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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Spatial variability in the seasonal south polar cap of Mars

The first comprehensive discussion of the south seasonal polar cap spectra obtained by the Mariner 7 infrared spectrometer in the short-wavelength region (2-4 microns) is presented. The infrared spectra is correlated with images acquired by the wide-angle camera. Significant spectral variation is noted in the cap interior and regions of varying water frost abundance, CO2 ice/frost cover, and CO2-ice path length can be distinguished. Many of these spectral variations correlate with heterogeneity noted in the camera images, but certain significant infrared spectral variations are not discernible in the visible. Simple reflectance models are used to classify the observed spectral variations into four regions. Region I is at the cap edge, where there is enhanced absorption beyond 3 microns inferred to be caused by an increased abundance of water frost. The increase in water abundance over that in the interior is on the level of a few parts per thousand or less. Region II is the typical cap interior characterized by spectral features of CO2 ice at grain sizes of several millimeters to centimeters. These spectra also indicate the presence of water frost at the parts per thousand level. A third, unusual region (III), is defined by three spectra in which weak CO2 absorption features are as much as twice as strong as in the average cap spectra and are assumed to be caused by an increased path length in the CO2. Such large paths are inconsistent with the high reflectance in the visible and at 2.2 microns and suggest layered structures or deposition conditions that are not accounted for in current reflectance models. The final region (IV) is an area of thinning frost coverage or transparent ice well in the interior of the seasonal cap. These spectra are a combination of CO2 and ground signatures.

Calvin, Wendy M.↗
NASA NTRS2004

Internal Structure of the Southern Polar Cap of Mars and Formation Implications

The surfaces of the Martian polar caps have been studied in detail but little is known about their internal structure. Exposures of the cap interior can be seen in the many troughs and scarps which incise them. The layered sequences visible in these topographic features have been known to exist for many years, however first order questions concerning the internal stratigraphy remain. We have identified a prominent bench forming layer near the top of the southern layered deposits. We have mapped its exposure in high-resolution MOC images on the eastern and western scarps. These images have been carefully registered to a MOLA derived DEM so topographic measurements along this bench can be extracted along with the location of each trace. What results are a set of measurements of the top of the bench forming layer in three dimensions. The top of this layer represents a distinct stratigraphic horizon. The prominent bench outcrops on both the eastern and western scarps which bound the highest portion of the southern layered deposits. Confirmation that these are two benches are indeed the same stratigraphic surface comes from the similarity of surrounding (nonbench forming) layers.

Byrne, S.↗
NASA NTRS1995

The response of ionospheric convection in the polar cap to substorm activity

We report multi-instrument observations during an isolated substorm on 17 October 1989. The European Incoherent Scatter (EISCAT) radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71 deg Lambda - 78 deg Lambda. Sub-Auroral Magnetometer Network (SAMNET) and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. Interplanetary Monitoring Platform-8 (IMP-8) magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux in the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71 deg Lambda by the time of the expansion phase onset. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the distant neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase.

Lester, M.↗
NASA NTRS1979

Seasonal recession of Mars' south polar cap as seen by Viking

The spring-summer retreat of the south polar cap of Mars is portrayed in photomosaics obtained by Viking Orbiter 2 during 1977. Comparisons of these data to Mariner 9 photos and to the record of telescopic observations attest that the polar retreat viewed by Viking was significantly slower than those previously reported. A global dust storm which occurred at an unusually early season may have effected this retarded recession by introducing dust into the atmosphere of Mars which modified the polar energy balance through scattering of incident radiation. The composition of the south residual cap cannot be unambiguously determined at this time; however, some data suggest that CO2 or clathrate survived the entire summer viewed by Viking.

James, P. B.↗
NASA NTRS1971

Mariner 7 ultraviolet spectrometer experiment - Photometric function and roughness of Mars' polar cap surface.

Review of some of the results of the Mariner 7 ultraviolet spectrometer observations of the south polar cap of Mars. The near ultraviolet polar spectrum shows the predominance of surface reflection over atmospheric scattering. The intensity of the reflected radiation decreased steeply for a change in solar elevation of only about 10 deg. Neither a haze layer nor ground inhomogeneity is considered a likely explanation for this observation. An unusual photometric function of the surface is more probable. An analysis of reflected radiation intensity as a function of incidence and emission angles was made, assuming a photometric function for the surface. The angular inversion revealed a 'smoothness factor' suggestive of an icy or glazed surface. A hypothesis is advanced to explain the observed phenomena and associated polar features.

Pang, K.↗
NASA NTRS2019

Formation of the Potential Jump Over the Geomagnetically Quiet Sunlit Polar Cap Region

We consider the formation of a potential drop over the Earth's polar cap duringgeomagnetically quiet daytime. The observed potential drop is primarily defined by the hydrogen,photoelectron, and polar rain fluxes ratios and depends strongly on the energy distribution of thephotoelectron flux. Polar rain is an essential component of the model required for plasma quasineutrality.The potential distribution along the magnetic field line has two regions, with a small, gradual, potentialdrop of 3–4 V and a potential jump. The value of the potential jump depends on the hydrogen ion tophotoelectron flux ratio and is also controlled by polar rain electrons. With quasineutrality required at itsupper boundary, the jump only occurs in the presence of polar rain and its location depends on the polarrain flux. Model predictions compare well with FAST observations presented by Kitamura et al.(2012, https://doi.org/10.1029/2011JA017459).

Khazanov, George V.↗
NASA NTRS2019

Formation of the Potential Jump over the Geomagnetically Quiet Sunlit Polar Cap Region

We consider the formation of a potential drop over the Earth's polar cap during geomagnetically quiet daytime. The observed potential drop is primarily defined by the hydrogen, photoelectron, and polar rain fluxes ratios and depends strongly on the energy distribution of the photoelectron flux. Polar rain is an essential component of the model required for plasma quasineutrality. The potential distribution along the magnetic field line has two regions, with a small, gradual, potential drop of 3 to 4 volts and a potential jump. The value of the potential jump depends on the hydrogen ion to photoelectron flux ratio and is also controlled by polar rain electrons. With quasineutrality required at its upper boundary, the jump only occurs in the presence of polar rain and its location depends on the polar rain flux. Model predictions compare well with FAST (Fast Auroral SnapshoT) observations presented by Kitamura et al.(2012, https://doi.org/10.1029/2011JA017459).

Khazanov, G. V.↗
NASA NTRS2023

Hemispheric Symmetry and Asymmetry of Poleward Moving Radar Auroral Forms (PMRAFs) and Associated Polar Cap Patches During a Geomagnetic Storm

Magnetopause reconnection is known to impact the dayside ionosphere by driving fast ionospheric flows, auroral transients, and high density plasma structures named polar cap patches. However, most of the observed reconnection impact is limited to one hemisphere, and a question arises as to how symmetric the impact is between hemispheres.

hemispheric symmetry/asymmetry↗
NASA NTRS2003

A One Billion Year Martian Climate Model: The Importance of Seasonally Resolved Polar Caps and the Role of Wind

Wind deflation and deposition are powerful agents of surface change in the present Mars climate regime. Recent studies indicate that, while the distribution of regions of potential deflation (or erosion) and deposition is remarkably insensitive to changes in orbital parameters (obliquity, timing of perihelion passage, etc.), rates of aeolian surface modification may be highly sensitive to these parameters even if the atmospheric mass remains constant. But previous work suggested the atmospheric mass is likely to be sensitive to obliquity, especially if a significant mass of carbon dioxide can be stored in the regolith or deposited in the form of massive polar caps. Deflation and erosion are highly sensitive to surface pressure, so feedback between orbit variations and surface pressure can greatly enhance the sensitivity of aeolian modification rates to orbital parameters. We used statistics derived from a 1 Gyr orbital integration of the spin axis of Mars, coupled with 3D general circulation models (GCMs) at a variety of orbital conditions and pressures, to explore this feedback. We also employed a seasonally resolved 1D energy balance model to illuminate the gross characteristics of the longterm atmospheric evolution, wind erosion and deposition over one billion years. We find that seasonal polar cycles have a critical influence on the ability for the regolith to release CO2 at high obliquities, and find that the atmospheric CO2 actually decreases at high obliquities due to the cooling effect of polar deposits at latitudes where seasonal caps form. At low obliquity, the formation of massive, permanent polar caps depends critically on the values of the frost albedo, A(sub frost), and frost emissivity, E(sub frost). Using our 1D model with values of A(sub frost) = 0.67 and E(sub frost) = 0.55, matched to the NASA Ames GCM results, we find that permanent caps only form at low obliquities (< 10 degrees). Thus, contrary to expectations, the Martian atmospheric pressure is remarkable static over time, and decreases both at high and low obliquity. Also, from our one billion year orbital model, we present new results on the fraction of time Mars is expected to experience periods of high and low obliquity. Finally, using GCM runs at a variety of pressures, we examine the likely role of wind erosion under an early more massive Martian atmosphere.

J C Armstrong↗
NASA NTRS2003

CryoScout: A Descent Through the Mars Polar Cap

CryoScout was proposed as a subsurface investigation of the stratigraphic climate record embedded in Mars North Polar cap. After landing on a gentle landscape in the midst of the mild summer season, CryoScout was to use the continuous polar sunlight to power the descent of a cryobot, a thermal probe, into the ice at a rate of about 1 m per day. CryoScout would probe deep enough into this time capsule to see the effects of planetary obliquity variations and discrete events such as dust storms or volcanic eruptions. By penetrating tens of meters of ice, the mission would explore at least one of the dominant "MOC layers" observed in exposed layered terrain.

Hecht, M. H.↗