Cold Spots

Cold Spots
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We observe a longitudinal heterogeneity in the cold spot distribution that reflects the Moon's synchronous rotation with a higher density of cold spots at the apex of motion. This could result from a shorter retention time for larger cold spots on the leading hemisphere due to the greater number of smaller, superposed impacts. Impact craters on the Moon modify the surfaces around them, resulting in patches of colder nighttime surface temperatures. Using the cold spots as markers to identify the most recent impacts that have occurred on the Moon, we measured the diameters of all the craters with cold spots.

Comparing the population of these craters with the expected impact rate, we estimate that the cold spots fade over a few hundred thousand years. The cold spots are also concentrated on the western hemisphere due to the Moon's synchronous rotation where the western half of the Moon always faces toward the direction of motion of the Moon orbiting the Earth. This suggests that a relatively slow population of objects impacted the Moon in the last few hundred thousand years.

The largest cold spots, however, are concentrated on the trailing hemisphere.

A new class of small, fresh impact craters has been recently identified on the Moon through the systematic mapping of lunar surface temperatures Bandfield et al. Cold spots appear to be common to all recent impacts and degrade relatively rapidly in the lunar space environment.

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Therefore, cold spots provide a means of uniquely identifying the most recent impact craters on the Moon, and thus yield information on the recent production of lunar impact craters. Cold spots were identified and cataloged by Bandfield et al. We surveyed this catalog containing 2, cold spot locations for source craters.

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A total of 2, craters associated with cold spots were identified including new cold spots that were not in the Bandfield et al. Approximately 6. Crater diameter estimates in these locations were based on WAC images or constrained based on the areal extent of the bright, immature regolith.

Lunar Cold Spots and Crater Production on the Moon

Additionally, five cold spots, representing 0. These craters were too small to be reliably identified in WAC images and were approximated indirectly from the size of their cold spot assuming their cold spot extended 20 crater radii from the crater. The results are insensitive to these craters as they are few in number and small in size. Since the initial survey of cold spots published by Bandfield et al. Modeling by Vasavada et al. Mapping of variations in the modeled H parameter value by Hayne et al.

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Cold spot may refer to: Cold spot (paranormal), an area of low temperature that allegedly indicates the presence of a ghost; CMB cold spot, a vast area of space . The CMB Cold Spot or WMAP Cold Spot is a region of the sky seen in microwaves that has been found to be unusually large and cold relative to the expected.

The model included a slope correction to account for the influence of topography on temperatures, and as a result, the H parameter mapping reveals the cold spots in greater detail than the regolith temperatures. The formation ages of the large craters were constrained using crater counts of the smaller crater populations superposed on their continuous ejecta. Counts were conducted using Arcmap with the Cratertools plugin Kneissel et al. Because of the relatively young age of the ejecta, only craters with diameters generally no larger than a few tens of meters have had time to accumulate.

Williams et al. There is no indication that any of the cold spots result from secondary impacts.

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The density of cold spots that have been identified diminishes with increasing latitude. The detection of cold spots becomes less reliable at higher latitudes due to the increasing topographic influence on surface temperatures, especially in the highlands. We therefore attribute the observed decline in cold spot density with latitude to a bias in observation. This suggests that the greater topographic variability of the highlands makes detection of smaller cold spots more difficult at higher latitudes relative to the maria and further suggest that the downturn in the CSFD is a result of incomplete cold spot detection at smaller sizes.

Additional heterogeneities are observed in the distribution of cold spots. These longitudes correspond to the centers of the leading and trailing hemispheres, respectively apex and antapex of motion for the synchronously rotating Moon. Cold spots with more subtle temperature contrasts are more apparent in the H parameter map Powell et al. This revealed an additional five cold spots that are not identifiable in nighttime regolith temperatures. The temperature anomalies of these craters are small, all with a temperature contrast of less than 2. South Ray crater does not have a definitive cold spot associated with it, providing evidence that cold spots do not survive beyond this age and are relatively ephemeral features on the lunar surface.

Applying the idealized crater retention age to the cold spot source crater distribution provides an estimate of the typical retention time of the cold spots detectible in the regolith nighttime temperature data. Deviations between the measured distribution and the model distributions could indicate variations in retention times for differing cold spot sizes. Additionally, the shallower CSFD slope observed at smaller diameters may result from the incomplete identification of cold spots at smaller sizes as the ability to discern cold spots from slope effects and other temperature heterogeneities becomes more difficult as noted above, or there may be additional factors in cold spot formation at smaller impact energies that influence the expression of cold spots and the magnitude of the associated thermal anomalies i.

These did not generate identifiable cold spots. As additional postimpact data are acquired, further analyses of new cold spots may enable a better understanding of the temporal evolution of the smallest cold spots. Morota et al.

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Such slow objects would therefore need to be continuously resupplied. The lunar meteorites provide evidence for the viability of lunar impact ejecta as such a source. Williams, Bandfield, et al. To test the significance of the distribution of this population of craters, we apply the Rayleigh z test to the distribution of longitudes i. The critical Z , typically defined by a p value of 0. As we exceed this value, we can conclude that the null hypothesis of no preferred longitude can be rejected with high confidence. This would be a conservative estimate as it assumes equal probability of craters forming at any longitude; however, the leading hemisphere is favored due to the synchronous rotation.

Our survey of the H parameter map revealed five additional large cold spots, four of which occur in the leading hemisphere Williams, Bandfield, et al. The cold spots apparent only in the H parameter map are all older than 0.

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The other cold spots are generally younger than 0. However, as seen with the smaller craters, the large cold spots should form preferentially in the leading hemisphere, which is not observed. Alternatively, the destruction rate of the large cold spots could be enhanced on the leading hemisphere.

The formation and destruction of cold spots is not well understood, making this scenario difficult to assess. Smaller impacts, down to the limit of Diviner spatial resolution, also appear to create cold spots, and it is not clear how their destruction results from the superposition of additional impacts. Further, Powell et al. Since cold spots are more difficult to detect at higher latitudes, we are unable to explore any latitude dependence on cold spots with any confidence.

The precise provenance on the lunar surface of the meteorites is unknown and they likely represent a sampling from both the nearside and farside. Because of the diversity of compositions and exposure ages, the meteorites likely derive from many craters, and the young ejection ages constrain the source craters to less than a few kilometers in diameter as there are not enough larger craters young enough to account for the diversity of meteorites Basilevsky et al.

Therefore, many of the known lunar meteorites likely originated from craters with cold spots.

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Hydrocode simulations find impact events forming craters with diameters as small 1. This is supported by generally shallow, less than a few meters, meteorite source depths and a large fraction of the meteorites being composed of regolith breccias formed within the regolith layer Basilevsky et al. Costello et al. Secondary craters, craters formed by fragments ejected by the original primary impact event, have been suggested to form a substantial fraction of the total population of craters e. This collectively suggests that secondary cratering is the predominant mechanism of mixing of the top meter of the lunar regolith.

Five large cold spots, not identifiable in the regolith temperatures, but apparent in the H parameter map, are all older than 0. Funders are aware of the need for support for community organisations within these areas and would like to respond to this need while at the same time ensuring their funding continues to fit within their own strategic priorities.

Following on from our Hot and Cold Spots event in March, we hosted a roundtable meeting to consider one possible response. This roundtable explored a potential pilot Cold Spot Collaboration CSC delivered with our member, The Fore , which could provide a low-cost, effective way for multiple funders to work together to get grants and skills into community organisations in funding cold spots.

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