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  • LUNAR AND PLANETARY EXPLORATION  (6)
  • comets  (2)
  • Astronomy; Lunar and Planetary Science and Exploration  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Infrared Spectroscopy of Comet Hale-Bopp (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 71-80 
    Details
    ISSN: 1573-0794
    Keywords: Infrared ; spectroscopy ; composition ; comets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract High resolution (λ/δλ ∼ 20,000) spectra of comet C/1995 O1 (Hale-Bopp) in the 2–5 μm region were obtained during UT 2–5 March 1997 using CSHELL at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The heliocentric and geocentric distances of the comet were ∼1.1 AU and ∼1.5 AU,respectively. We detected emission lines of the gas-phase molecules H2O, 4, C2H6, C2H2, HCN, and CO and derived absolute production rates and relative abundances for all species. We also used the 2-dimensional nature of the CSHELL data to investigate the spatial distribution of the molecules and find evidence that CO was derived at least partly from an extended source in the coma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006227530238
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Estimating the Size of Hale-Bopp's Nucleus (1997)
    Springer
    Earth, moon and planets 79 (1997), S. 17-33 
    Details
    ISSN: 1573-0794
    Keywords: Imaging ; comets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A variety of independent methods have been used to estimate the size of the nucleus of comet Hale-Bopp. Several groups have analyzed optical and infrared images of the comet and claim to detect the signature of the nucleus, despite the presence of a strong coma. A detection of the nucleus was also claimed during mm- and cm-wave observations of Hale-Bopp shortly before perihelion. A team of observers detected the occultation of a star by the nucleus of Hale-Bopp in October 1996. The maximum observed gas production rate of the comet near perihelion can be used to place a lower limit on the size of the nucleus. This paper critically reviews the many different methods used to constrain the size of Hale-Bopp's nucleus. All of the techniques are affected by systematic errors that can be difficult to quantify precisely. Nevertheless, the available evidence strongly suggests that the nucleus of Hale-Bopp has an effective radius of at least 15 km and is probably in the range 20–35 km. Thus, the prodigious gas and production rates from this comet are naturally explained by its unusually large size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006220930046
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  • 3
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    The spectrum of comets as derived from IUE observations (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Eight comets were observed with the IUE at various-heliocentric and geocentric distances. Their UV spectra are remarkably similar despite the large differences in the dust to gas ratios. Since all the dominant atomic species (except N) radicals and ions of the coma are detected in this spectral region, the total gaseous output of the nucleus can be estimated. The abundance of the carbon atom-bearing species is still not very well known and there are indications that the CO content of the coma could vary from comet to comet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: ESA 3rd European IUE Conf.; p 445-449
    Format: text
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  • 4
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    Rocket detection of ultraviolet emission from neutral oxygen and sulfur in the IO Torus (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 267; April 15
    Format: text
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  • 5
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    Vibrational and rotational excitation of CO in comets. Part 1: Non-equilibrium calculations. Part 2: Results of the calculation for standard bright comet, comet Iras-Araki-Alcock and comet Halley (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The vibrational and rotational excitation of the CO molecule in cometary comae were investigated using a model which includes IR vibrational pumping by the solar flux, vibrational and rotational radiative decay, and collisional coupling among rotational states. Steady state was not assumed in solving the rate equations. The evolution of a shell of CO gas was monitored as it expanded from the nucleus into the outer coma. Collisional effects were treated using a kinetic temperature profile derived from theoretical work on the coma energy balance. The kinetic temperature was assumed to be extremely cold in the inner coma; this has significant consequences for the CO excitation. If optical depth effects are ignored, only low J transitions will be significantly excited in comets observed at high spatial resolution. Ground-based observations of CO co-vibrational and rotational transitions will be extremely difficult due to lack of sensitivity and/or terrestrial absorption. However, CO should be detectable from a large comet with favorable observing geometry if the CO is a parent molecule present at the 10% level (or greater) relative to H2O. Observations using cooled, spaceborne instruments should be capable of detecting CO emission from even moderately bright comets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-86122 , NAS 1.15:86122
    Format: application/pdf
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  • 6
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    Spatial imaging of hydrogen Lyman-alpha emission from Jupiter (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A sounding rocket measurement of the H I L-alpha emission from Jupiter made on Dec. 1, 1978 shows limb darkening and an average disk brightness of 13 kR. This brightness is significantly higher than in previous measurements, and was confirmed by an IUE observation on Dec. 10, 1978. Comparison with a plane-parallel hydrogen layer model indicates that there is enhanced emission from the equatorial regions, reaching a peak near 80 deg longitude.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 240
    Format: text
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  • 7
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    Infrared molecular emissions from comets (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The possibility of detecting IR molecular line emission from cometary parent molecules is explored. Due to the non-LTE conditions in the inner coma and the large amount of near IR solar flux, IR fluorescence will be a significant source of cometary emission and, in fact, will dominate the grain radiation in a sufficiently high resolution instrument. The detection of this line emission will be difficult due to absorption in the terrestrial atmosphere, but it appears possible to measure cometary H2O emission from airplane altitudes. As IR molecular line emission represents one of the few promising methods of detecting cometary parent molecules directly, further research on this problem should be vigorously pursued.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-85067 , NAS 1.15:85067
    Format: application/pdf
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  • 8
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    Titan: Evidence for seasonal change - A comparison of Hubble Space Telescope and Voyager images (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A comparison of images of Titan obtained by the HST in August, 1990 with Voyager 1 and 2 images respectively obtained 10 and 9 years earlier has indicated a reversal of the seasonal hemispheric brightness asymmetry near 440 and 550 nm wavelengths; the northern hemisphere is in the more recent observations the brighter of the two, by about 10 percent. Titan's albedo pattern is therefore adequately explained by a seasonal model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 97; 1 Ma
    Format: text
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  • 9
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    The Small Satellites of Pluto as Observed by New Horizons (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of approx.40 kilometers for Nix and Hydra and approx. 10 kilometers for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of approx. 2. All four moons have high albedos (approx.50 to 90%) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages of at least 4 billion years. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary.
    Keywords: Astronomy; Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN40469 , Science (ISSN 0036-8075) (e-ISSN 1095-9203); 351; 6279
    Format: text
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