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  • Other Sources  (16)
  • 1
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    The absence of a color-distance trend in comets (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New near-IR J-H and H-K observations of 23 comets have been obtained in the heliocentric distance range of 1 to 6 AU. No evidence is found for a color-distance trend in the present sample. Significant differences between the grain populations in different comets are pointed out. The results indicate that the color distributions are unimodal, and that, unlike asteroids, the comets cannot be classified into distinct color-defined groups.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 96; 1723-173
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  • 2
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    Structure of the Uranian rings. I - Square-well model and particle-size constraints (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A least squares fitting is added to the diffraction model for the Uranian rings and the model is then used to determine the relative optical depths of the rings at visible and near-IR wavelengths. Light transmission is assumed constant on a scale of a few radial km in the rings. The amount of starlight passing through the rings is calculated from occultations with account taken of a monolayer ring, diffraction effects, and multiple ring layers. A diffracted occultation profile is generated with consideration given to the angular diameter of the star, the impulse response of the detector, and atmospheric aberrations. Calculation procedures which remove noise are outlined and results are compared with the observational data base. The wavelength dependence of optical depth is formulated. It is shown that occultation data do not support the presence of a large fraction of submicron particles. No optical depth variations are projected for 0.88-2.2 microns wavelengths. Unchopped data are needed to verify the model predictions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 89; 1587-160
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  • 3
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    The rings of Uranus - Occultation profiles from three observatories (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Occultation profiles for the nine confirmed Uranian rings obtained from Las Campanas, the European Southern Observatory, and Cerro Tololo on 15-16 August 1980 are compared. The alpha ring shows a 'double-dip' structure; the eta ring shows a broad and narrow component (similar to Saturn's F ring); and the epsilon ring shows six features that appear in the data from all three observatories. Diffraction fringes appear at the edges of several of the occultation profiles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 56; 202-208
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  • 4
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    Deep Impact, Stardust-NExT and the Behavior of Comet 9P/Tempel 1 from 1997 to 2010 (2011)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We present observational data for Comet 9P/Tempel 1 taken from 1997 through 2010 in an international collaboration in support of the Deep Impact and Stardust-NExT missions. The data were obtained to characterize the nucleus prior to the Deep Impact 2005 encounter, and to enable us to understand the rotation state in order to make a time of arrival adjustment in February 2010 that would allow us to image at least 25% of the nucleus seen by the Deep Impact spacecraft to better than 80 m/pixel, and to image the crater made during the encounter, if possible. In total, approx.500 whole or partial nights were allocated to this project at 14 observatories worldwide, utilizing 25 telescopes. Seventy percent of these nights yielded useful data. The data were used to determine the linear phase coefficient for the comet in the R-band to be 0.045 +/- 0.001 mag/deg from 1deg to 16deg. Cometary activity was observed to begin inbound near r approx. 4.0 AU and the activity ended near r approx. 4.6 AU as seen from the heliocentric secular light curves, water-sublimation models and from dust dynamical modeling. The light curve exhibits a significant pre- and post-perihelion brightness and activity asymmetry. There was a secular decrease in activity between the 2000 and 2005 perihelion passages of approx. 20%. The post-perihelion light curve cannot be easily explained by a simple decrease in solar insolation or observing geometry. CN emission was detected in the comet at 2.43 AU pre-perihelion, and by r = 2.24 AU emission from C2 and C3 were evident. In December 2004 the production rate of CN increased from 1.8 x 10(exp 23) mol/s to Q(sub CN) = 2.75 x 10(exp 23) mol/s in early January 2005 and 9.3 x 10(exp 24) mol/s on June 6, 2005 at r = 1.53 AU.
    Keywords: Astronomy
    Type: Icarus; 213; 323-344
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  • 5
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    The Composition of Comet C/2009 PI (Garradd) from Infrared Spectroscopy: Evidence for an Oxygen-Rich Heritage? (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Comets retain relatively primitive icy material remaining from the epoch of Solar System for111ation, however the extent to which their ices are modified remains a key question in cometary science. One way to address this is to measure the relative abundances of primary (parent) volatiles in comets (i.e., those ices native to the nucleus). High-resolution (lambda/delta lambda greater than 10(exp 4)) infrared spectroscopy is a powerful tool for measuring parent volatiles in comets through their vibrational emissions in the ~ 3-5 micrometer region. With modern instrumentation on worldclass telescopes, we can quantify a multitude of species (e.g., H2O, C2H2, CH4, C2H6 CO, H2CO, CH3OH, HCN, NH3), even in comets with modest gas production. In space environments, compounds of keen interest to astrobiology could originate from HCN and NH3 (leading to amino acids), H2CO (leading to sugars), or C2H6 and CH4 (suggested precursors of ethyl- and methylamine). Measuring the abundances of these precursor molecules and their variability among comets contributes to understanding the synthesis of the more complex prebiotic compounds.
    Keywords: Astronomy
    Type: GSFC.ABS.01161.2012 , Asteroids, Comets, Meteors (ACM) 2012; May 16, 2012 - May 20, 2012; Niigata; Japan
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  • 6
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    Temporal and Spatial Aspects of Gas Release During the 2010 Apparition of Comet 103P/Hartley-2 (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We report measurements of eight primary volatiles (H2O, HCN, CH4, C2H6, CH3OH, C2H2, H2CO, and NH3) and two product species (OH and NH2) in comet 103P/Hartley-2 using high dispersion infrared spectroscopy. We present production rates for individual volatiles species, their mixing ratios relative to water, and their spatial distributions in the coma on multiple dates that span the interval Sept. - Dec. 2010. The production rates vary strongly with nucleus rotation, but the mixing ratios remain constant throughout the campaign. The released primary volatiles exhibit diverse spatial properties which favor the presence of separate polar and apolar ice phases in the nucleus, establish dust and gas release from icy clumps (and also, directly from the nucleus), and provide insights into the driver for the cyanogen (CN) polar jet.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC.OVPR.4972.2011 , 43rd Annual DPS Meeting; Oct 02, 2011 - Oct 07, 2011; Nantes; France
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  • 7
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    The Formation Heritage of Jupiter Family Comet 10P/Tempel 2 as Revealed by Infrared Spectroscopy (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present spectral and spatial information for major volatile species in Comet 10P/Tempel 2, based on high-dispersion infrared spectra acquired on UT 2010 July 26 (heliocentric distance Rh = 1.44 AU) and September 18 (Rh = 1.62 AU), following the comet's perihelion passage on UT 2010 July 04. The total production rate for water on July 26 was (1.90 +/- 0.12) x 10(exp 28) molecules per sec, and abundances of six trace gases (relative to water) were: CH3OH (1.58% +/- 0.23%), C2H6 (0.39% +/- 0.04%), NH3 (0.83% +/- 0.20%), and HCN (0.13% +/- 0.02%). A detailed analysis of intensities for water emission lines provided a rotational temperature of 35 +/- 3 K. The mean OPR is consistent with nuclear spin populations in statistical equilibrium (OPR = 3.01 +/- 0.18), and the (1(sigma)) lower bound corresponds to a spin temperature greater than 38 K. Our measurements were contemporaneous with a jet-like feature observed at optical wavelengths. The spatial profiles of four primary volatiles display strong enhancements in the jet direction, which favors release from a localized vent on the nucleus. The measured IR continuum is much more sharply peaked and is consistent with a dominant contribution from the nucleus itself. The peak intensities for H2O, CH3OH, and C2H6 are offset by approx. 200 km in the jet direction, suggesting the possible existence of a distributed source, such as the release of icy grains that subsequently sublimed in the coma. On UT September 18, no obvious emission lines were present in our spectra, nevertheless we obtained a 3(sigma) upper limit Q(H2O) less than 2.86 x 10(exp 27) molecules per sec.
    Keywords: Exobiology
    Type: GSFC-E-DAA-TN8865 , Icarus (ISSN 0019-1035); 218; 1; 644-653
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  • 8
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    Development of Primary Volatile Production in COMET C/20O9 Pl (GARRADD) During its 2011-2O12 Apparition (2012)
    In:  CASI
    Details
    Publication Date: 2019-09-24
    Description: We quantified primary volatiles in comet C/2009 Pl (Garradd) through pre- and post-perihelion observations acquired during its apparition in 2011-12 [1,2,3]. Detected volatiles include H2O, CO, CH4, C2H2, C2H6, HCN, NH3, H2CO, and CH3OH. We present production rates and chemical abundance ratios (relative to water) for all species, and I-D spatial profiles for multiple primary volatiles. We discuss these findings in the context of an emerging taxonomy based on primary volatiles in comets [4]. We used three spectrometer/telescope combinations. On UT 20ll August 7 (Rh 2.4 AU) and September 17-21 (Rh 2.0 AU), we used CRIRES at ESO's Very Large Telescope (VLT) [1]. On September 8 and 9 (Rh 2.1 AU), we used NIRSPEC at Keck-2 and CSHELL at IRTF [2]. Using NIRSPEC on October 13 and 2012 January 08 (Rh 1.83 and 1.57 AU, respectively), we detected nine primary volatiles pre-perihelion, and six post-perihelion [3]. CO was enriched in Garradd while C2H2 was strongly depleted. C2H6 and CH3OH displayed abundances close to those measured for the majority of Oort cloud comets observed to date. The high fractional abundance of CO identifies comet C12009 P1 as a CO-rich comet. Spatial profiles revealed notable differences among individual primary species. Given the relatively large heliocentric distance of C/2009 Pl, we explored the effect of water not being fully sublimated within our field of view and we identi$, the "missing" water fraction needed to reconcile the retrieved abundance ratios with the mean values found for "organics-normal" comets.
    Keywords: Astrophysics
    Type: GSFC.ABS.6792.2012 , 44th Annual Meeting AAS Division of Planetary Sciences; Oct 14, 2012 - Oct 19, 2012; Reno, NV; United States
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  • 9
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    EPOXI: Comet 103p/Hartley 2 Observations from a Worldwide Campaign (2011)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales. at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P (Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was approximately 16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production.
    Keywords: Astrophysics
    Type: GSFC.JA.6404.2012 , Astrophysical Journal Letters; 734; L1
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  • 10
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    The 1983 June 15 occultation by Neptune. II - The oblateness of Neptune (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The oblateness and radius of Neptune were determined from an analysis of photoelectric observations of the June 15, 1983 occultation by Neptune at six stations, combined with the results of the Apr. 7, 1968 Neptune occultation of BD - 17 deg 4388. The oblateness is 0.0191 + or - 0.0017 and the equatorial radius is 25,268 + or - 12 km at the level probed by the occultation. The results are consistent with recent determinations of Neptune's rotation period and J2 (the second-order gravitational harmonic coefficient) and suggest that Neptune is far less centrally condensed than Uranus. Temperature profiles for Neptune's upper atmosphere were also derived from these data.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 90; 2624-263
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