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All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

A Science Rationale for Mobility in Planetary Environments

For the last several decades, the Committee on Planetary and Lunar Exploration (COMPLEX) has advocated a systematic approach to exploration of the solar system; that is, the information and understanding resulting from one mission provide the scientific foundations that motivate subsequent, more elaborate investigations. COMPLEX's 1994 report, An Integrated Strategy for the Planetary Sciences: 1995-2010,1 advocated an approach to planetary studies emphasizing "hypothesizing and comprehending" rather than "cataloging and categorizing." More recently, NASA reports, including The Space Science Enterprise Strategic Plan2 and, in particular, Mission to the Solar System: Exploration and Discovery-A Mission and Technology Roadmap,3 have outlined comprehensive plans for planetary exploration during the next several decades. The missions outlined in these plans are both generally consistent with the priorities outlined in the Integrated Strategy and other NRC reports,4-5 and are replete with examples of devices embodying some degree of mobility in the form of rovers, robotic arms, and the like. Because the change in focus of planetary studies called for in the Integrated Strategy appears to require an evolutionary change in the technical means by which solar system exploration missions are conducted, the Space Studies Board charged COMPLEX to review the science that can be uniquely addressed by mobility in planetary environments. In particular, COMPLEX was asked to address the following questions: (1) What are the practical methods for achieving mobility? (2) For surface missions, what are the associated needs for sample acquisition? (3) What is the state of technology for planetary mobility in the United States and elsewhere, and what are the key requirements for technology development? (4) What terrestrial field demonstrations are required prior to spaceflight missions?

Source record↗
NASA NTRS1999

Formation and Detection of Planetary Systems

Modern theories of star and planet formation and of the orbital stability of planetary systems are described and used to discuss possible characteristics of undiscovered planetary systems. The most detailed models of planetary growth are based upon observations of planets and smaller bodies within our own Solar System and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. These models predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed, and the methods that are being used and planned for detecting and characterizing extrasolar planets are reviewed.

Lissauer, Jack J.↗
NASA NTRS2005

Influence of Planetary Protection Guidelines on Waste Management Operations

Newly outlined missions in the Space Exploration Initiative include extended human habitation on Mars. During these missions, large amounts of waste materials will be generated in solid, liquid and gaseous form. Returning these wastes to Earth will be extremely costly, and will therefore likely remain on Mars. Untreated, these wastes are a reservoir of live/dead organisms and molecules considered to be "biomarkers" i.e., indicators of life). If released to the planetary surface, these materials can potentially confound exobiology experiments and disrupt Martian ecology indefinitely (if existent). Waste management systems must therefore be specifically designed to control release of problematic materials both during the active phase of the mission, and for any specified post-mission duration. To effectively develop waste management requirements for Mars missions, planetary protection guidelines must first be established. While previous policies for Apollo lunar missions exist, it is anticipated that the increased probability of finding evidence of life on Mars, as well as the lengthy mission durations will initially lead to more conservative planetary protection measures. To facilitate the development of overall requirements for both waste management and planetary protection for future missions, a workshop was conducted to identify how these two areas interface, and to establish a preliminary set of planetary protection guidelines that address waste management operations. This paper provides background regarding past and current planetary protection and waste management issues, and their interactions. A summary of the recommended planetary protection guidelines, anticipated ramifications and research needs for waste management system design for both forward (Mars) and backward (Earth) contamination is also provided.

Hogan, John A.↗
NASA NTRS2013

Planetary Data Systems (PDS) Imaging Node Atlas II

The Planetary Image Atlas (PIA) is a Rich Internet Application (RIA) that serves planetary imaging data to the science community and the general public. PIA also utilizes the USGS Unified Planetary Coordinate system (UPC) and the on-Mars map server. The Atlas was designed to provide the ability to search and filter through greater than 8 million planetary image files. This software is a three-tier Web application that contains a search engine backend (MySQL, JAVA), Web service interface (SOAP) between server and client, and a GWT Google Maps API client front end. This application allows for the search, retrieval, and download of planetary images and associated meta-data from the following missions: 2001 Mars Odyssey, Cassini, Galileo, LCROSS, Lunar Reconnaissance Orbiter, Mars Exploration Rover, Mars Express, Magellan, Mars Global Surveyor, Mars Pathfinder, Mars Reconnaissance Orbiter, MESSENGER, Phoe nix, Viking Lander, Viking Orbiter, and Voyager. The Atlas utilizes the UPC to translate mission-specific coordinate systems into a unified coordinate system, allowing the end user to query across missions of similar targets. If desired, the end user can also use a mission-specific view of the Atlas. The mission-specific views rely on the same code base. This application is a major improvement over the initial version of the Planetary Image Atlas. It is a multi-mission search engine. This tool includes both basic and advanced search capabilities, providing a product search tool to interrogate the collection of planetary images. This tool lets the end user query information about each image, and ignores the data that the user has no interest in. Users can reduce the number of images to look at by defining an area of interest with latitude and longitude ranges.

Stanboli, Alice↗
NASA NTRS2018

Planetary Spectrum Generator: An Accurate Online Radiative Transfer Suite for Atmospheres, Comets, Small Bodies and Exoplanets

We have developed an online radiative-transfer suite (https://psg.gsfc.nasa.gov) applicable to a broad range of planetary objects (e.g., planets, moons, comets, asteroids, TNOs, KBOs, exoplanets). The Planetary Spectrum Generator (PSG) can synthesize planetary spectra (atmospheres and surfaces) for a broad range of wavelengths (UV/Vis/near-IR/IR/far-IR/THz/sub-mm/Radio) from any observatory (e.g., JWST, ALMA, Keck, SOFIA), any orbiter (e.g., ExoMars, Juno), or any lander (e.g., MSL). This is achieved by combining several state-of-the-art radiative transfer models, spectroscopic databases and planetary databases (i.e., climatological and orbital). PSG has a 3D (three-dimensional) orbital calculator for most bodies in the solar system, and all confirmed exoplanets, while the radiative-transfer models can ingest billions of spectral signatures for hundreds of species from several spectroscopic repositories. It integrates the latest radiative-transfer and scattering methods in order to compute high resolution spectra via line-by-line calculations, and utilizes the efficient correlated-k method at moderate resolutions, while for computing cometary spectra, PSG handles non-LTE and LTE excitation processes. PSG includes a realistic noise calculator that integrates several telescope/instrument configurations (e.g., interferometry, coronagraphs) and detector technologies (e.g., CCD, heterodyne detectors, bolometers). Such an integration of advanced spectroscopic methods into an online tool can greatly serve the planetary community, ultimately enabling the retrieval of planetary parameters from remote sensing data, efficient mission planning strategies, interpretation of current and future planetary data, calibration of spectroscopic data, and development of new instrument/spacecraft concepts.

Villanueva, G. L.↗
NASA NTRS2017

The Evolution of Planetary Protection Implementation on Mars Landed Missions

NASA has developed requirements dedicated to the prevention of forward and backward contamination during space exploration. Historically, international agreements provided guidelines to prevent contamination of the Moon and other celestial bodies, as well as the Earth (e.g., sample return missions). The UN Outer Space Treaty was established in 1967 and the Committee on Space Research (COSPAR) maintains a planetary protection policy complying with Article IX of this treaty. By avoiding forward contamination, the integrity of scientific exploration is preserved. Planetary Protection mission requirements are levied on missions to control contamination. These requirements are dependent on the science of the mission and on the celestial bodies encountered or targeted along the way. Consequently, categories are assigned to missions, and specific implementation plans are developed to meet the planetary protection requirements. NASA missions have evolved over time with increasingly more demanding scientific objectives and more complex flight systems to achieve those objectives and, thus, planetary protection methods and processes used for implementation have become much more intricate, complicated, and challenging. Here, we will portray the evolution of planetary protection implementation at JPL in several important areas throughout the course of NASA sponsored robotic Mars lander or rover missions, starting from Mars Pathfinder through the beginning of Mars 2020. Highlighted in the discussion will be process changes in planetary protection requirements development and flow down. Development and implementation of new and improved methods used in the reduction of spacecraft bioburden will be discussed as well as approaches and challenges that come along with setting up remote laboratories to perform bioassays. The consequences and forward planning of delays on missions will be highlighted as well as lessons learned on the impact of communication and training in achieving planetary protection requirements. The evolution of methods used for the detection of microbial bioburden on spacecraft hardware will be considered. These methods use standard microbiology as well as the adaptation of advances in biotechnology, molecular biology, and bioinformatics. Technical approaches developed for the prevention of contamination and recontamination of hardware during Assembly, Test, and Launch Operations will be discussed.

Kazarians, Gayane A.↗
NASA NTRS2019

Planetary Science with Small Satellites: Opportunities and Challenges

Small satellites aren't anything particularly new. Earth orbiting small satellites go back 30 years or more. What is new is the proliferation and access to small satellite technologies and flight opportunities. This has been in large part due to the advent of the "cubesat" model, initially a means to develop student's engineering skills, but has since evolved into an industry and accepted method within government space agencies. Until very recently these smallsats were limited to Earth orbiting missions, but with the successful flight of the MarCO spacecraft and the upcoming launch of EM-1 cubesats, the Moon, Mars and beyond are now within reach. While all this is good news, we still have a ways to go before smallsats become true planetary science tools. One could argue that Deep Space 2 was the first planetary smallsat, launched in 1999 and having a mass of 2.3 kg (each probe) it hoped to demonstrate that "real" science could be done with a small (and less expensive) package. The DS2 failure shelved the idea of smallsats (even chilling some to "Class D" planetary missions in general) for nearly two decades. NASA has slowly come back around to smallsats for planetary missions, going so far as to support a range of mission studies (the Planetary Science Deep Space SmallSat Studies, or PSDS3, Program) and the creation of a new Program (SIMPLEx) to developed such missions for opportunistic flights. The MarCO success was hugely important in maintaining (and building) this forward momentum. However, we still have yet to demonstrate "real" science from a planetary smallsat and there are some fundamental disconnects between expectation and reality. This talk will discuss some of the opportunities and challenges that reside with planetary smallsats, focusing on two examples: LunaH-Map (the first SIMPLEx cubesat) and Aeolus (a Mars PSDS3 smallsat concept).

Colaprete, Anthony↗
DOE OSTI2021

A Lattice Boltzmann Scheme for Polarized Radiative Transfer in Planetary Atmospheres

Quantitative calculation of reflected polarized light from planets is of great significance to interpret the polarimetric observations of planetary atmospheres. In this work, we propose a lattice Boltzmann (LB) scheme for polarized radiative transfer in planetary atmospheres. The LB scheme obtains the Stokes vector through the vector LB equation performing simple collision and streaming processes. The vector radiative transfer equation is rigorously derived from the vector LB equation via the Maxwell iteration technique. Polarized radiative transfer of a single point on the planetary surface with Rayleigh and Mie scattering atmospheres are first accurately solved by our LB scheme. Afterward, we systematically investigate the disk-integrated polarization of finite and semi-infinite, conservative and nonconservative Rayleigh scattering planetary atmospheres. The disk-integrated phase curves of the Stokes parameters and degree of polarization and spherical and geometric albedos are produced, which are in good agreement with the benchmark results for different cases. The numerical results indicate that our LB scheme is efficient and accurate for polarized radiative transfer in planetary atmospheres. Our LB scheme is expected to provide a competitive numerical tool to interpret the polarimetric observations of planetary atmospheres.

47 OTHER INSTRUMENTATION↗
NASA NTRS2023

Tunable Laser Spectrometers for Planetary Science

Distinguishing planetary formation and evolution pathways and understanding the origins of volatiles on planetary bodies requires determination of relative abundances and isotope ratios in the noble gases, and also of the isotope ratios in C, H, N, O and S at high precisions. Traditional planetary mass spectrometers uniquely provide excellent survey capability including the noble gas relative abundances and their isotope ratios. However, to distinguish planetary evolution models for the outer planets, stable isotope ratios in C and O require precisions of ∼10 or better, readily achievable with a tunable laser spectrometer (TLS). As demonstrated on the Mars Curiosity rover, and as planned for a now-selected NASA Venus mission, tunable laser spectrometers play a unique role synergistic with the capabilities of planetary mass spectrometers. The TLS technique of recording infrared absorption spectra at ultrahigh resolution (resolving power λ/δλ ∼ 5 million) provides unambiguous detection of a wide variety of gases such as H2O, H2O2, H2CO, HOCl, NO, NO2, HNO3, N2O, O3, CO, CO2, NH3, N2H4, PH3, H2S, SO2, OCS, HCl, HF, O2, HCN, and CH4, C2H2, C2H4, C2H6 at parts-per-billion levels. Through line-depth or line-area ratio comparisons of adjacent spectral lines, planetary TLS instruments can achieve isotope ratio measurements in C, H, N, O, and S molecules at precisions of ∼1–2, including for the triple isotope components of O and S. Expected performance of TLS instruments for Venus, Saturn, Enceladus and Uranus will be described as constrained by actual measurements reported at Mars on the Curiosity rover.

Planetary↗
DOE OSTI2025

Non-traditional stable isotope measurements using laser desorption Orbitrap mass spectrometry: Implications for planetary missions.

Isotopic fractionation recorded in planetary materials provides insights into physical, chemical, and/or potential biological processes occurring on Solar System bodies. As we enter into the next decades of planetary exploration, the crucial information revealed by isotopic compositions of rocky and icy samples mandates that next generation spaceflight instrumentation possess the capability to measure isotope ratios in situ with sufficient precision/accuracy to distinguish between such processes. Here, in addition to identifying and fingerprinting complex organic materials with high accuracy and ultrahigh mass resolutions, laser desorption Orbitrap™ mass spectrometry (LD-O-MS) has the capability to determine the elemental and isotopic composition of solid planetary materials such as rock, regolith, organics, ice, etc. Here, we use a space-qualified LD-O-MS instrument comprising a 266 nm ultraviolet (UV) laser and Orbitrap mass analyzer ruggedized for planetary applications to investigate the stable isotopic composition of Ti and Zn metal plates. Based on the isotopic analyses, we constrain the performance of the CORALS instrument to sub per mille (‰) level accuracy and precision for Ti and at the per mille (‰) level for Zn. An LD-O-MS instrument is a versatile instrument capable of measuring isotopic composition of a variety of planetary samples and would constitute a critical instrument in the exploration of various planetary bodies including but not limited to Moon, Mars, Enceladus and other ocean or icy worlds, Ceres and other asteroids, and comets, thereby answering several high-priority questions pertaining to the formation and evolution of our Solar System.

58 GEOSCIENCES↗
NASA NTRS1984

Ultraviolet spectroscopy of the planetary nebula in the Fornax galaxy

The planetary nebula in the Fornax dwarf spheroidal galaxy is carbon rich, according to calculations based on measurements of the 1909 A emission line doublet of semiforbidden C III obtained with the International Ultraviolet Explorer. The ratio N(C)/N(O) is approximately equal to 3.7, comparable to the largest reliably determined carbon/oxygen ratios in high excitation planetaries of the Milky Way. The present result is based on four low-dispersion spectra with a combined exposure time of 27.2 hours; the Fornax planetary nebula is probably the most distant known planetary that can be observed with IUE. The IUE data were analyzed together with visible-wavelength emission-line fluxes reported by Danziger et al. (1978) to compute abundances for various elements. In terms of chemical composition, the Fornax nebula resembles planetary nebulae in the Magellanic Clouds more closely than it does typical or carbon-rich planetaries in the Galaxy.

Maran, S. P.↗
NASA NTRS1986

Effects of orography on planetary scale flow

The earth's orography is composed of a wide variety of scales, each contributing to the spectrum of atmospheric motions. A well studied subject (originating with Charney and Eliassen) is the direct forcing of planetary scale waves by the planetary scale orography: primarily the Tibetan plateau and the Rockies. However, because of the non-linear terms in the equations of dynamic meteorology, even the smallest scales of mountain induced flow can contribute to the planetary scale if the amplitude of the small scale disturbance is sufficintly large. Two possible mechanisms for this are illustrated. First, preferentially located lee cyclones can force planetary waves by their meridional transport of heat and momentum (Hansen and Chen). Recent theories are helping to explain the phenomena of lee cyclogenesis (e.g., Smith, 1984, J.A.S.). Second, mesoscale mountain wave and severe downslope wind phenomena produce such a large local drag, that planetary scale waves can be produced. The mechanism of upscale transfer is easy to understand in this case as the standing planetary scale wave has a wavelength which depends on the mean structure of the atmosphere, and not on the width of the mountain (just as in small scale lee wave theory). An example of a theoretical description of a severe wind flow with very large drag is shown.

Smith, R. B.↗
NASA NTRS1988

Planetary Geology: Goals, Future Directions, and Recommendations

Planetary exploration has provided a torrent of discoveries and a recognition that planets are not inert objects. This expanded view has led to the notion of comparative planetology, in which the differences and similarities among planetary objects are assessed. Solar system exploration is undergoing a change from an era of reconnaissance to one of intensive exploration and focused study. Analyses of planetary surfaces are playing a key role in this transition, especially as attention is focused on such exploration goals as returned samples from Mars. To assess how the science of planetary geology can best contribute to the goals of solar system exploration, a workshop was held at Arizona State University in January 1987. The participants discussed previous accomplishments of the planetary geology program, assessed the current studies in planetary geology, and considered the requirements to meet near-term and long-term exploration goals.

Source record↗
NASA NTRS1990

The effect of latent heat release on synoptic-to-planetary scale wave interactions and implications for satellite observations: Observational study

Researchers have been exploring methods to facilitate the prediction of rapidly intensifying surface cyclones. Recognizing that synoptic-scale systems, such as these cyclones, are less predictable at medium range and beyond than are planetary-scale circulations, researchers propose that the planetary-scale environment for explosive cyclogenesis could be better predicted than the cyclones themselves. Researchers have therefore constructed a planetary-scale climatology of explosive cyclogenesis by compositing together filtered 500 mb height fields (retaining planetary waves only) corresponding to a large sample of rapidly intensifying surface cyclones, stratified geographically and according to the direction of 500 mb geostrophic flow (southwesterly, northwesterly or westerly) over the cyclone center. The composites are calculated from five days preceding to five days following each rapid cyclogenesis event, and have climatology subtracted so that the evolution of planetary-scale anomalies before and after cyclogenesis can be followed. Whether the anomalies are distinct from background variability and thus provide predictive value is now being evaluated. Following explosive cyclogenesis over which the filtered 500 mb flow is southwesterly, there appear in the composites large positive 500 mb height anomalies downstream. In some cases, these anomalies are associated with blocking patterns. Whether the objectively-defined blocking patterns in the data set are preceded by upstream intense surface cyclone activity is being investigated. Finally, the contribution of synoptic-scale processes, notably warm air advection, to planetary-scale height rises during a block formation following an explosive cyclogenesis event is being diagnosed. Researchers hope to eventually evaluate the impact of satellite derived latent heat release upon the warm air advection in this case.

Colucci, Stephen J.↗
NASA NTRS1993

Ordinary planetary systems - Architecture and formation

Today we believe ordinary planetary systems to be an unremarkable consequence of star formation. The solar system, so far the only confidently known example in the universe of a planetary system, displays a set of striking structural regularities. These structural regularities provide fossil clues about the conditions and mechanisms that gave rise to the planets. The formation of our planetary system, as well as its general characteristics, resulted from the physical environment in the disk-shaped nebula that accompanied the birth of the sun. Observations of contemporary star formation indicate that the very conditions and mechanisms thought to have produced our own planetary system are widely associated with the birth of stars elsewhere. Consequently, it is reasonable to believe that planetary systems occur commonly, at least in association with single, sunlike stars. Moreover, it is reasonable to believe that many planetary systems have gross characteristics resembling those of our own solar system.

Levy, E. H.↗
NASA NTRS1993

Planetary protection implementation on future Mars lander missions

A workshop was convened to discuss the subject of planetary protection implementation for Mars lander missions. It was sponsored and organized by the Exobiology Implementation Team of the U.S./Russian Joint Working Group on Space Biomedical and Life Support Systems. The objective of the workshop was to discuss planetary protection issues for the Russian Mars '94 mission, which is currently under development, as well as for additional future Mars lander missions including the planned Mars '96 and U.S. MESUR Pathfinder and Network missions. A series of invited presentations was made to ensure that workshop participants had access to information relevant to the planned discussions. The topics summarized in this report include exobiology science objectives for Mars exploration, current international policy on planetary protection, planetary protection requirements developed for earlier missions, mission plans and designs for future U.S. and Russian Mars landers, biological contamination of spacecraft components, and techniques for spacecraft bioload reduction. In addition, the recent recommendations of the U.S. Space Studies Board (SSB) on this subject were also summarized. Much of the discussion focused on the recommendations of the SSB. The SSB proposed relaxing the planetary protection requirements for those Mars lander missions that do not contain life detection experiments, but maintaining Viking-like requirements for those missions that do contain life detection experiments. The SSB recommendations were found to be acceptable as a guide for future missions, although many questions and concerns about interpretation were raised and are summarized. Significant among the concerns was the need for more quantitative guidelines to prevent misinterpretation by project offices and better access to and use of the Viking data base of bioassays to specify microbial burden targets. Among the questions raised were how will the SSB recommendations be integrated with existing Committee on Space Research (COSPAR) policy and how will they apply to and affect Mars '94, Mars '96, MESUR Pathfinder, and MESUR Network missions? One additional topic briefly considered at the workshop was the identification of some issues related to planetary protection considerations for Mars sample return missions. These issues will form the basis for a follow-on joint U.S./Russian workshop on that subject.

Howell, Robert↗
NASA NTRS1993

Workshop on advanced technologies for planetary instruments

NASA's robotic solar system exploration program requires a new generation of science instruments. Design concepts are now judged against stringent mass, power, and size constraints--yet future instruments must be highly capable, reliable, and, in some applications, they must operate for many years. The most important single constraint, however, is cost: new instruments must be developed in a tightly controlled design-to-cost environment. Technical innovation is the key to success and will enable the sophisticated measurements needed for future scientific exploration. As a fundamental benefit, the incorporation of breakthrough technologies in planetary flight hardware will contribute to U.S. industrial competitiveness and will strengthen the U.S. technology base. The Workshop on Advanced Technologies for Planetary Instruments was conceived to address these challenges, to provide an open forum in which the NASA and DoD space communities could become better acquainted at the working level, and to assess future collaborative efforts. Over 300 space scientists and engineers participated in the two-and-a-half-day meeting held April 28-30, 1993, in Fairfax, Virginia. It was jointly sponsored by NASA's Solar System Exploration Division (SSED), within the Office of Space Science (OSS); NASA's Office of Advanced Concepts and Technology (OACT); DoD's Strategic Defense Initiative Organization (SDIO), now called the Ballistic Missile Defense Organization (BMDO); and the Lunar and Planetary Institute (LPI). The meeting included invited oral and contributed poster presentations, working group sessions in four sub-disciplines, and a wrap-up panel discussion. On the first day, the planetary science community described instrumentation needed for missions that may go into development during the next 5 to 10 years. Most of the second day was set aside for the DoD community to inform their counterparts in planetary science about their interests and capabilities, and to describe the BMDO technology base, flight programs, and future directions. The working group sessions and the panel discussion synthesized technical and programmatic issues from all the presentations, with a specific goal of assessing the applicability of BMDO technologies to science instrumentation for planetary exploration.

Appleby, J.↗
NASA NTRS1993

Nd-142/Nd-144 in bulk planetary reservoirs, the problem of incomplete mixing of interstellar components and significance of very high precision Nd-145/Nd-144 measurements

Apart from the challenge of very high precision Nd-142/Nd-144 ratio measurement, accurate applications of the coupled Sm-(146,147)-Nd-(142,143) systematics in planetary differentiation studies require very precise knowledge of the present-day (post-Sm-146 decay) Nd-142/Nd-144 ratios of bulk planetary objects (BP). The coupled systematics yield model ages for the time of formation of Sm/Nd-fractionated reservoirs by differentiation of Sm/Nd-unfractionated bulk planetary reservoirs. Estimates of (Nd-142/Nd-144)(sub BP) and (Nd-143/Nd-144)(sub BP) therefore provide the critical baseline relative to which these model ages are referenced. In the Sm-147-Nd-143 systematics, Nd-143/Nd-144 variations are mostly large; therefore, small variations in initial Nd-143/Nd-144 ratios generally can be ignored. However, in the case of Sm-146-Nd-142, the range of Nd-142/Nd-144 divergence for differentiated planetary reservoirs is much smaller. Consequently Sm-(146,147)-Nd-(142,143) model ages are sensitive to small variations in bulk planetary Nd-142/Nd-144 (both present-day and initial). One major unanswered question is whether or not Nd shelf standards (CIT Nd beta/Ames metal, La Jolla, NASA-JSC/Ames metal) have Nd-142/Nd-144 identical to the bulk Earth or otherwise might record some degree of radiogenic evolution in an early-fractionated reservoir. Our discussions of earth Earth differentiation based on Nd-142/Nd-144 in Isua and Acasta samples have employed a working assumption: (Nd-142/Nd-144)(sub Nd beta) = (Nd-142/Nd-144)(sub Bulk Earth). This requires experimental justification and is apparently contradicted by chondrite Nd-142/Nd-144 measurements, which have been interpreted to indicate: (Nd-142/Nd-144)(sub JSC/Ames metal) = ((Nd-142/Nd-144)(sub CHUR) = 35 plus or minus 8 ppm). At present, interpretations of the early Earth and Moon hinge largely on this issue. Because Ba in bulk chondrite samples exhibit similar magnitude nuclear anomalies, attributable to incomplete mixing of interstellar components, a critical question is whether or not nuclear effects are also present in Nd-142/Nd-144, both in bulk chondrites and between planetary objects.

Harper, C. L., Jr.↗