3 results
Dehydrated thin film media to rapidly estimate bioburden for planetary protection flight implementation
- Zachary S. Dean, Kristina Stott, Wayne Schubert, Emily P. Seto, Sailaja Chandrapati
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- Journal:
- International Journal of Astrobiology / Volume 22 / Issue 5 / October 2023
- Published online by Cambridge University Press:
- 03 July 2023, pp. 568-582
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- Article
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Planetary Protection (PP) is the practice of safeguarding solar system bodies from terrestrial biological contamination and screening the Earth against potentially harmful extraterrestrial biological contamination. On Earth, cleanrooms and spacecraft surfaces are assayed using swabs and wipes that are then heat shocked for 15 min at 80°C to select for spores. The samples are further processed using the pour-plate method and Petri plates (TSA plates), with trypticase soy agar (TSA) serving as the growth medium. This sampling and processing procedure, called the NASA Standard Assay (NSA), is used by PP engineers around the world. Recent years have seen an increase in the incorporation of state-of-the-art technology, such as membrane filtration, into the NSA, with a push for implementing environmentally friendly technology into day-to-day activities. Dehydrated thin film media, such as Petrifilm Rapid Aerobic Count (RAC) plates, suit these goals as an alternative method to TSA plates. RAC plates show bacterial growth (and distinguish colonies from foreign particles such as bubbles) faster than TSA plates due to the incorporation of chromogenic colour indicators in the media. RAC plates also possess a much smaller environmental footprint than TSA plates, and are designed to evaluate even some of the challenging-to-detect environmental organisms, including spreaders that fill over 25% of the plate area in only a few hours. With these benefits in mind the PP Group at the NASA Jet Propulsion Laboratory took on the task of comparing RAC plates directly to TSA plates within the context of the NSA. Not only were the RAC plates able to detect surface environmental samples and in vitro spiked samples equivalent to NSA-processed TSA plates, but spreader organisms were countable on RAC plates at culture densities 10- to 100-fold greater than on TSA plates. In addition, RAC plates showed a robust, linear detection capability when challenged with membrane filter incorporation and organisms were easily acquired from RAC plates for archiving or post-processing experiments including MALDI-TOF bacterial identification. With their ease of use, small footprint, and both rapid and accurate bioburden measurements, RAC plates have the potential to overcome limitations posed by current PP culturing protocols.
Biological safety in the context of backward planetary protection and Mars Sample Return: conclusions from the Sterilization Working Group
- Emily Craven, Martell Winters, Alvin L. Smith, Erin Lalime, Rocco Mancinelli, Brian Shirey, Wayne Schubert, Andrew Schuerger, Mariko Burgin, Emily P. Seto, Morgan Hendry, Amruta Mehta, J. Nick Benardini, Gary Ruvkun
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- Journal:
- International Journal of Astrobiology / Volume 20 / Issue 1 / February 2021
- Published online by Cambridge University Press:
- 13 January 2021, pp. 1-28
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The National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) are studying how samples might be brought back to Earth from Mars safely. Backward planetary protection is key in this complex endeavour, as it is required to prevent potential adverse effects from returning materials to Earth's biosphere. As the question of whether or not life exists on Mars today or whether it ever did in the past is still unanswered, the effort to return samples from Mars is expected to be categorized as a ‘Restricted Earth Return’ mission, for which NASA policy requires the containment of any unsterilized material returned to Earth. NASA is investigating several solutions to contain Mars samples and sterilize any uncontained Martian particles. This effort has significant implications for both NASA's scientific mission, and the Earth's environment; and so special care and vigilance are needed in planning and execution in order to assure acceptance of safety to Earth's biosphere. To generate a technically acceptable sterilization process across a wide array of scientific and other stakeholders, on 30–31 January 2019, 10–11 June 2019 and 19–20 February 2020, NASA informally convened a Sterilization Working Group (SWG) composed of experts from industry, academia and government to assess methods for sterilization and inactivation, to identify future work needed to verify these methods against biological challenges, and to determine their feasibility for implementation on robotic spacecraft in deep space. The goals of the SWG were:
(1) Understand what it means to sterilize and/or inactivate Martian materials and how that understanding can be applied to the Mars Sample Return (MSR) mission.
(2) Assess methods for sterilization and inactivation, and identify future work needed to verify these methods.
(3) Provide an effective plan for communicating with other agencies and the public.
This paper provides a summary of the discussions and conclusions of the SWG over these three workshops. It reflects a consensus position based on qualitative discussion of how agencies might approach the problem of sterilization of Mars material. The SWG reached a consensus that sterilization options can be considered on the basis of biology as we know it, and that sterilization modalities that are effective on terrestrial materials and organisms should be part of the MSR planetary protection strategy. Conclusions pointed to several industry standards for sterilization to include heat, chemical, UV radiation and low-heat plasma. Technical trade-offs for each sterilization modality were discussed while simultaneously considering the engineering challenges and limitations for spaceflight. Future work includes more in-depth discussions on technical trade-offs of sterilization modalities, identifying and testing Earth analogue challenge organisms and proteinaceous molecules against chosen modalities, and executing collaborative agreements between NASA and external working group partners to help close data gaps, and to establish strong, scientifically grounded sterilization and inactivation standards for MSR.
4 - Dreams of a stratocumulus sleeper
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- By David A. Randall, Wayne H. Schubert, Department of Atmospheric Science Colorado State University Fort Collins, USA
- Edited by Evgeni Fedorovich, University of Oklahoma, Richard Rotunno, National Center for Atmospheric Research, Boulder, Colorado, Bjorn Stevens, University of California, Los Angeles
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- Book:
- Atmospheric Turbulence and Mesoscale Meteorology
- Published online:
- 04 August 2010
- Print publication:
- 21 October 2004, pp 71-94
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Summary
Foggy recollections
When we were students at UCLA in the early 1970s, the California stratus deck frequently floated over our heads. There on the beautiful campus under the clouds, we studied Doug Lilly's (1968; hereafter L68) paper about cloud-topped mixed layers under strong inversions. The paper was recommended to us by our mentor, Professor Akio Arakawa, who recognized the relevance of Lilly's insights to climate dynamics. Whereas spectacular supercells leap from the boundary layer to the tropopause in a single bound, L68 analyzed “wimpy” stratus and stratocumulus clouds that are only a few hundred meters thick and barely manage to precipitate. L68 was a “sleeper.” It received little attention at first, but over the decades since then it has picked up many citations (417 as of June 2003), and it forms the groundwork for several currently thriving lines of research. L68's emergence as a classic research paper stems in part from the climatic importance of the cloud regimes it dealt with, but more importantly from the amazing prescience of Lilly's ideas and the clarity with which he expressed them.
Several ingredients, acquired over a number of years, came together in a two-week period during the summer of 1965 to produce the remarkable L68 paper. The first was personal experience and interest. Lilly's high-school physics teacher, at Sequoia Union High School in Redwood City, California, ran a weather club, which Lilly joined with enthusiasm. After becoming the club's student leader, Lilly began to evolve, by his own description, into a
weather junkie, keeping daily weather records, making forecasts, and testing their accuracy. When I learned to drive, I did something akin to tornado chasing, within the limits of California weather.[…]