Stereophotoclinometry (SPC) makes it possible to extract the shapes of surfaces by combining information from images, namely stereo parallax data and surface shading from slopes, with knowledge of the location of a spacecraft. This technique has been used extensively in the past few decades to describe the shapes of planets and small bodies, such as asteroids and comets. It has also been used to carefully navigate spacecraft around very small bodies, as in the case of the OSIRIS-REx mission to the ∼500 m diameter asteroid (101955) Bennu. This paper describes the mathematical foundation of SPC, with examples from the OSIRIS-REx mission.

Several sample-return missions such as OSIRIS-REx, Hayabusa2, and Mars 2020 recently have or are currently, collecting the most pristine planetary samples we can analyze on Earth since the Apollo missions. Therefore, it is essential to create instrumentation that will allow preliminary compositional analysis of these materials while preventing oxidation, alteration, or contamination from Earth's environment. At York University, a small, transportable environmental chamber with temperature, pressure, and atmosphere control has been integrated on an optical table with a combined UV (266 nm) and Green (532 nm) Raman, laser-induced fluorescence, and time-resolved laser-induced fluorescence instrument. This system can collect high-resolution 2D spectroscopic maps, long accumulation point analysis and time-resolved fluorescence 'fingerprinting'. The sample chamber is capable of pressures <10(-4) mbar, temperatures <-20 C-degrees, and different atmospheric compositions such nitrogen, argon, or carbon dioxide via gas hookup. The intended use of the system is to detect and identify minerals and organics within sensitive or fragile planetary samples using minimally destructive laser-based techniques, while maintaining specific environmental conditions to preserve and maintain the pristineness of the material being analyzed, such as samples returned from planetary missions.(c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

Several space missions from NASA, and ESA have visited and will land on Mars in the search for life. The last mission to arrive was the Mars 2020 Perseverance rover on 18 February 2021. The next mission to Mars will be ExoMars Rosalind Franklin rover, expected to touch down sometime after 2028. Both Mars2020 and ExoMars are equipped with Raman spectroscopic systems: SuperCam and SHER-LOC on Perseverance, and Raman Laser Spectrometer (RLS) on Rosalind Franklin (RF). These instruments will be tasked with iden-tifying rocks, minerals, and potential organic biosignatures on the Martian surface. There are many challenges associated with the qualitative and quantitative analysis of resulting data received from current missions on Mars. It is our belief that studies of new terres-trial Martian analogues can help to overcome these challenges. Here, we introduce Cha similar to das Caldeiras Outcrop, Fogo Island, Cabo Verde as a new volcanic terrestrial analog for Mars. We sampled several areas of relevance in Cha similar to das Caldeiras and conducted a complete band analysis of Raman spectra for targets from this site. Additional analyses included ATR-FTIR and XRD. We detected several pyroxene types (augite and diopside) and plagioclase feldspar species (orthoclase, bytownite, sanidine, albite, and anorthite), olivine (forsterite), oxides (magnetite), and leucite. The alteration and secondary minerals detected were carbonates (calcite and dolomite), oxides (goethite, anatase, and hematite), spinel (chromite), phosphate (apatite), various clays, and zeolites (chabazite and muscovite and analcime). We present the Cha similar to das Caldeiras site as a possible new volcanic analogue for Mars given: 1) the similarities to other volcanic places in the Canary Islands; 2) the exclusive geological evolution that is only present in the volcanic emplacement from the Macaronecia-group; 3) the pristine quality of the samples from the outcrop as well as the alteration volcanic minerals.(c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

We studied the tolerance of one species of quinoa achenes from ecotype RQ252 to simulated extraplanetary conditions in a vacuum chamber (high low-pressure 10-2 to 10-7 Torr, UV laser simulated plasma radiation, and cryogenic temperature). The selection of this ecotype of quinoa achenes was a condition to previous studies, where RQ252 shows evidence of high efficacy in grow adaptation in the South America Puna between 3800-4500 m asl subjected to low oxygen and increased UV radiation exposition. After extraplanetary experi-ment exposure, we evaluated quinoa tolerance to experimental conditions through germination and early growth responses under a controlled laboratory standard atmosphere. Rate and final germination subjected to high low-pressure treatments during 4 h, 8 h, and 16 h were not different to control. Laser plasma application accelerated the germination rates. Final germination always reaches values up to 90%. SEM-EDS analysis showed structural changes on the pericarp surface, especially in high low-pressure and high low pressure + plasma treatments. EDS revealed that the quinoa pericarp subjected to different treatments showed changes in mineral content. Potas-sium ions decreased under high low-pressure and high low pressure + laser plasma irradiation (between 32 and 42%) but increased in a prolonged vacuum (35%) and more when plasma was added (96%). Early growth was affected by the different treatments, being the radicle length the most affected parameter. Our results suggest that quinoa achene ecotype RQ252 viability has excellent tolerance to extraplanetary conditions.

The surface strength of small rubble-pile asteroids, which are aggregates of unconsolidated material under microgravity, is poorly constrained but critical to understanding surface evolution and geologic history of the asteroid. Here we use images of an impact ejecta deposit and downslope avalanche adjacent to a 70-m-diameter impact crater on the rubble-pile asteroid (101955) Bennu to constrain the asteroid’s surface properties. We infer that the ejecta deposited near the crater must have been mobilized with velocities less than Bennu’s escape velocity (20 cm s –1 ); such low velocities can be explained only if the effective strength of the local surface is exceedingly low, nominally ≤2 Pa. This value is four orders of magnitude below strength values commonly used for asteroid surfaces, but it is consistent with recent estimates of internal strength of rubble-pile asteroids and with the surface strength of another rubble-pile asteroid, Ryugu. We find a downslope avalanche indicating a surface composed of material readily mobilized by impacts and that has probably been renewed multiple times since Bennu’s initial assembly. Compared with stronger surfaces, very weak surfaces imply (1) more retention of material because of the low ejecta velocities and (2) lower crater-based age estimates—although the heterogeneous structure of rubble piles complicates interpretation.

The OSIRIS‐REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft sampled asteroid (101955) Bennu on 20 October 2020 and will return the collected regolith to Earth in 2023. Before sample collection, spectral observations of four regions of interest on Bennu's surface were acquired at high spatial resolution (2–9 m per spectrometer spot) to identify the most suitable site for sampling and provide contextual information for the returned sample. In this study, we investigate thermal‐infrared (6–50 μm) observations of these four regions, including the site that OSIRIS‐REx ultimately sampled, using the Advanced Thermophysical Model with input digital terrain models derived from laser altimetry. From model‐to‐measurement comparisons, we find that the observed brightness temperatures depend strongly on small‐scale topography, local variations in thermal inertia, and the observation phase angle. Thermal inertia mapping reveals spatial variations that distinguish the different boulder types found on Bennu. A boulder bearing carbonate veins has higher thermal inertia than average, suggesting that cementation processes reduced its porosity. The thermal inertia of the site sampled is 190 ± 30 J m −2 K −1 s −1/2 , which is consistent with observations of a fine‐grained regolith mixed with porous rocks. Thermophysical modeling of the site sampled predicts that the maximum temperatures experienced by the collected sample while on Bennu were 357 ± 3 and 261 ± 3 K for the surface and 50 cm depth, respectively. We predict that OSIRIS‐REx will return a sample with thermophysical properties unique from those of meteorites.

The LunaR concept study investigated the scientific value, feasibility, and deployment options for a Raman spectrometer on future lunar landed missions. It consists of a breadboard instrument that covers the 150–4000 cm−1 wavelength range with a resolution of ∼6 cm−1; Raman scattering is induced by a 532 nm continuous wave laser. The current conceptual design envisions the Raman spectrometer performing a downward-looking, 90-point one-dimensional across-track scan (±45°off nadir) of the lunar surface with the instrument mounted on the underside of a rover. A downward-looking context camera would provide information on the physical nature of targets interrogated by the Raman spectrometer and localization of the Raman spectra. Our laboratory investigations indicate that Raman spectroscopy is applicable to addressing a wide range of lunar surface exploration goals related to geology, in situ resource identification, and condensed volatile detection in diverse geological terrains, including permanently shadowed regions. Testing of a breadboard and commercial instrument on lunar samples and analogues indicates that a complete spectral scan of a target of interest can be completed in ∼90 min, permitting its use on even short-duration lunar landed missions. All of the major minerals present on the Moon can be detected, and in many cases their compositions can be quantified or constrained.

We propose a Bayesian Markov Chain Monte Carlo parameter estimation technique to determine frequency‐dependent complex dielectric permittivity and permeability of powdered planetary regolith analog materials from coaxial transmission line measurements. The technique uses either a flat (non‐dispersive) or a generalized dielectric response model to simultaneously determine the complex permittivity and permeability from measured scattering parameters. By exploring the parameter space, the technique reduces the dependence on good initial model parameters required by typical optimization methods. The technique can be used with either two‐port measurements or shorted measurements, where an additional one‐port shorted sample is measured. We find the technique is able to accurately determine electromagnetic parameters of low‐loss, high dielectric, and magnetic materials. The technique is also robust to half‐wavelength resonances in the sample as well as the presence of higher order modes.

We present systematic measurements of the frequency‐dependent complex dielectric permittivity of lunar regolith analogue samples with increasing amounts of the mineral ilmenite along with Bayesian model fits using a one‐pole Cole‐Cole model. We use these results to calculate a lower bound for the attenuation of radar signals in dB/m based on ilmenite content. We compare our measurement results with previous efforts to use Earth‐based radar maps to calculate the effect of ilmenite on radar attenuation and find that they are in agreement. We also revisit the ilmenite‐dependent loss tangent relationships of Carrier III et al. (1991) and demonstrate the significant frequency‐dependent effect of ilmenite content on signal attenuation as well as the effect of minor variations in loss tangent for depth‐to‐feature determinations. The results presented here are the first systematic laboratory measurements investigating the effect of ilmenite on radar attenuation and show future promise for the application of dielectric spectroscopy, or the identification of materials based on their electromagnetic properties in the radar and microwave range.

The surface of the rubble‐pile asteroid (101955) Bennu has been characterized in detail by the OSIRIS‐REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission. By examining global and local digital terrain models, we observed that Bennu possesses terraces, that is, a series of roughly latitude‐parallel, step‐like slope breaks. These partially circumscribe the poles and extend east‐west over several longitudinal quadrants at mid‐ to high (≥30°) latitudes. The terraces are subtle in amplitude, with heights ranging from 1 to 5 m. They often exhibit back‐wasting that results in V‐shaped scarps that open downslope in some locations. When boulders >5–10 m are absent at or near a terrace, the steeper portion (the drop) of the terrace lacks rocks, whereas the flatter portion (the bench) of the terrace has accumulations of rocks at its crest. When boulders >5–10 m are present, their steep downslope faces often make up the drop from the terrace crest, and they retain debris upslope, thereby enhancing the terrace structure. A geotechnical stability analysis indicates that Bennu's surface is likely unstable and that surface cohesion is <0.6 Pa. Bennu's terraces strongly resemble scarps generated in laboratory and numerical simulations of a cohesionless granular bed as the slope of the bed increases quasi‐statically. We conclude that terraces are probably actively forming on Bennu as its surface slowly fails owing to creep induced by spin acceleration.

When the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft collected a sample of surface material from asteroid Bennu in 2020 October, it was the first time that an autonomous optical navigation system relying on natural terrain features had been used to guide a spacecraft to a planetary surface. This system, called Natural Feature Tracking (NFT), works by rendering features from digital terrain models and then correlating them with the terrain in real-time navigation images to estimate the spacecraft's position and velocity with respect to the asteroid. Here we describe how the OSIRIS-REx mission built the catalog of features for NFT and how those features performed during rehearsals for and execution of the Touch-and-Go (TAG) sample collection event. Feature performance (quality and accuracy of match) in the rendering and correlation process is the basis of the NFT measurement. All features scored well above the minimum correlation threshold thanks to the effort invested in selecting and modeling them. Residuals across the TAG trajectory were small, indicating that features in the catalog were defined consistently relative to each other. NFT delivered the spacecraft to within 1 m of the targeted location, with a difference of only 3.5 cm and 1.4 s from the predicted location and time of touch. This exceptional performance was crucial for spacecraft safety given Bennu's rough and hazardous terrain.

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 sizefrequency 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 -500,000 years 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 setting indicates 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.

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission rendezvoused with asteroid (101955) Bennu in 2018 with the primary objective of collecting a sample of regolith from the surface. As the first NASA asteroid sample return mission, OSIRIS-REx deployed several new technologies to achieve program objectives. Here we present an overview of Natural Feature Tracking (NFT), a system developed to autonomously guide the spacecraft to the desired sampling site using optical navigation and the natural terrain on the surface of Bennu. NFT utilized a series of image-based digital terrain models (DTMs) constructed by means of stereophotoclinometry to represent patches on the surface of the asteroid. These DTMs were used to generate synthetic renderings of the terrain and identify features for use in navigating to the sampling location. In addition, high-resolution models of the sampling site constructed from scanning lidar data were used for predicting the time and location of contact with the surface. These models went through a series of validation tests to ensure the performance of the NFT system. When the spacecraft executed the sampling trajectory in 2020 October, NFT enabled real-time guidance updates that delivered it safely to the desired sampling location while also providing critical hazard avoidance capabilities in the rocky Bennu environment.

The impactor-to-crater size scaling relationships that enable estimates of planetary surface ages rely on an accurate formulation of impactor–target physics. An armouring regime, specific to rubble-pile surfaces, has been proposed to occur when an impactor is comparable in diameter to a target surface particle (for example, a boulder). Armouring is proposed to reduce crater diameter, or prevent crater formation in the asteroid surface, at small crater diameters. Here, using measurements of 1,560 craters on the rubble-pile asteroid (101955) Bennu, we show that the boulder population controls a transition from crater formation to armouring at crater diameters ~2–3 m, below which crater formation in the bulk surface is increasingly rare. By combining estimates of impactor flux with the armouring scaling relationship, we find that Bennu’s crater retention age (surface age derived from crater abundance) spans from 1.6–2.2 Myr for craters less than a few meters to ~10–65 Myr for craters >100 m in diameter, reducing the maximum surface age by a factor of >15 relative to previous estimates. The range of crater retention ages, together with latitudinal variations in large-crater spatial density, indicate that ongoing resurfacing processes render the surface many times younger than the bulk asteroid.

The OSIRIS-REx spacecraft collected a surface sample from Hokioi crater (55.8° N, 42.3° E; diameter ∼20 m) on the asteroid Bennu in 2020 October. We explore the geology of the sample collection site, known as Nightingale, by using digital terrain models, relative albedo maps, and images collected by the OSIRIS-REx spacecraft. Hokioi crater sits at the northwest edge of an older, larger (120 m diameter) crater between two north–south ridges respectively located at roughly 0° and 90° longitude, between which unconsolidated material generally migrates from the geopotential high at the north (+Z) pole to the geopotential low at the equator. The impact that formed Hokioi crater exposed relatively unweathered, fine-grained dark material that we observe within and ejected beyond the crater. The regional slope and steep crater walls to the north of the Nightingale site have enabled a mix of the dark debris and brighter material (which may include carbonates and/or exogenic basalts) surrounding Hokioi crater to migrate onto the crater floor, where the sample was collected; some of this material may be old ejecta excavated from up to 10 m depth when the 120 m diameter crater formed. We therefore expect the OSIRIS-REx sample to include materials of varying brightnesses, compositions, and exposure ages, derived primarily from the 0°–90° longitude quadrant and from as deep as 10 m. The sample may also include material derived from the impactor that formed Hokioi crater. We expect it to have low cohesion (≪0.6 Pa) and a friction angle between 32° and 39°.

The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft collected a sample from the asteroid Bennu in 2020. This achievement leveraged an autonomous optical navigation approach called Natural Feature Tracking (NFT). NFT provided spacecraft state updates by correlating asteroid surface features rendered from previously acquired terrain data with images taken by the onboard navigation camera. The success of NFT was the culmination of years of preparation and collaboration to ensure that feature data would meet navigation requirements. This paper presents the findings from ground testing performed prior to the spacecraft's arrival at Bennu, in which synthetic data were used to develop and validate the technical approach for building NFT features. Correlation sensitivity testing using synthetic models of Bennu enabled the team to characterize the terrain properties that worked well for feature correlation, the challenges posed by smoother terrain, and the impact of imaging conditions on correlation performance. The team found that models constructed from image data by means of stereophotoclinometry (SPC) worked better than those constructed from laser altimetry data, except when test image pixel sizes were more than a factor of 2 smaller than those of the images used for SPC, and when topography was underrepresented and resulted in incorrect shadows in rendered features. Degradation of laser altimetry data related to noise and spatial sampling also led to poor correlation performance. Albedo variation was found to be a key contributor to correlation performance; topographic data alone were insufficient for NFT.

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-meter-long elliptical crater. This exposed material is darker, spectrally redder, and more abundant in fine particulates than the original surface. The bulk density of the displaced subsurface material was 500 to 700 kilograms per cubic meter, which is about half that of the whole asteroid. Particulates that landed on instrument optics spectrally resemble aqueously altered carbonaceous meteorites. The spacecraft stored 250 ± 101 grams of material, which will be delivered to Earth in 2023.

K. Ishimaru1, D. S. Lauretta1, N. Porter1, D. R. Golish1, M. Al Asad2, R. L. Ballouz1, O. S. Barnouin3, K. N. Burke1, M. G. Daly4, D. N. DellaGiustina1, B. Rizk1, and K. J. Walsh5. 1Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ, 85721, USA, 2Department of Earth Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada, 3The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA, 4The Centre for Research in Earth and Space Science, York University, Toronto, Ontario, Canada, 5Southwest Research Institute, Boulder, CO, USA. (kana@orex.lpl.arizona.edu)

Exploration of asteroid (101955) Bennu by the OSIRIS-REx mission has provided an in-depth look at this rubble-pile near-Earth asteroid. In particular, the measured gravity field and the detailed shape model of Bennu indicate significant heterogeneities in its interior structure, compatible with a lower density at its center. Here we combine gravity inversion methods with a statistical rubble-pile model to determine the density and size-frequency distribution (SFD) index of the rubble that constitutes Bennu. The best-fitting models indicate that the SFD of the interior is consistent with that observed on the surface, with a cumulative SFD index of approximately $-2.9$. The rubble bulk density is approximately $1.35$ g/cm$^3$, corresponding to a $12$% macro-porosity. We find the largest rubble particle to be approximately $145$ m, whereas the largest void is approximately $10$ m.

The authors regret that in the printed version of the above article there are errors in Eqs. (3)–(5) and would therefore like to draw attention to the corresponding corrections. The correct and final version follows. In the original paper, Eqs.(3)–(5) appeared as [Formula presented]where [Formula presented]and [Formula presented] The correct equations should be: [Formula presented]where [Formula presented]and [Formula presented] These changes do not affect the results or discussion present in the article. The authors would like to apologise for any inconvenience caused.