Potentially habitable flow-like features from Martian dry ice geyser dune spots: Difference between revisions
Potentially habitable flow-like features from Martian dry ice geyser dune spots (edit)
Revision as of 15:52, 29 September 2018
, 5 years agono edit summary
No edit summary |
No edit summary |
||
Line 9:
This would happen later in the spring and through to the summer. The dark streaks from the geysers begin to extend further down the slopes, sometimes at a rate of meters per day. There are streaks in both hemispheres but the details of how they form differ.
In the Southern hemisphere, they form in the debris of the geysers, and both of the current models for this part of the process involve liquid water<ref name="MartínezRenno2013DarkDuneSpots"/>. In one of these modelsfresh water that forms as subsurface meltwater, at 0°C below snow-ice packs. These are optically thin in visible light but opaque to thermal infrared, so trapping heat in a solid state greenhouse effect familiar in similar situations in Antarctica. Insulated from the surface temperatures and from sublimation in the low pressure of the atmosphsere, the heat is retained from one day to the next gradually building up to thin layers of liquid water up to several centimeters deep, perhaps 10-20 cms below the surface.<ref name="MartínezRenno2013SubsurfaceMeltWater>{{cite journal|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3/fulltext.html|last1=Martínez|first1=G. M.|last2=Renno|first2=N. O.|title=Water and Brines on Mars: Current Evidence and Implications for MSL section 2.2.2 Subsurface Melt Water|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3#Sec6|journal=Space Science Reviews|volume=175|issue=1-4|year=2013|pages=29–51|issn=0038-6308|doi=10.1007/s11214-012-9956-3}}</ref>. The other model involves thin layers of ULI water (undercooled liquid water)<ref name="MartínezRenno2013ULIWater>{{cite journal|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3/fulltext.html|last1=Martínez|first1=G. M.|last2=Renno|first2=N. O.|title=Water and Brines on Mars: Current Evidence and Implications for MSL section 2.2.1 Undercooled Liquid Interfacial Water|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3#Sec5|journal=Space Science Reviews|volume=175|issue=1-4|year=2013|pages=29–51|issn=0038-6308|doi=10.1007/s11214-012-9956-3}}</ref> which form on the surface of solar heated grains, then flows downwards, supplying several litres of water per day to the features. In both cases they then pick out salts which let them remain liquid in the cold near surface conditions as they flow down the slopes.
The northern hemisphere flow like features begin as wind-blown features on steep slopes. They start to extend later in the year, similarly to the southern hemisphere features. However, if they involve brines, the temperatures are far lower, with surface temperatures around -90 °C, though in the models that involve water, the brines themselves would be at warmer temperatures than the surrounding dry ice. Also, though most of the models for the northern hemisphere features involve water, they can also be explained with dry ice and cascading dust. <ref name="MartínezRenno2013DarkDuneSpots"/>
| |||