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Neveu M, Coker RF, Lorenz RD, MacKenzie SM, Lunine JI, Davila AF. Planetary Protection Assessment of Radioisotope Thermoelectric Generator (RTG)-Powered Landed Missions to Ocean Worlds: Application to Enceladus. ASTROBIOLOGY 2022; 22:1047-1060. [PMID: 35972349 DOI: 10.1089/ast.2020.2432] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Landed missions to icy worlds with a subsurface liquid water ocean must meet planetary protection requirements and ensure a sufficiently small likelihood of any microorganism-bearing part of the landed element reaching the ocean. A higher bound on this likelihood is set by the potential for radioisotope thermoelectric generator (RTG) power sources, the hottest possible landed element, to melt through the ice shell and reach the ocean. In this study, we quantify this potential as a function of three key parameters: surface temperature, ice shell thickness (i.e., heat flux through the shell), and thickness of a porous (insulating) snow or regolith cover. Although the model we describe can be applied to any ocean world, we present results in the context of a landed mission concept to the south polar terrain of Saturn's moon Enceladus. In this particular context, we discuss planetary protection considerations for landing site selection. The likelihood of forward microbial contamination of Enceladus' ocean by an RTG-powered landed mission can be made sufficiently low to not undermine compliance with the planetary protection policy.
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Affiliation(s)
- Marc Neveu
- Department of Astronomy, University of Maryland, College Park, Maryland, USA
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Robert F Coker
- Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
| | - Ralph D Lorenz
- Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
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Lauretta DS, Adam CD, Allen AJ, Ballouz RL, Barnouin OS, Becker KJ, Becker T, Bennett CA, Bierhaus EB, Bos BJ, Burns RD, Campins H, Cho Y, Christensen PR, Church ECA, Clark BE, Connolly HC, Daly MG, DellaGiustina DN, Drouet d’Aubigny CY, Emery JP, Enos HL, Freund Kasper S, Garvin JB, Getzandanner K, Golish DR, Hamilton VE, Hergenrother CW, Kaplan HH, Keller LP, Lessac-Chenen EJ, Liounis AJ, Ma H, McCarthy LK, Miller BD, Moreau MC, Morota T, Nelson DS, Nolau JO, Olds R, Pajola M, Pelgrift JY, Polit AT, Ravine MA, Reuter DC, Rizk B, Rozitis B, Ryan AJ, Sahr EM, Sakatani N, Seabrook JA, Selznick SH, Skeen MA, Simon AA, Sugita S, Walsh KJ, Westermann MM, Wolner CWV, Yumoto K. Spacecraft sample collection and subsurface excavation of asteroid (101955) Bennu. Science 2022; 377:285-291. [DOI: 10.1126/science.abm1018] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Carbonaceous asteroids, such as (101955) Bennu, preserve material from the early Solar System, including volatile compounds and organic molecules. We report spacecraft imaging and spectral data collected during and after retrieval of a sample from Bennu’s surface. The sampling event mobilized rocks and dust into a debris plume, excavating a 9-m-long elliptical crater. This exposed material that is darker, spectrally redder, and more abundant in fine particulates than the original surface. The bulk density of the displaced subsurface material was 500–700 kg per cubic meter, about half that of the whole asteroid. Particulates that landed on instrument optics spectrally resemble aqueously altered carbonaceous meteorites. The spacecraft stored 250 ± 101 g of material, which will be delivered to Earth in 2023.
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Affiliation(s)
- D. S. Lauretta
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | - A. J. Allen
- Physics Department, University of Central Florida, Orlando, FL, USA
| | - R.-L. Ballouz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - O. S. Barnouin
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - K. J. Becker
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - T. Becker
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - C. A. Bennett
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | - B. J. Bos
- Goddard Space Flight Center, Greenbelt, MD, USA
| | - R. D. Burns
- Goddard Space Flight Center, Greenbelt, MD, USA
| | - H. Campins
- Physics Department, University of Central Florida, Orlando, FL, USA
| | - Y. Cho
- Department of Earth and Planetary Environmental Science, University of Tokyo, Tokyo, Japan
| | - P. R. Christensen
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
| | | | - B. E. Clark
- Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA
| | - H. C. Connolly
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
- Department of Geology, Rowan University, Glassboro, NJ, USA
| | - M. G. Daly
- Department of Earth and Space Science and Engineering, York University, Toronto, ON, Canada
| | | | | | - J. P. Emery
- Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ, USA
| | - H. L. Enos
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | | | | | - D. R. Golish
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | | | | | | | | | | | - H. Ma
- Lockheed Martin Space, Littleton, CO, USA
| | | | | | | | - T. Morota
- Department of Earth and Planetary Environmental Science, University of Tokyo, Tokyo, Japan
| | | | - J. O. Nolau
- Physics Department, University of Central Florida, Orlando, FL, USA
| | - R. Olds
- Lockheed Martin Space, Littleton, CO, USA
| | - M. Pajola
- INAF (Italian National Institute for Astrophysics) – Astronomical Observatory of Padova, Padova, Italy
| | | | - A. T. Polit
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | | | - B. Rizk
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - B. Rozitis
- School of Physical Sciences, Open University, Milton Keynes, UK
| | - A. J. Ryan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | - N. Sakatani
- Department of Physics, Rikkyo University, Tokyo, Japan
| | - J. A. Seabrook
- Department of Earth and Space Science and Engineering, York University, Toronto, ON, Canada
| | - S. H. Selznick
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | - A. A. Simon
- Goddard Space Flight Center, Greenbelt, MD, USA
| | - S. Sugita
- Department of Earth and Planetary Environmental Science, University of Tokyo, Tokyo, Japan
| | - K. J. Walsh
- Southwest Research Institute, Boulder, CO, USA
| | - M. M. Westermann
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - C. W. V. Wolner
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - K. Yumoto
- Department of Earth and Planetary Environmental Science, University of Tokyo, Tokyo, Japan
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