Juan A. Sanchez

Renewed interest in lunar exploration is creating a growing population of poorly tracked cislunar objects, some of which will ultimately impact the Moon. The ultimate fate of rocket upper stages or failed mission payloads is often unknown and unplanned. Determining the origin and physical properties of such objects will become increasingly important as sustained lunar exploration places humans and infrastructure on the surface. Here we present a ground-based physical and dynamical characterization of 2025-010D, a Falcon 9 upper stage predicted to impact the lunar farside on 2026 August 5. Backward propagation of its orbit independently links the object to the “Ghost Riders in the Sky” launch, while visible and near-infrared spectroscopy distinguishes it from natural objects and reveals absorption bands consistent with spacecraft thermal control materials. Photometric lightcurves confirm its elongated shape and reveal an unexpected change of more than 8 s in its ∼7 minute rotation period during observations. We predict an impact between Bell and Einstein craters at ∼2.36 km s ⁻¹ , producing a crater ≲25 m in diameter. Since its provenance is independently known, 2025-010D provides a benchmark for identifying and characterizing future cislunar objects of uncertain origin.

The study of S-complex near-Earth objects (NEOs), the parent bodies of ordinary chondrites, has shown that they are dominated by asteroids with LL chondrite-like compositions. This is surprising because among the three subtypes of ordinary chondrites (H, L, and LL), LL chondrites are the least common, representing only 10% of all ordinary chondrite falls. This discrepancy has been attributed to the size of the NEOs studied, which are likely too large to be the immediate precursors of the meteorites that fall on Earth. To test this hypothesis, we obtained near-infrared spectra (0.7–2.5 μ m) of a group of objects with absolute magnitudes 20.0 ≤ H ≤ 29.2 (sizes ∼4–343 m). The sample was divided into subgroups based on their H value, and the composition of the asteroids was determined. We found that the dominance of LL chondrite-like objects disappears at sizes of ∼31–49 m. At this size range, asteroids with L chondrite-like compositions become dominant, matching the fraction of L chondrite meteorite falls. In contrast, the fraction of H chondrite-like NEOs was found to be much lower than the proportion of H chondrite falls, even among the smallest objects. We determined an upper size limit of ∼18 m for the parent bodies of these meteorites. The same upper limit was established for the pre-atmospheric parent bodies of LL chondrites. These results constitute the first observational evidence for a size dependence in the composition of S-complex NEOs.

The Vera C. Rubin Observatory and the future NEO Surveyor infrared space telescope are expected to dramatically increase the number of near-Earth object discoveries. Among these new objects, we expect small (0.40). Despite this detectability, E-types remain among the rarest near-Earth asteroids (NEAs), with few published spectra to constrain their composition or firmly link them to their assumed meteorite analogs, the aubrites. This linkage is further complicated by noncompositional effects such as grain size, especially given growing evidence that small NEAs are regolith-free unlike their larger main belt counterparts. To better characterize this effect, we conducted a spectral study of eight aubrite meteorites from the ultraviolet-to-mid-infrared range (0.18–14.5 μ m; UV–VNIR–MIR) wavelengths, examining multiple grain sizes from μ m powders to slabs. We find that grain size significantly alters key spectral parameters used to interpret aubrite-like material, including albedo, spectral slope, and band depth of the 0.9 μ m feature. We also demonstrate how aubrite grain size data can aid in interpreting E-type NEAs 2023 DZ2 and 2015 TC25, as well as identifying possible connections to the main belt asteroids (434) Hungaria and (44) Nysa, respectively. Finally, we show that grain size affects the Bus–DeMeo taxonomic classification for nearly all of our aubrites, with implications that some small Q-type NEAs may be composed of aubrite-like material rather than ordinary chondrites.

Impacts are the most ubiquitous processes on planetary bodies in our solar system. During these impact events, shock waves can deposit enough energy to produce shock-induced darkening in the target material, resulting in an alteration of its spectral properties. This spectral alteration can lead to an ambiguous taxonomic classification of asteroids and an incorrect identification of meteorite analogs. In this study, we investigated the effects of shock darkening on the visible and near-infrared spectra of ordinary chondrites and members of the howardites, eucrites, and diogenites clan. A decrease in albedo and suppression of the absorption bands with increasing shock darkening was observed for all the samples. We found that adding $\gtrsim$50\% of shock-darkened material to an unaltered sample was enough to change the taxonomic classification of an ordinary chondrite from S-complex to C- or X-complex. A similar amount was sufficient to change the taxonomic classification of a eucrite from V-type to O-type, whereas a eucrite composed of 100\% shock-darkened material was classified as a Q-type. We discuss the limitations of using just albedo for taxonomic classification of asteroids, which has implications for future space-based infrared surveys. We also investigated if shock darkening is responsible for a bias against the discovery of near-Earth objects (NEOs) with H and L chondrite-like compositions, which could explain the abundance of LL chondrites among NEOs.

Impacts are the most ubiquitous processes on planetary bodies in our solar system. During these impact events, shock waves can deposit enough energy to produce shock-induced darkening in the target material, resulting in an alteration of its spectral properties. This spectral alteration can lead to an ambiguous taxonomic classification of asteroids and an incorrect identification of meteorite analogs. In this study, we investigated the effects of shock darkening on the visible and near-infrared spectra of ordinary chondrites and members of the howardites, eucrites, and diogenites clan. A decrease in albedo and suppression of the absorption bands with increasing shock darkening was observed for all the samples. We found that adding ≳50% of shock-darkened material to an unaltered sample was enough to change the taxonomic classification of an ordinary chondrite from S-complex to C- or X-complex. A similar amount was sufficient to change the taxonomic classification of a eucrite from V type to O type, whereas a eucrite composed of 100% shock-darkened material was classified as a Q type. We discuss the limitations of using just albedo for taxonomic classification of asteroids, which has implications for future space-based infrared surveys. We also investigated if shock darkening is responsible for a bias against the discovery of near-Earth objects (NEOs) with H and L chondrite-like compositions, which could explain the abundance of LL chondrites among NEOs.

Active asteroid (6478) Gault underwent outbursts between late 2018 and early 2019 with tails morphologically similar to the ejecta from Dimorphous following the Double Asteroid Redirection Test impact. Multiple studies investigated the dust properties, confirmed that Gault is an S-type Phocaea-family asteroid, and obtained a ∼2.5 hr rotation period consistent with being near the critical rotation period for breakup. We present results from near-infrared spectral monitoring of Gault on one night during a period of activity and five nights across 3 yr after activity ceased in order to understand the evolution of surface mineralogy over time. Spectral band parameters show an average Band I center of 0.920 ± 0.005 μm, Band II center of 2.04 ± 0.13 μm, and band area ratio of 1.33 ± 0.04. These values correspond to an olivine–pyroxene ratio of 0.40, 18.7 mol% fayalite, and 17.2 mol% ferrosilite—all of which are consistent with an H chondrite that has low levels of thermal metamorphism. Three meteorite analogs were identified that are H chondrites with petrologic types between H3.4 and H4. The low-level thermal metamorphism interpretation of Gault’s surface suggests that it formed from the outermost portion of the progenitor of the Phocaea family, assuming an “onion shell’ structure, which was catastrophically disrupted 1.2 Gyr ago. We discuss implications of Gault’s surface composition to better understand this H chondrite parent body, with the suggestion that more dynamical and spectral analyses be performed for members of the Phocaea family.

Linking near-Earth asteroids to associated meteorites can be a challenging process for many reasons, one being grain size differences. To address this issue for rarer meteorites, we studied visible and near-infrared (0.35–2.5 μm) reflectance spectra of 11 rare meteorite classes over five different grain size bins (45–90 μm, 90–150 μm, 150–300 μm, 300–500 μm, and 500–1000 μm). We analyzed the reflectance properties, diagnostic spectral band parameters (band centers and band area ratios), spectral slope, and taxonomic classification. The spectra were analyzed using principal component analysis to detect trends in principal component (PC) space and the impact on asteroid taxonomic classification in the Bus–DeMeo system. We found that the absolute reflectance (visual albedo) at 0.55 μm (photometric V band) typically decreases with increasing grain size, although there are some variations such as sharp increases for the slabs. Our EH4 and aubrite show a trend of increasing spectral slope with decreasing grain size. Our ureilite, angrite, winonaite, acapculoite, and mesosiderite show a general trend of a decrease in Band I (∼0.9 μm) depth with increasing grain size up to 500–1000 μm. Taxonomic classification of spectra of all grain sizes shows that classification tools generally struggle to differentiate grain size effects from mineralogical variations. This research demonstrates the need for a more robust taxonomic classification system that accounts for grain size and one that accurately classifies small near-Earth asteroids with regolith-free surfaces.

We present the results of a fourth planetary defense exercise, focused this time on the small near-Earth asteroid (NEA) 2023 DZ2 and conducted during its close approach to the Earth in 2023 March. The International Asteroid Warning Network (IAWN), with support from NASA's Planetary Defense Coordination Office (PDCO), has been coordinating planetary defense observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. The last campaign focused on the NEA Apophis, and an outcome of that exercise was the need for a short burst campaign to replicate a real-life near-Earth object impact hazard scenario. The goal of the 2023 DZ2 campaign was to characterize the small NEA as a potential impactor and exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication with a short notice of just 24 hr. The entire campaign lasted about 10 days. The campaign team was divided into several working groups based on the characterization method: photometry, spectroscopy, thermal IR photometry and optical polarimetry, radar, and risk assessment. Science results from the campaign show that 2023 DZ2 has a rotation period of 6.2745 ± 0.0030 minutes; visible wavelength color photometry/spectroscopy/polarimetry and near-IR spectroscopy all point to an E-type taxonomic classification with surface composition analogous to aubrite meteorites; and radar observations show that the object has a diameter of 30 ± 10 m, consistent with the high albedo (0.49) derived from polarimetric and thermal IR observations.

The study of small (ν ₆ resonance, 16% from the 3:1, and just 1% from the 5:2 resonance. Lightcurves and rotational periods were derived from the photometric data. No clear trend between the axis ratio and the absolute magnitude or rotational period of the NEOs was found.