Seasonal Polar Temperatures on the Moon

Williams, J. P.; Greenhagen, B. T.; Schörghofer, N.; Sefton‐Nash, E.; Hayne, P. O.; Lucey, P. G.; Siegler, M. A.; Aye, K.-M.

doi:10.1029/2019je006028

Cited by 113 publications

(95 citation statements)

References 86 publications

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“…These values are much smaller than the PSR areas of 12,866 and 16,055 km 2 (Mazarico et al, 2011). The area of seasonal cold traps implied from Williams et al (2019) is 17,500 km 2 for the north pole and 24,300 km 2 for the south. Hayne et al (2020) recently calculated the fractional area of cold traps at all size scales as a function of latitude.…”

Section: Previous Estimates Of Water Ice Deliverymentioning

confidence: 98%

Stratigraphy of Ice and Ejecta Deposits at the Lunar Poles

Cannon

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et al. 2020

Geophysical Research Letters

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Water ice has been delivered to the lunar poles from different sources over billions of years, but this accumulation was punctuated by large impacts that excavated dry regolith from depth and emplaced it in layers over the poles. Here, we model the resulting stratigraphies of ice and ejecta deposits in the lunar polar regions. Large polar craters were age dated, and their ejecta distributions calculated with standard scaling relations. We then created a Monte Carlo model for ice deposition and ejecta emplacement. Typical model runs showed that deposits in older cold traps (>4 Ga) are divided into two zones: buried ice-rich gigaton deposits and younger more gardened mantles. The latter are consistent with small crater morphometry measurements, but the existence of substantial ice buried at great depths is more difficult to confirm. Rare outlier model runs included Mercury-like cases with significant deposition events in recent history (<200 Ma). Plain Language Summary The polar regions of Earth's Moon have topographic depressions that are never directly exposed to the Sun, so they are cold enough for deposits of ice to exist. Water can get into these regions by water-bearing asteroids colliding with the Moon, or from lunar volcanoes erupting gases that travel to the poles. At the same time, large impact craters that form at the poles eject an enormous amount of soil and rock that could bury existing ice. It is not well understood how these two processes work together to build up deposits that may have alternating layers of ice-rich and ice-poor soil. In this study, we used computer simulations to predict what these layered deposits may look like. We found it is likely that large amounts of relatively pure ice are buried at depth in the oldest deposits, covered with thinner layers hosting less ice. Impact cratering has been the dominant process affecting the lunar poles, but the effects of large polar craters on nearby ice deposits have not been previously addressed. Impact effects have been considered for micrometeoroids (e.g.,

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Section: Previous Estimates Of Water Ice Deliverymentioning

confidence: 98%

Stratigraphy of Ice and Ejecta Deposits at the Lunar Poles

Cannon

Deutsch

Head

et al. 2020

Geophysical Research Letters

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“…4 summarize the PSR and cold-trap areas based on the results of this study. Including seasonal variations, which are neglected here, Williams et al 34 obtain 13,000 km 2 of cold-trap area poleward of 80° S and 5,300 km 2 for the north polar region based on a Diviner threshold of 110 K. Our model shows that many PSRs are not cold traps, particularly those equatorward of 80°, which tend to exceed 110 K. Over half a century ago, classical analysis by Watson, Murray and Brown 2,13 derived the shadow fraction using photographic data, and assumed a constant f = 0.5. We find that the overall PSR area fraction is 0.15% of the surface, smaller than the 0.51% found by Watson et al 13 (Table 1).…”

Section: Calculation Of Shadow Temperaturesmentioning

confidence: 99%

Micro cold traps on the Moon

2020

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Water ice is thought to be trapped in large permanently shadowed regions in the Moon's polar regions, due to their extremely low temperatures. Here, we show that many unmapped cold traps exist on small spatial scales, substantially augmenting the areas where ice may accumulate. Using theoretical models and data from the Lunar Reconnaissance Orbiter, we estimate the contribution of shadows on scales from 1 km to 1 cm, the smallest distance over which we find cold-trapping to be effective for water ice. Approximately 10-20% of the permanent cold-trap area for water is found to be contained in these micro cold traps, which are the most numerous cold traps on the Moon. Consideration of all spatial scales therefore substantially increases the number of cold traps over previous estimates, for a total area of ~40,000 km 2 , about 60% of which is in the south. A majority of cold traps for water ice is found at latitudes > 80° because permanent shadows equatorward of 80° are typically too warm to support ice accumulation. Our results suggest that water trapped at the lunar poles may be more widely distributed and accessible as a resource for future missions than previously thought.

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“…The Diviner Lunar Radiometer Experiment (Diviner), currently orbiting that Moon onboard LRO, is a nine‐channel visible and infrared instrument measuring the spectral brightness temperature at seven middle‐ to far‐infrared wavelengths (Paige, Foote, et al, ). It has been systematically mapping the Moon since 5 July 2009 at solar and infrared wavelengths covering a full range of latitudes, longitudes, local times, and seasons (Williams et al, ; Williams et al, ). Thermal properties of the lunar regolith have been studied by several researchers using Diviner (Bandfield et al, , ; Hayne et al, ; Vasavada et al, ), but these studies did not use a comparison to microwave data.…”

Section: Introductionmentioning

confidence: 99%

New Constraints on Thermal and Dielectric Properties of Lunar Regolith from LRO Diviner and CE‐2 Microwave Radiometer

2020

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We derive a new constraint on the thermal and dielectric properties of the lunar regolith layer by reconciling data from the Lunar Reconnaissance Orbiter (LRO) Diviner infrared radiometer and Chang'E-2 (CE-2) microwave radiometer (MRM). The bolometric Bond albedo of the lunar surface, which characterizes the ability of the lunar surface to reflect visible radiation, is a function of incidence angle. We determined the Bond albedo by using the Lunar Orbiter Laser Altimeter 1,064-nm normal albedo and the surface temperature at noon as a function of latitude. The results suggest a modification to existing regolith thermal conductivity models based on a fit to the diurnal variation of Diviner data. Based on the thermal model, a 1-D radiative transfer and dielectric properties model is developed to fit MRM data for the global Moon. With a new dielectric loss tangent equation for highland regolith applied, our model matches MRM data well at 19.35 and 37 GHz, which are generally accepted to be well calibrated. A global map of loss tangent of the Moon at these frequencies is also obtained by fitting the diurnal amplitude of microwave brightness temperature (T B ) of each location on the Moon. We find that the loss tangent of highlands regolith has a slight frequency dependence and is larger than previous studies. We also identify a large discrepancy between our theoretical model and T B obtained by CE-2 MRM at low frequencies, which is attributed to issues caused by contamination on calibration horn. Plain Language SummaryWe derive the physical properties of the dusty layer on the surface of the Moon by using the data from Lunar Reconnaissance Orbiter Diviner infrared radiometer, Lunar Orbiter Laser Altimeter, and Chang'E-2 microwave radiometer. Our results show that visible radiation reflected by the Moon surface is a function of incidence angle. The dusty layer is much less transparent at microwave band as we expected before. The dielectric properties of the layer vary a lot from bright highlands to dark Maria, which can be used to distinguish different compositions. We also recognize some calibration errors within the microwave radiometer data set.

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Seasonal Polar Temperatures on the Moon

Cited by 113 publications

References 86 publications

Stratigraphy of Ice and Ejecta Deposits at the Lunar Poles

Stratigraphy of Ice and Ejecta Deposits at the Lunar Poles

Micro cold traps on the Moon

New Constraints on Thermal and Dielectric Properties of Lunar Regolith from LRO Diviner and CE‐2 Microwave Radiometer

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