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Catalyst: Radiation Effects on Volatiles and Exploration of Asteroids and the Lunar Surface

2018; Elsevier BV; Volume: 4; Issue: 1 Linguagem: Inglês

10.1016/j.chempr.2017.12.004

2451-9308

Thomas M. Orlando, Brant M. Jones, C. S. Paty, Micah J. Schaible, John R. Reynolds, Phillip N. First, Stephen K. Robinson, Valeria La Saponara, Esther Beltran,

Radiation Therapy and Dosimetry

Prof. Thomas Orlando is currently a professor in the Georgia Institute of Technology (GIT) School of Chemistry and Biochemistry and an adjunct professor in the GIT School of Physics. He serves as director of the GIT Center for Space Technology and Research and as principal investigator (PI) of the NASA Solar System Exploration Research Virtual Institute Center on Radiation Effects on Volatiles and Exploration of Asteroids and Lunar Surfaces (REVEALS). Prof. Carol Paty and Dr. Esther Beltran are deputy PIs, and Dr. Brant Jones and Prof. Stephen Robinson are science theme leaders. Orlando, Jones, Paty, and Schaible focus on understanding radiation effects on the regolith and the solar-wind formation of volatiles. Profs. Valeria La Saponara, John Reynolds, and Robinson focus on mitigating health risks by developing nanocomposites for spacesuits and habitats. Prof. Phillip First explores 2D materials for radiation detection. Collectively, the efforts will help facilitate future human exploration of near-Earth destinations. Prof. Thomas Orlando is currently a professor in the Georgia Institute of Technology (GIT) School of Chemistry and Biochemistry and an adjunct professor in the GIT School of Physics. He serves as director of the GIT Center for Space Technology and Research and as principal investigator (PI) of the NASA Solar System Exploration Research Virtual Institute Center on Radiation Effects on Volatiles and Exploration of Asteroids and Lunar Surfaces (REVEALS). Prof. Carol Paty and Dr. Esther Beltran are deputy PIs, and Dr. Brant Jones and Prof. Stephen Robinson are science theme leaders. Orlando, Jones, Paty, and Schaible focus on understanding radiation effects on the regolith and the solar-wind formation of volatiles. Profs. Valeria La Saponara, John Reynolds, and Robinson focus on mitigating health risks by developing nanocomposites for spacesuits and habitats. Prof. Phillip First explores 2D materials for radiation detection. Collectively, the efforts will help facilitate future human exploration of near-Earth destinations. Recent space-exploration missions to a number of solar-system objects, including the Moon, Mars, Mercury, and near-Earth asteroids (NEAs), have revealed a wide variety of physical conditions that give rise to a diverse assortment of chemical environments and molecules. Because some of these objects are currently under consideration by NASA as strategic destinations for future human exploration missions, a more complete description of their respective surface conditions is desirable for mitigating human risk factors and determining the availability of in situ resources. Without an appreciable atmosphere, each of these potential destinations is constantly being bombarded by radiation from solar wind, galactic cosmic rays, and hypervelocity micrometeorite impacts from local (circumplanetary) or interplanetary sources.1Bennett C.J. Pirim C. Orlando T.M. Space-weathering of solar system bodies: a laboratory perspective.Chem. Rev. 2013; 113: 9086-9150Crossref PubMed Scopus (108) Google Scholar Ionizing radiation (IR) and micrometeorite impactors can deposit, transport, alter, and even produce volatiles, such as water and methane, in the surface materials of such bodies. Relevant to possible human exploration of these airless bodies, IR is known to produce DNA damage that is most likely linked to cancer susceptibility, neurodegenerative disorders, developmental abnormalities, inflammatory responses, and accelerated and/or premature aging.2Hoeijmakers J.H.J. DNA damage, aging, and cancer.N. Engl. J. Med. 2009; 361: 1475-1485Crossref PubMed Scopus (1490) Google Scholar Thus, the constant radiation assault presents obvious life-threatening and program-limiting health risks for humans, and these must be understood, quantified, and mitigated by the development of effective shielding materials, real-time radiation-detection systems, and radiation-hardened human habitats and spacesuits. Given that ionization and the inelastic scattering of secondary low-energy electrons (LEEs) contribute significantly to radiation damage in materials and living cells,3Alizadeh E. Orlando T.M. Sanche L. Biomolecular damage induced by ionizing radiation: The direct and indirect effects of low-energy electrons on DNA.in: Annual Review of Physical Chemistry. Volume 66. Annual Reviews, 2015: 379-398Google Scholar the use of nanoscale and 2D materials that scavenge LEEs effectively is required for both monitoring and mitigating IR damage. IR and micrometeorite bombardment of airless bodies can produce volatile resources for in situ utilization during an extended human mission. As shown in Figure 1, surface processing of solar-system bodies lacking protective atmospheres or magnetospheres—more generally referred to as space weathering—occurs when photon or charged-particle radiation and meteorite impacts modify the chemical and physical makeup of the dust, rocks, and ice that constitute the uppermost layer of the surface, called the regolith. If the incoming projectile is an electron, photon, or light ion, the energy deposition is primarily via electronic excitations and can lead to the breaking and rearrangement of chemical bonds and the removal of surface species through a process generally referred to as electronic sputtering. The interaction between solar protons and the regolith can lead to implantation, reactive scattering, and possibly the production of simple volatiles (e.g., water and methane). These, along with additional volatiles deposited by cometary or meteorite impacts, can be trapped and sequestered in the near-surface and polar regions of the lunar and NEA surfaces. The presence of significant abundances of water and methane would provide invaluable in situ resources for future human exploration missions. Studies pertaining to the physical interaction of water have directly measured the binding energy and sticking probability on the lunar regolith and determined that the rate of water thermal desorption is high, such that only a small distribution of molecules have binding energies greater than the interactions expected from a traditional multilayer ice system. A simple Arrhenius model using the measured binding energies has revealed that molecular water will not persist on the sun-lit side of the Moon over a lunar day even at high latitudes (areas of less solar flux) as a result of high thermal-desorption rates.4Poston M.J. Grieves G.A. Aleksandrov A.B. Hibbitts C.A. Dyar M.D. Orlando T.M. Temperature programmed desorption studies of water interactions with Apollo lunar samples 12001 and 72501.Icarus. 2015; 255: 24-29Crossref Scopus (44) Google Scholar This impedes the buildup and persistence of surficial water on the sun-lit side of the Moon surface and on the surfaces of airless bodies whose temperatures exceed 150 K. The interaction between electrons and photons and the regolith leads to electron-stimulated desorption and photon-stimulated desorption, respectively. These are known to contribute to the Moon glow and the migration of volatiles. Additionally, photoelectron emission tends to cause the day-side surface to charge positively, whereas solar-wind electron absorption on the night side leads to a negative charge buildup. In regions of obstructed plasma flow, such as the trailing plasma wake behind a body and within terminator craters, the solar-wind ion trajectories are diverted into the wake region via large negative potentials that develop across the plasma-void boundary.5Halekas J. Bale S. Mitchell D. Lin R. Electrons and magnetic fields in the lunar plasma wake.J. Geophys. Res. Space Phys. 2005; 110: A07222Crossref Scopus (116) Google Scholar This wake E-field makes surfaces charge even more strongly negative in relation to the unaltered plasma flow.6Farrell W. Stubbs T. Halekas J. Killen R. Delory G. Collier M. Vondrak R. Anticipated electrical environment within permanently shadowed lunar craters.J. Geophys. Res. Planets. 2010; 115: E03004Crossref Scopus (62) Google Scholar In unobstructed regions, the solar-wind plasma interacts directly with the surface. Experimental work has shown that interactions between the ∼keV H+ ions (protons) and the lunar regolith simulant can produce chemically bound hydroxyl (–OH), thus suggesting a potential solar-wind-induced formation mechanism for water precursors.7Schaible M.J. Baragiola R.A. Hydrogen implantation in silicates: the role of solar wind in SiOH bond formation on the surfaces of airless bodies in space.J. Geophys. Res. Planets. 2014; 119: 2017-2028Crossref Scopus (38) Google Scholar The chemically bound –OH groups cannot dissociate and recombine to form water, hydrogen, etc., under normal thermal conditions as a result of the high activation barrier. However, it has been demonstrated that molecular water is released from minerals with saturated –OH terminal sites and defects at high temperatures. This occurs by a process known as recombinative or associative desorption and involves the thermally activated reaction of two –OH groups that are in close proximity to one another. This reaction produces and releases water while healing the defect caused by the missing oxygen atom. In addition, the process can also result in the formation of molecular hydrogen, particularly if one of the neighboring defect sites is a hydride. Recombinative desorption in silicates typically requires a temperature of at least 450 K, well above the ambient temperature of the sun-lit side of the Moon or the surfaces of NEAs. Only regolith or minerals containing certain metal oxides (i.e., TiO2, Fe2O3, etc.) allow recombinative desorption below 450 K. Thus, under the thermal conditions of lunar and NEA surfaces, recombinative desorption from minerals containing mostly silicates does not contribute significantly to the formation of water. However, during meteorite impacts, the temperature of the regolith can locally reach ∼104 K depending on the velocity of impact, thus driving recombinative desorption and the formation of simple volatiles, such as water and methane. The lunar surface is known to contain a wide range of organic molecules. Methane has been observed within both the lunar regolith8Abell P.I. Eglinton G. Maxwell J.R. Pillinger C.T. Hayes J.M. Indigenous lunar methane and ethane.Nature. 1970; 226: 251-252Crossref PubMed Scopus (17) Google Scholar and the lunar exosphere.9Hodges R.R. Methane in the lunar exosphere: Implications for solar wind carbon escape.Geophys. Res. Lett. 2016; 43: 6742-6748Crossref Scopus (22) Google Scholar More complex organics have also been observed in situ by the Lunar Crater Observation and Sensing Satellite (LCROSS), which detected infrared absorption bands attributed to various saturated hydrocarbons.10Neish C.D. Bussey D.B.J. Spudis P. Marshall W. Thomson B.J. Patterson G.W. Carter L.M. The nature of lunar volatiles as revealed by Mini-RF observations of the LCROSS impact site.J. Geophys. Res. Planets. 2011; 116: E01005Crossref Scopus (46) Google Scholar Even the ubiquitous tar resulting from the radiolysis of organic molecules has been detected in the lunar regolith.11Thomas-Keprta K.L. Clemett S.J. Messenger S. Ross D.K. Le L. Rahman Z. McKay D.S. Gibson E.K. Gonzalez C. Peabody W. Organic matter on the Earth's Moon.Geochim. Cosmochim. Acta. 2014; 134: 1-15Crossref Scopus (22) Google Scholar How these molecules came to be under such harsh and isolated conditions is a question that has yet to be answered definitively. The delivery of organics via meteorites and interplanetary dust particles seems reasonable given the frequency of impacts on the Moon12Speyerer E.J. Povilaitis R.Z. Robinson M.S. Thomas P.C. Wagner R.V. Quantifying crater production and regolith overturn on the Moon with temporal imaging.Nature. 2016; 538: 215-218Crossref PubMed Scopus (105) Google Scholar and the fact that extraterrestrial organics have been identified on a variety of meteorites. Additionally, experiments have shown that large complex organics can be formed upon the energetic processing of volatile ice mixtures,13Herbst E. The synthesis of large interstellar molecules.Int. Rev. Phys. Chem. 2017; 36: 287-331Crossref Scopus (69) Google Scholar and a parallel avenue for production could be the exposure of ices to ionizing radiation in the form of galactic cosmic rays. As pointed out recently,14Crites S. Lucey P. Lawrence D. Proton flux and radiation dose from galactic cosmic rays in the lunar regolith and implications for organic synthesis at the poles of the Moon and Mercury.Icarus. 2013; 226: 1192-1200Crossref Scopus (22) Google Scholar galactic cosmic rays will easily deposit 10 eV per molecule within a relatively (geologically) short time into the ices (water, carbon monoxide, and methane) that exist in the permanently shadowed regions of the Moon. Lastly, volatiles such as methane could have been produced during the period of lunar geological activity through a Fischer-Tropsch-type process via the conversion of carbon monoxide and hydrogen gas into saturated hydrocarbons. However, the relative importance of the different formation mechanisms for organic molecules on the surfaces of airless bodies is largely unknown. In addition to needing in situ resources, human exploration missions beyond near-Earth orbit require a validated approach to addressing astronaut health risks due to radiation. Most human experience in spaceflight has been in low Earth orbit (LEO)—in fact, only about 0.5% of total human spaceflight time has occurred beyond LEO, during the Apollo lunar missions. In these future operations, real-time radiation monitoring will be especially critical given that astronauts can be far from radiation shelter in the event of a dynamic solar event. Now, with six decades of LEO experience behind us, planning for long-duration missions beyond LEO is a national priority. One of the chief technical barriers to feasible distant-destination missions by humans is space radiation and the ability to predict and monitor the radiation absorbed by astronauts on a real-time and mission-integrated basis. Although the deep-space radiation environment is reasonably well characterized, radiation-protection materials for human habitats and spacesuits have not been fully developed or characterized, and real-time radiation monitors remain in their infancy. For example, several types of real-time radiation monitors currently utilized on the International Space Station have produced inconsistent results, and they are not integrated with spacesuits. Current spacesuit designs have single-function layers—including pressure garments, air bladders, and restraint layers—along with thermal cooling, insulation, and micrometeoroid protective layers. These multilayer laminates limit the astronauts' dexterity. Moreover, radiation protection is limited to short-term exposure within a protective environment (Earth's magnetic field) and is therefore not adequate for human exploration missions beyond near-Earth orbit. New materials to facilitate and improve radiation protection are an essential component of being able to work and live safely in a deep-space environment. Design drivers of novel spacesuits should therefore include multifunctional, lightweight materials with optimal mobility and flexibility, robust radiation protection, and high durability, as well as provide special protection for particularly vulnerable human organs and engineering systems for critical operability. In light of these requirements, materials composed of a polymer-matrix composite reinforced with a combination of materials that control mechanical integrity, electrical properties, and radiation hardness are being developed and tested within the NASA Radiation Effects on Volatiles and Exploration of Asteroids and Lunar Surfaces (REVEALS) program. This process, shown schematically at the bottom of Figure 1, demonstrates how a processable resin matrix precursor can be combined with modified fibers and fillers that incorporate electrical transport and radiation protection. The process uses fiber surface functionality to control polarity and induce strong bonding interactions at material interfaces during processing. These interactions will utilize the ability of polar filler materials to be formed directly into composites. Ultimately, these composite materials will be formed into flexible sheets and patches that can bring multifunctionality to spacesuit applications. All human extraterrestrial missions will benefit from improvements in, and development of, new radiation-detection technologies in order to provide essential redundancy. Recent studies have dedicated special attention to the exposure of the human central nervous system to radiation because of its effects on human performance, cognitive effects, and late degenerative tissue processes. In addition to the development of new spacesuit materials, new 2D and topological materials for portable, organ-specific radiation-detection devices are needed. The quickest approach involves optimizing an existing graphene field-effect transistor and determining the device suitability for both pulse-counting and passive radiation detection. In parallel, changes in electronic properties and electrical conduction, which are induced by the irradiation of 2D and topological materials, will be monitored. Technologically advanced 2D materials, such as graphene, will be used for creating a prototype device and associated methodologies. The technological path established by this prototype will be leveraged for other promising materials, resulting in a reduction of the risk of human radiation exposure for missions beyond near-Earth orbit. In summary, experimental and theoretical efforts to address solar-wind irradiation and micrometeorite bombardment will reveal a level of detail regarding radiation processing and space weathering of the Moon, Phobos, Deimos, and NEA surfaces necessary for future human mission planning. To date, no program has systematically examined all of the non-thermal channels related to radiation processing of these human exploration targets. Moreover, human radiation risks and mitigation approaches for long-duration deep-space missions are only partially understood and are the subject of a variety of ongoing and long-term NASA and international-partner studies. Therefore, focused efforts should also be on the development and testing of new 2D materials, active radiation dosimetry, and the operationally practical integration of these results into extravehicular-activity spacesuits and crewed vehicle mobility on distant surfaces. Radiation Effects on Volatiles and Exploration of Asteroids and Lunar Surfaces (REVEALS) is supported by the NASA Solar System Exploration Research Virtual Institute cooperative agreement number NNH16ZDA001N. Reaction: Surviving on the Moon, Mars, and AsteroidsBernard H. FoingChemJanuary 11, 2018In BriefProf. Foing is an advisor to the director general of the European Space Agency (ESA), a space astrophysicist at the European Space Research & Technology Centre (ESTEC), executive director of the International Lunar Exploration Working Group (ILEWG), and research professor at Vrije Universiteit Amsterdam and Florida Tech. He was chief scientist, chairman of the ESTEC staff association, and lead scientist for the ESA SMART-1 mission to the Moon. He is co-investigator of ESA missions SOHO, COROT, Mars Express, ExoMars, and EXPOSE experiments (FOTON capsules and International Space Station. He is manager of ILEWG ExoGeoLab and EuroMoonMars field simulations in extreme terrestrial analogs. Full-Text PDF Open ArchiveReaction: Chemistry Driven by the Harsh Space EnvironmentWilliam M. FarrellChemJanuary 11, 2018In BriefDr. Bill Farrell is a plasma physicist at NASA's Goddard Space Flight Center. He is a co-investigator on the Cassini mission to Saturn and the Parker Solar Probe mission. He is also principal investigator of the DREAM2 Center for Space Environments ( http://ssed.gsfc.nasa.gov/dream/ ), which examines the exosphere formation, radiation effects, and plasma interactions of the Moon and other airless bodies. Dr. Farrell has authored or co-authored over 200 journal articles on various aspects of space science, including the hydroxylation at the Moon, the curious plasma effects within the Enceladus plume, and the possibility of electricity generated in Martian dust devils. Full-Text PDF Open Archive