SETI Institute Scientists Head to the 48th Annual DPS Meeting

The following is a list of posters and presentations by SETI Institute scientists attending the DPS meeting in Pasadena, CA, October 16-21, 2016.


1. M. S. Tiscareno*

SETI Institute

Propeller peregrinations: Ongoing observations of disk-embedded migration in Saturn’s rings

The "propeller" moons within Saturn's rings are the first objects ever to have their orbits tracked while embedded in a disk, rather than moving through empty space (Tiscareno et al. 2010, ApJL). The km-sized "giant propellers" whose orbits have been tracked in the outer-A ring, as well as their smaller 0.1-km-sized brethren swarming in the mid-A ring, are not seen directly; rather, their locations are inferred by means of the propeller-shaped disturbances they create in the surrounding ring material (Tiscareno et al. 2006, Nature; Sremcevic et al. 2007, Nature; Tiscareno et al. 2008, AJ). The orbits of giant propellers are primarily Keplerian, but with clear excursions of up to several degrees longitude over a decade of observations. Most theories that have been proposed to explain the non-Keplerian motion of propeller moons (e.g., Pan et al. 2012, MNRAS; Tiscareno 2013, P&SS) rely on gravitational and/or collisional interactions between the moon and the surrounding disk, and thus hold out the prospect for directly observing processes that are important in protoplanetary scenarios and other disk systems. We will review the current dynamical models and report on recent ongoing observations by the Cassini imaging camera.


2. Z. Zhang*; A. Hayes; M. A. Janssen; P. D. Nicholson; J. N. Cuzzi; I. de Pater; D. Dunn; M. M. Hedman; P. R. Estrada

Cornell University; Jet Propulsion Laboratory; NASA Ames Research Center; UC, Berkeley; Sierra College; University of Idaho; SETI Institute

Microwave Observations on Saturn's Main Rings
Despite considerable study, Saturn’s rings continue to challenge current theories for their provenance. Water ice comprises the bulk of Saturn’s rings, yet it is the small fraction of non-icy material that is arguably more valuable in revealing clues about the system’s origin and age. Herein, we present new measurements of the non-icy material fraction in Saturn’s main rings, determined from microwave observations obtained by Cassini Radar and EVLA.<br /><br />Our Cassini Radar observations in the C Ring show an exceptionally high brightness at near-zero azimuthal angles, suggesting a high porosity of 70%-75% for the particles. Furthermore, most regions in the C ring contain about 1-2% silicates while with an enhanced abundance concentrated in the middle C ring reaching a maximum of 6%-11%. We proposed that the C ring has been continuously polluted by meteoroid bombardment for 15-90Myr, while the middle C ring was further contaminated by an incoming Centaur disrupted by Saturn tidal force. Owing to the B ring’s high opacity, the particles there are likely to have 85% - 90% porosity, with corresponding non-icy material fractions of ~ 0.3% - 0.5% in the inner and outer B ring, and ~0.1% - 0.2% in the middle regions. For the A ring interior to the Encke gap, the derived non-icy material is ~0.2% - 0.3% everywhere for porosities ranging from 55% - 90%. Finally, our results for the Cassini Division indicate a non-icy material fraction of ~1% - 2% similar to most regions in the C ring, except that the Cassini Division particles are more likely to contain ~ 90% porosity due to the high opacity there. Our results here further support the idea that Saturn’s rings may be less than 150 Myr old suggesting an origin scenario in which the rings are derived from the relatively recent breakup of an icy moon.<br /><br />Furthermore, we calibrated and analyzed multi-wavelengths EVLA observation at wavelengths ranging from 0.7cm to 13cm. As the array operates in a wavelength regime where the absorption coefficient of water ice shows dramatic variation, the EVLA observations enable us to disentangle brightness temperature variations from changes in the particle size distribution and non-icy material abundance.


3. J. N. Spitale*; M. S. Tiscareno

Planetary Science Institute; SETI Institute

Localized Perturbations in Saturn's C Ring
Years of high-resolution imaging of Saturn's rings have revealed many examples of perturbations arising from local causes. For example, the presence of 100-m-scale and smaller moonlets is inferred in the A ring based on the propeller-shaped disturbances that they create (Tiscareno et al. 2006, 2010); the F ring is shaped by regular collisions with its shepherd Prometheus, as well as with other smaller bodies orbiting in the vicinity (Murray et al. 2005, 2008); the "wisps" on the outer edge of the Keeler gap (Porco et al. 2005) may mark the locations of small moonlets that have emerged from the A ring (Tiscareno and Arnault 2015); wakes in the Huygens ringlet imply the presence of two multi-km bodies, and the irregular shape of its inner edge suggests the presence of many smaller bodies (Spitale and Hahn 2016); based on shadow measurements, the B ring contains an embedded 300-m object that produces a small propeller-shaped disturbance (Spitale and Porco 2010; Spitale and Tiscareno 2012).<br /><br />Here, we present evidence for localized perturbations in the C ring. The ringlet embedded in the Bond gap, near 1.470 Saturn radii, shows discrete clumps orbiting at the Keplerian rate in images spanning about eight years. The clumps are not detected in all image sequences at the expected longitudes. The Dawes ringlet, near 1.495 Saturn radii, has an irregular edge that does not appear as a simple superposition of low-wavenumber normal modes.


4. P. R. Estrada*; R. H. Durisen; J. N. Cuzzi
SETI Institute; Indiana University; NASA Ames Research Center

The Evolution of Saturn's Rings Under the Influence of the Edgeworth-Kuiper Belt Micrometeoroid Flux: Tightening the Constraints on Ring Age
 Results of the Cassini Dust Analyzer (CDA) experiment indicate that the determined range of the micrometeoroid flux at infinity for Saturn (Altobelli et al., 2015) may be comparable to the nominal value of the incident, flat-plate and one-sided meteoroid flux value currently adopted for use in ballistic transport applications and models (e.g., Estrada et al., 2015). Moreover, the source of the micrometeoroid flux has been localized to the Edgeworth-Kuiper Belt (EKB) and is not cometary in origin as previously assumed. Apart from suggesting an altogether different composition for the ring pollutant, a major consequence of these new measurements is that the EKB flux is much more gravitationally focused than the cometary case because it is isotropic in the planet rather than the heliocentric frame. Thus, the lower velocities at infinity that characterize the EKB flux can increase the impact flux on the rings by a factor of ∼25. This means that even for the lower bound of the range of the newly measured flux, the amount of material hitting the rings may be considerably higher and thus the process of micrometeoroid bombardment and ballistic transport is likely even more influential in the rings' structural and compositional evolution over time. Here, we calculate the new EKB ejecta distribution using the model of Cuzzi and Durisen (1990) and compare this with the nominal cometary one, and then demonstrate using new simulations the consequences of the EKB flux on the evolution of ring composition and structure. The constraining of the micrometeoroid flux represents a very important step in being able to associate an absolute age for the rings. We argue that the new EKB flux poses a serious problem for "primordial" or "old" ring origin scenarios and favors more a scenario in which the rings, at least the way we see them today, cannot be much older than a few 100 Myrs.


5. F. Marchis*; J. Rameau; E. L. Nielsen; R. J. De Rosa; T. Esposito; Z. H. Draper; B. Macintosh; J. R. Graham
SETI Institute; Stanford University; UC Berkeley; University of Victoria; Universite de Montreal

Gemini Planet Imager Exoplanet Survey: Key Results Two Years Into The Survey
 The Gemini Planet Imager Exoplanet Survey (GPIES) is targeting 600 young, nearby stars using the GPI instrument. We report here on recent results obtained with this instrument from our team.Rameau et al. (ApJL, 822 2, L2, 2016) presented astrometric monitoring of the young exoplanet HD 95086 b obtained with GPI between 2013 and 2016. Efficient Monte Carlo techniques place preliminary constraints on the orbital parameters of HD 95086 b. Under the assumption of a coplanar planet–disk system, the periastron of HD 95086 b is beyond 51 AU. Therefore, HD 95086 b cannot carve the entire gap inferred from the measured infrared excess in the SED of HD 95086. Additional photometric and spectroscopic measurements reported by de Rosa et al. (2016, apJ, in press) showed that the spectral energy distribution of HD 95086 b is best fit by low temperature (T~800-1300 K), low surface gravity spectra from models which simulate high photospheric dust content. Its temperature is typical to L/T transition objects, but the spectral type is poorly constrained. HD 95086 b is an important exoplanet to test our models of atmospheric properties of young extrasolar planets.Direct detections of debris disk are keys to infer the collisional past and understand the formation of planetary systems. Two debris disks were recently studied with GPI:- Draper et al. (submitted to ApJ, 2016) show the resolved circumstellar debris disk around HD 111520 at a projected range of ~30-100 AU using both total and polarized H-band intensity. Structures in the disks such as a large brightness asymmetry and symmetric polarization fraction are seen. Additional data would confirm if a large disruption event from a stellar fly-by or planetary perturbations altered the disk density - Esposito et al. (submitted to ApJ, 2016) combined Keck NIRC2 data taken at 1.2-2.3 microns and GPI 1.6 micron total intensity and polarized light detections that probes down to projected separations less than 10 AU to show that the HD 61005 debris disk ("The Moth") support the premise of a planet-perturbed disk.These new data, and additional interesting targets, will be presented and discussed. This work is partially supported by NASA NNX14AJ80G.


6. H. Imanaka*; M. A. Smith; C. P. McKay; D. P. Cruikshank; M. S. Marley

SETI Institute; NASA Ames Research Center; University of Houston

Photochemical aerosols in warm exoplanetary atmospheres
Recent transit observations of exoplanets have demonstrated the possibility of a wide prevalence of haze/cloud layers at high altitudes. Hydrocarbon photochemical haze could be the candidate for such haze particles on warm sub-Neptunes, but the lack of evidence for methane poses a puzzle for such hydrocarbon photochemical haze. The CH4/CO ratios in planetary atmospheres vary substantially from their temperature and dynamics. We have conducted a series of laboratory simulations to investigate how atmospheric compositions, specifically CH4/CO ratios, affect the haze production rates and their optical properties. The mass production rates in the H2-CH4-CO gas mixtures are rather insensitive to the CH4/CO ratios larger than at 0.3. Significant formation of solid material is observed in a H2-CO gas mixture even without CH4. The complex refractive indices of the aerosol analogue from the H2-CO gas mixture show strong absorption at the visible near-IR wavelengths. These experimental facts imply that substantial carbonaceous aerosols may be generated in warm H2-CO-CH4 exoplanetary atmospheres, and that it might be responsible for the observed dark albedos at the visible wavelengths.

7. T. Fouchet*; R. Wiens; S. Maurice; J. R. Johnson; S. Clegg; S. Sharma; F. Rull; F. Montmessin; R. Anderson; O. Beyssac; L. Bonal; L. Deflores; G. Dromart; W. Fischer; O. Forni; O. Gasnault; J. P. Grotzinger; N. Mangold; J. Martinez-Frias; S. MacLennan; K. McCabe; P. cais; T. Nelson; S. Angel; P. Beck; K. Benzerara; S. Bernard; B. Bousquet; N. Bridges; E. Cloutis; C. Fabre; O. Grasset; N. Lanza; J. Lasue; S. Le Mouélic; R. Leveille; E. Lewin; T. H. McConnochie; N. Melikechi; P. Meslin; A. Misra; G. Montagnac; H. Newsom; A. Ollila; P. Pinet; F. Poulet; P. Sobron
Observatoire de Paris; LANL; IRAP/CNRS; APL/JHU; Univ. Hawaii; Univ. Valladolid; LATMOS/CNRS; USGS; IMPMC/CNRS; IPAG/CNRS; JPL; ENS Lyon; Caltech; LPG/CNRS; CSIC-UCM; Stony Brook; Univ. Bordeaux; Univ. South Carolina; Univ. Winnipeg; GeoRessources/CNRS; CSA; GSFC; Inv. Deleware; Univ. New Mexico; IAS/CNRS; SETI

The SuperCam Remote Sensing Suite for MARS 2020: Nested and Co-Aligned LIBS, Raman, and VISIR Spectroscopies, and color micro-imaging
As chartered by the Science Definition Team, the Mars 2020 mission addresses four primary objectives: A. Characterize the processes that formed and modified the geologic record within an astrobiologically relevant ancient environment, B. Perform astrobiologically relevant investigations to determine habitability, search for materials with biosignature presentation potential, and search for evidence of past life, C. Assemble a returnable cache of samples and D. Contribute to preparation for human exploration of Mars. The SuperCam instrument, selected for the Mars 2020 rover, as a suite of four instruments, provides nested and co-aligned remote investigations: Laser Induced Breakdown Spectroscopy (LIBS), Raman spectroscopy and time-resolved fluorescence (TRF), visible and near-infrared spectroscopy (VISIR), and high resolution color imaging (RMI). SuperCam appeals broadly to the four Mars 2020 objectives.
In detail, SuperCam will perform:
1. Microscale mineral identification by combining LIBS elemental and VISIR mineralogical spectroscopies, especially targeting secondary minerals
2. Determine the sedimental stratigraphy through color imaging and LIBS and VISIR spectroscopy
3. Search for organics and bio-signatures with LIBS and Raman spectroscopy
4. Quantify the volatile content of the rocks by LIBS spectroscopy to determine the degree of aquaeous alteration
5. Characterize the texture of the rocks by color imaging to determine their alteration processes
6. Characterize the rocks’ coatings by LIBS spectroscopy
7. Characterize the soil and its potential for biosignature preservation
8. Monitor the odd-oxygen atmospheric chemistry.
To meet these goals SuperCam will perform LIBS spectroscopy on 0.5 mm spot up to 7-meter distance, perform Raman and time-resolved fluoresence up to 12-m distance with a 0.8 mrad angular resolution, a 100 ns time gating in the 534-850 nm spectral range, acquire VISIR spectra in the range 0.4-0.85 μm with a resolution of 0.35 nm, and in the IR range over 1.3-2.6 μm, rich in mineral signatures, with a resolution of 20 nm, and provide RGB images with an angular resolution of 40 μrad over a FOV of 20 mrad.
We will present the science performances of SuperCam and the forecasted operation plans.


8. D. J. Osip*; A. S. Rivkin; P. Pravec; N. Moskovitz; A. Thirouin; P. Scheirich; D. A. Oszkiewicz; D. C. Richardson; D. Polishook; W. Ryan; C. Thomas; M. W. Busch; A. F. Cheng; P. Michel

Carnegie Observatories, Las Campanas Observatory; JHU/APL; Lowell Observatory; Ondrejov Observatory; University of Maryland; MIT; Magdalena Ridge Observatory; PSI; SETI; Obs. de La Cote D'Azur

The Observing Working Group for the Asteroid Impact & Delfection Assessment (AIDA) Mission
The Asteroid Impact & Deflection Assessment (AIDA) mission is a joint ESA-NASA mission concept currently under study. AIDA has two components: the Double Asteroid Redirect Test (DART) is the US component designed to demonstrate a kinetic impactor, while the Asteroid Impact Mission (AIM) spacecraft is on station to do a thorough pre- and post-impact survey of the Didymos system.
Members of the DART and AIM Investigation teams have been organized into several joint and independent working groups. While there is overlap in subject matter and membership between the groups, we focus here on the activities of the Observing Working Group.
The first work by the group was undertaken during the spring of 2015, before DART entered Phase A. During this period Didymos made an apparition reaching roughly V ~ 20.5 in brightness, and our top priority was constraining which of two very different pole positions for the Didymos system was correct. Several telescopes in the 2–4-m aperture range around the world attempted observations. An observed mutual event allowed the one pole position to be ruled out. Didymos is now thought to be a low-obliquity, retrograde rotator, similar to many other asteroid binary systems and consistent with expectations from a YORP-driven origin for the satellite.
We have begun planning for the 2017 apparition, occurring in the first half of the year. Didymos will be ~20% brighter at opposition than the 2015 apparition. Scaling from the successful observations with the 4.3-m Lowell Discovery Channel Telescope indicates that we will need telescopes at least 4 m (or larger, for some of the tasks, or at times longer before or after the opposition) in primary diameter for the advanced characterization in 2017.
Currently, we have four goals for this apparition: 1) confirming the preferred retrograde pole position; 2) gathering data to allow BYORP-driven changes in the mutual orbit to potentially be determined by later observations; 3) establishing whether or not the secondary is in synchronous rotation with the primary; and 4) constraining the inclination of the satellite orbit.


9. R. S. French*; M. R. Showalter; M. K. Gordon
SETI Institute

Precision Navigation of Cassini Images Using Rings, Icy Satellites, and Fuzzy Bodies
Before images from the Cassini spacecraft can be analyzed, errors in the published pointing information (up to ~110 pixels for the Imaging Science Subsystem Narrow Angle Camera) must be corrected so that the line of sight vector for each pixel is known. This complicated and labor-intensive process involves matching the image contents with known features such as stars, rings, or moons. Metadata, such as lighting geometry or ring radius and longitude, must be computed for each pixel as well. Both steps require mastering the SPICE toolkit, a highly capable piece of software with a steep learning curve. Only after these steps are completed can the actual scientific investigation begin.

We have embarked on a three-year project to perform these steps for all 400,000+ Cassini ISS images as well as images taken by the VIMS, UVIS, and CIRS instruments. The result will be a series of SPICE kernels that include accurate pointing information and a series of backplanes that include precomputed metadata for each pixel. All data will be made public through the PDS Ring-Moon Systems Node ( We expect this project to dramatically decrease the time required for scientists to analyze Cassini data.

In a previous poster (French et al. 2014, DPS #46, 422.01) we discussed our progress navigating images using stars, simple ring models, and well-defined icy bodies. In this poster we will report on our current progress including the use of more sophisticated ring models, navigation of "fuzzy" bodies such as Titan and Saturn, and use of crater matching on high-resolution images of the icy satellites.


10. L. Mayorga*; J. Jackiewicz; K. Rages; R. West; B. Knowles; M. Marley; N. Lewis
New Mexico State University; SETI Institute; Jet Propulsion Laboratory, California Institute of Technology; CICLOPS/Space Science Institute; NASA Ames Research Center; Space Telescope Science Institute; Department of Earth and Planetary Sciences, Johns Hopkins University

Jupiter's Phase Variations from Cassini: a testbed for future direct-imaging missions
Phase curves are important for our understanding of the energy balance and scattering behavior of an exoplanet's atmosphere. In preparation for future direct-imaging missions of Jupiter-like planets, we present phase curves of Jupiter from 0--150 degrees as measured in multiple optical bandpasses by Cassini/ISS during the Millennium flyby of Jupiter in late 2000 to early 2001. We demonstrate and confirm that Jupiter is not well represented by a Lambertian phase function and that its color is more variable with phase angle than predicted by Jupiter-like models. This indicates that a Jupiter-twin observed near quadrature may not be as straightforward to classify as a Jupiter-like planet.


11. H. B. Throop*; M. R. Showalter; H. C. Dones; D. Hamilton; H. A. Weaver; A. F. Cheng; S. A. Stern; L. Young; C. B. Olkin

SwRI; University of Maryland; APL; SETI; PSI

New Horizons Imaging of Jupiter's Main Ring
New Horizons took roughly 520 visible-light images of Jupiter's ring system during its 2007 flyby, using the spacecraft's Long-Range Reconnaissance Imager (LORRI). These observations were taken over nine days surrounding Jupiter close-approach. They span a range in distance of 30 - 100 RJ, and a phase angle range of 20 - 174 degrees. The highest resolution images -- more than 200 frames -- were taken at a resolution approaching 20 km/pix.
We will present an analysis of this dataset, much of which has not been studied in detail before. Our results include New Horizons' first quantitative measurements of the ring's intrinsic brightness and variability. We will also present results on the ring's azimuthal and radial structure. Our measurements of the ring's phase curve will be used to infer properties of the ring's dust grains.
Our results build on the only previous analysis of the New Horizons Jupiter ring data set, presented in Showalter et al (2007, Science 318, 232-234), which detected ring clumps and placed a lower limit on the population of undetected ring-moons.
This work was supported by NASA's OPR program.


12. M. R. Showalter*; I. de Pater; J. J. Lissauer; R. S. French

SETI Institute; UC Berkeley; NASA Ames Research Center

Hubble Observations of the Ongoing Evolution of Neptune's Ring-Moon System
We report on a new analysis of Hubble Space Telescope (HST) images of the Neptune system spanning 2004 to 2016. This expands upon an initial analysis we presented in 2013 (Showalter et al., DPS Meeting #45, abstract 206.01), based on HST images from 2004-2009. At that time we reported (1) the discovery of Neptune's fourteenth moon, S/2004 N 1, which orbits between Proteus and Larissa; (2) the recovery of Naiad, Neptune's innermost moon, although at an orbital longitude 90 degrees away from its prediction; and (3) the disappearance of the leading arcs in the Adams Ring, along with a marked decrease in the brightness of the trailing two arcs. Recent HST images extend the time baseline of the system by seven additional years, allowing us to expand upon prior results. We will report on our progress in refining the orbit, size and shape of S/2004 N 1, on understanding the orbital dynamics of Naiad, and on determining the ongoing evolution of the arcs and rings. 

13. A. J. Verbiscer*; M. W. Buie; R. Binzel; K. Ennico; W. M. Grundy; C. B. Olkin; M. R. Showalter; J. R. Spencer; S. A. Stern; H. A. Weaver; L. Young

University of Virginia; SWRI; MIT; NASA Ames; Lowell Observatory; SETI; JHU/APL

The Pluto System At Small Phase Angles
Hubble Space Telescope observations of the Pluto system acquired during the New Horizons encounter epoch (HST Program 13667, M. Buie, PI) span the phase angle range from 0.06 to 1.7 degrees, enabling the measurement and characterization of the opposition effect for Pluto and its satellites at 0.58 microns using HST WFC3/UVIS with the F350LP filter, which has a broadband response and a pivot wavelength of 0.58 microns. At these small phase angles, differences in the opposition effect width and amplitude appear. The small satellites Nix and Hydra both exhibit a very narrow opposition surge, while the considerably larger moon Charon has a broader opposition surge. Microtextural surface properties derived from the shape and magnitude of the opposition surge of each surface contain a record of the collisional history of the system. We combine these small phase angle observations with those made at larger phase angles by the New Horizons Long Range Reconnaissance Imager (LORRI), which also has a broadband response with a pivot wavelength of 0.61 microns, to produce the most complete disk-integrated solar phase curves that we will have for decades to come. Modeling these disk-integrated phase curves generates sets of photometric parameters that will inform spectral modeling of the satellite surfaces as well as terrains on Pluto from spatially resolved New Horizons Ralph Linear Etalon Imaging Spectral Array (LEISA) data from 1.2 to 2.5 microns. Rotationally resolved phase curves of Pluto reveal opposition effects that only appear at phase angles less than 0.1 degree and have widths and amplitudes that are highly dependent on longitude and therefore on Pluto's diverse terrains. The high albedo region informally known as Sputnik Planum dominates the disk-integrated reflectance of Pluto on the New Horizons encounter hemisphere. These results lay the groundwork for observations at true opposition in 2018, when the Pluto system will be observable at phase angles so small that an Earth transit across the solar disk will be visible from Pluto and its satellites.


14. I. Linscott*; S. Protopapa; D. P. Hinson; M. Bird; G. L. Tyler; W. M. Grundy; W. B. McKinnon; C. B. Olkin; S. A. Stern; J. A. Stansberry; H. A. Weaver

Stanford University; University of Maryland; SETI Institute; University of Bonn; Lowell Observatory; Washington University; SwRI; Space Telescope Science Institute; Johns Hopkins Applied Physics Lab

The structure and temperature of Pluto’s Sputnik Planum using 4.2 cm radiometry
New Horizons measured the radiometric brightness temperature of Pluto at 4.2 cm, during the encounter with two scans of the spacecraft’s high gain antenna shortly after closest approach. The Pluto mid-section scan included the region informally known as Sputnik Planum, now understood to be filled with nitrogen ice. The mean radiometric brightness temperature at 4.2 cm, obtained in this region is 25 K, for both Right Circular Polarization (RCP) and Left Circular Polarization (LCP), well below the sublimation temperature for nitrogen ice. Sputnik Planum was near the limb and the termination of the radiometric scan. Consequently, the thermal emission was measured obliquely over a wide range of emission angles. This geometry affords detailed modeling of the angular dependence of the thermal radiation, incorporating surface and subsurface electromagnetic scattering models as well as emissivity models of the nitrogen ice. In addition, a bistatic radar measurement detected the scattering of a 4.2 cm uplink transmitted from Earth. The bistatic specular point was within Sputnik Planum and the measurements are useful for constraining the dielectric constant as well as the surface and subsurface scattering functions of the nitrogen ice. The combination of the thermal emission’s angular dependence, RCP and LCP polarization dependence, and the bistatic scattering, yields estimates of the radiometric thermal emissivity, nitrogen ice temperature and spatial correlation scales. This work is supported by the NASA New Horizons Mission.


15. O. M. Umurhan*; W. Lyra; T. Wong; W. B. McKinnon; F. Nimmo; A. D. Howard; J. M. Moore; R. Binzel; O. White; S. A. Stern; K. Ennico; C. B. Olkin; H. A. Weaver; L. Young

NASA-Ames Research Center; SETI; JPL-NASA; Washington University, St. Louis; U C Santa Cruz; University of Virginia; Massachusetts Institute of Technology; Southwest Research Institute; JHU-APL

An Expanded Analysis of Nitrogen Ice Convection in Sputnik Planum
The New Horizons close-encounter flyby of Pluto revealed 20-35 km scale ovoid patterns on the informally named Sputnik Planum. These features have been recently interpreted and shown to arise from the action of solid-state convection of (predominantly) nitrogen ice driven by Pluto’s geothermal gradient. One of the major uncertainties in the convection physics centers on the temperature and grain-size dependency of nitrogen ice rheology, which has strong implications for the overturn times of the convecting ice. Assuming nitrogen ice in Sputnik Planum rests on a passive water ice bedrock that conducts Pluto’s interior heat flux, and, given the uncertainty of the grain-size distribution of the nitrogen ice in Sputnik Planum, we examine a suite of two-dimensional convection models that take into account the thermal contact between the nitrogen ice layer and the conducting water-ice bedrock for a given emergent geothermal flux. We find for nitrogen ice layers several km deep, the emerging convection efficiently cools the nitrogen-ice water-ice bedrock interface resulting in temperature differences across the convecting layer of 10-20 K (at most) regardless of layer depth. For grain sizes ranging from 0.01 mm to 5 mm the resulting horizontal size to depth ratios of the emerging convection patterns go from 4:1 up to 6:1, suggesting that the nitrogen ice layer in Sputnik Planum may be anywhere between 3.5 and 8 km deep. Such depths are consistent with Sputnik Planum being a large impact basin (in a relative sense) analogous to Hellas on Mars. In this grain-size range we also find, (i) the calculated cell overturn times are anywhere from 1e4 to 5e5 yrs and, (ii) there is a distinct transition from steady state to time dependent convection.


16. R. A. Beyer*; K. N. Singer; F. Nimmo; J. M. Moore; W. B. McKinnon; P. M. Schenk; J. R. Spencer; H. A. Weaver; C. B. Olkin; L. Young; K. Ennico; S. A. Stern

NASA Ames Research Center; Sagan Center at the SETI Institute; Southwest Research Institute; UCSC; Washington University; Lunar and Planetary Institute; JHU APL

Landslides on Charon and not on Pluto
Landslide features are observed on Charon but not on Pluto. This observation is another that reinforces the different strength regime of surface materials on the two bodies. Pluto's surface, although underlain by strong water ice, is primarily mantled with a variety of geologically weak ice species. Observations of these features indicate that they flow and move, but do so in a manner similar to glacial flow, and the strength and steepening required to precipitate a landslide simply isn't present in these materials under the pressure and temperature conditions on Pluto's surface. There are certainly areas of local mass-wasting, but no substantial landslide deposits. There are some locations on Pluto, notably along the fossae walls, and perhaps on the steeper montes surfaces that could have fostered landslides, but no landslide deposits have been observed nor are there obvious landslide alcoves that would have sourced them. The resolution of observations along the fossae may prevent identification there, and the toes of the steeper montes are embayed by geologically recent plains material which could be overlaying any landslide deposits.<br /><br />Charon, however, has a water-ice surface which exhibits many strength-dominated geologic features, and also exhibits landslide deposits. There are not many of these features and they are confined to the informally named Serenity Chasma, which has relatively steep, tall slopes, perfect for landslide initiation. We will discuss the physical characteristics of these landslide deposits and their context amongst other landslide features in the solar system.


17. S. P. Naidu*; L. A. Benner; M. Brozovic; J. D. Giorgini; J. S. Jao; C. G. Lee; M. A. Slade; L. G. Snedeker; M. W. Busch; F. D. Ghigo

Jet Propulsion Laboratory, California Institute of Technology; SETI Institute; NRAO

High-resolution Goldstone radar imaging of comet P/2016 BA14 (Pan-STARRS)
Comet P/2016 BA14 (Pan-STARRS) was discovered by Pan-STARRS on January 21, 2016 and approached Earth within 0.024 astronomical units (9.2 lunar distances) on March 22. It was originally classified as an asteroid but subsequent observations (Knight et al., CBET 4257, 2016) showed the presence of a faint, short tail suggesting that the object is a comet. The similarity of its orbit to that of comet 252P/LINEAR led to speculation of a common origin.<br /><br />We observed 2016 BA14 with radar using the 70-m DSS-14 (8560 MHz, 3.5 cm) and 34-m DSS-13 (7190 MHz, 4.2 cm) antennas at Goldstone as transmitters and the 100-m Green Bank Telescope in West Virginia as a receiver on four days spanning one week around close approach. The best images have range resolutions of 7.5 m/pixel and are the finest resolution comet images ever obtained at Goldstone. The maximum visible extent of the nucleus in the radar images is about 900 m, strongly implying that the diameter is more than 1 km. Its absolute magnitude of 19.5 and a diameter of at least 1 km imply an optical albedo of < 3%. The echo bandwidth is ~2.5 Hz, which suggests a slow rotation period of about 40 h that is consistent with the rotation evident in images obtained on each day. There are no obvious signatures of a coma in the radar data. The appearance of the leading edge of the nucleus varies significantly as it rotates: there are facets hundreds of meters in length, angular junctions between facets, depressions, and rounded regions. The radar images lack any prominent high-contrast surface features, but there are subtle signatures of linear ridges, concavities, and a raised region casting a radar shadow.


18. D. P. Hinson*; I. Linscott; L. Young; S. A. Stern; M. Bird; K. Ennico; R. Gladstone; C. B. Olkin; M. Pätzold; D. F. Strobel; M. Summers; G. L. Tyler; H. A. Weaver; W. Woods

SETI Institute; Stanford University; Southwest Research Inst.; University of Cologne; NASA Ames Research Center; Southwest Research Inst.; Johns Hopkins University; George Mason University; Applied Physics Laboratory

Radio Occultation Measurements of Pluto’s Atmosphere with New Horizons
The reconnaissance of the Pluto System by New Horizons in July 2015 included a radio occultation at Pluto. The observation was performed with signals transmitted simultaneously by four antennas of the NASA Deep Space Network, two at the Goldstone complex in California and two at the Canberra complex in Australia. Each antenna radiated 20 kW without modulation at a wavelength of 4.17 cm. New Horizons received the four signals with its 2.1-m high-gain antenna, where the signals were split into pairs and processed independently by two identical REX radio science instruments. Each REX relied on a different ultra-stable oscillator as its frequency reference. The signals were digitized and filtered, and the data samples were stored on the spacecraft for later transmission to Earth. Six months elapsed before all data had arrived on the ground, and the results reported here are the first to utilize the complete set of observations. Pluto’s tenuous atmosphere is a significant challenge for radio occultation sounding, which led us to develop a specialized method of analysis. We began by calibrating each signal to remove effects not associated with Pluto’s atmosphere, including the diffraction pattern from Pluto’s surface. We reduced the noise and increased our sensitivity to the atmosphere by averaging the results from the four signals, while using other combinations of the signals to characterize the noise. We then retrieved profiles of number density, pressure, and temperature from the averaged phase profiles at both occultation entry and exit. Finally, we used a combination of analytical methods and Monte Carlo simulations to determine the accuracy of the measurements. The REX profiles provide the first direct measure of the surface pressure and temperature structure in Pluto’s lower atmosphere. There are significant differences between the structure at entry (193.5°E, 17.0°S, sunset) and exit (15.7°E, 15.1°N, sunrise), which arise from spatial variations in surface composition coupled with the diurnal cycle of condensation and sublimation of nitrogen. This work is supported by the NASA New Horizons Mission.


19. S. C. Rafkin*; A. Soto; T. I. Michaels

Southwest Research Institute; SETI Institute

The Effect of Surface Ice and Topography on the Atmospheric Circulation and Distribution of Nitrogen Ice on Pluto
A newly developed general circulation model (GCM) for Pluto is used to investigate the impact of a heterogeneous distribution of nitrogen surface ice and large scale topography on Pluto’s atmospheric circulation. The GCM is based on the GFDL Flexible Modeling System (FSM). Physics include a gray model radiative-conductive scheme, subsurface conduction, and a nitrogen volatile cycle. The radiative-conductive model takes into account the 2.3, 3.3 and 7.8 μm bands of CH4 and CO, including non-local thermodynamic equilibrium effects. including non-local thermodynamic equilibrium effects. The nitrogen volatile cycle is based on a vapor pressure equilibrium assumption between the atmosphere and surface. Prior to the arrival of the New Horizons spacecraft, the expectation was that the volatile ice distribution on the surface of Pluto would be strongly controlled by the latitudinal temperature gradient. If this were the case, then Pluto would have broad latitudinal bands of both ice covered surface and ice free surface, as dictated by the season. Further, the circulation, and the thus the transport of volatiles, was thought to be driven almost exclusively by sublimation and deposition flows associated with the volatile cycle. In contrast to expectations, images from New Horizon showed an extremely complex, heterogeneous distribution of surface ices draped over substantial and variable topography. To produce such an ice distribution, the atmospheric circulation and volatile transport must be more complex than previously envisioned. Simulations where topography, surface ice distributions, and volatile cycle physics are added individually and in various combinations are used to individually quantify the importance of the general circulation, topography, surface ice distributions, and condensation flows. It is shown that even regional patches of ice or large craters can have global impacts on the atmospheric circulation, the volatile cycle, and hence, the distribution of surface ices. The work demonstrates that explaining Pluto’s volatile cycle and the expression of that cycle in the surface ice distributions requires consideration of atmospheric processes beyond simple vapor pressure equilibrium arguments.


20. W. M. Grundy*; R. Binzel; J. C. Cook; D. P. Cruikshank; C. M. Dalle Ore; A. M. Earle; K. Ennico; D. Jennings; C. Howett; R. Kaiser; I. Linscott; A. Lunsford; C. B. Olkin; A. H. Parker; J. W. Parker; S. Philippe; S. Protopapa; E. Quirico; D. Reuter; B. Schmitt; K. N. Singer; J. R. Spencer; J. A. Stansberry; S. A. Stern; C. Tsang; A. J. Verbiscer; H. A. Weaver; G. E. Weigle; L. Young

Lowell Obs.; Massachusetts Institute of Technology; Southwest Research Institute; NASA Ames Research Center; SETI Institute; NASA Goddard Space Flight Center; University of Hawai’i at Manoa; Stanford University; Université Grenoble Alpes, CNRS; University of Maryland; Space Telescope Science Institute; University of Virginia; Johns Hopkins University Applied Physics Laboratory; Southwest Research Institute

Pluto's Nonvolatile Chemical Compounds
Despite the migration of Pluto's volatile ices (N2, CO, and CH4) around the surface on seasonal timescales, the planet's non-volatile materials are not completely hidden from view. They occur in a variety of provinces formed over a wide range of timescales, including rugged mountains and chasms, the floors of mid-latitude craters, and an equatorial belt of especially dark and reddish material typified by the informally named Cthulhu Regio. NASA's New Horizons probe observed several of these regions at spatial resolutions as fine as 3 km/pixel with its LEISA imaging spectrometer, covering wavelengths from 1.25 to 2.5 microns. Various compounds that are much lighter than the tholin-like macromolecules responsible for the reddish coloration, but that are not volatile at Pluto surface temperatures such as methanol (CH3OH) and ethane (C2H6) have characteristic absorption bands within LEISA's wavelength range. This presentation will describe their geographic distributions and attempt to constrain their origins. Possibilities include an inheritance from Pluto's primordial composition (the likely source of H2O ice seen on Pluto's surface) or ongoing production from volatile precursors through photochemistry in Pluto's atmosphere or through radiolysis on Pluto's surface. New laboratory data inform the analysis.
This work was supported by NASA's New Horizons project.


21. C. B. Olkin*; D. Reuter; S. A. Stern; L. Young; H. A. Weaver; K. Ennico; R. Binzel; J. C. Cook; D. P. Cruikshank; C. M. Dalle Ore; A. M. Earle; W. Grundy; C. Howett; A. Parker; S. Protopapa; B. Schmitt; K. N. Singer; J. R. Spencer; J. A. Stansberry; S. Philippe

SWRI; GSFC; JHU/APL; NASA ARC; MIT; SETI; Lowell Observatory; U MD; Univ. J. Fourier,; STScI

The Color and Surface Composition of Mountains on Pluto
The New Horizons mission revealed that there are mountains along the western edge of the large glacier that dominates Pluto’s anti-Charon hemisphere. This talk will focus on the color and surface composition of the four large mountainous regions named Al Idrisi Montes, Bare Montes, Hillary Montes and Norgay Montes (all feature names are informal).
The Al Idrisi Montes are large blocks up to 40 km across and 5 km high that appear to be broken off of the ice crust and transported into Sputnik Planum (Moore et al. 2016). The color of this region as a function of latitude will be presented as well as the color differences between the blocks and the interstitial material between the blocks. Moving south along the edge of Sputnik Planum, the next mountainous region is Bare Montes. Part of the Bare Montes resembles Al Idrisi Montes with its chaotic blocky structure, but there is a significant difference in color between these regions. The Bare Montes are more red than Al Idrisi Montes and this region’s color more closely matches the nearby terrain of Cthulhu Regio. Continuing south, to the Hillary and Norgay Montes regions these topographic features become less red with both red and neutral colors on their slopes. The Hillary Montes show both red and neutral colors in the ices surrounding the peaks.
This work will provide a quantitative comparison of the color and composition across these 4 mountainous regions using data from the Ralph instrument. Ralph has 4 color filters: blue (400-550 nm), red (540-700 nm), near IR (780-975) and methane filter (860-910 nm) and collects infrared imaging spectrometric data (from 1.25-2.5 microns).
This work was supported by NASA's New Horizons project.


22. C. M. Dalle Ore*; J. C. Cook; D. P. Cruikshank; S. Protopapa; W. M. Grundy; C. B. Olkin; K. Ennico; S. A. Stern; H. A. Weaver; L. Young

NASA Ames Research Center; SETI Institute; Southwest Research Institute; Lowell Observatory; University of Maryland; Johns Hopkins University Applied Physics Laboratory

Charon's, Hydra's, and Nix's near IR spectra as seen by New Horizons
Charon, Pluto's largest satellite, is a predominantly grey-color icy world covered mostly in H2O ice, with spectral evidence for NH3 and/or its hydrates, as previously reported (Cook et al. 2007, ApJ. 663, 1406; Verbiscer et al. 2007, LPSC 38, 2318; Merlin et al. 2010, Icarus, 210, 930; Cook et al. 2014, AAS/DPS Abstracts, 46, #401.04; Holler et al. 2016, submitted, arXiv:1606.05695). In their 2010 work, Merlin et al. reported the presence of ammonia species along with H2O ice both in crystalline and amorphous phase. They introduced a blue component to model the slope present in their near-IR observations, which could not be otherwise reproduced without the adoption of an ad hoc component. The presence of ammonia and H2O in its crystalline form prompted Cook et al. (2007) to suggest cryovolcanism as a favored mechanism of resurfacing although the geological evidence for volcanism reported from New Horizons imaging observations does not appear to be recent (Moore et al. Science, 351, 1284).
We analyze one of New Horizons' observations of Charon taken with the LEISA imaging spectrometer from a distance of ~82,000 km at high spatial resolution (4.9 km/pixel). Images from the New Horizons spacecraft reveal a surface with terrains of seemingly different ages and a moderate degree of localized coloration.
Hydra was observed by New Horizons at a distance 240,000 and 370,000 hardly resolving its disk. Nix on the other hand was observed from a much more favorable distance of 60,000 and 162,000 km revealing a nearly uniform surface coloration and structure.
Although Hydra could hardly be resolved at the flyby distance we have obtained its spectral signature and we compare it with those of Charon and Nix. A feature at ~2.2 µm, corresponding to the NH3 and/or NH3 hydrates, is visible subtly on Charon and clearly on Hydra and Nix hinting at the possibility that NH3 might be less volatile than previously thought and making the need for recent cryovolcanism less crucial.
Preliminary modeling indicates uniformity in amounts and grain sizes of most components, a homogeneity that seems to be the trademark of Charon’s surface.
This work was supported by NASA's New Horizons project.


23. A. S. Bosh*; E. W. Dunham; C. Zuluaga; S. Levine; M. J. Person; J. E. Van Cleve

MIT; Lowell Observatory; SETI Institute

Stellar Occultations from Airborne Platforms: 1988 to 2016
Observing a stellar occultation by a solar system body with an airborne telescope requires precise positioning of the observer within the shadow cast onto the Earth. For small bodies like Pluto and Kuiper Belt objects, smaller than the Earth, the challenge is particularly intense, with the accuracy of the astrometric and flight planning determining whether the observation succeeds or fails. From our first airborne occultation by Pluto in 1988 aboard the Kuiper Airborne Observatory (KAO), to our most recent event by Pluto in 2015 aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA), we have refined our astrometric and flight planning systems to the point where we can now place an airborne observer into the small central flash zone. We will discuss the history of airborne observation of occultations while detailing the improvements in the astrometric processes.  Support for this work was provided by NASA SSO grant NNX15AJ82G to Lowell Observatory.


24. E. Van Heerden*; N. Erasmus; A. Greenberg; E. Nesvold; J. Galache; E. Dahlstrom; F. Marchis

University of Oxford; South African Astronomical Observatory; University of California, Los Angeles; Carnegie Institute of Washington, Department of Terrestrial Magnetism; Minor Planet Center, Smithsonian Astrophysical Observatory; International Space Consultants; SETI Institute

The Deflector Selector: A Machine Learning Framework for Prioritizing Deflection Technology Development
On 15 February, 2013, a ~15 m diameter asteroid entered the Earth’s atmosphere over Russia. The resulting shockwave injured nearly 1500 people, and incurred ~33 million (USD) in infrastructure damages. The Chelyabinsk meteor served as a forceful demonstration of the threat posed to Earth by the hundreds of potentially hazardous objects (PHOs) that pass near the Earth every year. Although no objects have yet been discovered on an impact course for Earth, an impact is virtually statistically guaranteed at some point in the future. While many impactor deflection technologies have been proposed, humanity has yet to <i>demonstrate</i> the ability to divert an impactor when one is found. Developing and testing any single proposed technology will require significant research time and funding. This leaves open an obvious question – towards which technologies should funding and research be directed, in order to maximize our preparedness for when an impactor is eventually found?<br /><br />To help answer this question, we have created a detailed framework for analyzing various deflection technologies and their effectiveness. Using an n-body integrator (REBOUND), we have simulated the attempted deflections of a population of Earth-impacting objects with a variety of velocity perturbations (∂Vs), and measured the effects that these perturbations had on impact probability. We then mapped the ∂Vs applied in the orbital simulations to the technologies capable of achieving those perturbations, and analyzed which set of technologies would be most effective at preventing a PHO from impacting the earth. As a final step, we used the results of these simulations to train a machine learning algorithm. This algorithm, combined with a simulated PHO population, can predict which technologies are most likely to be needed. The algorithm can also reveal which impactor observables (mass, spin, orbit, etc.) have the greatest effect on the choice of deflection technology. These results can be used as a tool to inform funding decisions for both deflection technology development and PHO characterization missions.


25. M. Brozovic*; L. A. Benner; S. P. Naidu; P. A. Taylor; M. W. Busch; J. Margot; M. C. Nolan; E. S. Howell; A. Springmann; J. D. Giorgini; M. K. Shepard; C. Magri; J. E. Richardson; E. G. Rivera-Valentin; L. A. Rodriguez-Ford; L. F. Zambrano Marin

Jet Propulsion Laboratory/Caltech; SETI; Univeristy of Arizona; Univeristy of California, Los Angeles; Bloomsburg University; University of Maine, Farmington; Planetary Science Institute; Arecibo Observatory, USRA

Population trends of binary near-Earth asteroids based on radar and lightcurves observations
The Arecibo and Goldstone planetary radars are invaluable instruments for the discovery and characterization of binary and triple asteroids in the near-Earth asteroid (NEA) population. To date, 41 out of 56 known binaries and triples (~73% of the objects) have been discovered by radar and 49 of these multiple systems have been detected by radar. Their absolute magnitudes range from 12.4 for (1866) Sisyphus to 22.6 for 2015 TD144 and have a mean and rms dispersion of 18.1+-2.0. There is a pronounced decrease in the abundance of binaries for absolute magnitudes H>20. One of the smallest binaries, 1994 CJ1, with an absolute magnitude H=21.4, is also the most accessible binary for a spacecraft rendezvous. Among 365 NEAs with H<22 (corresponding to diameters larger than ~ 140 m) detected by radar since 1999, ~13% have at least one companion. Two triple systems are known, (15391) 2001 SN263 and (136617) 1994 CC, but this is probably an underestimate due to low signal to noise ratios (SNRs) for many of the binary radar detections. Taxonomic classes have been reported for 41 out of 56 currently known multiple systems and some trends are starting to emerge: at least 50% of multiple asteroid systems are S, Sq, Q, or Sk, and at least 20% are optically dark (C, B, P, or U). Thirteen V-class NEAs have been observed by radar and six of them are binaries. Curiously, a comparable number of E-class objects have been detected by radar, but none is known to be a binary.


26. D. H. Wooden*; S. M. Lederer; E. Jehin; B. Rozitis; J. D. Jefferson; T. W. Nelson; J. L. Dotson; E. L. Ryan; E. S. Howell; Y. R. Fernandez; A. J. Lovell; C. E. Woodward; D. E. Harker

NASA Ames Research Center; NASA Johnson Space Center; Université de Liège; The Open University; University of California, Santa Cruz; University of Southern Maine; SETI Institute; Lunar and Planetary Laboratory; Univ. of Central Florida; Agnes Scott College; Univ. of Minnesota; UC, San Diego

Characterization of the high-albedo NEA 3691 Bede
Characterization of NEAs provides important inputs to models for atmospheric entry, risk assessment and mitigation. Diameter is a key parameter because diameter translates to kinetic energy in atmospheric entry. Diameters can be derived from the absolute magnitude, H(PA=0deg), and from thermal modeling of observed IR fluxes. For both methods, the albedo (pv) is important – high pv surfaces have cooler temperatures, larger diameters for a given Hmag, and shallower phase curves (larger slope parameter G). Thermal model parameters are coupled, however, so that a higher thermal inertia also results in a cooler surface temperature. Multiple parameters contribute to constraining the diameter. Observations made at multiple observing geometries can contribute to understanding the relationships between and potentially breaking some of the degeneracies between parameters. We present data and analyses on NEA 3691 Bede with the aim of best constraining the diameter and pv from a combination of thermal modeling and light curve analyses. We employ our UKIRT+Michelle mid-IR photometric observations of 3691 Bede's thermal emission at 2 phase angles (27&43 deg 2015-03-19 & 04-13), in addition to WISE data (33deg 2010-05-27, Mainzer+2011).<br />Observing geometries differ by solar phase angles and by moderate changes in heliocentric distance (e.g., further distances produce somewhat cooler surface temperatures). With the NEATM model and for a constant IR beaming parameter (eta=constant), there is a family of solutions for (diameter, pv, G, eta) where G is the slope parameter from the H-G Relation. NEATM models employing Pravec+2012's choice of G=0.43, produce D=1.8 km and pv≈0.4, given that G=0.43 is assumed from studies of main belt asteroids (Warner+2009). We present an analysis of the light curve of 3691 Bede to constrain G from observations. We also investigate fitting thermophysical models (TPM, Rozitis+11) to constrain the coupled parameters of thermal inertia (Gamma) and surface roughness, which in turn affect diameter and pv. Surface composition can be related to pv. This study focuses on understanding and characterizing the dependency of parameters with the aim of constraining diameter, pv and thermal inertia for 3691 Bede.


27. E. L. Ryan*; C. E. Woodward; B. N. Sharkey

SETI Institute; University of Minnesota

Rotational properties of L4 Trojan asteroids from K2
Our understanding of solar system formation is undergoing a renaissance as new planetary systems are found, often unlike our own. Many questions now ask how the giant planets and their satellite systems accreted and if there is evidence that they migrated to new orbital positions. One of the keys to understanding these questions within our own solar system is the Jupiter Trojan population which is co-orbital with Jupiter. The two Trojan clouds at the stable L4 and L5 Lagrangian points are in orbits which are stable over the age of the Solar System, unlike many other present epoch small body populations. Planetary migration models suggest that the Trojan asteroids, and the dynamically hot (i.e. "scattered"), population of Kuiper Belt objects originate from the same region in the early solar system. While these objects would have started with the same compositions, establishing compositional linkages is challenging and complicated due to a paucity of distinct and easily identifiable mineralogical features in the optical, where these objects are the brightest. While the surface compositions and colors of the Trojans match objects in the inner solar system, as well as the Kuiper Belt, physical characterization of this large population of objects has been scarce. During Campaign 6 in late 2015, the 115 square degree K2 spacecraft field of view overlapped with the L4 Trojan cloud, allowing for long term monitoring. We report on the fitted rotational periods and lightcurve amplitudes from 56 Trojan asteroids that were observed for an average of 11 days by K2. We find ~20% of objects have rotational periods longer than 50 hours and ~40% of the objects have lightcurves with shapes characteristic of contact binary systems.


28. C. Raissi*; M. Lamee; O. Mosiane; C. Vassallo; M. W. Busch; A. Greenberg; L. A. Benner; S. P. Naidu; N. Duong

INRIA; University of Minnesota; SKA South Africa; University of Texas, Austin; SETI; UCLA; JPL; JPL; University of Louisville; North West University

New Approaches For Asteroid Spin State and Shape Modeling From Delay-Doppler Radar Images
Delay-Doppler radar imaging is a powerful technique to characterize the trajectories, shapes, and spin states of near-Earth asteroids; and has yielded detailed models of dozens of objects. Reconstructing objects’ shapes and spins from delay-Doppler data is a computationally intensive inversion problem. Since the 1990s, delay-Doppler data has been analyzed using the SHAPE software. SHAPE performs sequential single-parameter fitting, and requires considerable computer runtime and human intervention (Hudson 1993, Magri et al. 2007). Recently, multiple-parameter fitting algorithms have been shown to more efficiently invert delay-Doppler datasets (Greenberg & Margot 2015) – decreasing runtime while improving accuracy. However, extensive human oversight of the shape modeling process is still required. We have explored two new techniques to better automate delay-Doppler shape modeling: Bayesian optimization and a machine-learning neural network.<br />One of the most time-intensive steps of the shape modeling process is to perform a grid search to constrain the target’s spin state. We have implemented a Bayesian optimization routine that uses SHAPE to autonomously search the space of spin-state parameters. To test the efficacy of this technique, we compared it to results with human-guided SHAPE for asteroids 1992 UY4, 2000 RS11, and 2008 EV5. Bayesian optimization yielded similar spin state constraints within a factor of 3 less computer runtime.<br />The shape modeling process could be further accelerated using a deep neural network to replace iterative fitting. We have implemented a neural network with a variational autoencoder (VAE), using a subset of known asteroid shapes and a large set of synthetic radar images as inputs to train the network. Conditioning the VAE in this manner allows the user to give the network a set of radar images and get a 3D shape model as an output. Additional development will be required to train a network to reliably render shapes from delay-Doppler images.<br />This work was supported by NASA Ames, NVIDIA, Autodesk and the SETI Institute as part of the NASA Frontier Development Lab program.


29. R. D. Cameron*; L. Barge; K. B. Chin; I. J. Doloboff; E. Flores; A. C. Hammer; P. Sobron; M. J. Russell; I. Kanik

NASA Jet Propulsion Laboratory; Oberlin College; SETI Institute

Catalytic Diversity in Alkaline Hydrothermal Vent Systems on Ocean Worlds
Hydrothermal systems formed by serpentinization can create moderate-temperature, alkaline systems and it is possible that this type of vent could exist on icy worlds such as Europa which have water-rock interfaces. It has been proposed that some prebiotic chemistry responsible for the emergence of life on Earth and possibly other wet and icy worlds could occur as a result ofredox potential and pH gradients in submarine alkaline hydrothermal vents (Russell et al., 2014). Hydrothermal chimneys formed in laboratory simulations of alkaline vents under early Earth conditions have precipitate membranes that contain minerals such as iron sulfides, which are hypothesized to catalyze reduction of CO2 (Yamaguchi et al. 2014, Roldan et al. 2014) leading to further organic synthesis. This CO2 reduction process may be affected by other trace components in the chimney, e.g. nickel or organic molecules. We have conducted experiments to investigate catalytic properties of iron and iron-nickel sulfides containing organic dopants in slightly acidic ocean simulants relevant to early Earth or possibly ocean worlds. We find that the electrochemical properties of the chimney as well as the morphology/chemistry of the precipitate are affected by the concentration and type of organics present. These results imply that synthesis of organics in water-rock systems on ocean worlds may lead to hydrothermal precipitates which can incorporate these organic into the mineral matrix and may affect the role of gradients in alkaline vent systems.Therefore, further understanding on the electroactive roles of various organic species within hydrothermal chimneys will have important implications for habitability as well as prebiotic chemistry. This work is funded by NASA Astrobiology Institute JPL Icy Worlds Team and a NAI Director’s Discretionary Fund award.
Yamaguchi A. et al. (2014) Electrochimica Acta, 141, 311–318.
Russell, M. J. et al. (2014), Astrobiology, 14, 308-43.
Roldan, A. (2014) Chem. Comm. 51, 35: 7501-7504.


30. L. A. Lebofsky*; D. McCarthy; E. DeVore; P. Harman

University of Arizona; Planetary Science Institute; SETI Institute

Leadership Workshops for Adult Girl Scout Leaders
This year, the University of Arizona is conducting its first two Leadership Workshops for Girl Scout adult leaders. These workshops are being supported by a five-year NASA Collaborative Agreement, Reaching for the Stars: NASA Science for Girl Scouts (, through the SETI Institute in collaboration with the University of Arizona, Girl Scouts of the USA (GSUSA), the Girl Scouts of Northern California, the Astronomical Society of the Pacific, and Aries Scientific, Inc. These workshops are an outgrowth of Astronomy Camp for Girl Scout Leaders, a 14-year “Train the Trainer” program funded by NASA through the James Webb Space Telescope’s Near Infrared Camera (NIRCam) education and outreach team. We are continuing our long-term relationship with all Girl Scout Councils to engage girls and young women not only in science and math education, but also in the astronomical and technological concepts relating to NASA’s scientific mission. Our training aligns with the GSUSA Journey: It’s Your Planet-Love It! and introduces participants to some of the activities that are being developed by the Girl Scout Stars team for GSUSA’s new space science badges for all Girl Scout levels being developed as a part of Reaching for the Stars: NASA Science for Girl Scouts.
The workshops include hands-on activities in basic astronomy (night sky, stars, galaxies, optics, telescopes, etc.) as well as some more advanced concepts such as lookback time and the expansion of the Universe. Since the inception of our original Astronomy Camp in 2003, our team has grown to include nearly 280 adult leaders, staff, and volunteers from over 79 Councils in 43 states and the District of Columbia so they can, in turn, teach young women essential concepts in astronomy, the night sky environment, applied math, and engineering. Our workshops model what astronomers do by engaging participants in the process of science inquiry, while equipping adults to host astronomy-related programs with local Girl Scouts.
Reaching for the Stars: NASA Science for Girl Scouts is supported by NASA Science Mission Directorate’s Education Cooperative Agreement # NNX16AB90.


31. M. Gordon*; M. R. Showalter; L. Ballard; M. S. Tiscareno; N. Heather

SETI Institute

OPUS – Outer Planets Unified Search with Enhanced Surface Geometry Parameters – Not Just for Rings
In recent years, with the massive influx of data into the PDS from a wide array of missions and instruments, finding the precise data you need has been an ongoing challenge. For remote sensing data obtained from Jupiter to Pluto, that challenge is being addressed by the Outer Planets Unified Search, more commonly known as OPUS.
OPUS is a powerful search tool available at the PDS Ring-Moon Systems Node (RMS) – formerly the PDS Rings Node. While OPUS was originally designed with ring data in mind, its capabilities have been extended to include all of the targets within an instrument’s field of view. OPUS provides preview images of search results, and produces a zip file for easy download of selected products, including a table of user specified metadata. For Cassini ISS and Voyager ISS we have generated and include calibrated versions of every image.
Currently OPUS supports data returned by Cassini ISS, UVIS, VIMS, and CIRS (Saturn data through June 2010), New Horizons Jupiter LORRI, Galileo SSI, Voyager ISS and IRIS, and Hubble (ACS, WFC3 and WFPC2).
At the RMS Node, we have developed and incorporated into OPUS detailed geometric metadata, based on the most recent SPICE kernels, for all of the bodies in the Cassini Saturn observations. This extensive set of geometric metadata is unique to the RMS Node and enables search constraints such as latitudes and longitudes (Saturn, Titan, and icy satellites), viewing and illumination geometry (phase, incidence and emission angles), and distances and resolution.
Our near term plans include adding the full set of Cassini CIRS Saturn data (with enhanced geometry), New Horizons MVIC Jupiter encounter images, New Horizons LORRI and MVIC Pluto data, HST STIS observations, and Cassini and Voyager ring occultations. We also plan to develop enhanced geometric metadata for the New Horizons LORRI and MVIC instruments for both the Jupiter and the Pluto encounters.


32. M. Devogele*; P. Tanga; P. Bendjoya; J. Rivet; J. Surdej; S. J. Bus; J. M. Sunshine; A. Cellino; H. Campins; J. Licandro; N. Pinilla-Alonso; B. Carry

Université de Liège; Laboratoire Lagrange, Observatoire de la Côte d'Azur; Institute for Astronomy; University of Maryland; Osservatorio Astrofisico di Torino; Univ. of Central Florida; Instituto De Astrofísica De Canarias; SETI Institute

Linking CAI abundance to polarimetric response in a population of ancient asteroids
Polarimetry constitutes one of the fundamental tools for characterizing the surface texture and composition of airless Solar System bodies. In 2006, polarimetric observations led to the discovery of a new type of asteroids, which displays a peculiar polarimetric response. These asteroids are collectively known as “Barbarians”, from (234) Barbara the first discovered one.
The most commonly accepted explanation for this perculiar polarization response seems to be the presence of a high percentage of fluffy-type Calcium Aluminium-rich Inclusions (CAIs), whose optical properties could produce the observed polarization. Their reflectance spectra also exibit an absorption feature in the near-infrared around 2.1-2.2 microns, that is characteristic of this peculiar group.
Based on these results, we organized a systematic polarimetric and near-infrared observational campaign of known Barbarians or candidate asteroids. These campaigns include members of the family of 1040 Klumpkea, 2085 Henan and 729 Watsonia, which are known to contain Barbarian and/or L-type asteroids also suspected to have such a polarimetric behaviour. We have made use of the ToPo polarimeter at the 1m telescope of the Centre pédagogique Planète et Univers (C2PU, Observatoire de la Côte d’Azur, France). The spectroscopic observations in the near-infrared were obtained with the SpeX instrument at the NASA’s InfraRed Telescope Facility (IRTF).
By combining polarimetry and spectroscopy we find a correlation between the abundance of CAIs and the inversion angle of the phase-polarization curve of Barbarian asteroids. This is the first time that a direct link has been established between a specific polarimetric response and the surface composition of asteroids. In addition, we find a considerable variety of CAI abundance from one object to the other, consistent with a wide range of possible albedos. Since these asteroids constitute a reservoir of primitive Solar System material, understanding their origin can shed light on the processes driving the formation and transport of the refractory minerals that first condensed in the protoplanetary disk.


33. P. Vernazza*; M. Marsset; P. Beck; R. Binzel; F. DeMeo; M. Birlan; R. Brunetto; O. Groussin; F. Marchis; J. P. Emery

Laboratoire d'Astrophysique de Marseille; MIT; IPAG; IMCCE; IAS; SETI; Univ. Of Tennessee

C-complex asteroids: Two main compositional families?
An important goal of asteroid science is to link extraterrestrial materials (meteorites, IDPs) to their parent bodies in order to constrain their formation and evolution. To accomplish this task, we need to combine data from several different disciplines: ground based spectroscopic observations, laboratory studies (petrology, mineralogy), and thermal modeling. Here we report the result of a large observing campaign aimed at investigating the surface composition of the most massive C-complex Main Belt Asteroids (MBAs). We observed more than 100 of these C-types with SpeX/IRTF in the near-infrared thus complementing the existing visible part of the spectrum. We also analyzed their spectral properties in the mid-infrared, when available. We will show that by comparing the mineralogical composition of these C-type asteroids with the composition of CC meteorites and IDPs we are able to identify two main compositional families among C-types (CM-like and IDP-like). A further comparison with thermal evolution models supports the idea that these two populations likely formed in two different environments.


34. A. Yen*; D. Blake; T. Bristow; S. Chipera; R. Downs; R. Gellert; J. P. Grotzinger; D. Ming; R. Morris; S. Morrison; L. Rampe; L. Thompson; A. Treiman; D. Vaniman

JPL/Caltech; NASA-Ames; SETI Institute; Chesapeake Energy; University of Arizona; University of Guelph; Caltech; NASA-JSC; University of New Brunswick; LPI; PSI

Fluid migration through sandstone fractures in Gale Crater, Mars
The Curiosity Mars rover encountered numerous occurrences of light-toned fractures in lithified sediments along its traverse in Gale Crater. These alteration zones can be traced for tens of meters across the landscape and are generally less than a meter in width. Two of these features were investigated in detail by the rover instruments, including drilling to acquire samples both within and immediately outside the lighter-toned areas.
The chemical composition established by the Alpha Particle X-ray Spectrometer (APXS) on the arm of the rover shows that the alteration zones are significantly enhanced in silica (40% increase) and sulfur (factor of ~5) relative to the surrounding rocks. Concentrations of Fe, Mg, Al, Mn, Ni and Zn are reduced by a factor of two or more. The correlation between Ca and SO3 indicates the presence of Ca-sulfates, but with up to 15% SO3 (and only 6% to 9% CaO) in the APXS data, the presence of Mg and Fe sulfates in the altered fractures is likely.
The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument analyzed the drill fines and found mostly plagioclase feldspar, pyroxenes and magnetite in the unaltered sandstones. X-ray amorphous material and minor hematite and Ca-sulfates are also present. Samples from the alteration zones, however, show a factor of two decrease in the pyroxene to feldspar ratio, abundant Ca-sulfates in various hydration states, and a majority fraction of amorphous material rich in silica and mixed-cation sulfates.
The direct comparison of samples within and adjacent to the light toned fractures indicates an alteration process involving the dissolution of pyroxenes and removal of metal cations. The mobility of Al and the likely presence of Fe-sulfates suggest alteration in an acidic environment, but additional moderate pH episodes cannot be ruled out. These features post-date the sandstone lithification and are among the youngest fluid events studied thus far in Gale Crater.


35. N. Glines*; V. C. Gulick

SETI Institute; NASA Ames Research Center

How did the icy mantle of Mars contribute to the origins of gullies and FSVs?
Compared to the Martian valley networks, Fresh Shallow Valleys (FSVs) and gullies formed quite recently - in the Late Amazonian period. Recent studies propose that FSVs may be formed by meltwater flowing beneath ice, supported by evidence for the channels ignoring the constraints of drainage divides and often being found with ridges and mounds analogous to terrestrial esker environments. Our studies of gullies show that while multiple processes have contributed to their formation and modification over time, the key sources include groundwater flow, ground ice melt, or ice/snow surface melt, which includes the possibility of meltwater from ice-rich LDM. FSVs and gullies have been found to be spatially associated with viscous flow features (VFFs), mantle deposits, and various peri/paraglacial features such as arcuate ridges. It is important to note that the mid-latitude bands within which the FSVs and gullies concentrate are both near enough to the poles to experience frozen depositions during periods of high obliquity, and near enough to the equator to experience melt induced by peak temperatures, possible today where surface pressure is also favorable. While FSVs and gullies are often found dissecting into mantle deposits, it is possible that the easily-erodible ice-rich LDM simply provides insulation and protective blanketing to promote or enable water flow and ice melt from the near-subsurface. We are looking to identify any changes to channels and ice-rich LDM within FSVs and gullies to help determine whether the water's source is from the ice-rich mantling unit, the subsurface, or both.


36. V. C. Gulick*; N. Glines

NASA Ames Research Center; SETI Institute

Understanding Gully Formation and Seasonal Flows on Recent and Current Mars
The discoveries of gullies and seasonal slope flows (RSL) have re-ignited the debate over various channel, valley, and gully formation mechanisms on Mars. The controversy over whether liquid water was involved with gully formation, harkens back to the mid-1970s to early 2000s, where catastrophic flooding, surface runnoff and ground-water sapping processes were strongly debated along with other mechanisms as the primary processes responsible for channel and valley formation on Mars. However, over the past decade, the value of multiple working hypotheses has again become apparent, this time in understanding the formation of Martian gullies and Recurring Slope Lineae. Various mechanisms put forth to explain these landforms include liquid H2O/ice erosion, CO2 ice/frost sublimation, CO2 ice block sliding, water and brine flows, salt deliquescence, and dry granular flows, among others.
We carried out detailed morphologic/morphometric studies of gullies in various environmental settings on Mars to evaluate the potential formation processes. Using HiRISE images and DTMs, we mapped and generated detailed longitudinal and cross-sectional profiles of gully systems and estimated volumes for both the gullies and their debris aprons. Several gullies form highly integrated patterns similar to fluvial systems. Additionally, RSL are often found either in the tributaries of these integrated systems or in adjacent regions, implying that RSL may play a role in initiating gully formation or mark the last vestiges of water activity in these locations. We also find that the more highly integrated gullies have volumes significantly larger than their aprons, suggesting that the missing volumes (~40-60% or more) were likely the volatiles involved in gully formation. Additionally, THEMIS and TES surface temperatures of these integrated gully sites, many of which also contain RSL, are at or above freezing seasonally suggesting that the volatile component may be consistent with H2O although CO2 cannot be ruled out. Other less integrated systems have apron volumes that equal or exceed the gully volumes suggesting that dry flows, avalanching, gully infill, or other dry processes may have been more important in these environments.


37. H. C. Dones*; J. Alvarellos; E. B. Bierhaus; W. Bottke; M. Cuk; P. Hamill; D. Nesvorny; S. J. Robbins; K. Zahnle

Southwest Research Inst.; San Jose State Univ.; Space Systems Loral; Lockheed Martin; SETI Institute; NASA Ames Research Center

Could the Craters on the Mid-Sized Moons of Saturn Have Been Made by Satellite Debris?
Saturn's mid-sized moons have usually been assumed to be primordial. However, Charnoz et al. (2011) and Crida and Charnoz (2012) showed that the steep trend of mass vs. distance of the moons out to Rhea is consistent with the spreading of an early massive ring (e.g., Canup 2010) beyond Saturn's Roche limit. In this model, these moons would be billions of years old, but with Mimas forming perhaps 1 Gyr after Rhea.
Cuk et al. (2016) investigated the dynamical evolution of the, mid-sized saturnian moons due to tides. They infer that the moons have migrated little. Tethys and Dione probably did not cross their 3:2 resonance, but the system likely did cross a Dione-Rhea 5:3 resonance and a Tethys-Dione secular resonance. These crossings would have happened recently; for Q = 1500 (Lainey et al. 2012), within the past 100 Myr. Cuk et al. suggested that a previous generation of moons underwent an orbital instability, perhaps due to a solar evection resonance, leading to catastrophic collisions between them (Movshovitz et al. 2016). Today's moons would have reaccreted from the debris. This model implies that most craters on the moons were formed by this debris, with impacts taking place at much lower speeds than applies for impacts by comets.
Many crater properties, such as the depth-to-diameter ratio (Bray and Schenk 2015) and the amount of melting and vaporization (Kraus et al. 2011), depend on the impact velocity. We will discuss how measurements of craters in Cassini images of saturnian moons can be used to distinguish between the Cuk et al. scenario and the view in which the largest craters are made by comets and planetocentric debris makes only smaller craters (Alvarellos et al. 2005).
We thank the Cassini Data Analysis Program for support and Amy Barr Mlinar for discussions.
Alvarellos, J.L., Zahnle, K.J., Dobrovolskis, A.R., Hamill,
P. (2005). Icarus 178, 104
Bray, V.J., Schenk, P.M. (2015). Icarus 246, 156
Canup, R.M. (2010). Nature 468, 943
Charnoz, S., et al. (2011). Icarus 216, 535
Crida, A., Charnoz, S. (2012). Science 338, 1196
Cuk, M., Dones, L., Nesvorny, D. (2016). Astrophys. J. 820:97
Kraus, R.G., Senft, L.E., Stewart, S.T. (2011). Icarus 214, 724
Lainey, V., et al. (2012). Astrophys. J. 752:14
Movshovitz, N., et al. (2016). Icarus 275, 85


38. M. Cuk*; D. P. Hamilton

SETI Institute; University of Maryland

Cuckoo in the Nest: The Fate of the Original Moons of Neptune
Neptune's moon Triton is the largest captured satellite in the solar system, as indicated by its inclined retrograde orbit. The most likely mechanism for its capture is binary disruption, which ejected its former binary companion and placed Triton on a large, eccentric orbit around Neptune (Agnor and Hamilton 2006). While the tides would in principle circularize Triton's orbit (Goldreich et al. 1989), Triton's early orbit would have evolved much faster through interactions with preexisting moons of Neptune (Cuk and Gladman 2005). Assuming that the pre-existing moons of Neptune were similar to those of Uranus, analytical estimates are unclear on which outcome is most likely during moon-moon scattering. Cuk and Gladman (2005) suggested that collisions among the regular moons happen first, while Nogueira et al. (2011) find that collisions between Triton and an old moon, or an ejection should happen first. Here we use the general purpose (T+U) symplectic integrator to explore this short-lived epoch of orbit crossing in the Neptunian system. Our preliminary results indicate that Triton might have collided with one of the preexisting moons of Neptune before the regular satellites could have been destroyed in mutual collisions. Goldreich et al. (1989) claimed that a collision with a moon larger than Miranda would destroy Triton and therefore could be ruled out. However, using modern collisional disruption estimated from Stewart and Leinhardt (2012), we find that Triton could have accreted a 1000-km moon at relevant velocities without being disrupted. The product of this merger would have a much tighter orbit as the accreted moon would not have been retrograde like Triton. At the meeting we will present a more detailed exploration of possible post-capture configurations, and report quantitative probabilities for different outcomes of this exciting and violent episode of Triton's history.