Kathleen Mandt | Johns Hopkins University Applied Physics Lab (original) (raw)

Papers by Kathleen Mandt

Journal of Geophysical Research: Space Physics

The Planetary Science Journal

The current composition of giant planet atmospheres provides information on how ... more The current composition of giant planet atmospheres provides information on how such planets formed, and on the origin of the solid building blocks that contributed to their formation. Noble gas abundances and their isotope ratios are among the most valuable pieces of evidence for tracing the origin of the materials from which the giant planets formed. In this review we first outline the current state of knowledge for heavy element abundances in the giant planets and explain what is currently understood about the reservoirs of icy building blocks that could have contributed to the formation of the Ice Giants. We then outline how noble gas isotope ratios have provided details on the original sources of noble gases in various materials throughout the solar system. We follow this with a discussion on how noble gases are trapped in ice and rock that later became the building blocks for the giant planets and how the heavy element abundances could have been locally enriched in the protosolar nebula. We then provide a review of the current state of knowledge of noble gas abundances and isotope ratios in various solar system reservoirs, and discuss measurements needed to understand the origin of the ice giants. Finally, we outline how formation and interior evolution will influence the noble gas abundances and isotope ratios observed in the ice giants today. Measurements that a future atmospheric probe will need to make include (1) the 3He/4He isotope ratio to help constrain the protosolar D/H and 3He/4He; (2) the 20Ne/22Ne and 21Ne/22Ne to separate primordial noble gas reservoirs similar to the approach used in studying meteorites; (3) the Kr/Ar and Xe/Ar to determine if the building blocks were Jupiter-like or similar to 67P/C-G and Chondrites; (4) the krypton isotope ratios for the first giant planet observations of these isotopes; and (5) the xenon isotopes for comparison with the wide range of values represented by solar system reservoirs.Mandt, K. E., Mousis, O., Lunine, J., Marty, B., Smith, T., Luspay-Kuti, A., & Aguichine, A. (2020). Tracing the origins of the ice giants through noble gas isotopic composition. Space Science Reviews, 216(5), 1-37.

Solar Lyman-a emission re-radiated from H atoms incoming to... more Solar Lyman-a emission re-radiated from H atoms incoming to the heliosphere from interstellar medium is a powerful tool to probe globally plasma properties both at the heliosphere boundary and near the Sun. H Lyman-&#945; line profiles reflect velocity distributions of low energy H atoms in the heliosphere which hold information about the plasma near the heliopause. H Lyman &#945; intensities as observed at 1 AU serve as diagnostic of global properties of the solar wind.&#160;In this talk we will review what we have learned about the global heliospheric interaction from H Lyman-a observations from inside the heliosphere on SWAN/SOHO, Voyages/UVS and New Horizons/Alice missions. Outward trajectory of Interstellar Probe going through the outer heliosphere to the interstellar medium (ISM) up to 1000 AU enable unique science opportunities to explore global interaction between the solar wind and local ISM by observing for the first time Lyman-a emission from outside of the heliosphere. We will report a progress of UV working group in outlining primary science questions on the nature of the global heliosphere and Local Interstellar Cloud, planning observation strategy, measurement requirements and synergies with planetary UV observations for potential KBO fly-by.

The global nature of the interaction of the heliosphere and the Local Interstell... more The global nature of the interaction of the heliosphere and the Local Interstellar Medium (LISM) is among one of the most outstanding space physics problems of today. Ultimately, our magnetic bubble is upheld by the expanding solar wind born in the solar corona that is now accessible by Parker Solar Probe. At the other extreme boundary, a completely new regime of physical interactions is at work that shape the unseen global structure of the entire heliosphere. Voyager 1 and 2 are soon nearing their end of operations inside of 170 AU and their payloads dedicated to planetary science have uncovered a region of space that defies our understanding. At the same time, IBEX and Cassini have obtained complementary &#8220;inside-out&#8221; ENA images of the heliospheric boundary region that cannot be fully explained. An Interstellar Probe through the heliospheric boundary, in to the LISM would be the first dedicated mission to venture into this largely unexplored frontier of space. With a dedicated suite of in-situ and remote-sensing instrumentation, such a probe would not only open the door for a new regime of space physics acting at the boundary and in other astrospheres, but would also obtain the very first images from the outside of the global structure of the heliosphere that, in context with the in-situ measurements would enable a quantum leap in understanding the global nature of our own habitable astrosphere. Beyond the Heliopause, the Interstellar Probe would offer the first sampling of the properties of the Local Interstellar Cloud and interstellar dust that are completely new scientific territories. Relatively modest contributions across divisions would offer historic science returns, including a flyby of one or two Kuiper Belt Objects, first insights in to the structure of the circum-solar dust disk, and the first measurements of the Extra-galactic Background Light beyond the obscuring Zodiacal cloud. In summary, an Interstellar Probe would represent humanity&#8217;s first step in to the galaxy and become the farthest space exploration ever undertaken. The idea of an Interstellar Probe and a Solar Probe shares a common beginning as two of the &#8220;Special Probes&#8221; that the Simpson Committee carried forward in their Interim Report to the Space Studies Board in 1960. Since then, an Interstellar Probe has scientifically been highly rated in the Solar and Space Physics Decadal Surveys, but the lack of propulsion technologies and launch vehicles have presented a stumbling block for its realization. However, this bottleneck is now being removed with the development of the Space Launch System (SLS) Block 2 with first launch projected to end of the 2020&#8217;s. A study funded by NASA is now progressing towards its third year of developing realistic mission architectures for an Interstellar Probe using technology ready for launch beginning 2030. An SLS Block 2, with an Atlas Centaur 3rdstage, a Star 48 4th stage &#160;could propel a spacecraft up to about 8.5 AU/year, which would be more than twice the fastest escaping spacecraft (Voyager 1 at 3.6 AU/year). The scenario would use a direct inject to Jupiter followed by a Jupiter Gravity assist powered by the 4th stage. The mission trade space is bound by requirements to be able to operate out to 1000 AU, 600 W of power beginning of mission, and survive up to 50 years. Here, we discuss the outstanding science questions that could be addressed by a mission to the LISM, notional science payload and report on realistic mission architectures, design concepts and trades, enabling technologies, and programmatic challenges.

An Interstellar Probe beyond our heliosphere in to the largely unexplored inters... more An Interstellar Probe beyond our heliosphere in to the largely unexplored interstellar medium (ISM) would be the furthest and boldest step in robotic space exploration ever taken. A dedicated payload of in-situ and remote sensing instruments would uncover the new regime of physics at work in the heliospheric boundary region and offer the first external view of the global heliosphere that is currently missing in the family portrait of all other types of astrospheres observed. Beyond about 400 AU the Probe would reach the ISM and for the first time begin its sampling of the properties of the local interstellar cloud (LIC) that our Sun and neighboring star systems are immersed in. An Interstellar Probe has been discussed since around 1960 in several NASA and international studies. The compelling science objectives have remained almost unchanged and are focused on understanding the plasma physics in the interaction region between the heliosphere and the ISM. Their importance have been amplified by the recent unexpected findings by the Voyager 1 and 2 spacecraft that are nearing their end of life at less than 150 AU from the Sun. Remote observations in Energetic Neutral Atoms (ENAs) by the NASA IBEX and Cassini missions have made the remarkable discoveries of ENA emission morphologies that have come as a complete surprise and still lack a satisfactory explanation. Hubble Space Telescope observations have now also made it clearer that the Sun is about to exit the LIC and perhaps already has, which is a unique event of astronomical scales that an Interstellar Probe could explore in-situ for the first time. In addition to these top-priority objectives, contributions of unprecedented science value to planetary sciences and astrophysics are possible including flybys of at least one Kuiper Belt Object, in-situ and remote observations of the dust debris disk, and the extra-galactic background light. Here we review the outstanding questions and current state of understanding of the global heliosphere, the ISM and what planetary and astrophysics augmentations can offer. We summarize the compelling science case for an Interstellar Probe, including a range of possible science payloads and the associated operation scenarios. The results stem from the study of a Pragmatic Interstellar Probe currently underway, funded by NASA, and led by The Johns Hopkins University Applied Physics Laboratory with active participation from a large, international team of scientists and engineers. The study focuses on finding realistic mission architectures among a trade space of propulsion options, trajectories, risks and reliability challenges. The study considers operation out to 1000 AU, a survival probability of 85% over 50 years and electrical power of no less than 400 W at the beginning of mission. Over twice the speed of Voyager 1 (the fastest spacecraft currently) has already been achieved in the design using conventional propulsion, with a direct inject to Jupiter followed by a Jupiter Gravity Assist. In order to provide input requirements to the mission study, several possible payloads with different mass allocations and associated mission requirements, trade-offs and risks have been identified.

Planetary and Space Science

Monthly Notices of the Royal Astronomical Society

In light of the recent New Horizons flyby measurements, we present a coupled ion-neutralphotochem... more In light of the recent New Horizons flyby measurements, we present a coupled ion-neutralphotochemistry model developed for simulating the atmosphere of Pluto. Our model results closely match the observed density profiles of CH 4 , N 2 and the C 2 hydrocarbons in the altitude range where available New Horizons measurements are most accurate (above ∼100-200 km). We found a high eddy coefficient of 10 6 cm 2 s −1 from the surface to an altitude of 150 km, and 3 × 10 6 cm 2 s −1 above 150 km for Pluto's atmosphere. Our results demonstrate that C 2 hydrocarbons must stick to and be removed by aerosol particles in order to reproduce the C 2 profiles observed by New Horizons. Incorporation into aerosols in Pluto's atmosphere is a significantly more effective process than condensation, and we found that condensation alone cannot account for the observed shape of the vertical profiles. We empirically determined the sticking efficiency of C 2 hydrocarbons to aerosol particles as a function of altitude, and found that the sticking efficiency of C 2 hydrocarbons is inversely related to the aerosol surface area. Aerosols must harden and become less sticky as they age in Pluto's atmosphere. Such hardening with ageing is both necessary and sufficient to explain the vertical profiles of C 2 hydrocarbons in Pluto's atmosphere. This result is in agreement with the fundamental idea of aerosols hardening as they age, as proposed for Titan's aerosols.

The Titan ionosphere has proven to be chemically complex beyond our wildest dreams. Large positiv... more The Titan ionosphere has proven to be chemically complex beyond our wildest dreams. Large positively and negatively charged organic ions have been identified at altitudes above 950 km altitude. The corresponding neutral chemistry is equally as complex and tracks the ion chemistry with a high degree of correlation. This suggests a major role for ion/neutral chemistry in the production of

ABSTRACT The atmosphere of Titan, Saturn’s largest moon, is an analog for the Earth’s atmosphere ... more ABSTRACT The atmosphere of Titan, Saturn’s largest moon, is an analog for the Earth’s atmosphere in the distant past when life first emerged, and may also be used to study the distant future when the abundance of water in the atmosphere may be reduced by photochemical loss processes associated with climate change. This Dissertation investigates the evolution of Titan’s atmosphere utilizing measurements of the stable isotope ratios in molecular nitrogen and methane. The Cassini Ion Neutral Mass Spectrometer (INMS) measures the composition of the ionosphere and neutral atmosphere as it flies through the atmosphere, approaching altitudes as low as 950 km above the surface. INMS measurements of the 14N/15N in N2 as a function of altitude for 30 Titan flybys are compared, using a basic diffusion model, to the Huygens Gas Chromatograph Mass Spectrometer (GCMS) measurement of the 14N/15N in N2 on the surface. This comparison provides the input parameters needed to extrapolate the INMS measurements of 12C/13C in CH4 from the upper atmosphere to the surface where the ratio is within the range of expected primordial values. Although the 12C/13C at Titan is close to the primordial value, vi escape and photochemistry fractionate the isotope ratio over time. This suggests that methane has been present in Titan’s atmosphere for no more than one billion years. A cross-calibration of INMS ion densities with the electron densities measured by the Cassini Radio Plasma Wave Spectrometer (RPWS) constrains the energy response of INMS and provides a new approach for determining the densities of ions in Titan’s ionosphere. These ion densities validate an updated coupled Ion-Neutral-Thermal model that constrains the fractionation of the nitrogen isotopes due to photochemistry. Modeling the evolution of the nitrogen isotopes over geological times scales based on chemistry and escape limits the initial 14N/15N to a heavier ratio than the 14N/15N observed in the Earth’s atmosphere. The methodologies developed for this Dissertation are relevant not only to Titan, but also to Earth. They can be used to evaluate dynamics and photochemistry of the nitrogen isotopes in the upper atmosphere and to define future missions to study the composition of the Earth’s thermosphere.

Current isotopic ratios in planetary atmospheres have played an important role in determining how... more Current isotopic ratios in planetary atmospheres have played an important role in determining how that atmosphere has evolved over geologic time scales (e.g. Donahue et al. 1997, Lunine et al. 1999). The current 12C/13C ratio in methane is a particularly useful indicator of Titan&amp;#39;s atmospheric evolutionary history (Mandt et al. 2009). Primordial 12C/13C ratios throughout the solar system are limited

Independent, simultaneous positive ion measurements have been obtained by the Cassini Plasma Spec... more Independent, simultaneous positive ion measurements have been obtained by the Cassini Plasma Spectrometer (CAPS) and the Ion and Neutral Mass Spectrometer (INMS) during fourteen Cassini encounters with Titan&amp;#39;s upper atmosphere. Significant densities of positive ions with masses greater than 100 Daltons have been observed. The overlap of the CAPS and INMS spectra is utilized to accurately determine the mass identity.

LRO-LAMP far-UV albedo maps show global spectral evidence for surficial water frost/hydration, an... more LRO-LAMP far-UV albedo maps show global spectral evidence for surficial water frost/hydration, and probe PSRs using an innovative nightside observing technique.

$Research paper thumbnail of 13C and 15N fractionation of CH4/N2 mixtures during photochemical aerosol formation: Relevance to Titan$

Icarus, 2015

ABSTRACT The ratios of the stable isotopes that comprise each chemical species in Titan’s atmosph... more ABSTRACT The ratios of the stable isotopes that comprise each chemical species in Titan’s atmosphere provide critical information towards understanding the processes taking place within its modern and ancient atmosphere. Several stable isotope pairs, including 12C/13C and 14N/15N, have been measured in situ or probed spectroscopically by Cassini-borne instruments, space telescopes, or through ground-based observations. Current attempts to model the observed isotope ratios incorporate fractionation resulting from atmospheric diffusion, hydrodynamic escape, and primary photochemical processes. However, the effect of a potentially critical pathway for isotopic fractionation – organic aerosol formation and subsequent deposition onto the surface of Titan – has not been considered due to insufficient data regarding fractionation during aerosol formation. To better understand the nature of this process, we have conducted a laboratory study to measure the isotopic fractionation associated with the formation of Titan aerosol analogs, commonly referred to as ‘tholins’, via far-UV irradiation of several methane (CH4) and dinitrogen (N2) mixtures. Analysis of the δ13C and δ15N isotopic signatures of the photochemical aerosol products using an isotope ratio mass spectrometer (IRMS) show that fractionation direction and magnitude are dependent on the initial bulk composition of the gas mixture. In general, the aerosols showed enrichment in 13C and 14N, and the observed fractionation trends can provide insight into the chemical mechanisms controlling photochemical aerosol formation.

Journal of Geophysical Research: Space Physics

The Planetary Science Journal

Planetary and Space Science

Monthly Notices of the Royal Astronomical Society

$Research paper thumbnail of 13C and 15N fractionation of CH4/N2 mixtures during photochemical aerosol formation: Relevance to Titan$

Icarus, 2015