Search

Apophis’s current trajectory takes it safely past our planet at a distance of several Earth radii on 2029 April 13. Here the possibility is considered that Apophis could collide with a small asteroid, like the ones that frequently and unpredictably strike Earth, and the resulting perturbation of its trajectory. The probability of an impact that could significantly displace Apophis relative to its keyholes is found to be less than one in 10 ^6 , requiring a Δ v ≳ 0.3 mm s ^−1 , while for an impact that could significantly displace Apophis compared to its miss distance in 2029, it is less than one in 10 ^9 , requiring a Δ v ≳ 5 cm s ^−1 . These probabilities are below the usual thresholds considered by asteroid impact warning systems. Apophis is in the daytime sky and unobservable from mid-2021 to 2027. It will be challenging to determine from single-night observations in 2027 if Apophis has moved on the target plane enough to enter a dangerous keyhole, as the deviation from the nominal ephemeris might be only a few tenths of an arcsecond. An impending Earth impact would, however, be signaled clearly in most cases by deviations of tens of arcseconds of Apophis from its nominal ephemeris in 2027. Thus, most of the impact risk could be retired by a single observation of Apophis in 2027, though a minority of cases present some ambiguity and are discussed in more detail. Charts of the on-sky position of Apophis under different scenarios are presented for quick assessment by observers.

Among binary asteroids, (35107) 1991VH stands out as unique given the likely chaotic rotation within its secondary component. The source of this excited dynamical state is unknown. In this work, we demonstrate that a past close encounter with Earth could have provided the necessary perturbation to allow the natural internal dynamics, characterized by spin–orbit coupling, to evolve the system into its current dynamical state. In this hypothesis, the secondary of 1991VH was previously in a classical 1:1 spin–orbit resonance with an orbit period likely between 28 and 35 hr before being perturbed by an Earth encounter within ∼80,000 km. We find that if the energy dissipation within the secondary is relatively inefficient, this excited dynamical state could persist to today and produce the observed ground-based measurements. Coupled with the orbital history of 1991VH, we can then place a constraint on the tidal dissipation parameters of the secondary.

On 2022 September 26, the Double Asteroid Redirection Test (DART) mission was the first successful demonstration of a kinetic impactor for planetary defense. The DART mission utilized a novel autonomous data processing pipeline architecture to quickly produce and analyze the quality of raw and calibrated images from the camera mounted on board the spacecraft. Optimization of the data processing pipeline allowed the final 150 images prior to impact to be calibrated and delivered to the Investigation Team and the press within 15 minutes of acquisition. A data quality analysis pipeline allowed for rapid identification of detector misconfigurations, missing data, and other adverse events. DART data products, along with data from LICIACube and data from ground observatories, used common file formats to facilitate the development of analysis and archiving software. This architecture is described for future missions with large volumes of data and an emphasis on quick-turnaround applications such as planetary defense.

NASA’s Near-Earth Object Surveyor mission, scheduled for launch in 2027 September, is designed to detect and characterize at least two-thirds of the potentially hazardous asteroids with diameters larger than 140 m in a nominal 5 yr mission. We describe a model to estimate the survey performance using a faster approach than the time domain survey simulator described in Mainzer et al. (2023). This model is applied to explain how the completeness for 5 and 10 yr surveys varies with orbit type and asteroid size and to identify orbits with notably high or low likelihoods of detection. Size alone is an incomplete proxy for impact hazard, so for each asteroid orbit, we also calculate the associated hazard based on the impact velocity and the relative likelihood of impact. We then estimate how effective the mission will be at anticipating impacts as a function of impact energy, finding that a 5 yr mission will identify 87% of potential impacts larger than 100 Mt (Torino-9, “Regional Devastation”). For a 10 yr mission, this increases to 94%. We also show how the distribution of warning time varies with impact energy.

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.

Characterization of near-Earth objects (NEOs) is critical for Earth-impact hazard assessment. Particularly crucial to our physical understanding of NEOs are laboratory spectral measurements of meteorites as they are the best and most widely available analog materials, barring sample return missions. However, most meteorites do not have direct orbital links to specific asteroids, making it challenging to identify their source body in the NEO or main-belt asteroid populations. Near-Earth asteroid (NEA) 2024 BX1 was discovered on 2024 January 20 at 21:48 UTC from MPC code K88, impacting the Earth (west of Berlin, Germany) 165 minutes later. The incoming bolide was observed by multiple meteor cameras, which enabled successful reconstruction of its exo-atmospheric orbit and quick recovery. We present results from laboratory spectral characterization of the Ribbeck meteorite in the UV–mid-infrared wavelengths (0.2–14.2 μ m) over seven grain size bins (

On 2022 September 26 (UTC), NASA's Double Asteroid Redirection Test (DART) mission achieved a successful impact on Dimorphos, the secondary component of the near-Earth binary asteroid system (65803) Didymos. Subsequent ground-based observations suggest a significant reshaping of Dimorphos, with its equatorial axis ratio changing from 1.06 to ∼1.3. Here we report the effects of this reshaping event on Dimorphos's orbit and attitude. Given the reported reshaping magnitude, our mutual dynamics simulations show that approximately 125 s of the observed 33 minute orbit period change after the DART impact may have resulted from reshaping. This value, however, is sensitive to the precise values of Dimorphos's post-impact axis ratios and may vary by up to 2 times that amount, reaching approximately 250 s within the current uncertainty range. While the rotational state of the body is stable at the currently estimated axis ratios, even minor changes in these ratios or the introduction of shape asymmetry can render its attitude unstable. The perturbation to Dimorphos’s orbital and rotational state delivered by the impact directly, combined with any reshaping, leads to a strong possibility for a tumbling rotation state. To accurately determine the momentum enhancement factor ( β ) through measurements by the European Space Agency’s Hera spacecraft and to evaluate the effectiveness of the kinetic deflection technique for future planetary defense initiatives, the effects of reshaping should not be overlooked.

The study of small (

The world’s first planetary defense test mission was carried out in late 2022 by NASA’s Double Asteroid Redirection Test (DART) mission. The main DART spacecraft, which was accompanied by the ASI-provided LICIACube cubesat, intentionally impacted Dimorphos, the smaller secondary of the near-Earth object binary system (65803) Didymos, on 2022 September 26. The impact released a large amount of ejecta, which, combined with the spacecraft’s momentum, produced the observed 33 ± 1 minute period change that was subsequently observed from ground-based telescopes. The DART mission, in addition to having successfully changed the orbital period of Dimorphos, also activated the asteroid as a result of the impact but under known conditions, unlike other impacts on asteroids. We have conducted long-term monitoring over 5 months following the impact with the Las Cumbres Observatory Global Telescope (LCOGT) network and Magdalena Ridge Observatory (MRO). This was supplemented by almost 3 months of more sparsely sampled data, primarily from educational users of the LCOGT network during the period from 2022 July 5 to 2022 September 25, prior to the impact date of 2022 September 26. Here we report the observations of the Didymos system and DART impact ejecta with the telescopes of the LCOGT network from T+1.93 days to T+151.3 days after impact, and we study the evolving morphology of the ejecta cloud and evolving tail over the entire length of the data set. In addition, we combined these intensive data sets with the earlier sparse observations over the ∼90 days prior to impact to derive a new disk-integrated phase function model using the H , G _1 , G _2 parameterization.

We report radar, photometric, and visible-wavelength spectrophotometry observations of NEA 2018 EB obtained in 2018. The radar campaign started at Goldstone (8560 MHz, 3.5 cm) on April 7, and it was followed by more extensive observations from October 5 to 9 by both Arecibo (2380 MHz, 12.6 cm) and Goldstone. 2018 EB was observed optically on April 5, 8, and 9 and again on October 18. Spectrophotometry was obtained on October 19 with the SOAR telescope, and the data suggest that 2018 EB is an Xk-class object. The echo power spectra and delay-Doppler radar images revealed that 2018 EB is a binary system. Radar images constrained the satellite's diameter to ${0.15}_{-0.05}^{+0.02}$ km, but the data were not sufficient for shape modeling. Shape modeling of lightcurves and radar data yielded an oblate primary with an effective diameter D = 0.30 ± 0.04 km and a sidereal rotation period of ${4.3}_{-0.5}^{+0.6}$ hr. Measurements of delay-Doppler separations between the centers of mass of the primary and the satellite, along with the timing of a radar eclipse observed on October 9, resulted in an orbit fit for the satellite with a semimajor axis of ${0.50}_{-0.01}^{+0.04}$ km, an eccentricity of 0.15 ± 0.04, a period of ${16.85}_{-0.26}^{+0.33}$ hr, and an orbit pole constrained to the ecliptic longitudes and latitudes of $\lambda ={93}_{-{43}^{^\circ }}^{+{27}^{^\circ }}$ and $\beta ={48}_{-{18}^{^\circ }}^{+{7}^{^\circ }}$ . The system mass was estimated to be ${2.03}_{-0.08}^{+0.52}\times {10}^{10}$ kg, which yielded a bulk density of ${1.4}_{-0.5}^{+0.6}$ g cm ^−3 . Our analysis suggests that 2018 EB has a low optical albedo of p _V = 0.028 ± 0.016 and a relatively high radar albedo of η _OC = 0.29 ± 0.11 at Arecibo and η = 0.22 ± 0.10 at Goldstone.

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the moon Dimorphos of the [65803] Didymos binary system and changed the binary orbit period, demonstrating asteroid deflection by a kinetic impact and indicating that more momentum was transferred to Dimorphos by escaping impact ejecta than was incident with DART. Images of the DART impact ejecta plume were obtained by the Light Italian cubesat for Imaging of Asteroids (LICIACube) in the first few minutes after the DART impact. The ejecta plume imaged by LICIACube 158 s after the DART impact prior to closest approach shows no evidence for plume clearing at low altitude. The ejecta plume imaged 175 s after the DART impact is optically thick up to projected altitudes of 200 m above the surface of Dimorphos. These observations are compared with models of the impact ejecta plume optical depth, structure, and evolution, which are developed from point-source scaling models fitted to numerical simulations of the DART impact into a rubble pile Dimorphos with different material strengths. The observations of the impact plume optical depth and the high momentum transfer from the DART impact are not consistent with impact and ejecta plume models assuming the Dimorphos cohesive strength to be as high as 5000 Pa. Models with 5 and 50 Pa Dimorphos cohesive strength provide the overall best consistency with plume opacity observations and high momentum transfer.

Asteroids with low orbital perihelion distances experience extreme heating from the Sun that can modify their surfaces and trigger nontypical activity mechanisms. These objects are generally difficult to observe from ground-based telescopes due to their frequent proximity to the Sun. The Near-Earth Object (NEO) Surveyor mission, however, will regularly survey down to solar elongations of 45° and is well suited for the detection and characterization of low-perihelion asteroids. Here, we use the survey simulation software tools developed for mission verification to explore the expected sensitivity of NEO Surveyor to these objects. We find that NEO Surveyor is expected to be >90% complete for near-Sun objects larger than D ∼ 300 m. Additionally, if the asteroid (3200) Phaethon underwent a disruption event in the past to form the Geminid meteor stream, Surveyor will be >90% complete to any fragments larger than D ∼ 200 m. For probable disruption models, NEO Surveyor would be expected to detect dozens of objects on Phaethon-like orbits, compared to a predicted background population of only a handful of asteroids, setting strong constraints on the likelihood of this scenario.

The ASI cubesat LICIACube has been part of the first planetary defense mission DART, having among its scopes to complement the DRACO images to better constrain the Dimorphos shape. LICIACube had two different cameras, LEIA and LUKE, and to accomplish its goal, it exploited the unique possibility of acquiring images of the Dimorphos hemisphere not seen by DART from a vantage point of view, in both time and space. This work is indeed aimed at constraining the tridimensional shape of Dimorphos, starting from both LUKE images of the nonimpacted hemisphere of Dimorphos and the results obtained by DART looking at the impacted hemisphere. To this aim, we developed a semiautomatic Computer Vision algorithm, named VADER, able to identify objects of interest on the basis of physical characteristics, subsequently used as input to retrieve the shape of the ellipse projected in the LUKE images analyzed. Thanks to this shape, we then extracted information about the Dimorphos ellipsoid by applying a series of quantitative geometric considerations. Although the solution space coming from this analysis includes the triaxial ellipsoid found by using DART images, we cannot discard the possibility that Dimorphos has a more elongated shape, more similar to what is expected from previous theories and observations. The result of our work seems therefore to emphasize the unique value of the LICIACube mission and its images, making even clearer the need of having different points of view to accurately define the shape of an asteroid.

Since the dawn of the Space Age, hundreds of payloads have been launched into heliocentric space. As near-Earth object (NEO) surveys search deeper for small asteroids, more artificial objects in heliocentric orbits are being discovered. We now face a challenge to identify the true nature of these objects and avoid contaminating the NEO catalog. Here, we present the methods used to characterize one such object. 2020 SO was discovered by the Pan-STARRS1 survey on 2020 September 17. Originally classified as a NEO, the object’s artificial nature became evident due to its low velocity relative to Earth and solar radiation pressure affecting its orbit about the Sun. Based on a backward propagation of its orbit, 2020 SO is thought to be a Centaur rocket body (R/B) from the launch of the Surveyor 2 mission to the Moon. We characterized 2020 SO using a range of ground-based optical and near-infrared telescopes to constrain its true nature. We find that its reflectance spectrum is consistent with that of other Centaur R/B launched during a similar time frame, and we identify 1.4, 1.7, and 2.3 μ m absorption bands consistent with polyvinyl fluoride used on the aft bulkhead radiation shield exterior of Centaur-D R/B at the time.

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission recently returned a sample of rocks and dust collected from asteroid Bennu. We analyzed the highest-resolution thermal data obtained by the OSIRIS-REx Thermal Emission Spectrometer (OTES) to gain insight into the thermal and physical properties of the sampling site, including rocks that may have been sampled, and the immediately surrounding Hokioi Crater. After correcting the pointing of the OTES data sets, we find that OTES fortuitously observed two dark rocks moments before they were contacted by the spacecraft. We derived thermal inertias of 100–150 (±50) J m ^−2 K ^−1 s ^−1/2 for these two rocks—exceptionally low even compared with other previously analyzed dark rocks on Bennu (180–250 J m ^−2 K ^−1 s ^−1/2 ). Our simulations indicate that monolayer coatings of sand- to pebble-sized particles, as observed on one of these rocks, could significantly reduce the apparent thermal inertia and largely mask the properties of the substrate. However, the other low-thermal-inertia rock that was contacted is not obviously covered in particles. Moreover, this rock appears to have been partially crushed, and thus potentially sampled, by the spacecraft. We conclude that this rock may be highly fractured and that it should be sought in the returned sample to better understand its origin in Bennu’s parent body and the relationship between its thermal and physical properties.

On 2022 September 26, NASA's Double Asteroid Redirection Test (DART) successfully hit Dimorphos, the smaller companion of the binary system formed with the asteroid (65803) Didymos. Both the binary system and the impact event were imaged by the Light Italian Cubesat for Imaging of Asteroids, detached from DART 15 days before the impact. Images from the onboard LUKE red, green, and blue camera together with ground-based observations enabled the reconstruction of Didymos's brightness phase curve, with phase angles ranging from 2.35° to 107.7°. The opposition effect regime was studied using the exponential-linear equation, the “Shevchenko” function and the linear-by-parts model while the IAU-official HG1G2 magnitude system was applied to the full phase curve. The opposition effect indicates an unusual asteroid surface for an S type, with characteristics similar to M-type asteroids. While the HG1G2 parameters from the full phase curve place Didymos well among asteroids of the taxonomic C complex. Didymos’s phase curve parameters when compared to near-Earth asteroids are very close to the Q type (1862) Apollo, indicating possible depletion of fine submicrometric grains through resurfacing. Didymos's geometric albedo (0.15 ± 0.01) is reported to be 30%–45% smaller than the average geometric albedo for near-Earth S types (0.26 ± 0.04). We propose that Didymos might be an LL ordinary chondrite analog containing albedo-suppressing, shock-darkened/impact melt minerals that have undergone resurfacing processes in the past. A comparison with meteorites indicates that, less likely, Didymos could also contain materials analog to carbon-bearing brecciated L3 ordinary chondrites.

This study provides a pre-impact map of the albedo of the Double Asteroid Redirection Test (DART) target Dimorphos corrected for all the effects of viewing geometry, as well as an estimate of photometric roughness for the hemisphere imaged by DART. Other photometric properties are derived for the (65803) Didymos binary system based on DART and ground-based measurements obtained at JPL’s Table Mountain Observatory. The roughness, geometric albedo, phase curve and phase integral, and single particle phase function are typical of the S-family of asteroids. The major remaining uncertainty lies in the behavior of the phase curve below 7°. These results provide a baseline for comparison with Hera measurements, leading to an understanding of the quantitative effects of the kinetic impactor mitigation strategy.

Asteroid 99942 Apophis will pass near Earth in 2029 April. Expected to miss our planet by a safe margin, that could change if Apophis's path were perturbed by a collision with another asteroid in the interim. Though the statistical chance of such a collision is minuscule, the high risk associated with Apophis motivates us to examine even this very unlikely scenario. In this work, we identify encounters between known asteroids and Apophis up to 2029 April. Here we show that Apophis will encounter the 1300 m diameter asteroid 4544 Xanthus in 2026 December. Their minimum orbit intersection distance is less than 10,000 km, with Apophis passing that closest point just 4 hr before Xanthus. Though a direct collision is ruled out, the encounter is close enough that material accompanying Xanthus (if any) could strike Apophis. We also identify other asteroid encounters that deserve monitoring.

We present a series of numerical simulations using a shock physics smoothed particle hydrodynamics code, investigating energetic impacts on small celestial bodies characterized by diverse internal structures, ranging from weak and homogeneous compositions to rubble-pile structures with varying boulder volume packing. Our findings reveal that the internal structure of these rubble-pile bodies significantly influences the impact outcomes. Specifically, we observe that the same impact energy can either catastrophically disrupt a target with a low boulder packing (≲30 vol%), or result in the ejection of only a small fraction of material from a target with the same mass but high boulder packing (≳40 vol%). This finding highlights the pivotal role played by the rubble-pile structure, effectively acting as a bulk shear strength, which governs the size and behavior of the resulting impact. Consequently, understanding and characterizing the internal structure of asteroids will be of paramount importance for any future efforts to deflect or disrupt an asteroid on a collision course with Earth.

The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos, on 2022 September 26 UTC. We estimate the changes in the orbital and physical properties of the system due to the impact using ground-based photometric and radar observations, as well as DART camera observations. Under the assumption that Didymos is an oblate spheroid, we estimate that its equatorial and polar radii are 394 ± 11 m and 290 ± 16 m, respectively. We estimate that the DART impact instantaneously changed the along-track velocity of Dimorphos by −2.63 ± 0.06 mm s ^−1 . Initially, after the impact, Dimorphos’s orbital period had changed by −32.7 minutes ± 16 s to 11.377 ± 0.004 hr. We find that over the subsequent several weeks the orbital period changed by an additional 34 ± 15 s, eventually stabilizing at 11.3674 ± 0.0004 hr. The total change in the orbital period was −33.25 minutes ±1.5 s. The postimpact orbit exhibits an apsidal precession rate of 6.7 ± 0.°2 day ^−1 . Under our model, this rate is driven by the oblateness parameter of Didymos, J _2 , as well as the spherical harmonics coefficients, C _20 and C _22 , of Dimorphos’s gravity. Under the assumption that Dimorphos is a triaxial ellipsoid with a uniform density, its C _20 and C _22 estimates imply axial ratios, a / b and a / c , of about 1.3 and 1.6, respectively. Preimpact images from DART indicate Dimorphos’s shape was close to that of an oblate spheroid, and thus our results indicate that the DART impact significantly altered the shape of Dimorphos.

We present results from observations of 238 near-Earth objects (NEOs) obtained with the RATIR instrument on the 1.5 m robotic telescope at San Pedro Martir’s National Observatory in Mexico, in the frame of our multiobservatory, multifilter campaign. Our project is focused on rapid response photometric observations of NEOs with absolute magnitudes in the range 18.1–27.1 (diameter ≈ 600 and 10 m, respectively). Data with coverage in the near-infrared and visible range were analyzed with a nonparametric classification algorithm, while visible-only data were independently analyzed via Monte Carlo simulations and a 1-Nearest Neighbor method. The rapid response and the use of spectrophotometry allows us to obtain taxonomic classifications of subkilometer objects with small telescopes, representing a convenient characterization strategy. We present taxonomic classifications of the 87 objects observed in the visible and near-infrared. We also present the taxonomic distribution of an additional 151 objects observed in the visible. Our most accurate method suggests a nonfeatured-to-featured ratio of ≈0.75, which is consistent with the value found by the Mission Accessible Near-Earth Object Survey, which conducted a similar study using a spectral analysis. The results from the Monte Carlo method suggest a ratio of ≈0.8, although this method has some limitations. The 1-Nearest Neighbor method showed to be not suitable for NEO classifications.

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the secondary body of the binary asteroid (65803) Didymos on 2022 September 26 and altered its orbit about the primary body. Before the DART impact, we performed visible and mid-infrared observations to constrain the pre-impact thermophysical properties of the Didymos system and to model its Yarkovsky effect. Analysis of the photometric phase curve derives a Bond albedo of 0.07 ± 0.01, and a thermophysical analysis of the mid-infrared observations derives a thermal inertia of 320 ± 70 J m ^−2 K ^−1 s ^−1/2 and a thermal roughness of 40° ± 3° rms slope. These properties are compatible with the ranges derived for other S-type near-Earth asteroids. Model-to-measurement comparisons of the Yarkovsky orbital drift for Didymos derives a bulk density of 2750 ± 350 kg m ^−3 , which agrees with other independent measures based on the binary mutual orbit. This bulk density indicates that Didymos is spinning at or near its critical spin-limit at which self-gravity balances equatorial centrifugal forces. Furthermore, comparisons with the post-impact infrared observations presented in Rivkin et al. indicate no change in the thermal inertia of the Didymos system following the DART impact. Finally, orbital temperature simulations indicate that subsurface water ice is stable over geologic timescales in the polar regions if present. These findings will be investigated in more detail by the upcoming ESA Hera mission.

The apparent velocities of near-Earth asteroids (NEAs) are usually high when they pass by Earth. Observing these fast-moving objects with long exposure times would cause their images to streak and significantly decrease the precision of astronomical measurements. The rotating-drift-scan (RDS) charge-coupled device technique is a promising approach to observe fast-moving NEAs during their close approaches to Earth. By rotating the camera of a telescope, an NEA can be observed in the time delay integration mode. This allows the asteroid to be imaged as a point source, even with a long exposure time. Here, we thoroughly present the RDS follow-up observation and orbit determination of a newly discovered NEA 2023 BJ _7 . This technique makes an impactful contribution to improving the NEA's orbit accuracy by extending the observation arc. A detailed statistical analysis of the astrometric error was conducted, revealing that RDS observations can achieve a competitive accuracy with an rms error of 0.″24 in right ascension and 0.″32 in declination. The instability of the telescope is thought to be the main reason affecting the internal precision. Furthermore, the RDS technique excels at observing fast-moving NEAs, as well as newly discovered NEAs without accurate ephemerides. For NEAs with rates of motion exceeding 10 deg day ^−1 , the rms of RDS observation residuals is 0.″35 in the along-track direction and 0.″23 in the cross-track. With this technique, a network of small-aperture telescopes would substantially benefit our global NEAs monitoring system to ensure Earth’s safety from any asteroid impacts.

We explore binary asteroid formation by spin-up and rotational disruption considering the NASA DART mission's encounter with the Didymos–Dimorphos binary, which was the first small binary visited by a spacecraft. Using a suite of N -body simulations, we follow the gravitational accumulation of a satellite from meter-sized particles following a mass-shedding event from a rapidly rotating primary. The satellite’s formation is chaotic, as it undergoes a series of collisions, mergers, and close gravitational encounters with other moonlets, leading to a wide range of outcomes in terms of the satellite's mass, shape, orbit, and rotation state. We find that a Dimorphos-like satellite can form rapidly, in a matter of days, following a realistic mass-shedding event in which only ∼2%–3% of the primary's mass is shed. Satellites can form in synchronous rotation due to their formation near the Roche limit. There is a strong preference for forming prolate (elongated) satellites, although some simulations result in oblate spheroids like Dimorphos. The distribution of simulated secondary shapes is broadly consistent with other binary systems measured through radar or lightcurves. Unless Dimorphos's shape is an outlier, and considering the observational bias against lightcurve-based determination of secondary elongations for oblate bodies, we suggest there could be a significant population of oblate secondaries. If these satellites initially form with elongated shapes, a yet-unidentified pathway is needed to explain how they become oblate. Finally, we show that this chaotic formation pathway occasionally forms asteroid pairs and stable triples, including coorbital satellites and satellites in mean-motion resonances.

NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1 σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β , resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.

The successful impact of NASA’s DART mission with Dimorphos, the secondary body of binary asteroid system (65803) Didymos, altered the attitude, shape, and orbit of Dimorphos. In addition to perturbing the immediate short-term dynamics of the system, these changes have major implications for the binary Yarkovsky–O’Keefe–Radzievskii–Paddack (BYORP) effect and resulting long-term secular evolution. In this study, we assess the range of possible reshaping-induced changes in BYORP. We produce high-fidelity numerical simulations of the orbit-attitude coupled tidal-BYORP dynamical evolution of the Didymos system to constrain how the secular evolution changed from its preimpact behavior. We find that the nature of the dynamics is highly dependent on a variety of initial conditions and assumptions, and it is difficult to fully predict how the system will secularly evolve following the impact. Rather, we provide a range of feasible possibilities within the bounds of observations and current best estimates of the Didymos system parameters. ESA’s Hera mission will help reduce uncertainties surrounding the postimpact state and shape of Dimorphos in 2027, allowing our predictions of the secular evolutionary effects and long-term fate of the Didymos system to be better refined.

Stereophotoclinometry (SPC) was the prime method of shape modeling for NASA’s OSIRIS-REx mission to asteroid Bennu. Here we describe the extensive testing conducted before launch to certify SPC as NASA Class B flight software, which not only validated SPC for operational use but also quantified the accuracy of this technique. We used a computer-generated digital terrain model (DTM) of a synthetic asteroid as the truth input to render simulated truth images per the planned OSIRIS-REx observing campaign. The truth images were then used as input to SPC to create testing DTMs. Imaging sets, observational parameters, and processing techniques were varied to evaluate their effects on SPC's performance and their relative importance for the quality of the resulting DTMs. We show that the errors in accuracy for SPC models are of the order of the source images’ smallest pixel sizes and that a DTM can be created at any scale, provided there is sufficient imagery at that scale. Uncertainty in the spacecraft’s flight path has minimal impact on the accuracy of SPC models. Subtraction between two DTMs (truth and simulated) is an effective approach for measuring error but has limitations. Comparing the simulated truth images with images rendered from the SPC-derived DTMs provides an excellent metric for DTM quality at smaller scales and can also be applied in flight by using real images of the target. SPC has limitations near steep slopes (e.g., the sides of boulders), leading to height errors of more than 30%. This assessment of the accuracy and sensitivity of SPC provides confidence in this technique and lessons that can be applied to future missions.

The OSIRIS-REx mission used stereophotoclinometry (SPC) to generate digital terrain models (DTMs) of its target asteroid, Bennu. Here we present a suite of preflight tests conducted to identify the observing geometry and number of images needed to create DTMs that would enable successful navigation around and to the surface of the asteroid. We demonstrate that high-quality DTMs can be generated by using only five images: four that are focused on topography, in which the spacecraft’s viewing geometry brackets the target (north, south, east, and west), and a fifth that measures the target’s albedo variation, taken from near local noon. We further show that the first 10 iterations of the SPC process can meaningfully improve DTM quality, including in the case of a suboptimal input image set, whereas after 10 iterations the DTM quality approaches an asymptotic maximum. We distill our findings into recommendations for observation planning that can be applied by other missions intending to use SPC to model the shape and terrain of their target.

The Lucy LOng Range Reconnaissance Imager (L’LORRI) took 1549 images of the Didymos–Dimorphos binary system, starting 12 hr before the Double Asteroid Redirection Test (DART) impact event on 2022 September 26 and ending 24 hr after it. The Lucy imaging campaign provided pre-impact monitoring of the baseline brightness of the Didymos system, as well as intensive 1 s cadence imaging starting 3 minutes prior to impact and extending until 4 minutes after impact, and then continued monitoring at increasing cadences and image exposure times to measure the Didymos system brightness changes produced by ejecta released during the impact. One of the L’LORRI images encompassed the exact time when the DART spacecraft impacted Dimorphos, but there is no evidence of a thermally generated optical flash in the image. L’LORRI observed a shell of fast-moving ejecta, and we derive a range of projected speeds (∼0.26–3.6 km s ^−1 ) for that material. The much slower moving ejecta (≲1 m s ^−1 ) stayed within a single L’LORRI pixel for the entire duration of the Lucy-DART program. We find that the slow ejecta were responsible for 57.4% ± 2.2% of the total post-impact brightness increase measured by L’LORRI, while the fast ejecta were responsible for 42.6% ± 2.3% of the post-impact brightness increase. The initial brightness increase relative to the pre-impact Didymos system brightness was significantly smaller for L’LORRI compared to that measured by some ground-based observers, which is plausibly explained by differences in phase angles and different responses to sodium emission depending on the camera spectral bandwidths.

On 2020 April 29, the near-Earth object (52768) 1998 OR2 experienced a close approach to Earth at a distance of 16.4 lunar distances (LD). 1998 OR2 is a potentially hazardous asteroid of absolute magnitude H = 16.04 that can currently come as close to Earth as 3.4 LD. We report here observations of this object in polarimetry, photometry, and radar. Our observations show that the physical characteristics of 1998 OR2 are similar to those of both M- and S-type asteroids. Arecibo’s radar observations provide a high radar albedo of ${\hat{\sigma }}_{\mathrm{OC}}\,=$ 0.29 ± 0.08, suggesting that metals are present in 1998 OR2 near-surface. We find a circular polarization ratio of μ _c = 0.291 ± 0.012, and the delay-Doppler images show that the surface of 1998 OR2 is a top-shape asteroid with large-scale structures such as large craters and concavities. The polarimetric observations display a consistent variation of the polarimetric response as a function of the rotational phase, suggesting that the surface of 1998 OR2 is heterogeneous. Color observations suggest an X-complex taxonomy in the Bus–DeMeo classification. Combining optical polarization, radar, and two epochs from the NEOWISE satellite observations, we derived an equivalent diameter of D = 1.80 ± 0.1 km and a visual albedo p _v = 0.21 ± 0.02. Photometric and radar data provide a sidereal rotation period of P = 4.10872 ± 0.00001 hr, a pole orientation of (332.°3 ± 5°, 20.°7 ± 5°), and a shape model with dimensions of $({2.08}_{-0.10}^{+0.10},{1.93}_{-0.10}^{+0.10},{1.60}_{-0.05}^{+0.05})$ km.

The NASA Double Asteroid Redirection Test (DART) has demonstrated the capability of successfully conducting kinetic impact-based asteroid deflection missions. The changes in the Didymos–Dimorphos mutual orbit as a result of the DART impact have already been measured. To fully assess the heliocentric outcome of deflection missions, the heliocentric momentum enhancement parameter, β _⊙ , needs to be determined and disentangled from other nongravitational phenomena such as the Yarkovsky effect. Here we explore the measurability of β _⊙ resulting from DART, which we estimate simultaneously with nongravitational accelerations using a least-squares filter. Results show that successful stellar occultation measurements of the Didymos system in the second half of 2024 in addition to the ones in the 2022–2023 campaigns can achieve a statistically significant estimate of β _⊙ , with an uncertainty slightly above 20% for an assumed β _⊙ = 3. Adding additional occultation measurements and pseudorange measurements from the Hera spacecraft operations at Didymos starting in 2027 decreases this relative uncertainty to under 6%. We find that pre-impact occultation observations combined with post-impact occultations would have yielded substantially higher signal-to-noise ratios on the heliocentric deflection. Additionally, pre-impact occultations would also have enabled a statistically significant β _⊙ estimate using only one additional occultation in 2023 September. Therefore, we conclude that future asteroid deflection missions would greatly benefit from both pre- and post-deflection occultation measurements to help assess the resulting orbital changes.

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG _1 G _2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.

We analyze the polarization observations of the Didymos–Dimorphos system before and after the impact by the NASA Double Asteroid Redirection Test spacecraft on Dimorphos. We fit empirical polarization phase curve models and statistically confirm the discovery by Gray et al. about the degree of linear polarization of the system decreasing on the impact and remaining altered for at least 30 days post-impact. With numerical simulations of particles in the geometric optics domain, we estimate the dominant size of the particles either in the regolith of Didymos and Dimorphos or in the impact-driven ejecta cloud to be several hundred micrometers. The observed change between the pre-impact and post-impact systems indicates either a decrease in average particle size of some tens of micrometers or a decreased level of space weathering.

Dimorphos was the target of the Double Asteroid Redirection Test (DART) mission. This paper summarizes the properties of an updated shape model of Dimorphos, describes the differences between the updated shape model and an earlier version published by Daly, Ernst, Barnouin et al. (doi: https://doi.org/10.1038/s41586-023-05810-5 ), summarizes the data products associated with this model, and explains where the products can be accessed. The updated shape model benefited from improved methods of incorporating limb information, which will accelerate future shape modeling efforts for other objects with limited imaging data. The updated shape model is similar to the earlier model but slightly smaller (−2.8% change in volume) than the previous Dimorphos global shape model, and the updated shape is slightly more elongated. The additional analysis reported here supports an oblate preimpact shape for Dimorphos. This result indicates that the postimpact elongation of Dimorphos derived from ground-based observations is evidence for a large crater or global reshaping of the asteroid due to the DART impact. The updated global shape model of Dimorphos, as well as the earlier version, will be available in the Planetary Data System Small Bodies Node and through the public Small Body Mapping Tool.

The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the moonlet of the binary asteroid 65803 Didymos, on 2022 September 26 and successfully tested a kinetic impactor as an asteroid deflection technique. The success of the deflection was partly due to the momentum of the excavated ejecta material, which provided an extra push to change Dimorphos’s orbital period. Preimpact images provided constraints on the surface but not the subsurface morphology of Dimorphos. DART observations indicated that Dimorphos contained a boulder-strewn surface, with an impact site located between a cluster of large surface boulders. In order to better understand the momentum enhancement factor ( β ) resulting from the impact, we performed impact simulations into two types of targets: idealized homogeneous targets with a single boulder of varying size and buried depth at the impact site and an assembly of boulders at the impact site with subsurface layers. We investigated the relative effects of surface morphology to subsurface morphology to put constraints on the modeling phase space for DART following impact. We found that surface features created a 30%–96% armoring effect on β , with large surface boulders measuring on the order of the spacecraft bus creating the largest effect. Subsurface effects were more subtle (3%–23%) and resulted in an antiarmoring effect on β , even when layers/boulders were close to the surface. We also compared our 2D axisymmetric models to a 3D rectilinear model to understand the effects of grid geometry and dimension on deflection efficiency computational results.

The NASA Double Asteroid Redirection Test spacecraft successfully impacted the Didymos–Dimorphos binary asteroid system on 2022 September 26 UTC. We provide an update to its preimpact mutual orbit and estimate the postimpact physical and orbital parameters, derived using ground-based photometric observations taken from 2022 July to 2023 February. We found that the total change of the orbital period was −33.240 ± 0.072 minutes (all uncertainties are 3 σ ). We obtained the eccentricity of the postimpact orbit to be 0.028 ± 0.016 and the apsidal precession rate was 7.3 ± 2.0 degrees day ^−1 from the impact to 2022 December 2. The data taken later in 2022 December to 2023 February suggest that the eccentricity dropped close to zero or the orbit became chaotic approximately 70 days after the impact. Most of the period change took place immediately after the impact, but in the few weeks following the impact it was followed by an additional change of $-{27}_{-58}^{+19}$ s or −19 ± 18 s (the two values depend on the approach we used to describe the evolution of the orbital period after the impact—an exponentially decreasing angular acceleration or the assumption of a constant orbital period, which changed abruptly some time after the impact, respectively). We estimate the preimpact Dimorphos–Didymos size ratio was 0.223 ± 0.012 and the postimpact is 0.202 ± 0.018, which indicate a marginally significant reduction of Dimorphos’ volume by (9 ± 9)% as the result of the impact.

We have monitored the Didymos–Dimorphos binary system in imaging polarimetric mode before and after the impact from the Double Asteroid Redirection Test mission. A previous spectropolarimetric study showed that the impact caused a dramatic drop in polarization. Our longer-term monitoring shows that the polarization of the post-impact system remains lower than the pre-impact system even months after the impact, suggesting that some fresh ejecta material remains in the system at the time of our observations, either in orbit or settled on the surface. The slope of the post-impact polarimetric curve is shallower than that of the pre-impact system, implying an increase in albedo of the system. This suggests that the ejected material is composed of smaller and possibly brighter particles than those present on the pre-impact surface of the asteroid. Our polarimetric maps show that the dust cloud ejected immediately after the impact polarizes light in a spatially uniform manner (and at a lower level than pre-impact). Later maps exhibit a gradient in polarization between the photocentre (which probes the asteroid surface) and the surrounding cloud and tail. The polarization occasionally shows some small-scale variations, the source of which is not yet clear. The polarimetric phase curve of Didymos–Dimorphos resembles that of the S-type asteroid class.

We present rotational periods of four Potentially Hazardous Asteroids, 2021 HC3, 2001 EC, (7482) 1994 PC1 and (99942) Apophis, from two observatories. From these new CCD observations we derived some information about the internal structure of the asteroids. [ABSTRACT FROM AUTHOR]

Exoplanet detection typically relies on expensive space-based or large ground-based telescopes. A large problem is a lack of telescope time for detection. A network of amateur telescopes, with measuring devices comprised of lowcost spectroscopes and smartphones, was combined with an automated data analysis process involving a custom YOLOv3 AI to collect, clean, and prepare the data. The detection process implemented Doppler spectroscopy and transit photometry, and these two methods were cross-correlated for higher accuracy. In addition, they were used to calculate a variety of orbital parameters and predict exoplanet habitability. This system was then used to evaluate five-star systems, including stars both with and without exoplanets. The AI was 87.63% accurate at identifying stellar spectral lines compared to generally accepted spectra for the stars in question, which shows the high practicality of this system, and a comparison of the calculated values with the generally accepted ones using Spearman's Rho test shows the high accuracy of the system overall, with a p-value of 0.043. Now that this method has been shown to be usable and relatively accurate, this method can be applied to myriad astronomical tasks, such as mapping the spectral classes of star clusters, or scanning for Near-Earth Objects. [ABSTRACT FROM AUTHOR]

The observation of small bodies in the Space Environment is an ongoing important task in astronomy. While nowadays new objects are mostly detected in larger sky surveys, several follow-up observations are usually needed for each object to improve the accuracy of orbit determination. In particular objects orbiting close to Earth, so called Near-Earth Objects (NEOs) are of special concern as a small but not negligible fraction of them can have a non-zero impact probability with Earth. Additionally, the observation of manmade space debris and tracking of satellites falls in the same class measurements. Telescopes for these follow-up observations are mainly in a aperture class between 1 m down to approximately 25 cm. These telescopes are often hosted by amateur observatories or dedicated companies like 6ROADS specialized on this type of observation. With upcoming new NEO search campaigns by very wide field of view telescopes, like the Vera C. Rubin Observatory, NASA’s NEO surveyor space mission and ESA’s Flyeye telescopes, the number of NEO discoveries will increase dramatically. This will require an increasing number of useful telescopes for follow-up observations at different geographical locations. While well-equipped amateur astronomers often host instruments which might be capable of creating useful measurements, both observation planning and scheduling, and also analysis are still a major challenge for many observers. In this work we present a fully robotic planning, scheduling and observation pipeline that extends the widely used open-source cross-platform software KStars/Ekos for Instrument Neutral Distributed Interface (INDI) devices. The method consists of algorithms which automatically select NEO candidates with priority according to ESA’s Near-Earth Object Coordination Centre (NEOCC). It then analyses detectable objects (based on limiting magnitudes, geographical position, and time) with preliminary ephemeris from the Minor Planet Center (MPC). Optimal observing slots during the night are calculated and scheduled. Immediately before the measurement the accurate position of the minor body is recalculated and finally the images are taken. Besides the detailed description of all components, we will show a complete robotic hard- and software solution based on our methods.

We report observations of the Didymos–Dimorphos binary asteroid system using the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Compact Array (ACA) in support of the Double Asteroid Redirection Test mission. Our observations on UT 2022 September 15 provided a preimpact baseline and the first measure of Didymos–Dimorphos’s spectral emissivity at λ = 0.87 mm, which was consistent with the handful of siliceous and carbonaceous asteroids measured at millimeter wavelengths. Our postimpact observations were conducted using four consecutive executions each of ALMA and the ACA spanning from T+3.52 to T+8.60 hr, sampling thermal emission from the asteroids and the impact ejecta. We scaled our preimpact baseline measurement and subtracted it from the postimpact observations to isolate the flux density of millimeter-sized grains in the ejecta. Ejecta dust masses were calculated for a range of materials that may be representative of Dimorphos’s S-type asteroid material. The average ejecta mass over our observations is consistent with 1.3–6.4 × 10 ^7 kg, with the lower and higher values calculated for amorphous and crystalline silicates, respectively. Owing to the likely crystalline nature of S-type asteroid material, the higher value is favored. These ejecta masses represent 0.3%–1.5% of Dimorphos’s total mass and are in agreement with lower limits on the ejecta mass based on measurements at optical wavelengths. Our results provide the most sensitive measure of millimeter-sized material in the ejecta and demonstrate the power of ALMA for providing supporting observations to spaceflight missions.

The Near-Earth Object Surveyor (NEO Surveyor) mission has a requirement to find two-thirds of the potentially hazardous asteroids larger than 140 m in size. In order to determine the mission’s expected progress toward this goal during design and testing, as well as the actual progress during the survey, a simulation tool has been developed to act as a consistent and quantifiable yardstick. We test that the survey simulation software is correctly predicting on-sky positions and thermal infrared fluxes by using it to reproduce the published measurements of asteroids from the NEOWISE mission. We then extended this work to find previously unreported detections of known near-Earth asteroids in the NEOWISE data archive, a search that resulted in 21,661 recovery detections, including 1166 objects that had no previously reported NEOWISE observations. These efforts demonstrate the reliability of the NEO Surveyor Survey Simulator tool and the perennial value of searchable image and source catalog archives for extending our knowledge of the small bodies of the solar system.

The Near-Earth Object (NEO) Surveyor mission is a NASA Observatory designed to discover and characterize asteroids and comets. The mission’s primary objective is to find the majority of objects large enough to cause severe regional impact damage (>140 m in effective spherical diameter) within its 5 yr baseline survey. Operating at the Sun–Earth L1 Lagrange point, the mission will survey to within 45° of the Sun in an effort to find objects in the most Earth-like orbits. The survey cadence is optimized to provide observational arcs long enough to distinguish near-Earth objects from more distant small bodies that cannot pose an impact hazard reliably. Over the course of its survey, NEO Surveyor will discover ∼200,000–300,000 new NEOs down to sizes as small as ∼10 m and thousands of comets, significantly improving our understanding of the probability of an Earth impact over the next century.

We present an approach for the inclusion of nonspherical constituents in high-resolution N -body discrete element method (DEM) simulations. We use aggregates composed of bonded spheres to model nonspherical components. Though the method may be applied more generally, we detail our implementation in the existing N -body code pkdgrav . It has long been acknowledged that nonspherical grains confer additional shear strength and resistance to flow when compared with spheres. As a result, we expect that rubble-pile asteroids will also exhibit these properties and may behave differently than comparable rubble piles composed of idealized spheres. Since spherical particles avoid some significant technical challenges, most DEM gravity codes have used only spherical particles or have been confined to relatively low resolutions. We also discuss the work that has gone into improving performance with nonspherical grains, building on pkdgrav 's existing leading-edge computational efficiency among DEM gravity codes. This allows for the addition of nonspherical shapes while maintaining the efficiencies afforded by pkdgrav 's tree implementation and parallelization. As a test, we simulated the gravitational collapse of 25,000 nonspherical bodies in parallel. In this case, the efficiency improvements allowed for an increase in speed by nearly a factor of 3 when compared with the naive implementation. Without these enhancements, large runs with nonspherical components would remain prohibitively expensive. Finally, we present the results of several small-scale tests: spin-up due to the YORP effect, tidal encounters, and the Brazil nut effect. In all cases, we find that the inclusion of nonspherical constituents has a measurable impact on simulation outcomes.

In the event of a potentially catastrophic asteroid impact, with sufficient warning time, deploying a nuclear device remains a powerful option for planetary defense if a kinetic impactor or other means of deflection proves insufficient. Predicting the effectiveness of a potential nuclear deflection or disruption mission depends on accurate multiphysics simulations of the device's X-ray energy deposition into the asteroid and the resulting material ablation. The relevant physics in these simulations span many orders of magnitude, require a variety of different complex physics packages, and are computationally expensive. Having an efficient and accurate way of modeling this system is necessary for exploring a mission's sensitivity to the asteroid's range of physical properties. To expedite future simulations, we present a completed X-ray energy deposition model developed using the radiation-hydrodynamics code Kull that can be used to initiate a nuclear mitigation mission calculation. The model spans a wide variety of possible mission initial conditions: four different asteroid-like materials at a range of porosities, two different source spectra, and a broad range of radiation fluences, source durations, and angles of incidence. Using blowoff momentum as the primary metric, the model-initiated simulation results match the full radiation-hydrodynamics results to within 10%.

The known near-Earth object (NEO) population consists of over 32,000 objects, with a yearly discovery rate of over 3000 NEOs per year. An essential component of the next generation of NEO surveys is an understanding of the population of known objects, including an accounting of the discovery rate per year as a function of size. Using a near-Earth asteroid (NEA) reference model developed for NASA’s NEO Surveyor (NEOS) mission and a model of the major current and historical ground-based surveys, an estimate of the current NEA survey completeness as a function of size and absolute magnitude has been determined (termed the Known Object Model; KOM). This allows for understanding of the intersection of the known catalog of NEAs and the objects expected to be observed by NEOS. The current NEA population is found to be ∼38% complete for objects larger than 140 m, consistent with estimates by Harris & Chodas. NEOS is expected to catalog more than two-thirds of the NEAs larger than 140 m, resulting in ∼76% of NEAs cataloged at the end of its 5 yr nominal survey, making significant progress toward the US Congressional mandate. The KOM estimates that ∼77% of the currently cataloged objects will be detected by NEOS, with those not detected contributing ∼9% to the final completeness at the end of its 5 yr mission. This model allows for placing the NEOS mission in the context of current surveys to more completely assess the progress toward the goal of cataloging the population of hazardous asteroids.

Ejecta from Dimorphos following the DART mission impact significantly increased the brightness of the Didymos–Dimorphos system, allowing us to examine subsurface material. We report daily near-IR spectroscopic observations of the Didymos system using NASA’s IRTF that follow the evolution of the spectral signature of the ejecta cloud over 1 week, from 1 day before the impact. Overall, the spectral features remained fixed (S-type classification) while the ejecta dissipated, confirming that both Didymos and Dimorphos are constructed from the same silicate material. This novel result strongly supports binary asteroid formation models that include the breaking up of a single body due to rotational breakup of kilometer-wide bodies. At impact time +14 and +38 hr, the spectral slope decreased, but the following nights presented an increasing spectral slope that almost returned to the preimpact slope. However, the parameters of the 1 μ m band remained fixed, and no “fresh”/Q-type-like spectrum was measured. We interpret this as follows. (1) The ejecta cloud is the main contributor (60%–70%) to the overall light during the ∼40 hr after impact. (2) Coarser debris (≥100 μ m) dominated the ejecta cloud, decreasing the spectral slope (after radiation pressure removed the fine grains ≤10 hr after impact). (3) After approximately 1 week, the ejecta cloud dispersed enough to make the fine grains on Didymos’s surface the dominant part of the light, increasing the spectral slope to the preimpact level. (4) A negligible amount of nonweathered material was ejected from Dimorphos’s subsurface, suggesting that Dimorphos was accumulated from weathered material ejected from Didymos’s surface.

Studying small near-Earth asteroids is important in order to understand their dynamical histories and origins as well as to mitigate the damage caused by asteroid impacts on Earth. We report the results of multicolor photometry of the tiny near-Earth asteroid 2015 RN _35 using the 3.8 m Seimei telescope in Japan and the TRAPPIST-South telescope in Chile over 17 nights in 2022 December and 2023 January. We observed 2015 RN _35 across a wide range of phase angles from 2° to 30° in the g , r , i , and z bands in the Pan-STARRS system. These lightcurves show that 2015 RN _35 is in a nonprincipal axis spin state with two characteristic periods of 1149.7 ± 0.3 s and 896.01 ± 0.01 s. We found that the slope of the visible spectrum of 2015 RN _35 is as red as asteroid (269) Justitia, one of the very red objects in the main belt, which indicates that 2015 RN _35 can be classified as an A- or Z-type asteroid. In conjunction with the shallow slope of the phase curve, we suppose that 2015 RN _35 is a high-albedo A-type asteroid. We demonstrated that surface properties of tiny asteroids could be well constrained by intensive observations across a wide range of phase angles. 2015 RN _35 is a possible mission-accessible A-type near-Earth asteroid with a small Δ v of 11.801 km s ^−1 in the launch window between 2030 and 2035.