In the permanently shadowed craters, where radar observations have pointed to the presence of ice, the altimeter recorded dark patches of diminished laser reflectance. “We never see in these regions the large increase of return energy that you would see if it were so cold that ice were exposed on the surface,” Neumann said. One possibility is that the radar-bright deposits, widely believed to be ice, could be overlaid by a dark material, such as a hydrocarbon, that can tolerate somewhat higher temperatures.
That hypothesis was supported by David Paige of the University of California, Los Angeles. He and his colleagues calculated surface and subsurface temperatures for the locations where radar-bright features tend to form and inferred a probable composition of ice pockets blanketed by regolith darkened by organic compounds. Peak temperatures in the shadowed craters, which can often be too warm for exposed water ice, mesh well with conditions at which dark organic molecules would be stable. But just below the surface, temperatures in radar-bright craters tend to be colder, hovering near –170 degrees C. That is exactly the temperature at which water ice would be expected to remain stable, Paige said. MESSENGER's new look at the features long ago spotted by Earth-based radars, he added, demonstrate “fairly conclusively now that they are predominantly composed of thermally stable water ice.”
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5 Comments
Add CommentDo we have en estimate on the volume (area at minimum) of the largest ice block?
Reply | Report Abuse | Link to thisI have to wonder, if there are mini-environments where frozen water can persist that are adjacent to areas where the temperature is too high for for frozen water, might not there be some tiny temperate spaces within the boundary layers between the two extremes where liquid water might exist, at least part of the time?
Reply | Report Abuse | Link to thisAs far as I am aware,water boils at 100 C at sea level. As the air pressure decrease with altitude, so the boiling point gets lower. In space above the atmosphere, water presumably boils instantaneously. So, how do you get ice in space? Answer please
Reply | Report Abuse | Link to thisComets may be the only answer. No atmosphere to heat them up so if they survive the impact energy and do not see the sun, they could survive and survive as they are seen.
Reply | Report Abuse | Link to thisIf the sun touches them and they go over the boiling point which may be a lot lower with out an atmosphere it would turn to steam and be gone. But Comets seem feasible.
Jim, if there is no or very little atmosphere water boils away as steam. Saw that in experiments in college and HS in near vacuum environments. It is a two state system unless you have an atmosphere and the right temperature range. Even on Mars if water were to show itself after an impact event it has two choices to make very quickly freeze or steam.
Reply | Report Abuse | Link to thisTitan is a good example of what is involved in a triple state particle. Of course on Venus maybe lead has a triple state. Hmmm, I don't remember seeing atmospheric lead in the readings but maybe it is trace.