Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.c33b..06h&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #C33B-06
Physics
0473 Paleoclimatology And Paleoceanography (3344, 4900), 0724 Ice Cores (4932)
Scientific paper
We describe experiments using a low-power thermal drill capable of autonomously retrieving and analyzing meltwater samples from an ice sheet with a vertical resolution of a centimeter or less. The drill operates by passively creating a melt front at the nose, then pumping the melt water to an analytical instrument on the surface. This "open hole" strategy minimizes thermal contact between the drill and the ice, limiting the power consumption to little more than is necessary to melt the ice. Even in the cold martian ice sheet (<175K) a 7.5 cm diameter drill can descend at speeds of 25 cm per hr using only about 250W. In relatively warm terrestrial ice the technique is useful only to a few hundred meters, below which the hole would collapse. The drill has successfully been tested in Greenland to a depth of 50 m. In cold martian ice, given enough time, such a drill could penetrate two or more kilometers to the base of the northern ice sheet. For Mars, the primary objective of such a drill is to explore the climate record through visual inspection of layering and analysis of isotopic ratios in the meltwater. A secondary objective would be to seek biomarkers through detection of relevant chemical signatures such as methane or fluorescent molecules. To this end, studies were performed to determine the limits of vertical resolution imposed by tube flow of the meltwater from the drill to the surface. Mixing in the tube could dilute a localized biomarker to the point of undetectability, or could degrade the ability to associate such a signal with a specific historical climate marker. Chemical markers (salts, detected by conductivity changes) and fluorescent markers (including quantum dots) were introduced abruptly into the meltwater stream, and the effluent at the end of the tube was then analyzed to determine the persistence of the signature. Theoretically, the transfer function is strongly dependent on factors that are difficult to quantify such as turbulence and wall interactions. In the configuration studied, the detected signal was significantly more abrupt than might have been expected from a purely laminar tube flow model.
Aharonson Oded
Engelhardt Hermann
Fisher Andrew
Hecht Michael H.
Smith Marcie
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