Contamination Management of Sample Collection Devices for Life Detection on Icy World Plume Fly-through Missions
Abstract
Life detection missions to the Ocean Worlds Jupiter and Saturn, such as Europa and Enceladus, will collect ice samples by either landing on the surface, or flying through the moon plumes using sample collection devices. Ice particles plumes, ejected into space from the underlying ocean, have been mapped on Enceladus [1-2] and, most recently, detected on Europa [3].A key issue for highly sensitive life-detection instruments for sample analysis (e.g., capillary electrophoresis with laser-induced fluorescence, gas chromatography-mass spectrometry, and antibody microarray chips) is how to determine that a positive signal of life in a sample is intrinsic to the planetary body and not a result of exogenous contamination from Earth. Contamination management methods involve the use of blank control samples to calibrate the instrument against biomarker contamination just prior to receiving samples. However, in space or planetary surface environments, it is difficult or impossible to run blanks that fully sample the collection-and-handling devices, limiting the efficacy of this contamination management tool. In addition, the instrument detection sensitivity for target organics must be adequate for the lower limit of the anticipated concentration range of cellular and organic biomarkers in the target Ocean World, which can be very low, e.g., less than 80-120 cells/mL, in the range of the lowest values detected in the Antarctic subglacial Lake Vostok ice counterpart [4].In this context, NASA Ames Research Center (ARC) has been simulating plume fly-throughs of prototype collectors of ice particles as well as surface ice sampling. During these impact tests at ARC's Vertical Gun Range (AVGR), basic ancillary experiments involve measurement of microbial and biomarker survival, and simultaneous management/monitoring of contamination levels of the prototype collectors and the AVGR chamber using NASA-approved practices [5]. The objective was to evaluate cleaning and microbial reduction techniques. These involved an ultrasensitive adenosine 5_ triphosphate (ATP) luminometry assay (limit of detection: 0.2_10-15 moles (femtomoles, or fmol) for pre-screening of collector surfaces, which is below the threshold cleanliness limit of 2.3_10_11 mmol ATP/ 25 cm2 (0.9 fmol/cm2) [6], and bioburden monitoring. The ATP does not survive cellular death and is a proxy for recent biological activity being used for bioburden monitoring in spacecraft [5] and cross-contamination during field trials. Furthermore, we used protocols that enabled mitigation of false negatives (kinetic-inhibited) and false positives (by reaction enhancement) in salt-rich samples. During sampling of the target sea ice (< 2 to 0.3 fmol ATP/100 μL) and on collector surfaces (< 0.2 to < 0.9 fmol/cm2), contamination levels were negligible and did not affect scientific evaluation of biomarker survival upon impact in natural and synthetic seawater experiments (e.g., 5_103 fmol ATP/100 μL). These results are preliminary as test data are still being analyzed.References: [1] Krupp N. et al (2012) Icarus 433-447. [2] Porco et al., 2006. Science. 311:1393-1401. [3] Europa Lander Science Definition Team, 2017. [4] Christner et al. 2006. Limnology and Oceanography 51(6): 2485-2501 [5] NASA (2010) NASA-HDBK-6022. [6] Benardini &Venkateswaran (2016) AMB Expr. 6:113.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3665W