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NASA NTRS2011

Assessing the Age of an Asteroid's Surface with Data from the International Rosetta Mission

Rosetta is an international mission led by the European Space Agency (ESA) with key support and instrumentation from the National Aeronautics and Space Administration (NASA). Rosetta is currently on a ten-year mission to catch comet 67P/Churyumov-Gerasimenko (C-G); throughout its voyage, the spacecraft has performed flybys of two main belt asteroids (MBA): Steins and Lutetia. Data on the physical, chemical, and geological properties of these asteroids are currently being processed and analyzed. Accurate interpretation of such data is fundamental in the success of Rosetta's mission and overall objectives. Post-flyby data analyses strive to correlate the size, shape, volume, and rotational rate of Lutetia, in addition to interpreting its multi-color imagining, albedo, and spectral mapping. Although advancements in science have contributed to the examination of celestial bodies, methods to analyze asteroids remain largely empirical, not semi-empirical, nor ab initio. This study aims to interpret and document the scientific methods currently utilized in the characterization of asteroid (21) Lutetia in order to render these processes and methods accessible to the public. Examples include a standardized technique for assessing the age of an asteroid surface, complete with clickable reference maps, methodology of grouping surface characteristics together, and a standardized power law equation for the age. Other examples include determining the density of an object. Context for what both density and age mean is a bi-product of this study. Results of the study will aid in the development of pedagogical material on asteroids for public use, and in creation of an academic database for selected targets that might be used as a reference.

asteriods↗
NASA NTRS2011

Asteroid Return Mission Feasibility Study

This paper describes an investigation into the technological feasibility of finding, characterizing, robotically capturing, and returning an entire Near-Earth Asteroid (NEA) to the International Space Station (ISS) for scientific investigation, evaluation of its resource potential, determination of its internal structure and other aspects important for planetary defense activities, and to serve as a testbed for human operations in the vicinity of an asteroid. Reasonable projections suggest that several dozen candidates NEAs in the size range of interest (approximately 2-m diameter) will be known before the end of the decade from which a suitable target could be selected. The conceptual mission objective is to return an approximately 10,000-kg asteroid to the ISS in a total flight time of approximately 5 years using a single Evolved Expendable Launch Vehicle. Preliminary calculations indicate that this could be accomplished using a solar electric propulsion (SEP) system with high-power Hall thrusters and a maximum power into the propulsion system of approximately 40 kW. The SEP system would be used to provide all of the post-launch delta V. The asteroid would have an unrestricted Earth return Planetary Protection categorization, and would be curated at the ISS where numerous scientific and resource utilization experiments would be conducted. Asteroid material brought to the ground would be curated at the NASA Johnson Space Center. This preliminary study identified several areas where additional work is required, but no show stoppers were identified for the approach that would return an entire 10,000-kg asteroid to the ISS in a mission that could be launched by the end of this decade.

near Earth asteriods (NEA)↗
NASA NTRS2015

Linear Covariance Analysis For Proximity Operations Around Asteroid 2008 EV5

The NASA initiative to collect an asteroid the Asteroid Robotic Redirect Mission (ARRM) is currently investigating the option of retrieving a boulder off an asteroid, demonstrating planetary defense with an enhanced gravity tractor technique and returning it to a lunar orbit. Techniques for accomplishing this are being investigated by the Satellite Servicing Capabilities Office (SSOO) and NASA GSFC in colloboration with JPL, NASA, JSC, LaRC, and Draper Laboratories Inc. Two critical phases of the mission are the descent to the boulder and the Enhanced Gravity Tractor-enhanced gravity tractor demonstration. A linear covariance analysis was done for these phases to assess the feasibility of these concepts with the proposed design of the sensor and actuaor suite of the Asteroid Redirect Vehicle (ARV). The sensor suite for this analysis will include a wide field of view camera, Lidar, and a MMU. The proposed asteroid of interest is currently the C-type asteroid 2008 EV5, a carbonaceous chondrite that is of high interest to the scientific community. This paper will present an overview of the analysis discuss sensor and actuator models and address the feasibility of descending to the boulder within the requirements as the feasibility of maintaining the halo orbit in order to demonstrate the Enhanced Gravity Tractor-enhanced gravity tractory technique.

Guidance↗
NASA NTRS2016

Structural Design Considerations for a 50 kW-Class Solar Array for NASA's Asteroid Redirect Mission

NASA is planning an Asteroid Redirect Mission (ARM) to take place in the 2020s. To enable this multi-year mission, a 40 kW class solar electric propulsion (SEP) system powered by an advanced 50 kW class solar array will be required. Powered by the SEP module (SEPM), the ARM vehicle will travel to a large near-Earth asteroid, descend to its surface, capture a multi-metric ton (t) asteroid boulder, ascend from the surface and return to the Earth-moon system to ultimately place the ARM vehicle and its captured asteroid boulder into a stable distant orbit. During the years that follow, astronauts flying in the Orion multipurpose crew vehicle (MPCV) will dock with the ARM vehicle and conduct extra-vehicular activity (EVA) operations to explore and sample the asteroid boulder. This paper will review the top structural design considerations to successfully implement this 50 kW class solar array that must meet unprecedented performance levels. These considerations include beyond state-of-the-art metrics for specific mass, specific volume, deployed area, deployed solar array wing (SAW) keep in zone (KIZ), deployed strength and deployed frequency. Analytical and design results are presented that support definition of stowed KIZ and launch restraint interface definition. An offset boom is defined to meet the deployed SAW KIZ. The resulting parametric impact of the offset boom length on spacecraft moment of inertias and deployed SAW quasistatic and dynamic load cases are also presented. Load cases include ARM spacecraft thruster plume impingement, asteroid surface operations and Orion docking operations which drive the required SAW deployed strength and damping. The authors conclude that to support NASA's ARM power needs, an advanced SAW is required with mass performance better than 125 W/kg, stowed volume better than 40 kW/cu m, a deployed area of 200 sq m (100 sq m for each of two SAWs), a deployed SAW offset distance of nominally 3-4 m, a deployed SAW quasistatic strength of nominally 0.1 g in any direction, a deployed loading displacement under 2 m, a deployed fundamental frequency above 0.1 Hz and deployed damping of at least 1%. These parameters must be met on top of challenging mission environments and ground testing requirements unique to the ARM project.

solar arrays↗
NASA NTRS2017

Spacecraft Mission Design for the Mitigation of the 2017 PDC Hypothetical Asteroid Threat

This paper presents a detailed mission design analysis results for the 2017 Planetary Defense Conference (PDC) Hypothetical Asteroid Impact Scenario, documented at https:cneos.jpl.nasa.govpdcspdc17. The mission design includes campaigns for both reconnaissance (flyby or rendezvous) of the asteroid (to characterize it and the nature of the threat it poses to Earth) and mitigation of the asteroid, via kinetic impactor deflection, nuclear explosive device (NED) deflection, or NED disruption. Relevant scenario parameters are varied to assess the sensitivity of the design outcome, such as asteroid bulk density, asteroid diameter, momentum enhancement factor, spacecraft launch vehicle, and mitigation system type. Different trajectory types are evaluated in the mission design process from purely ballistic to those involving optimal midcourse maneuvers, planetary gravity assists, and/or low-thrust solar electric propulsion. The trajectory optimization is targeted around peak deflection points that were found through a novel linear numerical technique method. The optimization process includes constrain parameters, such as Earth departure date, launch declination, spacecraft, asteroid relative velocity and solar phase angle, spacecraft dry mass, minimum/maximum spacecraft distances from Sun and Earth, and Earth-spacecraft communications line of sight. Results show that one of the best options for the 2017 PDC deflection is solar electric propelled rendezvous mission with a single spacecraft using NED for the deflection.

Barbee, Brent W.↗
NASA NTRS2017

Evidence of Collisional Histories of Asteroids, Comets and Meteorites: Comparisons with Shocked Minerals

Evidence of the collisional history of comets and asteroids has been emerging from analyses of cometary forsterite and enstatite returned from Comet Wild 2 by the Stardust mission (Keller et al.Geochim. Cosmochim. Acta 72, 2008; Tomeoka et al. MAPS 43, 2008; Jacobs et al. MAPS 44, 2009). Likewise, shock metamorphism is observed in many meteoritic forsterites and enstatites (McCausland et al. AGU, 2010), suggesting similar collisional histories for asteroids. Further exploration of the effects of collisions is slated for the upcoming Asteroid Impact Mission/Double Asteroid Redirection Test (AIM/DART) mission, expected for launch in 2020. DART will impact Didymoon, the companion of the larger 65803 Didymos (1996 G2) asteroid, and AIM will use its instrumentation to characterize the impact. A suite of relevant impact experiments have been carried out in the Experimental Impact Laboratory at the NASA Johnson Space Center at velocities ranging from approx. 2.0 - 2.8 km/s and temperatures from 25 C to -100 C. Targets include a suite of minerals typically found in cometary dust and in asteroids and meteorites: Mg-rich forsterite (olivine), enstatite (orthopyroxene), diopside (clinopyroxene), magnesite (Mg-rich carbonate), and serpentine (phyllosilicate). Transmission Electron Microscope (TEM) imaging indicates evidence of shock similar to that seen in forsterite and enstatite from Comet Wild 2. Fourier Transform Infrared (FTIR) Spectroscopy will also be used for comparisons with meteorite spectra. A quantitative analysis of the shock pressures required to induce planar dislocations and spectral effects with respect to wavelength will also be presented.

Lederer, Susan M.↗
NASA NTRS2018

Precious Dust Two Mission Converge on Asteroid Sample Returns

Far-flung spacecraft deliver incredible views of distant worlds. But there's nothing like bringing samples back to Earth. Instruments carried by spacecraft have limitations-of power, complexity, size, and number. Their investigations leave many fundamental questions unanswered, questions that we might be able to answer if only we had samples. This summer marks the beginning of an exciting new era in sample-return missions: NASA's OSIRIS-REx spacecraft arrives at asteroid Bennu, and the Japanese Hayabusa2 spacecraft arrives at asteroid Ryugu. Both are primitive asteroids-dark remnants of Solar System formation that carry carbon and water-a type of asteroid that's never been visited before. After thoroughly mapping their respective asteroids for geology and mineralogy, each probe will collect surface samples and return them to Earth. I can't wait to study them in my laboratory. Cosmic-dust pioneer Kazu Tomeoka introduced me to the dream of sample-return missions 20 years ago. In those days, the only returned extraterrestrial samples were from the Moon. He said to his students, "In the near future, we will be able to collect samples from asteroids and comets. There will be no need to wait for meteorites or cosmic dust to come and fall from the sky. And some of you might be the first to look at those samples." This inspired my life's work: laboratory analysis of returned astromaterials.

Nakamura-Messenger, Keiko↗
NASA NTRS2019

Risk Estimation of Threatening Asteroids

When faced with the question of designing an asteroid deflection mission or with the decision of launching it, significant uncertainties are present in the asteroid’s physical properties, and its orbit solution. The success of the deflection mission relies heavily on these aspects. For example, a heavier than expected asteroid will reduce the imparted deflection DV. So will a larger porosity value by reducing the beta factor [1]. Here, we present a new capability that estimates asteroid impact risk under consideration of these uncertainties. The new method samples the uncertainty space along multiple dimensions, performs a predetermined deflection, propagates the deflected samples to the Earth, models the impact damage, and estimates the overall risk outcome. The work builds on the Probabilistic Asteroid Impact Risk (PAIR) assessment tool [2] by including orbital uncertainty and deflection capabilities. We demonstrate this risk estimation approach for threatening asteroids using the example of the fictitious impactor 2019 PDC. Such analysis provides a quantitative basis for the work of decision makers and disaster managers. It may further find application in areas such as mitigation mission planning where projected post-mitigation risk can be compared to premitigation levels as a means of cost-benefit analysis formitigation options.

Rumpf, Clemens↗
NASA NTRS2017

Characteristics of a high-power ion beam deflection system necessary to deflect the hypothetical asteroid 2017 PD

The July 2027 impact date for the hypothetical asteroid 2017 PDC, that is the subject of an emergency response exercise, leaves just over ten years to implement a deflection approach. The analyses herein allocates four years to the design, fabrication, assembly, test and launch of a notional high-power Ion Beam Deflection (IBD) vehicle to meet a launch readiness date no later than May 2021. Using this launch date along with estimates for the vehicle mass and performance characteristics of the electric propulsion system, low-thrust trajectory analyses indicate a 2.56-year flight time to rendezvous with 2017 PDC. This would leave 3.6 years to execute the actual deflection phase. A 160-kW IBD vehicle could deflect 2017 PDC by at least one Earth radius within this time provided the asteroid’s actual diameter was less than about 140 m and its density was 2 g/cm3 or less. Larger diameters and/or higher densities would require a higher power IBD vehicle, multiple IBD vehicles, or a longer deflection phase. Ion beam deflection is largely independent of the characteristics of the threat object, but its effectiveness, like all deflection approaches, is sensitive to both the asteroid mass and the time available for deflection. The characteristics of IBD, i.e., large standoff distance between the spacecraft and the asteroid surface, as well as ion beam divergence angles of a few degrees, facilitates the possible simultaneous use of multiple IBD vehicles to improve the performance and robustness of the asteroid deflection. The 65-cm diameter, 20-kW NEXIS ion thruster developed in support of the Jupiter Icy Moons Orbiter mission concept is particularly well suited for application to a high-power IBD system. It has demonstrated an ion beam divergence angle of approximately 2 degrees and operation at 20 kW for over 2,000 hours. Completion of the development and flight qualification of this technology would significantly reduce the risk and time necessary to respond to the discovery of potentially hazardous asteroid in the size range of 50- to 100-m diameter.

Reeves, David↗
NASA NTRSDate not supplied

The Aguas Zarcas Breccia - Similarities to Surface Features of Asteroids Ryugu and Bennu

At 21:07 local time on 23rd April 2019, a meteorite fall occurred in Aguas Zarcas, San Carlos County, Alajuela province, Costa Rica. The rapid recovery of this brecciated carbonaceous chondrite after its fall provides an opportunity to investigate a freshly-fallen, relatively uncontaminated and highly-brecciated meteorite for comparison to the samples returned from C-group asteroids by the Hayabusa2 and OSIRIS-REx spacecraft. The study includes several pre-rain fragments. Our X-ray Computed Tomography(XCT) results show many different lithologies. In this study we describe the petrography and mineralogy of five different lithologies of the Aguas Zarcas meteorite. We also present bulk oxygen isotope data of some lithologies and results concerning the organic matter. We describe all the fragments in detail and attempt a classification of each lithology in order to understand the origin and the history of formation of the Aguas Zarcas' parent body. Our results show some lithologies of Aguas Zarcas similar to those in CM chondrites, but others are unique. The different lithologies [1] represent different levels of hydration and heating as well, which are good analogues for the types of materials returned from asteroids Bennu and Ryugu. Spectroscopic observations of the Ryugu and Bennu asteroids compared to laboratory measurements of meteorites suggest that the asteroids show some similarities to heated CM, heated CI or, CI chondrites [2-5]. Both asteroids are regarded to consist of materials altered by aqueous alteration (e.g., [5]) and formed by re-accretion after impact destruction and brecciation (e.g., [6-7]). Considering the various different lithologies in Aguas Zarcas [2] and other CM chondrites [8-9] these types of carbonaceous chondrites may be regarded as good analogues for samples from the Ryugu and Bennu asteroids. The presence of unique and rare lithologies in the Aguas Zarcas, that are distinct from typical CM chondrite lithologies, indicates a complex mixing of various materials in a highly dynamic environment.

Imene Kerraouch↗
NASA NTRS2021

Mineralogy and Surface Modification of Small Grains Recovered from the Asteroid 162173 Ryugu

Surface material on airless bodies exposed to the interplanetary space experienced the bombardment by low-energy (~1 keV/nucleon) solar wind particles and micrometeoroid impacts. These processes, alongside the resultant surface modifications, and spectral darkening and reddening are called space weathering [1]. Space weathering of the Moon and the asteroid 25143 Itokawa belonging to S-type asteroids have been investigated intensively [e.g. 1-5]. The Hayabusa 2 spacecraft returned samples from the asteroid 162173 Ryugu C-type asteroid. The Ryugu samples give us the first opportunity to investigate space weathering of C-type asteroids. The Mineralogy-Petrology Fine (M-P F or Sand) sub-team mainly investigates small grains (typically ~100 μm across). The main purposes of the M-P F sub-team are to understand the variationof mineralogy of the allocated grains and the nature of space weathering of the asteroid Ryugu. The M-P F sub-team is comprised of 51 members belonging to 25 universities and laboratories

T. Noguchi↗
NASA NTRSDate not supplied

Aqueous alteration of Cb-type asteroid Ryugu

The samples from the asteroid Ryugu, which returned to Earth in the winter of 2020 [1], were stored under pure Nitrogen conditions at the Extraterrestrial Materials Curation Center of ISAS. After basic description [2-3], they were distributed to six initial analysis teams in Japan in June 2021. The initial analysis "Stone" team, which was responsible for the analysis of coarse particles (>1 mm in size), consisted of about 150 scientists from Japan and abroad, and conducted a series of analyses We analyzed sixteen coarse Ryugu particles 1 ~ 8 mm in size: six from the 1st touch-down site and ten from the 2nd touch-down site. Individual coarse samples were cut by Xe-FIB or wire-saw to expose particular objects or textures to be exposed on the surface based on 3D structure and element distribution obtained by synchrotron X-ray CT analysis and XRF analysis, respectively. FE-SEM/EDS and FE-EPMA/WDS analysis were made on all polished sections. TEM observation of many FIB sections was made to see microstructures and to compare with carbonaceous chondrites. Many other analyses were carried out to characterize mineralogical and compositional properties and summary of the analysis procedures is described in [4]. X-ray CT analysis showed that all sixteen Ryugu particles are composed of fine-grained material, with no chondrules and CAIs larger than 100 μm in size. FE-EPMA observation showed that Ryugu samples are breccias, consisting of many small rock fragments of different compositions, lithologies, and histories. The most common lithology includes Mg-rich saponite and serpentine, dolomite, magnesite, hydroxyapatite, pyrrhotite, and magnetite as main constituents. The mineralogy of this major lithology supports the classification of Ryugu samples as CI chondrites, which experienced extensive aqueous alteration in Ryugu’s parent asteroid. Based on the obtained mineralogical properties, we performed chemical modeling of aqueous alteration of Ryugu’s parent asteroid [5]. Numerical simulations [6-8] to reproduce thermal history and impact-induced destruction of the Ryugu’s parent asteroid were also carried out using mineralogical and physical properties of the Ryugu samples. In the talk, I would like to explain the conditions of aqueous alteration occurred in the parent asteroid of Ryugu in order to show how the water in the asteroid changed the mineralogy and chemistry of the nebular dust.

T. Nakamura↗
NASA NTRS2022

Global geologic map of asteroid (101955) Bennu indicates heterogeneous resurfacing in the past 500,000 years

Global geologic maps are useful tools for efficient interpretation of a planetary body, and they provide global context for the diversity and evolution of the surface. We used data acquired by the OSIRIS-REx spacecraft to create the first global geologic map of the near-Earth asteroid (101955) Bennu. As this is the first geologic map of a small, non-spherical, rubble-pile asteroid, we discuss the distinctive mapping challenges and best practices that may be useful for future exploration of similar asteroids, such as those to be visited with the Hera and Janus missions. By mapping on two centimeter-scale global image mosaics (2D projected space) and a centimeter-scale global shape model (3D space), we generated three input maps respectively describing Bennu’s shape features, geologic features, and surface texture. Based on these input maps, we defined two geologic units: the Smooth Unit and the Rugged Unit. The units are differentiated primarily on the basis of surface texture, concentrations of boulders, and the distributions of lineaments, mass movement features, and craters. They are bounded by several scarps. The Rugged Unit contains abundant boulders and signs of recent mass movement. It also has fewer small(<20 m), putatively fresh craters than the Smooth Unit, suggesting that such craters have been erased in the former. Based on these geologic indicators, we infer that the Rugged Unit has the younger surface of the two. Differential crater size-frequency distributions and the distribution of the freshest craters suggest that both unit surfaces formed ~10–65 million years ago, when Bennu was located in the Main Asteroid Belt, and the Smooth Unit has not been significantly resurfaced in the past 2 million years. Meanwhile, the Rugged Unit has experienced resurfacing within the past ~500,000years during Bennu’s lifetime as a near-Earth asteroid. The geologic units are consistent with global diversity in slope, surface roughness, normal albedo, and thermal emission spectral characteristics. The site on Bennu where the OSIRIS-REx mission collected a regolith sample is located in the Smooth Unit, in a small crater nested within a larger one. So although the Smooth Unit is an older surface than the Rugged Unit, the impact-crater settingindicates that the material sampled was recently exposed. Several similarities are apparent between Bennu and asteroid (162173) Ryugu from a global geologic perspective, including two geologic units distinguishable by variations in the number density of boulders, as well as in other datasets such as brightness.

E R Jawin↗
NASA NTRSDate not supplied

The Aguas Zarcas Breccia - Similarities to Surface Features of C-Complex Asteroids Ryugu and Bennu

Knowledge of the materials originally present in the proto-solar nebula is one of the most significant constraints for models concerning the formation of our solar system. The physicochemical properties of these original materials can be determined through two distinct and complementary approaches: astronomical observations of nascent stellar systems and the dense clouds from which they originated; and laboratory studies of available astromaterials such as meteorites, interplanetary dust particles, comets, as well as returned mission samples (e.g., from Hayabusa -1 -2;OSIRIS -Rex). Laboratory study of these extraterrestrial materials provides valuable information about the first solids portion of the early solar system and their evolution. Here, we present petrographic and mineralogical characteristics of the polymic beccias Aguas Zarcas based on the research results of [1].On April 23, 2019, at 21:07 local time, a meteorite fall occurred in Aguas Zarcas, San Carlos County, Alajuela province, Costa Rica. The rapid recovery of this brecciated carbonaceous chondrite after its fall provides an opportunity to study a freshly fallen, relatively uncontaminated, and highly brecciated meteorite to compare with samples returned by theHayabusa2 and OSIRIS-REx spacecraft from C-group asteroids. The study includes several pre-rain fragments [1].The X-ray Computed Tomography (XCT) results show many different lithologies. We describe the petrography and mineralogy of five different lithologies of the Aguas Zarcas meteorite. We also present data on bulk oxygen isotopes. We describe all fragments in detail and attempt to classify each lithology in order to understand the origin and formation history of the Aguas Zarcas parent body. Our results show that some lithologies of Aguas Zarcas are similar to those in CM chondrites, but others are unique. The different lithologies [1] also represent different degrees of hydration and heating, which are good analogues for the types of materials returned by the Bennu and Ryugu asteroids. Spectroscopic observations of the Ryugu and Bennu asteroids compared to laboratory measurements of meteorites suggest that the asteroids have some similarities to heated CM, heated CI, or CI chondrites[2-5]. Both asteroids are thought to be composed of materials altered by aqueous alteration (e.g., [5]) and formed by reaccretion after destruction by impacts and brecciation (e.g., [6-7]). Considering the different lithologies in Aguas Zarcas [2] and other CM chondrites [8-9], these types of carbonaceous chondrites can be considered good analogues for samples from the Ryugu and Bennu asteroids. The presence of unique and rare lithologies in the Aguas Zarcas, different from the typical CM chondrite lithologies, suggests complex mixing of different materials in a highly dynamic environment.

Imene Kerraouch↗
NASA NTRSDate not supplied

Results of the Preliminary Analyses of Asteroid Ryugu Regolith Samples Returned by the Hayabusa2 Mission

The Hayabusa2 spacecraft returned 5.5g of regolith material from asteroid 162173 Ryugu in December 2021. The samples were maintained in near-vacuum conditions up to and even during many analyses, a factor that was critical for comparisons of Ryugu lithologies to meteorites because of ubiquitous terrestrial alteration of the latter. Observations of asteroid Ryugu by the Hayabusa2 spacecraft found that it is spinning, top-shaped rubble pile, formed from re-accretion of a (probably) small subset of fragments from a disrupted parent asteroid. Samples retrieved from Ryugu by the spacecraft during two brief touchdowns were expected to contain a record of this history, including the formation and early evolution of the parent body, its subsequent impact destruction and partial re-accretion, and later space weathering. The composition of Ryugu was expected to be similar to that of naturally-heated Ivuna-type carbonaceous chondrite meteorites (CI chondrites), based on ground- and spacecraft-based spectroscopy. Six preliminary examination teams investigated the formation history of Ryugu through laboratory analysis of the returned samples over the past 18 months. Specifically, we sought to determine (1) when and where in the Solar System the parent asteroid of Ryugu formed; (2) the original mineralogy, bulk elemental abundances, and chemical compositions of the accreted materials; (3) how these materials evolved through chemical and physical processing of the parent asteroid; and (4) how the parent asteroid was disrupted during impact and reaccumulated into Ryugu. This brief report mainly summarizes results from the mineralogy and petrology subteams, although results of the composition and isotope subteams are also mentioned. To address these issues, we analyzed numerous Ryugu particles up to ~8 mm in size.

Michael Zolensky↗
NASA NTRSDate not supplied

The Nature of Space Weathering in Samples From Asteroid (162173) Ryugu Revealed By Coordinated Analysis

Space weathering, driven primarily by micrometeorite bombardment and solar wind ion irradiation, alters the morphology, microstructure, and chemistry of the surface regolith on airless bodies. The accumulation of microstructural and chemical space weathering features, including melt deposits, amorphous rims, and nanophase iron-bearing particles (npFe), are associated with alterations of the spectral properties of the regolith. In particular, space weathering changes the spectral slope and reflectance of surface materials, and causes the attenuation of characteristic absorption bands in the visible to near-infrared wave-lengths, as well as a shift towards longer wavelengths of the Christiansen feature (CF)in thermal infrared spectra. Previous studies of space weathering characteristics have focused on siliceous bodies like the Moon and S-type asteroid Itokawa. However, observations of asteroid Ryugu by the JAXA Hayabusa2 spacecraft and subsequent analyses of returned samples revealed carbonaceous and hydrated materials. These samples provided our first opportunity to constrain the effects of space weathering processes on primitive, C-type asteroids. Analyses of returned samples to understand the space weathering of carbonaceous materials are important for accurately interpreting remote sensing observations of carbonaceous asteroids. In addition, the analysis of Hayabusa2 samples from Ryugu paved the way for the analysis of samples from the asteroid Bennu, re-turned by the NASA OSIRIS-REx mission. As space weathering impacts the microstructure, chemistry, and spectral characteristics of asteroidal surfaces, here we report the results of a coordinated analytical study of the micro-and nano-scale signatures of space weathering in samples returned from Ryugu.

L E Melendez↗
NASA NTRS2017

Near Earth Asteroid Characterization for Threat Assessment

Physical characteristics of NEAs are an essential input to modeling behavior during atmospheric entry and to assess the risk of impact but determining these properties requires a non-trivial investment of time and resources. The characteristics relevant to these models include size, density, strength and ablation coefficient. Some of these characteristics cannot be directly measured, but rather must be inferred from related measurements of asteroids and/or meteorites. Furthermore, for the majority of NEAs, only the basic measurements exist so often properties must be inferred from statistics of the population of more completely characterized objects. The Asteroid Threat Assessment Project at NASA Ames Research Center has developed a probabilistic asteroid impact risk (PAIR) model in order to assess the risk of asteroid impact. Our PAIR model and its use to develop probability distributions of impact risk are discussed in other contributions to PDC 2017 (e.g., Mathias et al.). Here we utilize PAIR to investigate which NEA characteristics are important for assessing the impact threat by investigating how changes in these characteristics alter the damage predicted by PAIR. We will also provide an assessment of the current state of knowledge of the NEA characteristics of importance for asteroid threat assessment. The relative importance of different properties as identified using PAIR will be combined with our assessment of the current state of knowledge to identify potential high impact investigations. In addition, we will discuss an ongoing effort to collate the existing measurements of NEA properties of interest to the planetary defense community into a readily accessible database.

Asteroid characterization↗
NASA NTRS2011

Optimal Asteroid Mass Determination from Planetary Range Observations: A Study of a Simplified Test Model

Mars ranging observations are available over the past 10 years with an accuracy of a few meters. Such precise measurements of the Earth-Mars distance provide valuable constraints on the masses of the asteroids perturbing both planets. Today more than 30 asteroid masses have thus been estimated from planetary ranging data (see [1] and [2]). Obtaining unbiased mass estimations is nevertheless difficult. Various systematic errors can be introduced by imperfect reduction of spacecraft tracking observations to planetary ranging data. The large number of asteroids and the limited a priori knowledge of their masses is also an obstacle for parameter selection. Fitting in a model a mass of a negligible perturber, or on the contrary omitting a significant perturber, will induce important bias in determined asteroid masses. In this communication, we investigate a simplified version of the mass determination problem. Instead of planetary ranging observations from spacecraft or radar data, we consider synthetic ranging observations generated with the INPOP [2] ephemeris for a test model containing ~25000 asteroids. We then suggest a method for optimal parameter selection and estimation in this simplified framework.

asteroids↗