共查询到20条相似文献，搜索用时 15 毫秒
1.
Lawrence DJ Eke VR Elphic RC Feldman WC Funsten HO Prettyman TH Teodoro LF 《Science (New York, N.Y.)》2011,334(6059):1058-105c
Based on a study of high-energy epithermal (HEE) neutrons in data from the Lunar Exploration Neutron Detector (LEND) on NASA's Lunar Reconnaissance Orbiter (LRO), the background from HEE neutrons is larger than initially estimated. Claims by Mitrofanov et al. (Reports, 22 October 2010, p. 483) of enhanced hydrogen abundance in sunlit portions of the lunar south pole and quantitative hydrogen concentration values in south pole permanently shaded regions are therefore insufficiently supported. 相似文献
2.
Colaprete A Schultz P Heldmann J Wooden D Shirley M Ennico K Hermalyn B Marshall W Ricco A Elphic RC Goldstein D Summy D Bart GD Asphaug E Korycansky D Landis D Sollitt L 《Science (New York, N.Y.)》2010,330(6003):463-468
Several remote observations have indicated that water ice may be presented in permanently shadowed craters of the Moon. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was designed to provide direct evidence. On 9 October 2009, a spent Centaur rocket struck the persistently shadowed region within the lunar south pole crater Cabeus, ejecting debris, dust, and vapor. This material was observed by a second "shepherding" spacecraft, which carried nine instruments, including cameras, spectrometers, and a radiometer. Near-infrared absorbance attributed to water vapor and ice and ultraviolet emissions attributable to hydroxyl radicals support the presence of water in the debris. The maximum total water vapor and water ice within the instrument field of view was 155 ± 12 kilograms. Given the estimated total excavated mass of regolith that reached sunlight, and hence was observable, the concentration of water ice in the regolith at the LCROSS impact site is estimated to be 5.6 ± 2.9% by mass. In addition to water, spectral bands of a number of other volatile compounds were observed, including light hydrocarbons, sulfur-bearing species, and carbon dioxide. 相似文献
3.
Paige DA Siegler MA Zhang JA Hayne PO Foote EJ Bennett KA Vasavada AR Greenhagen BT Schofield JT McCleese DJ Foote MC DeJong E Bills BG Hartford W Murray BC Allen CC Snook K Soderblom LA Calcutt S Taylor FW Bowles NE Bandfield JL Elphic R Ghent R Glotch TD Wyatt MB Lucey PG 《Science (New York, N.Y.)》2010,330(6003):479-482
Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies. 相似文献
4.
Mitrofanov IG Boynton WV Litvak ML Sanin AB Starr RD 《Science (New York, N.Y.)》2011,334(6059):1058-105d
Critical comments from Lawrence et al. are considered on the capability of the collimated neutron telescope Lunar Exploration Neutron Detector (LEND) on NASA's Lunar Reconnaissance Orbiter (LRO) for mapping lunar epithermal neutrons, as presented in our paper. We present two different analyses to show that our previous estimated count rates are valid and support the conclusions of that paper. 相似文献
5.
Hayne PO Greenhagen BT Foote MC Siegler MA Vasavada AR Paige DA 《Science (New York, N.Y.)》2010,330(6003):477-479
The Lunar Reconnaissance Orbiter (LRO) Diviner instrument detected a thermal emission signature 90 seconds after the Lunar Crater Observation and Sensing Satellite (LCROSS) Centaur impact and on two subsequent orbits. The impact heated a region of 30 to 200 square meters to at least 950 kelvin, providing a sustained heat source for the sublimation of up to ~300 kilograms of water ice during the 4 minutes of LCROSS post-impact observations. Diviner visible observations constrain the mass of the sunlit ejecta column to be ~10(-6) to 10(-5) kilograms per square meter, which is consistent with LCROSS estimates used to derive the relative abundance of the ice within the regolith. 相似文献
6.
Recent radar observations of Mercury have revealed the presence of anomalous radar reflectivity and polarization features near its north and south poles. Thermal model calculations show that, despite Mercury's proximity to the sun, the temperatures of flat, low-reflectivity surfaces at Mercury's poles are not expected to exceed 167 kelvin. The locations of the anomalous polar radar features appear to be correlated with the locations of large, high-latitude impact craters. Maximum surface temperatures in the permanently shadowed regions of these craters are expected to be significantly colder, as low as 60 kelvin in the largest craters. These results are consistent with the presence of water ice, because at temperatures lower than 112 kelvin, water ice should be stable to evaporation over time scales of billions of years. 相似文献
7.
Feldman WC Boynton WV Tokar RL Prettyman TH Gasnault O Squyres SW Elphic RC Lawrence DJ Lawson SL Maurice S McKinney GW Moore KR Reedy RC 《Science (New York, N.Y.)》2002,297(5578):75-78
Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO2 in the uppermost meter of the martian surface. Poleward of +/-60 degrees latitude is terrain rich in hydrogen, probably H2O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO2 layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H2O and/or OH. 相似文献
8.
Lunar surface magnetic fields and their interaction with the solar wind: results from lunar prospector 总被引：1，自引：0，他引：1
RP Lin DL Mitchell DW Curtis KA Anderson CW Carlson J McFadden MH Acuna LL Hood A Binder 《Science (New York, N.Y.)》1998,281(5382):1480-1484
The magnetometer and electron reflectometer experiment on the Lunar Prospector spacecraft has obtained maps of lunar crustal magnetic fields and observed the interaction between the solar wind and regions of strong crustal magnetic fields at high selenographic latitude (30 degreesS to 80 degreesS) and low ( approximately 100 kilometers) altitude. Electron reflection maps of the regions antipodal to the Imbrium and Serenitatis impact basins, extending to 80 degreesS latitude, show that crustal magnetic fields fill most of the antipodal zones of those basins. This finding provides further evidence for the hypothesis that basin-forming impacts result in magnetization of the lunar crust at their antipodes. The crustal magnetic fields of the Imbrium antipode region are strong enough to deflect the solar wind and form a miniature (100 to several hundred kilometers across) magnetosphere, magnetosheath, and bow shock system. 相似文献
9.
Lack of exposed ice inside lunar south pole Shackleton Crater 总被引：2，自引：0，他引：2
Haruyama J Ohtake M Matsunaga T Morota T Honda C Yokota Y Pieters CM Hara S Hioki K Saiki K Miyamoto H Iwasaki A Abe M Ogawa Y Takeda H Shirao M Yamaji A Josset JL 《Science (New York, N.Y.)》2008,322(5903):938-939
The inside of Shackleton Crater at the lunar south pole is permanently shadowed; it has been inferred to hold water-ice deposits. The Terrain Camera (TC), a 10-meter-resolution stereo camera onboard the Selenological and Engineering Explorer (SELENE) spacecraft, succeeded in imaging the inside of the crater, which was faintly lit by sunlight scattered from the upper inner wall near the rim. The estimated temperature of the crater floor, based on the crater shape model derived from the TC data, is less than approximately 90 kelvin, cold enough to hold water-ice. However, at the TC's spatial resolution, the derived albedo indicates that exposed relatively pure water-ice deposits are not on the crater floor. Water-ice may be disseminated and mixed with soil over a small percentage of the area or may not exist at all. 相似文献
10.
Langevin Y Poulet F Bibring JP Schmitt B Douté S Gondet B 《Science (New York, N.Y.)》2005,307(5715):1581-1584
The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) visible-infrared imaging spectrometer extensively observed regions of Mars with latitudes above 70 degrees N in late 2004 (heliocentric longitude from Ls 93 degrees to Ls 127 degrees ). The extent of water ice at the surface and the size of ice grains were monitored as a function of time. Bright, small-grained frost, which initially covered a large fraction of the polar cap, waned in favor of large-grained ice. In outlying regions, dominated by large-grained ice, the albedo increased over the period. Evaluating the dust content was model dependent. However, contamination of ice by dust was low. 相似文献
11.
Spectra of the region just above the bright limb of the Moon show weak emission features that are attributed to resonant scattering of sunlight from sodium and potassium vapor in the lunar atmosphere. The maximum omnidirectional emission flux above the bright limb is 3.8 +/- 0.4 kilorayleighs for sodium and 1.8 +/- 0.4 kiloray-leighs for potassium. The zenith column densities above the subsolar point are estimated to be 8 +/- 3 x 10(8) atoms cm(-2) for sodium 1.4 +/- 0.3 x 10(8) atoms cm(-2) for potassium. Corresponding surface densities are 67 +/- 12 atoms cm(-3) and 15 +/- 3 atoms cm(-3), respectively. The scale height for the sodium atmosphere is 120 +/- 42 kilometers, and for potassium 90 +/- 20 kilometers, which implies that the effective temperature of the sodium and potassium is close to the lunar surface temperature. The sodium density at the south polar region was found to be similar to that at the subsolar point, indicating wide-spread distribution of sodium vapor over the lunar surface. The ratio of the density of sodium to the density of potassium is (6 +/- 3) to 1, which is close to the sodium to potassium ratio in the lunar surface, suggesting that the atmosphere originates from the vaporization of surface minerals. 相似文献
12.
Mitrofanov IG Zuber MT Litvak ML Boynton WV Smith DE Drake D Hamara D Kozyrev AS Sanin AB Shinohara C Saunders RS Tretyakov V 《Science (New York, N.Y.)》2003,300(5628):2081-2084
Observations of seasonal variations of neutron flux from the high-energy neutron detector (HEND) on Mars Odyssey combined with direct measurements of the thickness of condensed carbon dioxide by the Mars Orbiter Laser Altimeter (MOLA) on Mars Global Surveyor show a latitudinal dependence of northern winter deposition of carbon dioxide. The observations are also consistent with a shallow substrate consisting of a layer with water ice overlain by a layer of drier soil. The lower ice-rich layer contains between 50 and 75 weight % water, indicating that the shallow subsurface at northern polar latitudes on Mars is even more water rich than that in the south. 相似文献
13.
Kivelson MG 《Science (New York, N.Y.)》2006,311(5766):1391-1392
Instruments on the Cassini spacecraft reveal that a heat source within Saturn's moon Enceladus powers a great plume of water ice particles and dust grains, a geyser that jets outward from the south polar regions and most likely serves as the dominant source of Saturn's E ring. The interaction of flowing magnetospheric plasma with the plume modifies the particle and field environment of Enceladus. The structure of Saturn's magnetosphere, the extended region of space threaded by magnetic-field lines linked to the planet, is shaped by the ion source at Enceladus, and magnetospheric dynamics may be affected by the rate at which fresh ions are created. 相似文献
14.
Spahn F Schmidt J Albers N Hörning M Makuch M Seiss M Kempf S Srama R Dikarev V Helfert S Moragas-Klostermeyer G Krivov AV Sremcevic M Tuzzolino AJ Economou T Grün E 《Science (New York, N.Y.)》2006,311(5766):1416-1418
During Cassini's close flyby of Enceladus on 14 July 2005, the High Rate Detector of the Cosmic Dust Analyzer registered micron-sized dust particles enveloping this satellite. The dust impact rate peaked about 1 minute before the closest approach of the spacecraft to the moon. This asymmetric signature is consistent with a locally enhanced dust production in the south polar region of Enceladus. Other Cassini experiments revealed evidence for geophysical activities near Enceladus' south pole: a high surface temperature and a release of water gas. Production or release of dust particles related to these processes may provide the dominant source of Saturn's E ring. 相似文献
15.
Spencer JR Pearl JC Segura M Flasar FM Mamoutkine A Romani P Buratti BJ Hendrix AR Spilker LJ Lopes RM 《Science (New York, N.Y.)》2006,311(5766):1401-1405
The Cassini spacecraft completed three close flybys of Saturn's enigmatic moon Enceladus between February and July 2005. On the third and closest flyby, on 14 July 2005, multiple Cassini instruments detected evidence for ongoing endogenic activity in a region centered on Enceladus' south pole. The polar region is the source of a plume of gas and dust, which probably emanates from prominent warm troughs seen on the surface. Cassini's Composite Infrared Spectrometer (CIRS) detected 3 to 7 gigawatts of thermal emission from the south polar troughs at temperatures up to 145 kelvin or higher, making Enceladus only the third known solid planetary body-after Earth and Io-that is sufficiently geologically active for its internal heat to be detected by remote sensing. If the plume is generated by the sublimation of water ice and if the sublimation source is visible to CIRS, then sublimation temperatures of at least 180 kelvin are required. 相似文献
16.
Neutron activation analyses of gallium, germanium, indium, and iridium in eight lunar samples and in meteorites and rocks (including four calciulnrich achondrites and five terrestrial basalts) with similar bulk compositions are reported. Lunar gallium concentrations are remarkably constant at about 5 parts per million, three times higher and four times lower than those in eucritic (calcium-rich) achondrites and terrestrial basalts, respectively. Lunar germanium concentrations range from 相似文献
17.
The clementine mission to the moon: scientific overview 总被引：4，自引：0，他引：4
Nozette S Rustan P Pleasance LP Kordas JF Lewis IT Park HS Priest RE Horan DM Regeon P Lichtenberg CL Shoemaker EM Eliason EM McEwen AS Robinson MS Spudis PD Acton CH Buratti BJ Duxbury TC Baker DN Jakosky BM Blamont JE Corson MP Resnick JH Rollins CJ Davies ME Lucey PG Malaret E Massie MA Pieters CM Reisse RA Simpson RA Smith DE Sorenson TC Breugge RW Zuber MT 《Science (New York, N.Y.)》1994,266(5192):1835-1839
In the course of 71 days in lunar orbit, from 19 February to 3 May 1994, the Clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths. These data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side. In addition, laser-ranging measurements provided the first view of the global topographic figure of the moon. The topography of many ancient impact basins has been measured, and a global map of the thickness of the lunar crust has been derived from the topography and gravity. 相似文献
18.
Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO(2) or H(2)O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth. 相似文献
19.
The South pole region of the moon as seen by clementine 总被引：2，自引：0，他引：2
The Clementine mission has provided the first comprehensive set of high-resolution images of the south pole region of the moon. Within 5 degrees of latitude of the pole, an area of an estimated 30,000 square kilometers remained in shadow during a full lunar rotation and is a promising target for future exploration for ice deposits. The Schr?dinger Basin (320 kilometers in diameter), centered at 75 degrees S, is one of the two youngest, least modified, great multiring impact basins on the moon. A large maar-type volcano localized along a graben within the Schr?dinger Basin probably erupted between 1 and 2 billion years ago. 相似文献
20.
Lunar meteorites represent a more random sampling of lunar material than the Apollo or Luna collections and, as such, lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the lunar cataclysm hypothesis. Within the lunar meteorite breccias MAC 88105, QUE 93069, DaG 262, and DaG 400, seven to nine different impact events are represented with 40Ar-39Ar ages between 2.76 and 3.92 billion years ago (Ga). The lack of impact melt older than 3.92 Ga supports the concept of a short, intense period of bombardment in the Earth-moon system at approximately 3.9 Ga. This was an anomalous spike of impact activity on the otherwise declining impact- frequency curve. 相似文献