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  • Lunar and Planetary Science and Exploration  (11)
  • Astronomy  (10)
  • 1
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    Polar and Non-Polar Layers on Mars: A Single Mechanism for Formation? (2003)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The recent discovery of vast quantities of near-subsurface ice in both polar regions of Mars by the Mars Odyssey Gamma Ray Spectrometer (GRS) has presented us with an interesting quandary. On one hand, these deposits, found poleward of 60 deg in both hemispheres, are consistent with thermal models suggesting ice will be best protected in these regions during periods of high obliquity. On the other hand, the current paradigm regarding the placement of these deposits, i.e., diffusive deposition of water vapor, appears to be inconsistent with the large volume mixing ratios (approx. 90%) inferred from the GRS data. This incongruity argues that diffusion alone cannot be the primary mechanism for the creation of these reservoirs, and that an alternate, large-scale process should be considered.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Third International Conference on Mars Polar Science and Exploration; LPI-Contrib-1184
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  • 2
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    The Polar Regions and Martian Climate: Studies with a Global Climate Model (2003)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Much of the interest in the polar regions centers on the fact that they likely contain the best record of Martian climate change on time scales from years to eons. This expectation is based upon the observed occurrence of weathering product deposits and volatile reservoirs that are coupled to the climate. Interpretation and understanding of these records requires understanding of the mechanisms that involve the exchange of dust, water, and carbon dioxide between the surface and atmosphere, and the atmospheric redistribution of these species. We will summarize our use of the GFDL Mars general circulation model (MGCM), to exploration aspects of the interaction between the global climate and the polar regions. For example, our studies have shown that while the northern polar cap is the dominant seasonal source for water, it can act as a net annual source or sink for water, depending upon the cap temperatures and the bulk humidity of the atmosphere. This behavior regulates the annual and global average humidity of the atmosphere, as the cap acts as a sink if the atmosphere is too wet and a source if it is too dry. We will then focus our presentation on the ability of the MGCM to simulate the observed diurnal variations of surface temperature. We are particularly interested in assessing the influence of dust aerosol and water ice clouds on simulated surface temperature and the comparison with observations. Surface thermal inertia and albedo are critical boundary inputs for MGCM simulations. Thermal inertia is also of intrinsic interest as it may be related to properties of the surface such as particle size and surface character.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Third International Conference on Mars Polar Science and Exploration; LPI-Contrib-1184
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  • 3
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    The Effects of Atmospheric Opacity on the Seasonal Variation of Martian Surface Temperature (2005)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The daily and seasonal variation of surface temperature is a central element in the description of martian climate. Surface thermal inertia and albedo are critical boundary inputs for simulating surface temperature in Mars general circulation models (MGCMs). Thermal inertia (TI) is also of intrinsic interest as it may be related to regolith properties such as particle size and surface character and so high spatial resolution is desirable. The recent mapping of TI at very high (0.25 deg) spatial resolution was achieved by fitting a thermal model to surface temperature observations obtained over a broad range of several martian years. However, varying atmospheric opacity (dust and water ice clouds) can significantly influence the estimated TI field and this effect was not fully compensated for. Opacity leads to an increase in morning temperature and a decrease in afternoon temperature, thus increasing the apparent thermal inertia.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXVI, Part 21; LPI-Contrib-1234-Pt-21
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  • 4
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    Daily to interannual variability in Mars' surfare pressure (2002)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Keywords: Lunar and Planetary Science and Exploration
    Type: American Geophysical Union Annual Fall Meeting; San Francisco, CA; United States
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  • 5
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    Explaining the Mid-Latitude Ice Deposits with a General Circulation Model (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: We have examined the influence of a regolith on the water cycle with a focus on high obliquity periods on Mars. Our findings show that while the regolith will almost certainly interact with the atmosphere initially, it is only a transient effect, and ice will form on the surface once the regolith is effectively isolated from the atmosphere. These low latitude deposits could conceivably be ice deposits formed at high obliquity and are certainly presently out of thermal equilibrium, but remain due to the insulating effect of a dust lag.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Special Session: Mars Climate Change; LPI-Contrib-1197
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  • 6
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    Modeling Viking Era Water Ice Clouds (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Padua; Italy
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  • 7
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    Long-Term Observations of Her X-1 with BATSE (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: Pulsed emission from Her X-1 has been observed by BATSE during each Main High state throughout the CGRO (Compton Gamma-Ray Observatory) mission . This long observation set by a single instrument provides new information on long-term behavior of the Her X-1 system. The luminosity varies by more than a factor of 3 between different 35d cycles. Frequency and flux histories do not show a simple relationship between the source intensity and spin behavior, but do show that only spindown occurs when the source is in its lowest intensity state. Orbital analyses will be presented, including tests for consistency of the observed orbital epoch with the long-term ephemeris reported by (Deeter 1991). The intensity profile and onset times of cycles observed by both BATSE and the RXTE ASM (All Sky Monitor) will be compared. Behavior of the cycle start times versus source Main High peak intensity will be presented.
    Keywords: Astronomy
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  • 8
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    A Search for Short-Period Accreting Pulsars with BATSE (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: Accreting X-ray pulsar systems can be detected and monitored by the BATSE Pulsar Monitor at full sensitivity only above the Nyquist period of 2.048 s, since it uses the DISCLA data type. Systems with shorter periods than 2 s can be observed, but with a reduced sensitivity, since only the aliased power is measured. While persistent sources in the period range below that have been found by earlier spacecraft, transient systems may still be undiscovered, due to limited time coverage of the galactic plane with all-sky instruments. BATSE data with a time resolution of 31 ms (PSR single-sweep mode) has been collected for four energy channels spanning 20-50 keV , at scheduled times for particular detectors and detector combinations which view the galactic plane. The data spans Nov 1993 to present, with a typical exposure of 15000 s per day to approximately 1/8 of the plane. An accelerated FFT-based search is in progress on these data. Data are segmented into approximately 300 second intervals, barycentered for 3 possible source directions spaced by 30 degrees about the detector normal, with the time series accelerated for each of 15 steps, each spaced by 5 x 10(exp -5). To avoid loss of coherence due to system orbital velocities, FFTs are averaged over each 1/4 day interval separately. Results of this search are presented, including examples of detection of Her X-1, Cen X-3, and other pulsars.
    Keywords: Astronomy
    Type: Apr 12, 1999 - Apr 15, 1999; Charleston, SC; United States
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  • 9
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    Discovery and Orbital Determination of the Transient X-Ray Pulsar GRO J1750-27 (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We report on the discovery and hard X-ray (20-70 keV) observations of the 4.45 second period transient X-ray pulsar GRO J1750-27 with the BATSE all-sky monitor on board CCRO. A relatively faint outburst (〈 30 mCrab peak) lasting at least 60 days was observed during which the spin-up rate peaked at 38 pHz/sec and was correlated with the pulsed intensity. An orbit with a period of 29.8 days was found. The large spin-up rate, spin period and orbital period together suggest that accretion is occurring from a disk and that the outburst is a 'giant' outburst typical of a Be/X-ray transient system. No optical counterpart has been reported yet.
    Keywords: Astronomy
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  • 10
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    Observations of 4U 1700-37 with BATSE (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The eclipsing binary X-ray source 4U 1700-37 has been continually monitored by the BATSE experiment on the Compton Gamma Ray Observatory since the spring of 1991. Using source measurements at times of Earth occultation, we observe an average (uneclipsed) flux of 0.23 crab in the 20-120 keV band. The flux is highly variable, with occasional flaring behavior on timescales from hundreds of seconds to several hours and intensities as bright as 1 crab. The uneclipsed spectrum is well represented by an optically thin thermal bremsstrahlung model with a temperature of 25 keV independent of source intensity or orbital phase. An upper limit of 4% on the pulse fraction has been obtained for pulse periods between 2 and 700 s. Average orbital light curves from almost 1000 days of occultation measurements have been constructed. These profiles are used to measure: (1) the eclipse semiangle, Theta(sub E) = 28.6 deg +/- 2.1 deg in the 20-120 keV band, and (2) the decrease in orbital period, P(dot)/P = -(3.3 +/- 0.6) x 10(exp -7) 1/ yr. Estimates of system physical parameters are obtained using Monte Carlo simulations to propagate errors in measured and assumed parameters. For the X-ray source mass we find M(sub x) = 2.6(sub -1.4)(sup +2.3) solar mass, and for the mass and radius of the optical companion, M(sub 0) = 30(sub -7)(sup +11) solar mass and R(sub 0) = 18(sub -2)(sup +2) solar radius.
    Keywords: Astronomy
    Type: NASA-TM-112507 , NAS 1.15:112507 , The Astrophysical Journal; 459; 259-270
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