arXiv subjects

William F. Bottke

Publications and source records attributed to William F. Bottke.

At least 37 records · Page 2Linked to original sources

arXiv2023

Dynamical feasibility of (3) Juno as a parent body of the H chondrites

We test the hypothesis that (3) Juno is a parent body of the H chondrites with dynamical modeling of an asteroid-family-forming impact and comparison to current observational data. Using a dynamical model that includes the Yarkovsky force on a simulated Juno family and a simplified cosmic ray exposure age model we examine the expected distribution of Juno family members in both the main belt and near-Earth orbits over 300 Myrs and the cosmic ray exposure distribution for fragments exiting the main belt via the 3:1J, 5:2J, and 8:3J mean motion resonances. We find that the smallest modeled ($D<$10 m) family members of (3) Juno cannot be directly responsible for the observed H chondrite flux and that the breakup of larger family members creates an CRE distribution that resembles the measured H chondrite CRE distribution but is still unable to adequately explain the significant number of H chondrites with CRE ages of 6-8 Myrs. A similar model was performed for the asteroid (6) Hebe, another parent body candidate, and produced a CRE age distribution that is inconsistent with the measured H chondrite CRE ages. We also find from our dynamical models that we can expect $<$7 km-scale Juno family members in near-Earth orbits in the present day, consistent with the recent discovery of the shock-darkened H chondrite-like asteroid (52768) 1998 OR$_{2}$.

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arXiv2023

Validation of the Survey Simulator tool for the NEO Surveyor mission using NEOWISE data

The Near Earth Object Surveyor mission has a requirement to find two-thirds of the potentially hazardous asteroids larger than 140 meters 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 1,166 objects that had no previously reported NEOWISE observations. These efforts demonstrate the reliability of the NEOS 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.

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arXiv2023

NEOMOD: A New Orbital Distribution Model for Near Earth Objects

Near Earth Objects (NEOs) are a transient population of small bodies with orbits near or in the terrestrial planet region. They represent a mid-stage in the dynamical cycle of asteroids and comets, which starts with their removal from the respective source regions -- the main belt and trans-Neptunian scattered disk -- and ends as bodies impact planets, disintegrate near the Sun, or are ejected from the Solar System. Here we develop a new orbital model of NEOs by numerically integrating asteroid orbits from main belt sources and calibrating the results on observations of the Catalina Sky Survey. The results imply a size-dependent sampling of the main belt with the $ν_6$ and 3:1 resonances producing $\simeq 30$\% of NEOs with absolute magnitudes $H = 15$ and $\simeq 80$\% of NEOs with $H = 25$. Hence, the large and small NEOs have different orbital distributions. The inferred flux of $H<18$ bodies into the 3:1 resonance can be sustained only if the main-belt asteroids near the resonance drift toward the resonance at the maximal Yarkovsky rate ($\simeq 2 \times 10^{-4}$ au Myr$^{-1}$ for diameter $D=1$ km and semimajor axis $a=2.5$~au). This implies obliquities $θ\simeq 0^\circ$ for $a<2.5$~au and $θ\simeq 180^\circ$ for $a>2.5$~au, both in the immediate neighborhood of the resonance (the same applies to other resonances as well). We confirm the size-dependent disruption of asteroids near the Sun found in previous studies. An interested researcher can use the publicly available NEOMOD Simulator to generate user-defined samples of NEOs from our model.

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arXiv2023

Early Bombardment of the Moon: Connecting the Lunar Crater Record to the Terrestrial Planet Formation

The lunar crater record features $\sim 50$ basins. The radiometric dating of Apollo samples indicates that the Imbrium basin formed relatively late -- from the planet formation perspective -- some $\simeq 3.9$ Ga. Here we develop a dynamical model for impactors in the inner solar system to provide context for the interpretation of the lunar crater record. The contribution of cometary impactors is found to be insignificant. Asteroids produced most large impacts on the terrestrial worlds in the last $\simeq 3$ Gyr. The great majority of early impactors were rocky planetesimals left behind at $\sim 0.5$--1.5 au after the terrestrial planet accretion. The population of terrestrial planetesimals was reduced by disruptive collisions in the first $t \sim 20$ Myr after the gas disk dispersal. We estimate that there were $\sim 4 \times 10^5$ diameter $d>10$ km bodies when the Moon formed (total planetesimal mass $\sim 0.015$ $M_{\rm Earth}$ at $t \sim 50$ Myr). The early bombardment of the Moon was intense. To accommodate $\sim 50$ known basins, the lunar basins that formed before $\simeq 4.35$--4.41 Ga must have been erased. The late formation of Imbrium occurs with a $\sim 15$--35\% probability in our model. About 20 $d>10$-km bodies were expected to hit the Earth between 2.5 and 3.5 Ga, which is comparable to the number of known spherule beds in the late Archean. We discuss implications of our model for the lunar/Martian crater chronologies, Late Veneer, and noble gases in the Earth atmosphere.

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arXiv2022

Formation of Lunar Basins from Impacts of Leftover Planetesimals

The Moon holds important clues to the early evolution of the Solar System. Some 50 impact basins (crater diameter D>300 km) have been recognized on the lunar surface, implying that the early impact flux was much higher than it is now. The basin-forming impactors were suspected to be asteroids released from an inner extension of the main belt (1.8-2.0 au). Here we show that most impactors were instead rocky planetesimals left behind at 0.5-1.5 au after the terrestrial planet accretion. The number of basins expected from impacts of leftover planetesimals largely exceeds the number of known lunar basins, suggesting that the first 200 Myr of impacts is not recorded on the lunar surface. The Imbrium basin formation (age 3.92 Gyr; impactor diameter d~100 km) occurs with a 15-35% probability in our model. Imbrium must have formed unusually late to have only two smaller basins (Orientale and Schrodinger) forming afterwards. The model predicts 20 d>10-km impacts on the Earth 2.5-3.5 Gyr ago (Ga), which is comparable to the number of known spherule beds in the late Archean.

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arXiv2022

Implications of Jupiter Inward Gas-Driven Migration for the Inner Solar System

The migration history of Jupiter in the sun's natal disk remains poorly constrained. Here we consider how Jupiter's migration affects small-body reservoirs and how this constrains its original orbital distance from the Sun. We study the implications of large-scale and inward radial migration of Jupiter for the inner solar system while considering the effects of collisional evolution of planetesimals. We use analytical prescriptions to simulate the growth and migration of Jupiter in the gas disk. We assume the existence of a planetesimal disk inside Jupiter's initial orbit. This planetesimal disk received an initial total mass and size-frequency distribution (SFD). Planetesimals feel the effects of aerodynamic gas drag and collide with one another, mostly while shepherded by the migrating Jupiter. Our main goal is to measure the amount of mass in planetesimals implanted into the main asteroid belt (MAB) and the SFD of the implanted population. We also monitor the amount of dust produced during planetesimal collisions. We find that the SFD of the planetesimal population implanted into the MAB tends to resemble that of the original planetesimal population interior to Jupiter. We also find that unless very little or no mass existed between 5 au and Jupiter's original orbit, it would be difficult to reconcile the current low mass of the MAB with the possibility that Jupiter migrated from distances beyond 15 au. This is because the fraction of the original disk mass that gets implanted into the MAB is very large. Finally, we discuss the implications of our results in terms of dust production to the so-called NC-CC isotopic dichotomy.

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arXiv2022

Implications for the collisional strength of Jupiter Trojans from the Eurybates family

In this work, we model the collisional evolution of the Jupiter Trojans and determined under which conditions the Eurybates-Queta system survives. We show that the collisional strength of the Jupiter Trojans and the age of the Eurybates family and by extension Queta are correlated. The collisional grinding of the Jupiter Trojan population over 4.5 Gy results in a size-frequency distribution (SFD) that remains largely unaltered at large sizes (>10 km) but is depleted at small sizes (10 m to 1 km). This results in a turnover in the SFD, the location of which depends on the collisional strength of the material. It is to be expected that the Trojan SFD bends between 1 and 10 km. Based on the SFD of the Eurybates family, we find that the family was likely the result of a catastrophic impact onto a 100 km rubble pile target. This corresponds to objects with a rather low collisional strength (10 times weaker than that of basaltic material studied in Benz & Asphaug1999). Assuming this weak strength, and an initial cumulative slope of the size frequency distribution of 2.1 between diameters of 2 m and 100 km when the Trojans were captured, the existence of Queta, the satellite of Eurybates, implies an upper limit for the family age of 3.7 Gy. Alternatively, we demonstrate that an unconventional collisional strength with a minimum at 20 m is a plausible candidate to ensure the survival of Queta over the age of the Solar System. Finally, we show how different collisional histories change the expected number of craters on the targets of the Lucy mission and that Lucy will be able to differentiate between them.

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arXiv2022

Predictions for the Dynamical States of the Didymos System before and after the Planned DART Impact

NASA's Double Asteroid Redirection Test (DART) spacecraft is planned to impact the natural satellite of (65803) Didymos, Dimorphos, around 23:14 UTC on 26 September 2022, causing a reduction in its orbital period that will be measurable with ground-based observations. This test of kinetic impactor technology will provide the first estimate of the momentum transfer enhancement factor $β$ at a realistic scale, wherein ejecta from the impact provides an additional deflection to the target. Earth-based observations, the LICIACube spacecraft (to be detached from DART prior to impact), and ESA's follow-up Hera mission to launch in 2024, will provide additional characterization of the deflection test. Together Hera and DART comprise the Asteroid Impact and Deflection Assessment (AIDA) cooperation between NASA and ESA. Here the predicted dynamical states of the binary system upon arrival and after impact are presented. The assumed dynamically relaxed state of the system will be excited by the impact, leading to an increase in eccentricity and slight tilt of the orbit together with enhanced libration of Dimorphos with amplitude dependent on the currently poorly known target shape. Free rotation around the moon's long axis may also be triggered and the orbital period will experience variations from seconds to minutes over timescales of days to months. Shape change of either body due to cratering or mass wasting triggered by crater formation and ejecta may affect $β$ but can be constrained through additional measurements. Both BYORP and gravity tides may cause measurable orbital changes on the timescale of Hera's rendezvous.

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arXiv2021

Physical Characterization of Metal-rich Near-Earth Asteroids 6178 (1986 DA) and 2016 ED85

Metal-rich near-Earth asteroids (NEAs) represent a small fraction of the NEA population that is mostly dominated by S- and C-type asteroids. Because of this, their identification and study provide us with a unique opportunity to learn more about the formation and evolution of this particular type of bodies, as well as their relationship with meteorites found on Earth. We present near-infrared (NIR) spectroscopic data of NEAs 6178 (1986 DA) and 2016 ED85. We found that the spectral characteristics of these objects are consistent with those of metal-rich asteroids, showing red slopes, convex shapes, and a weak pyroxene absorption band at $\sim$0.93 $μ$m. The compositional analysis showed that they have a pyroxene chemistry of Fs$_{40.6\pm3.3}$Wo$_{8.9\pm1.1}$ and a mineral abundance of $\sim$15% pyroxene and 85% metal. We determined that these objects were likely transported to the near-Earth space via the 5:2 mean motion resonance with Jupiter. Asteroid spectra were compared with the spectra of mesosiderites and bencubbinites. Differences in the NIR spectra and pyroxene chemistry suggest that bencubbinites are not good meteorite analogs. Mesosiderites were found to have a similar pyroxene chemistry and produced a good spectral match when metal was added to the silicate component. We estimated that the amounts of Fe, Ni, Co, and the platinum group metals present in 1986 DA could exceed the reserves worldwide.

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arXiv2021

Dark Primitive Asteroids Account for a Large Share of K/Pg-Scale Impacts on the Earth

A dynamical model for large near-Earth asteroids (NEAs) is developed here to understand the occurrence rate and nature of Cretaceous-Paleogene (K/Pg) scale impacts on the Earth. We find that 16--32 (2--4) impacts of diameter $D>5$ km ($D>10$ km) NEAs are expected on the Earth in 1 Gyr, with about a half of impactors being dark primitive asteroids (most of which start with semimajor axis $a>2.5$ au). These results explain why the Chicxulub crater, the third largest impact structure found on the Earth (diameter $\simeq180$ km), was produced by impact of a carbonaceous chondrite. They suggest, when combined with previously published results for small ($D \lesssim 1$ km) NEAs, a size-dependent sampling of the main belt. We conclude that the impactor that triggered the K/Pg mass extinction $\simeq 66$ Myr ago was a main belt asteroid that quite likely ($\simeq 60$\% probability) originated beyond 2.5 au.

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arXiv2021

Characterization of Exogenic Boulders on Near-Earth Asteroid (101955) Bennu from OSIRIS-REx Color Images

A small number of anomalously bright boulders on the near-Earth, rubble-pile asteroid (101955) Bennu were recently identified as eucritic material originating from asteroid (4) Vesta. Building on this discovery, we explored the global presence of exogenic boulders on Bennu. Our analysis focused on boulders larger than 1 m that show the characteristic 1-micron pyroxene absorption band in the four-color MapCam data from the OSIRIS-REx mission. We confirm the presence of exogenic boulders similar to eucrites and find that mixtures of eucrites with carbonaceous material is also a possible composition for some boulders. Some of the exogenic boulders have spectral properties similar to those of ordinary chondrite (OC) meteorites, although the laboratory spectra of these meteorites have a higher albedo than those measured on Bennu, which could be explained by either a grain size effect, the presence of impact melt, or optical mixing with carbonaceous material owing to dust coating. Our Monte Carlo simulations predict that the median amount of OC mass added to the parent body of Bennu is 0.055% and 0.037% of the volume of a 100- and 200-km-diameter parent body, respectively. If Bennu was a uniformly mixed byproduct of parent body and S-type projectiles, the equivalent mass of OC material would be a sphere with a diameter of 36 to 40 m (or a volume of 24,200 to 33,600 m3). The total amount of OC material in the interior of Bennu estimated from the MapCam data is slightly higher (91,000-150,000 m3).

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arXiv2020

Establishing Earth's Minimoon Population through Characterization of Asteroid 2020 CD$_3$

We report on our detailed characterization of Earth's second known temporary natural satellite, or minimoon, asteroid 2020 CD3. An artificial origin can be ruled out based on its area-to-mass ratio and broadband photometry, which suggest that it is a silicate asteroid belonging to the S or V complex in asteroid taxonomy. The discovery of 2020 CD3 allows for the first time a comparison between known minimoons and theoretical models of their expected physical and dynamical properties. The estimated diameter of 1.2+0.4-0.2 m and geocentric capture approximately a decade after the first known minimoon, 2006 RH120, are in agreement with theoretical predictions. The capture duration of 2020 CD3 of at least 2.7 yr is unexpectedly long compared to the simulation average, but it is in agreement with simulated minimoons that have close lunar encounters, providing additional support for the orbital models. 2020 CD3's atypical rotation period, significantly longer than theoretical predictions, suggests that our understanding of meter-scale asteroids needs revision. More discoveries and a detailed characterization of the population can be expected with the forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time.

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arXiv2020

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Proximity observations by OSIRIS-REx and Hayabusa2 provided clues on the shape evolution processes of the target asteroids, (101955) Bennu and (162173) Ryugu. Their oblate shapes with equatorial ridges, or the so-called top shapes, may have evolved due to their rotational conditions at present and in the past. Different shape evolution scenarios were previously proposed; Bennu's top shape may have been driven by surface processing, while Ryugu's may have been developed due to large deformation. These two scenarios seem to be inconsistent. Here, we revisit the structural analyses in earlier works and fill a gap to connect these explanations. We also apply a semi-analytical technique for computing the cohesive strength distribution in a uniformly rotating triaxial ellipsoid to characterize the global failure of top-shaped bodies. Assuming that the structure is uniform, our semi-analytical approach describes the spatial variations in failed regions at different spin periods; surface regions are the most sensitive at longer spin periods, while interiors fail structurally at shorter spin periods. This finding suggests that the shape evolution of a top shape may vary due to rotation and internal structure, which can explain the different evolution scenarios of Bennu's and Ryugu's top shapes. We interpret our results as the indications of top shapes' various evolution processes.

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arXiv2020

Debiased albedo distribution for Near Earth Objects

We extend the most recent orbital and absolute magnitude Near Earth Object (NEO) model (Granvik et al., 2018) to provide a statistical description of NEO geometric albedos. Our model is calibrated on NEOWISE albedo data for the NEO population and reproduces these data very well once a simple model for the NEOWISE observational biases is applied. The results are consistent with previous estimates. There are about 1,000 NEOs with diameter D>1km and the mean albedo to convert absolute magnitude into diameter is 0.147. We do not find any statistically significant evidence that the albedo distribution of NEOs depends on NEO size. Instead, we find evidence that the disruption of NEOs at small perihelion distances found in Granvik et al. (2016) occurs preferentially for dark NEOs. The interval between km-sized bodies striking the Earth should occur on average once every 750,000 years. Low and high albedo NEOs are well mixed in orbital space, but a trend remains with higher albedo objects being at smaller semimajor axes and lower albedo objects more likely found at larger semimajor axes.

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arXiv2019

Earth's Minimoons: Opportunities for Science and Technology

(modified from published version) Twelve years ago the Catalina Sky Survey discovered Earth's first known natural geocentric object other than the Moon, a few-meter diameter asteroid designated 2006 RH120. Despite significant improvements in ground-based telescope and detector technology in the past decade the asteroid surveys have not discovered another temporarily-captured orbiter (TCO; colloquially known as minimoons). Within a few years the Large Synoptic Survey Telescope (LSST) will either begin to regularly detect TCOs or force a re-analysis of the creation and dynamical evolution of small asteroids in the inner solar system. The first studies of the provenance, properties, and dynamics of Earth's minimoons suggested that there should be a steady state population with about one 1- to 2-meter diameter captured objects at any time. That model was then improved and extended to include the population of temporarily-captured flybys (TCFs), objects that fail to make an entire revolution around Earth while energetically bound to the Earth-Moon system. Several different techniques for discovering TCOs have been considered but their small diameters, proximity, and rapid motion make them challenging targets for existing ground-based optical, meteor, and radar surveys. We expect that if the TCO population is confirmed, and new objects are frequently discovered, they can provide new opportunities for 1) studying the dynamics of the Earth-Moon system, 2) testing models of the production and dynamical evolution of small asteroids from the asteroid belt, 3) rapid and frequent low delta-v missions to multiple minimoons, and 4) evaluating in-situ resource utilization techniques on asteroidal material. Here we review the past decade of minimoon studies in preparation for capitalizing on the scientific and commercial opportunities of TCOs in the first decade of LSST operations.

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arXiv2018

Evidence for Very Early Migration of the Solar System Planets from the Patroclus-Menoetius binary Jupiter Trojan

The orbital distribution of trans-Neptunian objects provides strong evidence for the radial migration of Neptune. The outer planets' orbits are thought to have become unstable during the early stages with Jupiter having scattering encounters with a Neptune-class planet. As a consequence, Jupiter jumped inward by a fraction of an au, as required from inner solar system constraints, and obtained its current orbital eccentricity. The timing of these events is often linked to the lunar Late Heavy Bombardment that ended ~700 Myr after the dispersal of the protosolar nebula (t_0). Here we show instead that planetary migration started shortly after t_0. Such early migration is inferred from the survival of the Patroclus-Menoetius binary Jupiter Trojan. The binary formed at t <~ t_0 within a massive planetesimal disk once located beyond Neptune. The longer the binary stayed in the disk, the greater the likelihood that collisions would strip its components from one another. The simulations of its survival indicate that the disk had to have been dispersed by migrating planets within <100 Myr of t_0. This constraint implies that the planetary migration is unrelated to the formation of the youngest lunar basins.

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arXiv2016

Modeling the Historical Flux of Planetary Impactors

The impact cratering record of the Moon and the terrestrial planets provides important clues about the formation and evolution of the Solar System. Especially intriguing is the epoch 3.8-3.9 Gyr ago (Ga), known as the Late Heavy Bombardment (LHB), when the youngest lunar basins such as Imbrium and Orientale formed. The LHB was suggested to originate from a slowly declining impactor flux or from a late dynamical instability. Here we develop a model for the historical flux of large asteroid impacts and discuss how it depends on various parameters, including the time and nature of the planetary migration/instability. We find that the asteroid impact flux dropped by 1 to 2 orders of magnitude during the first 1 Gyr and remained relatively unchanged over the last 3 Gyr. The early impacts were produced by asteroids whose orbits became excited during the planetary migration/instability, and by those originating from the inner extension of the main belt (E-belt; semimajor axis 1.6<a<2.1 au). The profiles obtained for the early and late versions of the planetary instability initially differ, but end up being similar after ~3 Ga. Thus, the time of the instability can only be determined by considering the cratering and other constraints during the first ~1.5 Gyr of the Solar System history. Our absolute calibration of the impact flux indicates that asteroids were probably not responsible for the LHB, independently of whether the instability happened early or late, because the calibrated flux is not large enough to explain Imbrium/Orientale and a significant share of large lunar craters. Comets and leftovers of the terrestrial planet formation provided additional, and probably dominant source of impacts during early epochs.

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arXiv2016

Physical Characterization of ~2-meter Diameter Near-Earth Asteroid 2015 TC25: A possible boulder from E-type Asteroid (44) Nysa

Small near-Earth asteroids (>20 meters) are interesting because they are progenitors for meteorites in our terrestrial collection. Crucial to our understanding of the effectiveness of our atmosphere in filtering low-strength impactors is the physical characteristics of these small near-Earth asteroids (NEAs). In the past, characterization of small NEAs has been a challenge because of the difficulty in detecting them prior to close Earth flyby. In this study we physically characterized the 2-meter diameter near-Earth asteroid 2015 TC25 using ground-based optical, near-infrared and radar assets during a close flyby of the Earth (distance 69,000 miles) in Oct. 2015. Our observations suggest that its surface composition is similar to aubrites, a rare class of high albedo differentiated meteorites. Aubrites make up only 0.14 % of all know meteorites in our terrestrial meteorite collection. 2015 TC25 is also a very fast rotator with a rotation period of 133 seconds. We compared spectral and dynamical properties of 2015 TC25 and found the best candidate source body in the inner main belt to be the 70-km diameter E-type asteroid (44) Nysa. We attribute difference in spectral slope between the two objects to the lack of regolith on the surface of 2015 TC25. Using the albedo of E-type asteroids (50-60%) we refine the diameter of 2015 TC25 to 2-meters making it one of the smallest NEA ever to be characterized.

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