disk model describing the radial transport of volatiles. We show that N2/CO ratios reproducing the value estimated in this comet can be found in grains condensed in the vicinity of the CO and N2 ice lines. Moreover, high CO/H2O ratios (>100 times the initial gas-phase value) can be found in grains condensed in the vicinity of the CO ice line. If the building blocks of a comet assembled from such grains, they should present N2/CO and CO/H2O ratios consistent with the measurements made in R2's coma. Our scenario indicates that R2 formed in a colder environment than the other comets that share more usual compositions. Our model also explains the unusual composition of the interstellar comet 2l/Borisov.

Olivier Mousis↗
NASA NTRS2019

Comparison of Neutral Outgassing of Comet 67P/Churyumov-Gerasimenko Inbound and Outbound Beyond 3 Au From ROSINA/DFMS

Context. Pre-equinox measurements of comet 67P/Churyumov-Gerasimenko with the mass spectrometer ROSINA/DFMS on board the Rosetta spacecraft revealed a strongly heterogeneous coma. The abundances of major and various minor volatile species were found to depend on the latitude and longitude of the nadir point of the spacecraft. The observed time variability of coma species remained consistent for about three months up to equinox. The chemical variability could be generally interpreted in terms of surface temperature and seasonal effects superposed on some kind of chemical heterogeneity of the nucleus. Aims. We compare here pre-equinox (inbound) ROSINA/DFMS measurements from 2014 to measurements taken after the outbound equinox in 2016, both at heliocentric distances larger than 3 AU. For a direct comparison we limit our observations to the southern hemisphere. Methods. We report the similarities and differences in the concentrations and time variability of neutral species under similar insolation conditions (heliocentric distance and season) pre- and post-equinox, and interpret them in light of the previously published observations. In addition, we extend both the pre- and post-equinox analysis by comparing species concentrations with a mixture of CO2 and H2O. Results. Our results show significant changes in the abundances of neutral species in the coma from pre- to post-equinox that are indicative of seasonally driven nucleus heterogeneity. Conclusions. The observed pre- and post-equinox patterns can generally be explained by the strong erosion in the southern hemisphere that moves volatile-rich layers near the surface.

comets↗
NASA NTRS2018

Origin of Molecular Oxygen in Comets: Current Knowledge and Perspectives

The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument onboard the Rosetta spacecraft has measured molecular oxygen (O 2 ) in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) in surprisingly high abundances. These measurements mark the first unequivocal detection of O 2 in a cometary environment. The large relative abundance of O 2 in 67P/C-G despite its high reactivity and low interstellar abundance poses a puzzle for its origin in comet 67P/C-G, and potentially other comets. Since its detection, there have been a number of hypotheses put forward to explain the production and origin of O 2 in the comet. These hypotheses cover a wide range of possibilities from various in situ production mechanisms to protosolar nebula and primordial origins. Here, we review the O2 formation mechanisms from the literature, and provide a comprehensive summary of the current state of knowledge of the sources and origin of cometary O 2 .

Molecular oxygen↗
NASA NTRSDate not supplied

The Role of Isotopes in Understanding of the Formation and Evolution of the Solar System

Comparative planetology via isotope geochemistry has played a critical role in advancing our understanding of the inventories of both volatiles and organics in the atmospheres of solar system bodies. For example, the 12 C/ 13 C measured from atmospheric methane in Titan provided upper limits on the amount of time that methane has been present in the atmosphere, demonstrating that methane was only present in Titan’s atmosphere during at most the last 1 billion years (Gyr). As another example, measurements of 14 N/ 15 N in atmospheric HCN and N 2 provide direct evidence of how photochemistry influences stable isotopes. These observations were used to determine that Titan’s nitrogen originated as NH 3 in the protosolar nebula, thus constraining the origin and delivery of volatiles to the Saturnian moon Titan. These measurements of 12 C/ 13 C and 14 N/ 15 N in Titan’s atmosphere were obtained with remote and in situ observations from the Cassini spacecraft in Saturn orbit. However, combining spacecraft observations like these throughout the solar system with Earth-based telescope observations, including both ground-based and from orbiting telescopes, produces far more powerful results. For example, the lower limit obtained for 14 N/ 15 N in HCN in Pluto’s atmosphere by ALMA combined with New Horizons observations of the atmospheric composition provides a valuable tool for determining the origin of nitrogen for Pluto if the influences of condensation and aerosol trapping on isotopes can be constrained. Isotopes measured at Jupiter and Saturn and their moons, combined with composition measurements from comets provide information on giant planet formation processes and primordial conditions when the solar system was forming. In all of these studies, measurements of isotope ratios in comets have served as a reference for processes in the protosolar nebula.

Kathleen E. Mandt↗