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NASA NTRS2005

[Stellar Occultation Studies of Small Bodies in the Outer Solar System: Accomplishments, Status, and Plans]

Bodies residing in the outer solar system exhibit unique physical processes, and some of the lessons learned from them can be applied to understanding what occurred in the outer solar system during its formation and early evolution. Pluto, the largest known Kuiper Belt object (KBO), and its near twin Triton--an ex-KBO that has been captured by Neptune--have nitrogen atmospheres that are in vapor-pressure equilibrium with surface ice. These atmospheres are most sensitively probed from Earth by the technique of Stellar occultations, which can provide the temperature and pressure profiles of these atmospheres at a spatial resolution of a few kilometers. Recent results from occultations show that the surface pressure of Triton's atmosphere has been increasing and that the shape of the atmosphere deviates from its expected spherical figure. With the occultation technique we can also learn the sizes of smaller bodies that have formed in the outer solar system: Charon, the Centaurs, and KBOs. Our proposed program involves identifying occultation candidates, predicting occultations, observing occultations, analysis of the data, and synthesis of the occultation results with other data. The main goals for our proposed work are to (i) further observe occultations by Triton with the objectives of understanding its pressure changes, distortion, and enigmatic thermal structure (ii) determine whether the abrupt drop in Pluto's stellar occultation light curve is caused by a sharp thermal gradient near its surface or by atmospheric haze, (iii) further observations to characterize the potential collapse of Pluto's atmosphere as it recedes from the sun (information that should be of interest to the Pluto-Kuiper Express), ( iv ) determine Charon's radius more accurately than can be done with the mutual events to derive a better estimate of Charon's density, and ( v ) directly determine the size (and albedo) of Centaurs with the goal of more accurately estimating the sizes of KBOS.

Elliott, James↗
NASA NTRS2006

Volume Ice Radiolysis in the Outer Solar System

The primary energy flux of charged particle components of the heliospheric and magnetospheric environments of the solar system is primarily carried by highly penetrating energetic particles. Although laboratory experiments on production of organics and oxidants typically only address effects on very thin surface layers, energy deposition occurs on surfaces of icy bodies of the outer solar system to meters in depth. Time scales for significant radiolytic deposition vary from thousands of years at millimeter depths on Europa to billions of years in the meters-deep regolith of Kuiper Belt Objects. Radioisotope decay (e.g., K-40) also contributes to volume radiolysis as the only energy source at much greater depths. Radiolytic oxygen is a potential resource for life within Europa and a partial source of oxygen for Saturn's magnetosphere and Titan's upper atmosphere. Interactions of very high energy cosmic rays with ices at Titan's surface may provide one of the few sources of oxidants in that highly reducing environment. The red colors of low-inclination classical Kuiper Belt Objects at 40-50 AU, and Centaur objects originating from this same population, may arise from volume radiolysis of deep ice layers below more refractory radiation crusts eroded away by surface sputtering and micrometeoroid impacts. A variety of techniques are potentially available to measure volume radiolysis products and have been proposed for study as part of the new Space Physics of Life initiative at NASA Goddard Space Flight Center. The technique of Electron Paramagnetic Resonance (EPR) has been used in medical studies to measure oxidant production in irradiated human tissue for cancer treatment. Other potential techniques include optical absorption spectroscopy and standard wet chemical analysis. These and other potential techniques are briefly reviewed for applicability to problems in solar system ice radiolysis and astrobiology.

Cooper, John F.↗
NASA NTRS2007

Radiolytic Gas-Driven Cryovolcanism in the Outer Solar System

Water ices in surface crusts of Europa, Enceladus, Saturn's main rings, and Kuiper Belt Objects can become heavily oxidized from radiolytic chemical alteration of near-surface water ice by space environment irradiation. Oxidant accumulations and gas production are manifested in part through observed H2O2 on Europa. tentatively also on Enceladus, and found elsewhere in gaseous or condensed phases at moons and rings of Jupiter and Saturn. On subsequent chemical contact in sub-surface environments with significant concentrations of primordially abundant reductants such as NH3 and CH4, oxidants of radiolytic origin can react exothermically to power gas-driven cryovolcanism. The gas-piston effect enormously amplifies the mass flow output in the case of gas formation at basal thermal margins of incompressible fluid reservoirs. Surface irradiation, H2O2 production, NH3 oxidation, and resultant heat, gas, and gas-driven mass flow rates are computed in the fluid reservoir case for selected bodies. At Enceladus the oxidant power inputs are comparable to limits on nonthermal kinetic power for the south polar plumes. Total heat output and plume gas abundance may be accounted for at Enceladus if plume activity is cyclic in high and low "Old Faithful" phases, so that oxidants can accumulate during low activity phases. Interior upwelling of primordially abundant NH3 and CH4 hydrates is assumed to resupply the reductant fuels. Much lower irradiation fluxes on Kuiper Belt Objects require correspondingly larger times for accumulation of oxidants to produce comparable resurfacing, but brightness and surface composition of some objects suggest that such activity may be ongoing.

Cooper, John F.↗
NASA NTRS2007

Solar System Science with JWST

JWST will enable breakthroughs in our understanding of the physical characteristics of cold bodies in the outer reaches of the Solar System. These objects include Pluto and other Kuiper Belt Objects (KBOs), the icy moons of the giant planets, and distant cometary nuclei. Recent discoveries of large objects in the Kuiper belt, along with many smaller members, make it clear that this region represents a major constituent of our Solar System, one that was hidden until recently because it is so remote and challenging to observe. The near-IR and mid-IR performance of JWST will be unique in its power to probe this region. This poster describes the science drivers for JWST observations of Solar System objects and plans for implementing this capability.

Sonneborn, G.↗
NASA NTRS2009

Icy Satellites of Saturn: Impact Cratering and Age Determination

Saturn is the first giant planet to be visited by an orbiting spacecraft that can transmit large amounts of data to Earth. Crater counts on satellites from Phoebe inward to the regular satellites and ring moons are providing unprecedented insights into the origin and time histories of the impacting populations. Many Voyager-era scientists concluded that the satellites had been struck by at least two populations of impactors. In this view, the Population I impactors, which were generally judged to be comets orbiting the Sun, formed most of the larger and older craters, while Population II impactors, interpreted as Saturn-orbiting ejecta from impacts on satellites, produced most of the smaller and younger craters. Voyager data also implied that all of the ring moons, and probably some of the midsized classical moons, had been catastrophically disrupted and reaccreted since they formed. We examine models of the primary impactor populations in the Saturn system. At the present time, ecliptic comets, which likely originate in the Kuiper belt/scattered disk, are predicted to dominate impacts on the regular satellites and ring moons, but the models require extrapolations in size (from the observed Kuiper belt objects to the much smaller bodies that produce the craters) or in distance (from the known active Jupiter family comets to 9.5 AU). Phoebe, Iapetus, and perhaps even moons closer to Saturn have been struck by irregular satellites as well. We describe the Nice model, which provides a plausible mechanism by which the entire Solar System might have experienced an era of heavy bombardment long after the planets formed. We then discuss the three cratering chronologies, including one based upon the Nice model, that have been used to infer surface ages from crater densities on the saturnian satellites. After reviewing scaling relations between the properties of impactors and the craters they produce, we provide model estimates of the present-day rate at which comets impact, and catastrophically disrupt, the saturnian moons. Finally, we present crater counts on the satellites from two different groups. Many of the heavily cratered terrains appear to be nearly saturated, so it is difficult to infer the provenance of the impactors from crater counts alone. More large craters have been found on Iapetus than on any other satellite. Enceladus displays an enormous range of surface ages, ranging from the old mid-latitude plains to the extremely young South Polar Terrain. Cassini images provide some evidence for the reality of Population II. Most of the observed craters may have formed in one or more cataclysms, but more work is needed to determine the roles of heliocentric and planetocentric bodies in creating the craters.

Dones, L.↗
NASA NTRS2010

Comparison of the Mineralogy of Comet Wild 2 Coma Grains to Other Astromaterials

We propose that Kuiper Belt samples (in this case comet coma grains from the Jupiter family comet Wild 2) are recognizably different from the bulk of materials in outer belt asteroids, because of their different formation positions and times in the early solar system. We believe this despite similarities found between some Wild 2 grains and components of carbonaceous chondrites (i.e. some CAI and chondrules). Kuiper Belt samples must preserve measurable mineralogical and compositional evidence of formation at unique positions and times in the early solar nebula, and these formational differences must have imparted recognizable special characteristics. We hypothesize that these characteristics include: (1) Unique major element compositional ranges of common astromaterial minerals, especially olivine and pyroxene; (2) Unique minor element compositions of major silicate phases, especially olivine and low-Ca pyroxene; (3) Degree and effects of radiation processing -- including amorphous rims, metal coatings, and Glass with Embedded Metal and Sulfides (GEMS); (4) Presence of abundant presolar silicate grains as recognized by anomalous oxygen in silicates; (5) Oxidation state of the mineral assemblage. We are working our way through all available Wild 2 samples, selecting 1-2 non-consecutive viable TEM grids from each possible extracted Wild 2 grain. We especially prefer TEM grids from grains for which complete mineralogical details have not been published (which is to say the majority of the extracted grains). We are performing a basic mineralogic survey by E-beam techniques, to establish the essential features of the extracted Wild 2 grains. We are making a particular effort to carefully and accurately measure minor elements of olivine and pyroxene, as these minerals are widespread in astromaterials, and comparisons of their compositions will serve to place the Wild 2 silicates in contact with asteroids, meteorites and chondritic interplanetary dust particles processing. We are also making a special effort to search for mineralogical products of aqueous alteration, since their presence would reveal that Wild 2 was once internally heated, a result with dramatic implications for models of early solar system primitive bodies. Thus far carbonates are the only potential evidence for aqueous alteration for Wild 2.

Frank, David↗
NASA NTRS2011

Collisional Processing of Comet Surfaces: Impact Experiments into Olivine

A new paradigm has emerged where 3.9 Ga ago, a violent reshuffling reshaped the placement of small bodies in the solar system (the Nice model). Surface properties of these objects may have been affected by collisions caused by this event, and by collisions with other small bodies since their emplacement. In addition, objects in the Kuiper Belt are believed to undergo extensive collisional processing while in the Kuiper Belt. Physical manifestations of shock effects (e.g., planar dislocations) in minerals typically found in comets will be correlated with spectral changes (e.g. reddening, loss and shift of peaks, new signatures) to allow astronomers to better understand geophysical impact processing that has occurred on small bodies. Targets will include solid and granular olivine (forsterite), impacted over a range of impact speeds with the Experimental Impact Laboratory at NASA JSC. Analyses include quantification of the dependence of the spectral changes with respect to impact speed, texture of the target, and temperature.

Lederer, S. M.↗
NASA NTRS2012

Comets as Messengers from the Early Solar System - Emerging Insights on Delivery of Water, Nitriles, and Organics to Earth

The question of exogenous delivery of water and organics to Earth and other young planets is of critical importance for understanding the origin of Earth's volatiles, and for assessing the possible existence of exo-planets similar to Earth. Viewed from a cosmic perspective, Earth is a dry planet, yet its oceans are enriched in deuterium by a large factor relative to nebular hydrogen and analogous isotopic enrichments in atmospheric nitrogen and noble gases are also seen. Why is this so? What are the implications for Mars? For icy Worlds in our Planetary System? For the existence of Earth-like exoplanets? An exogenous (vs. outgassed) origin for Earth's atmosphere is implied, and intense debate on the relative contributions of comets and asteroids continues - renewed by fresh models for dynamical transport in the protoplanetary disk, by revelations on the nature and diversity of volatile and rocky material within comets, and by the discovery of ocean-like water in a comet from the Kuiper Belt (cf., Mumma & Charnley 2011). Assessing the creation of conditions favorable to the emergence and sustenance of life depends critically on knowledge of the nature of the impacting bodies. Active comets have long been grouped according to their orbital properties, and this has proven useful for identifying the reservoir from which a given comet emerged (OC, KB) (Levison 1996). However, it is now clear that icy bodies were scattered into each reservoir from a range of nebular distances, and the comet populations in today's reservoirs thus share origins that are (in part) common. Comets from the Oort Cloud and Kuiper Disk reservoirs should have diverse composition, resulting from strong gradients in temperature and chemistry in the proto-planetary disk, coupled with dynamical models of early radial transport and mixing with later dispersion of the final cometary nuclei into the long-term storage reservoirs. The inclusion of material from the natal interstellar cloud is probable, for comets formed in the outer solar system.

Mumma, Michael J.↗
NASA NTRS2011

Spitzer Evidence for a Late Heavy Bombardment and the Formation of Urelites in {eta}Corvi at Approximately 1 Gyr

We have analyzed Spitzer and NASA/IRTF 2 - 35 micrometer spectra of the warm, ~350 K circumstellar dust around the nearby MS star eta Corvi (F2V, 1.4 plus or minus 0.3 Gyr). The spectra show clear evidence for warm, water- and carbon-rich dust at ~3 AU from the central star, in the system's Terrestrial Habitability Zone. Spectral features due to ultra-primitive cometary material were found, in addition to features due to impact produced silica and high temperature carbonaceous phases. At least 9 x 10(exp 18) kg of 0.1 - 100 micrometer warm dust is present in a collisional equilibrium distribution with dn/da ~ a(exp -3.5), the equivalent of a 130 km radius KBO of 1.0 grams per cubic centimeter density and similar to recent estimates of the mass delivered to the Earth at 0.6 - 0.8 Gyr during the Late Heavy Bombardment. We conclude that the parent body was a Kuiper-Belt body or bodies which captured a large amount of early primitive material in the first Myrs of the system's lifetime and preserved it in deep freeze at approximately 150 AU. At approximately 1.4 Gyr they were prompted by dynamical stirring of their parent Kuiper Belt into spiraling into the inner system, eventually colliding at 5-10 kilometers per second with a rocky planetary body of mass less than or equal to M(sub Earth at approximately 3 AU, delivering large amounts of water (greater than 0.1 % of M(sub Earth's Oceans)) and carbon-rich material. The Spitzer spectrum also closely matches spectra reported for the Ureilite meteorites of the Sudan Almahata Sitta fall in 2008, suggesting that one of the Ureilite parent bodies was a KBO.

Lisse, C. M.↗
NASA NTRS2014

How Dusty Is Alpha Centauri? Excess or Non-excess over the Infrared Photospheres of Main-sequence Stars

Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the Cen system. This requires knowledge of their photospheres.Having already detected the temperature minimum, Tmin, of CenA at far-infrared wavelengths, we here attempt to do the same for the moreactive companion Cen B. Using the Cen stars as templates, we study the possible eects that Tmin may have on the detectability of unresolveddust discs around other stars. Methods.We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in thefar infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunctionwith radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than Cen, a fractional dust luminosity fd LdustLstar 2 107 could account for SEDs that do not exhibit the Tmin eect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared,slight excesses at the 2:5 level are observed at 24 m for both CenA and B, which, if interpreted as due to zodiacal-type dust emission, wouldcorrespond to fd (13) 105, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dustgrains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the Cen stars, viz.4106 M$ of 4 to 1000 msize grains, distributed according to n(a) a3:5. Similarly, for filled-in Tmin emission, corresponding Edgeworth-Kuiper belts could account for103 M$ of dust. Conclusions. Our far-infrared observations lead to estimates of upper limits to the amount of circumstellar dust around the stars CenA and B.Light scattered andor thermally emitted by exo-Zodi discs will have profound implications for future spectroscopic missions designed to searchfor biomarkers in the atmospheres of Earth-like planets. The far-infrared spectral energy distribution of Cen B is marginally consistent with thepresence of a minimum temperature region in the upper atmosphere of the star. We also show that an Cen A-like temperature minimum mayresult in an erroneous apprehension about the presence of dust around other, more distant stars.

metallicities↗
NASA NTRS2016

Craters of the Pluto-Charon System

NASA's New Horizons flyby mission of the Pluto-Charon binary system and its four moons provided humanity with its first spacecraft-based look at a large Kuiper Belt Object beyond Triton. Excluding this system, multiple Kuiper Belt Objects (KBOs) have been observed for only 20 years from Earth, and the KBO size distribution is unconstrained except among the largest objects. Because small KBOs will remain beyond the capabilities of ground-based observatories for the foreseeable future, one of the best ways to constrain the small KBO population is to examine the craters they have made on the Pluto-Charon system. The first step to understanding the crater population is to map it. In this work, we describe the steps undertaken to produce a robust crater database of impact features on Pluto, Charon, and their two largest moons, Nix and Hydra. These include an examination of different types of images and image processing, and we present an analysis of variability among the crater mapping team, where crater diameters were found to average +/-10% uncertainty across all sizes measured (approx.0.5-300 km). We also present a few basic analyses of the crater databases, finding that Pluto's craters' differential size-frequency distribution across the encounter hemisphere has a power-law slope of approximately -3.1 +/- 0.1 over diameters D approx. = 15-200 km, and Charon's has a slope of -3.0 +/- 0.2 over diameters D approx. = 10-120 km; it is significantly shallower on both bodies at smaller diameters. We also better quantify evidence of resurfacing evidenced by Pluto's craters in contrast with Charon's. With this work, we are also releasing our database of potential and probable impact craters: 5287 on Pluto, 2287 on Charon, 35 on Nix, and 6 on Hydra.

Robbins, Stuart J.↗
NASA NTRSDate not supplied

NASA’s Space Launch System: New Launch Capability for Artemis Lunar and Deep Space Science Missions

With stacking and integration of the initial Block 1 Space Launch System (SLS) expected to begin in 2020, NASA’s powerful new launch vehicle is ready to take center stage in the agency’s Artemis program to return astronauts to the Moon. Combining the highest launch thrust and largest payload capacity ever developed, SLS also enables a new generation of high-C3 science missions to destinations such as the gas and ice giants, the Kuiper Belt, and even beyond the solar system. Block 1 is only the beginning, as the vehicle has a planned evolution path to progressively more powerful variants. In addition to these block upgrades providing increased lift capability, the vehicle can be configured to fly in crew configuration with the Orion spacecraft or in cargo configuration with payload fairings for launching science mission or large infrastructure, providing a flexible launch option. For Artemis I, the first SLS flight, the Block 1 vehicle in the crew configuration will send an uncrewed Orion spacecraft to lunar orbit for a thorough systems checkout before the crewed Artemis II flight. The Block 1 vehicle uses a proven propulsion system consisting of solid rocket boosters and RS-25 engines to lift more than 27 metric tons [t] to trans-lunar injection (TLI). In its cargo configuration, Block 1 can be fitted with a 5 m payload fairing. The second variant, Block 1B, uses a more powerful upper stage to increase payload mass to TLI to 38-42 t, depending on crew or cargo configuration. In the crew configuration, a co-manifested payload of up to 10 t can ride along in the Universal Stage Adapter (USA), which has as much volume for payloads as a 5 m-class payload fairing. The Block 2 evolved variant will lift 43-46 t to TLI, depending on crew or cargo configuration. The Block 1B and Block 2 vehicles can be outfitted with an 8.4 m-diameter payload fairing, available in 19.1 m and 27.4 m lengths, providing unprecedented volume for payloads. Larger-diameter 10 m fairings may also be an option in the future on the Block 2 vehicle. The unrivalled mass, volume and high-energy launches of SLS can provide significant mission flexibility for payloads and/or additional upper stages to open trade space for a new generation of exploration missions. SLS was designed to meet requirements for launching large-volume infrastructure as outlined in numerous studies of missions to cislunar space or Mars. Mission concept studies from the science community also point toward new possibilities enabled by SLS. Probes with more robust science packages can be sent to the gas giants. Dual spacecraft can be manifested for missions to Uranus and Neptune. Additional third or fourth payload stages can be encapsulated in the payload fairings to achieve missions to the Kuiper Belt or beyond. In addition, the large volume can be used to design and deploy wide-aperture mirrors on future space telescopes and to enable nuclear-thermal propulsion missions. At AIAA Ascend, the SLS Program will provide technical information on vehicle capabilities as well as descriptions of ongoing discussions with mission planners for utilizing the vehicle for an array of deep space missions.

Stephen Creech↗
NASA NTRS2019

The HST Lightcurve of (486958) 2014 MU69

We report Hubble Space Telescope (HST) lightcurve observations of the New Horizons spacecraft encounter Kuiper Belt object (KBO) (486958) 2014 MU69 acquired near opposition in July 2017. In order to plan the optimum flyby sequence the New Horizons mission planners needed to learn as much as possible about the target in advance of the encounter. Specifically, from lightcurve data, encounter timing could be adjusted to accommodate a highly elongated, binary, or rapidly rotating target. HST astrometric (Porter et al., 2018) and stellar occultation (Buie et al., 2018) observations constrained MU69's orbit and diameter (21–41 km for an albedo of 0.15–0.04), respectively. Photometry from the astrometric dataset suggested a variability of ≥0.3 mags, but they did not determine the period or provide shape information. To that end we strategically spaced 24 HST orbits over 9 days to investigate rotation periods from approximately 2–100 h and to better constrain the lightcurve amplitude. Until New Horizons detected MU69 in its optical navigation images beginning in August 2018, this HST lightcurve campaign provided the most accurate photometry to date. The mean variation in our data is 0.15 magnitudes which suggests that MU69 is either nearly spherical (a:b axis ratio of 1:1.15), or its pole vector is pointed near the line of sight to Earth; this interpretation does not preclude a near-contact binary or bi-lobed object. However, image stacks do conclude that MU69 does not have a binary companion ≥2000 km with a sensitivity to 29th magnitude (an object a few km in size for an albedo of 0.04–0.15). Our data are not of sufficient signal to noise to uniquely determine the period or amplitude, however, they did provide the necessary information for spacecraft planning. We report with confidence that MU69 is not both rapidly rotating and highly elongated (which we define as a lightcurve amplitude ≥ 0.5 magnitude). Since this paper is being published post fly-by, we note that our results are consistent with the fly-by imagery and orientation of MU69 (Stern et al., 2019). The combined dataset also suggests that within the KBO lightcurve literature there are likely other objects which share a geometric configuration like MU69 resulting in an underestimate of the contact binary fraction for the Cold Classical Kuiper Belt.

S D Benecchi↗
NASA NTRS2021

Triton: Fascinating Moon, Likely Ocean World, Compelling Destination!

Triton is an important signpost in understanding the diverse populations of both Ocean Worlds and Kuiper Belt Objects. As a likely ocean world, it is unique by virtue of its kidnapped history from the Kuiper Belt: its large orbital inclination makes it the only ocean world thought to be primarily heated by obliquity tides (Nimmo and Spencer, 2015). It is volatile-rich due to its formation in the outer Solar System and its unusual surface geology may be the product of cryovolcanism. Observations from New Horizons and Cassini motivate re-examination of Triton datasets and models, with value for comparative planetology of ocean worlds and KBOs, most notably with Europa, Enceladus, Titan, and Pluto. We re-explore old datasets with the new perspective of the importance of ocean worlds in our Solar System and the search for life.

J Castillo-Rogez↗
NASA NTRS2021

Numerical Modeling and Design of Gaseous Propellant Acquisition System for the Triton Hopper

Triton, the largest moon around Neptune, is a captured Kuiper Belt Object with a dynamic rarified atmosphere, active geysers, and unique “cantaloupe” like terrain. Little is known about Kuiper Belt Objects in the scientific community with most of the information coming from Pluto. Currently, NASA is designing an unmanned probe to explore the atmosphere and surface of Triton. This vehicle is unique in that it repeatedly takes off and lands (hops) using nitrogen propellant collected from its surroundings on Triton. This paper presents preliminary conceptual system design and numerical modeling of the atmospheric collection process. Four concepts are presented: a cryocooler-based system, a pump-based system, a sublimation and pump-based system, and a cryocooler and sublimation system. Numerical modeling takes into account the mass and energy transfer between all the relevant nodes in the system and is able to calculate the amount of nitrogen ice collected and ice accumulation rate as a function of time for each concept. The models are ultimately used to assess the feasibility of traversing from equator to pole in under two years using a gaseous propellant acquisition system for the Hopper.

Hopper↗
NASA NTRS2021

Neptune Odyssey: A Flagship Concept for the Exploration of the Neptune–Triton System

The Neptune Odyssey mission concept is a Flagship-class orbiter and atmospheric probe to the Neptune–Triton system. This bold mission of exploration would orbit an ice-giant planet to study the planet, its rings, small satellites, space environment, and the planet-sized moon Triton. Triton is a captured dwarf planet from the Kuiper Belt, twin of Pluto, and likely ocean world. Odyssey addresses Neptune system-level science, with equal priorities placed on Neptune, its rings, moons, space environment, and Triton. Between Uranus and Neptune, the latter is unique in providing simultaneous access to both an ice giant and a Kuiper Belt dwarf planet. The spacecraft—in a class equivalent to the NASA/ESA/ASI Cassini spacecraft—would launch by 2031 on a Space Launch System or equivalent launch vehicle and utilize a Jupiter gravity assist for a 12 yr cruise to Neptune and a 4 yr prime orbital mission; alternatively a launch after 2031 would have a 16 yr direct-to-Neptune cruise phase. Our solution provides annual launch opportunities and allows for an easy upgrade to the shorter (12 yr) cruise. Odyssey would orbit Neptune retrograde (prograde with respect to Triton), using the moonʼs gravity to shape the orbital tour and allow coverage of Triton, Neptune, and the space environment. The atmospheric entry probe would descend in ∼37 minutes to the 10 bar pressure level in Neptune’s atmosphere just before Odysseyʼs orbit-insertion engine burn. Odysseyʼs mission would end by conducting a Cassini-like “Grand Finale,” passing inside the rings and ultimately taking a final great plunge into Neptuneʼs atmosphere.

Abigail M. Rymer↗
NASA NTRS2022

29P/Schwassmann–Wachmann 1: A Rosetta Stone for Amorphous Water Ice and CO↔CO 2 Conversion in Centaurs and Comets?

Centaur 29P/Schwassmann–Wachmann 1 (SW1) is a highly active object orbiting in the transitional "Gateway" region between the Centaur and Jupiter-family comet (JFC) regions. SW1 is unique among the Centaurs in that it experiences quasi-regular major outbursts and produces CO emission continuously; however, the source of the CO is unclear. We argue that, due to its very large size (∼32 km radius), SW1 is likely still responding, via amorphous water ice (AWI) conversion to crystalline water ice (CWI), to the "sudden" change in its external thermal environment produced by its Myrs-long dynamical migration from the Kuiper Belt to its current location at the inner edge of the Centaur region. It is this conversion process that is the source of the abundant CO and dust released from the object during its quiescent and outburst phases. If correct, these arguments have a number of important predictions testable via remote sensing and in situ spacecraft characterization, including the quick release on Myr timescales of CO from AWI conversion for any few kilometer-scale scattered disk Kuiper Belt Objects transiting into the inner system; that to date SW1 has only converted between 50% and 65% of its nuclear AWI to CWI; that volume changes on AWI conversion could have caused subsidence and cave-ins, but not significant mass wasting or crater loss; that SW1's coma should contain abundant amounts of CWI+CO 2 "dust" particles; and that when SW1 transits into the inner system within the next 10,000 yr, it will be a very different kind of JFC.

Centaur 29P/Schwassmann–Wachmann 1(SW1)↗
NASA NTRS2024

StarNAV: An Architecture for Autonomous Spacecraft Navigation by the Relativistic Perturbation of Starlight

Exploration missions to the outer Solar System (e.g., Neptune, Kuiper belt objects) or to the interstellar medium present several challenges for conventional spacecraft designs. One of the greatest challenges is a means for navigation, as Earth-based tracking with the Deep Space Network (DSN) becomes less desirable due to high cost, decreased performance at long ranges, and long light-time delays. Indeed, light time delays at Neptune are over four hours (one way), making control of spacecraft during critical events nearly impossible—and this problem only becomes worse as we move to the Kuiper belt or to interstellar space. The need for autonomous spacecraft navigation is well established and is prominently featured in the 2015 NASA Technology Roadmap (e.g., TA 5.4.2.6 & 5.4.2.8). This has led to investment in various technologies to accomplish this task, with the majority of recent work focusing on optical navigation (OPNAV; TA 5.4.4.1) [1], X-ray pulsar navigation (XNAV; TA 5.6.1) [2], or DSN one-way ranging with the Deep Space Atomic Clock (DSAC; TA 5.4.1.1) [3]. This NIAC study suggests a new (and completely different) way of autonomously navigating a spacecraft anywhere in the Solar System or beyond. We call this new technique StarNAV.

NIAC Phase I↗