2010 Annual Science Report
NASA Jet Propulsion Laboratory - Icy Worlds Reporting | SEP 2009 – AUG 2010
Our goal in the Astrobiology of the Icy Worlds Investigation is to advance our understanding of the role of ice in the broad context of astrobiology through a combined laboratory, numerical, analytical, and field investigations. Icy Worlds team will pursue this goal through four major investigations namely, the habitability, survivability, and detectability of life of icy worlds coupled with “Path to Flight” Technology demonstrations.
A search for life linked to the search for water should naturally “follow the ice”. Can life emerge and thrive in a cold, lightless world beneath hundreds of kilometers of ice? And if so, do the icy shells hold clues to life in the subsurface? These questions are the primary motivation of our science investigations which are as follows:
- Habitability of Icy Worlds investigates the habitability of liquid water environments in icy worlds, with a focus on what processes may give rise to life, what processes may sustain life, and what processes may deliver that life to the surface.
- Survivability of Icy Worlds investigates the survivability of biological compounds under simulated icy world surface conditions, and compare the degradation products to abiotically synthesized compounds resulting from the radiation chemistry on icy worlds.
- Detectability of Icy Worlds investigates the detectability of life and biological materials on the surface of icy worlds, with a focus on spectroscopic techniques, and on spectral bands that are not in some way connected to photosynthesis.
- Our technology investigation, a Path to Flight for astrobiology, utilizes instrumentation built with non-NAI funding to carry out the science investigations discussed above. The search for life requires instruments and techniques that can detect biosignatures from orbit and in-situ under harsh conditions. Advancing this capacity is the focus of our Technology Investigation.
The following sections highlight some of our accomplishments for the above investigations.
As far as the Habitability of Icy Worlds Progress is concerned, we have reproduced the kind of submarine exhalations predicted for wet/icy, rocky worlds and found at the Lost City hydrothermal site but with the addition of bisulfide on reaction with iron sulfide. We have shown that such fluids produce transition metal-bearing chimneys and compartments exhibiting regular external ornamentations to be expected in far-from-equilibrium conditions and indicative of physicochemical self-organization.
We demonstrated detectability of methyl mercaptan and ethane using the Carbon Isotope Laser Spectrometer (CILS) and by extension, by the Curiosity Mars rover using the Tunable Laser Spectrometer (TLS) instrument on the Sample Acquisition Mission (SAM) package. (Vance et al., 2010)
Dr. Goodman and Mr. Lenferink installed a supercomputer system at Wheaton College and implemented a three-dimensional plume dynamics model, comparing the size, velocity, and temperature of turbulent plumes with theoretical predictions over a wide range of parameter space. Goodman also developed a single-column convection model, which will allow exploration the overall vertical structure of Europa’s ocean on a global scale. Drs. Goodman and Vance converted equation-of-state information garnered from FREZCHEM and laboratory experiments into a form useful for physical ocean modeling, and have successfully incorporated MgSO4 brine density data into the single-column model.
Reports from previous experiments on the stability of methane clathrates were published this year. These clathrates were found to be increasingly unstable with the addition of ammonia to aqueous solutions. A model for storage and cryovolcanic release of methane on Titan is discussed in this publication (Choukroun et al., 2010), which had just been accepted at the time of last year’s progress report.
During year 2, we have conducted numerical simulations in 3D spherical coordinates and 3D Cartesian coordinates (thin shell) which allows us to run simulations on a (256×256×256) grid. We were interested in the scaling of the vertical velocity for realistic values of the viscosity. During year 2, we have run 10 simulations with two different values of the viscosity at melting temperature (1013 and 1014 Pa.s) and 5 different values of the activation energy. The velocities will allow us to address the question of how much time it takes for the particles embeded into the freezing ice at the base of the ice crust to reach the base of the conductive lid. A second aspect of our numerical simulations is to investigate the horizontal stress applied by the convection process at the base of the conductive lid and to compare it with the yield stress necessary to break the ice lid. We have calculated these values for each of the 10 numerical simulations and data are being processed.
We also reported the first discovery of the deepest high-temperature hydrothermal activity which may berelevant to prebiotic chemistry and the origins of life (German et al, 2010). The evidence for previously unknown, diverse, and very deep hydrothermal vents along the ~110 km long, ultraslow spreading Mid-Cayman Rise (MCR) has recently been reported (ref). Our data indicate that the MCR hosts at least three discrete hydrothermal sites, each representing a different type of water-rock interaction, including both mafic and ultramafic systems and, at ~5,000 m, the deepest known hydrothermal vent.
As part of our Survivability of icy Worlds investigation, Co-Investigator Murthy Gudipati and his group continued studying the photodegradation of PAH molecules in ices using UV radiation and electrons. they found that electrons high energy electrons (up to 2 keV) can damage organic molecules far deeper in ice that what models predict. For example, organic probe molecules (Pyrene in this case) are completely destroyed after electron irradiation, no significant UV absorption due to any new product could be indicating that the PAHs are not only ionized in the first step, but then also degraded through consecutive radiation induced chemistry.
Investigators Paul Johnson, Robert Hodyss and Isik Kanik have continued studying the photolysis of organic molecules in icy matrices relevant to solar system bodies.
An extensive set of data have been collected on pholoysis of glycine, phenylalanine, oleic acid and SLPC. The data are now being prepared for publication.
Photochemical studies of thin cryogenic ice films composed of N2 and CH4 in ratios analogous to those on the surfaces of Neptune’s largest satellite, Triton, and on Pluto have been completed. Experiments were performed using a hydrogen discharge lamp, which provides an intense source of ultraviolet light in order to elucidate the solar induced photochemistry of these icy bodies. Initial characterization via infrared spectroscopy showed that C2H6, C2H4 and C2H2 are formed by the dissociation of CH4 into H, CH2 and CH3 and the subsequent reaction of these radicals within the ice (see figure 2.3). Acetylene, C2H2,, is further photodissociated into C2. Other radical species, such as C2, C2-, CN, NCN and CNN are observed in the visible and UV regions of the spectrum. These species imply a rich chemistry based on reactions of atomic carbon with the N2 matrix. Ultimately, this work suggests that C2-, CN, and CNN may be found in significant quantities on the surfaces of Triton and Pluto and that new observations of these objects in the appropriate wavelength regions are warranted.
In addition, a study of UV stimulated fluorescence of benzene, toluene and the isomers of xylene has been conducted. These results have implications for exploiting such phenomena for in situ detection of organics is solar system ices. This work is summarized in a manuscript that will be submitted to Astrobiology this fall.
In the upcoming year, our team will continue to explore the detailed, wavelength dependant photolysis of amino acids and lipids.
Co-I Paul Cooper of George Mason university has developed methodology to deposit hydroxy radicals into icy planetary surfaces and used these OH radicals to understand the formation of methanol in solar system ices. Recent modeling by Tim Cassidy (JPL) has shown that this OH abundance is comparable to the tenuous atmospheres of the icy Saturnian satellites.
The lack of H2O2 at 80 K is likely a result of chemical destruction with depositing OH to form O2. We observe some O2 that is trapped in the ice that we have yet to quantify but there will also be some (perhaps the majority?) that is lost to the vacuum. In the case of a planetary surface this would be a source of O2 in an atmosphere. This would be applicable to both icy satellites and icy ring systems throughout the solar system.
In collaboration with colleagues at The University of Western Australia, we have shown in matrix-isolation experiments that methanol formation can occur in H2O and CH4 mixtures by the unusual O atom insertion reaction with CH4. This has been shown by using various isotopologues of water and methane. Previous reports of irradiated ices have assumed a reaction between the methyl and OH radicals. In light of these results we are preparing to begin electron-irradiation experiments to conclusively determine the reaction mechanism in an irradiated ice sample.
Co-Investigators Ponce and Hand continued to study the behavior of microbial spores under energetic conditions, We expect samples to be ready for irradiation in the next couple of months.
In the area of Detection of Life in the Field, the Astrobiology of Icy Worlds team conducted a roughly 1-month field campaign in the Barrow, Alaska region during April, 2010. Much of the successful campaign was organized and carried out by postdoctoral researchers and graduate students working with the Co-investigators. Along with our fieldwork we visited a school in remote Atqasuk, Alaska and gave a heavily attended public talk in Barrow.
Limnological analyses were largely conducted by our Montana State Univeristy team. Water and ice samples were collected in April 2010 and the characterization of ice nutrients and bacteria are currently under way at the sub-zero ice core facility at MSU.
The ratio of emission at 470 nm to emission at 520 nm, when excited at 370 nm can be used as a fluorescence index (FI) that reveals the source of fluorescing organic matter in the sample. FIs in our samples were all near 1.5 indicating that the DOC is derived equally from both terrestrial and microbial sources.
Bacterial activity was measured as both leucine incorporation and methane oxidation. Optimum concentrations of leucine (20 nM) and length of incubation (2 to 6 hrs) for measuring bacterial population (BP) have been determined and preliminary temperature incubations indicate large differences in response by bacterial communities in different lakes. All lakes showed a general increase of BP with increasing temperatures.
Much of the microbial activity and DNA/RNA analyses for both Alaska and the Sierra snowpack is being conducted by the team at the Desert Research Institute in Reno, NV. There were unique phylotypes of for both bacteria and eukarya that were observed. In addition we recently created a ribosomal RNA gene clone library for bacteria and eukarya from one sample each to get a more detailed look into the identies of life in the summer-time snow field. Also, chlorophyll a concentration (0.05-0.6 mg mL-1) correlated with numbers of algal cells throughout the vertical profile, although no correlation was found between the two variables along the horizontal transect. Likewise, the concentration of inorganic sources of nitrogen and dissolved organic carbon (DOC) varied along the horizontal transect. However, these concentrations showed a tendency to increase with depth in the vertical profile, particularly in those layers were the presence of microorganisms was shown to decline, suggesting a lack of consumption.
The second field program concerning life detection is taking place in the Arctic tundra lakes of the North Slope of Alaska. A number of these lakes release ebullient methane. It should be pointed out that methane has been detected in the atmosphere of icy worlds such as Saturn’s moon Titan, and although not known if of biologic origin, it could be a feasible signature of life based on chemical rather than photosynthetic energy. Methane can be originated from three different sources and can be discriminated by age of production from current day – biogenic origins, to ancient in which the methane can be associated with coal beds or is associated with methane hydrates. Our team is working to characterize different lakes of the North slope in terms of their methane source using stable and 14-C isotope signatures. Lakes with biogenic methane harbor Archaea – the microorganisms that perform methanogenesis.
Back in the laboratory at the Desert Research Institute (DRI), gas samples collected to determine in situ rates of methane production were determined by gas chromatography (GC). Results obtained indicated the presence of methane in lakes Ikroavik, Qalluuraq, and Sukok, with the highest concentrations detected in lakes Qalluuraq and Sukok, though no significant production was observed.
Spectroscopic characterization of the methane bubbles in the ice above the lakes and of the non-ice components within the ice has been conducted largely by our team at JPL. Near-infrared spectra were collected at several of the above mentioned lakes during the April campaign. Spectra were collected both on the surface of the lake ice and in depth profile down the ice cores drilled in the ice. Spectra from the surface revealed differences between the bubble-rich and clear ice.
Geochemical analyses for the Alaska fieldwork is largely being conducted by our team at the University of California, Riverside. Sediment core samples collected during fieldwork in April 2010 have all been freeze-dried and gently homogenized, completing the first step of the protocol developed for this project. Sedimentological descriptions of the cores have been compiled for communal use. Initial lipid biomarker results from the Sukok Lake seep (S1) sediment core are determined.
As a part of Path to Flight investigation, we completed our first publication on the laboratory based, high pressure, low temperature Hydrothermal Vent Simulator (HVS). (Mielke et al, 2010). Gas produced by the JPL HVS was analyzed using a slightly modified version of TLS (Tunable Laser Spectrometer) that is a part of the SAM GC/MS instrument on the upcoming Mars rover, MSL. The modification made is possible to detect dimethyl sulfoxide (DMS) and methyl mercaptan (CH3SH). Liquid and dissolved gas analysis of the vent fluid is still under development.
In addition to the JPL Hydrothermal Vent Simulator, mineralogical analysis was performed on lab-grown chimneys. One iron-sulfide mineral of particular interest is the formation of makinawite which may be used to catalyze organic reactions. However, another iron-sulfide, pyrite, inhibits this catalysis. To determine the iron-sulfide being created, a sample of the iron-sulfide based chimney was placed into a nitrogen purged quartz cylinder to prevent alteration by oxidation. Using the new JPL multi-wavelength Raman imaging spectrometer, we were able detect nano-crystalline makinawite.
During the last ANtarctic Search for METeorites (ANSMET), our collaborator, Marc Fries (Planetary Science Institute), fielded a deep UV native fluorescence instrument to detect organics present either through human or natural contamination. The benefit of this instrument is its 1-3 meter standoff capability and a high affinity to detect organics. The instrument did perform, however the UV from the sun was much greater than previously anticipated. Aside from providing new accurate UV radiation information, this affected the dynamic range of the instrument. However, organics were detected and analysis is presently underway.
As a part of Investigation 4 activities, the Robotic Chemistry Analysis Laboratory (RCAL) has been field tested. It was mounted on the SRR-2K rover and all power and controls now come from the rover to give more reliable and precise control, coupled with appropriate changes to the operations software.
We reported on the use of a small light-weight hand-held field portable mass spectrometer (MS) for chemical analysis of organic material directly from solution or from the solid state with potential value in future planetary missions (Sokol et al., 2010). Detection and identification of small organic molecules, including some that might be prebiotics, was achieved using methods relevant to in situ and remote sensing applications. Tandem mass spectrometry (MS2) was successfully applied to confirm trace detection of target compounds in mixtures. Multiple stage (MSn) analysis, where n = 3–5, was employed for molecular structure confirmation and to demonstrate the high chemical specificity as well as the sensitivity of the instrumentation.