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Oded Aharonson


Associate Professor of
Planetary Science

B.S. 1994, Cornell University

M.Eng. 1995, Cornell University

Ph.D. 2002, Massachusetts Institute of Technology

Mars Surface: Simulations& Experiments

 

Mars Surface Simulations and Experiments

The Cryobot Instrument


Layered deposits in both residual polar caps on Mars suggest that a record of past climate exists there, analogous to climate histories derived from terrestrial ice cores.  The visible expression arises from alternation between relatively dust-rich and dust-poor layers, while the invisible variation of isotopic ratios therein record conditions during past climates.

Cryobot team testing a prototype instrument designed to core, sample, and analyze the Mars polar cap ice. The tests were conducted at the Athabasca Glacier of the Columbia Ice Field, Alberta, Canada. The Cryobot probe is seen suspended within the borehole. From left to right: Donna, Oded Aharonson (Caltech), Hermann Engelhardt (Caltech), Greg Cardell (JPL), Scott Anderson (HIGP), Frank Carsey (JPL), and Mike Hecht (JPL).

 

The Ice and Mars and Ice Simulation Laboratory

The regolith of Mars represents a significant reservoir of water in the form of ice, adsorbed water, and surface frosts and mantles.  The subsurface can couple strongly with atmospheric water vapor and the exchange between the two is an important process on timescales from diurnal to hundreds of thousands of years.  Exchange rates for the gain and loss of ice depend on the thermal characteristics of the regolith and its geometric structure.  The latter of these is characterized by the diffusion coefficient; a parameter which is difficult to fully characterize in idealized models, and is most often determined empirically for terrestrial soils.

 

The IceLab at Caltech consists of two walk-in freezers (-12 and -40 Celsius) which are used to grow and preserve custom ices with particular characteristics, serve as temperature control for Mars-environment chambers used in diffusion experiments, and store Arctic and Antarctic ice cores for future analysis.  Two anterooms are used for sample preparation and instrument construction.  One room also houses the recirculating chiller used in experiments where initially dry regolith is filled with ice via vapor diffusion.

      
Ice Lab Anteroom outside the walk-in freezers where computers, dataloggers, and instrument and sample preparation stations are kept.

   Within the -20 Celsius freezer, one of two Mars environment chambers bristles with data, power, and fluid feedthroughs.  The internal environment is maintained at 6 mbar pressure and very low relative humidity.  This mimics the Mars surface conditions at a hypothetical location where buried ice is unstable with respect the the vapor content in the atmosphere.  Much of Mars' present-day subsurface ice is at or near its equilibrium depth and does not migrate.
 

 

Within the chamber, two samples (here, two salt-encrusted discs of fine sand) overlie pure ice and retard its loss through their effect on the diffusion of vapor.  Each sample is monitored for mass (to deduce flux), ice temperature, and both air temperature and relative humidity at their upper surfaces.

 

 

 

The Mars Odyssey spacecraft has observed high concentrations of hydrogen (interpreted as subsurface ice) in the high-latitude regions.  Though the data are difficult to interprete, the ice concentration appears in some regions to be higher than the effective available pore space.  This has led investigators to invoke climate epochs different from present-day Mars to deposit ice which is subsequently buried.  In the IceLab, we investigate the possibility that atmospherically derived water vapor can deposit ice via diffusion into a cold soil and may in fact be able to fill all available pore space without the need for liquid phases or substantially different climates.

A computer-actuated series of mass-flow controllers flows carbon dioxide gas through a humidifying bubbler (glass sphere at bottom) and into the chamber which is continuously evacuated to maintain pressure.  A methanol recirculating chiller (behind the table) cools a plate within the chamber to -90 Celsius.  This coupled with a heating lamp in a negative feedback loop creates a stable temperature gradient; the driving force behind the diffusion both in the experiment and on Mars.

 

The image at below shows epitaxially grown ice on the surface of a coarse sand simulant at the conclusion of an ice-filling experiment.  The custom-built temperature probe for monitoring temperature as a function of depth in-situ is visible at the top.  On the left, the push-pop style extractor used to accurately shave layers of the ice-filled samples for gravimetric water content analysis.

 

 More information about this and other research is available in the form of published manuscripts here.