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  • 1
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    Cometesimals in the inner solar system (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Spectra obtained by the ultraviolet spectrometer on the Voyager 2 spacecraft between 1 and 2.5 AU are shown to provide evidence for a very large number of 'cometesimals' with radii between a few meters and a few tens of meters in the neighborhood of the earth. The evidence consists of a component in the interplanetary Lyman-alpha radiation that decreases rapidly with heliocentric distance. It is proposed that the source consists of cometesimals which are ice-coated, porous, low-density refractory boulders that may be the building blocks of ordinary comet nuclei. It is shown that the cometesimals required to produce the observed Lyman-alpha emission can also account for all the lunar craters with diameters between 200 m and 1500 m produced during the phase 3200 million years at sites such as Mare Tranquillitatis.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 330; 548-550
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  • 2
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    Escape of atmospheres and loss of water (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The properties and limitations of several loss processes for atmospheric gases are presented and discussed. They include thermal loss (Jeans and hydrodynamic); nonthermal loss (all processes involve charged particles); and impact erosion, including thermal escape from a molten body heated by rapid accretion. Hydrodynamic escape, or 'blowoff', is of particular interest because it offers the prospect of processing large quantities of gas and enriching the remainder in heavy elements and isotopes. In a second part, the water budgets and likely evolutionary histories of Venus, Earth and Mars are assessed. Although it is tempting to associate the great D/H enrichment on Venus with loss of a large initial endowment, a steady state with juvenile water (perhaps from comets) is equally probable.
    Keywords: ASTROPHYSICS
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  • 3
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    Ultraviolet absorption experiment MA-059 (1976)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The ultraviolet absorption experiment performed during the Apollo Soyuz mission involved sending a beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation, all filling the same 3 deg-wide field of view from the Apollo to the Soyuz. The radiation struck a retroreflector array on the Soyuz and was returned to a spectrometer onboard the Apollo. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Information concerning oxygen densities was also obtained by observation of resonantly fluorescent light. The absorption experiments for atomic oxygen and atomic nitrogen were successfully performed at a range of 500 meters, and abundant resonance fluorescence data were obtained.
    Keywords: ASTROPHYSICS
    Type: Apollo-Soyuz Test Project; 22 p
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  • 4
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    Observations of Comet Halley at H-alpha and 6300 A (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: High spectral resolution measurements of Comet Halley at H-alpha and OD-1 were obtained in March, 1986 using a small aperture telescope with the Fabry-Perot interferometer at the Arecibo Observatory. It is suggested that the highly structured spectral signature observed at H-alpha is due to collimation of atomic hydrogen in the inner hydrogen corona, following photodissociation of parent species, and that the emission is due to resonance fluorescence of solar Lyman-beta radiation. A feature at 6300.8 A accompanying the OD-1 emission at 6300.3 A is attributed to NH2. For a 6-arcmin field of view, a brightness for the OD-1 emission of 260 + or - 50 rayleighs is found for both March 15 and 17.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 53-56
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  • 5
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    High spectral resolution Fabry-Perot interferometer measurements of Comet Halley at H-alpha and 6300 A (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A 40.6-cm Newtonian telescope was interfaced to the Fabry-Perot interferometer at the Arecibo Observatory to make high-spectral-resolution measurements of Comet Halley emissions at 6562.72 A (H-alpha) and 6300.3 A (O I). The atomic hydrogen outflow velocity was found to be approximately 7.9 + or - 1.0 km/s. In general, the H-alpha spectra are highly structured, and indicative of a multiple component atomic hydrogen velocity distribution. For O (1D), implied production rates of 6.44 + or - 3.0 x 10 to the 28th/s and 5.66 + or - 2.7 x 10 to the 28th/s were found on March 15 and 17, respectively.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 5; 12 1; 283-287
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