Asteroid Population Research Articles

On the inclinations of the Jupiter Trojans

Jupiter Trojans are a resonant asteroidal population characterised by photometric colours that are compatible with trans-Neptunian objects, high inclinations, and an asymmetric distribution of the number of asteroids between the two swarms. Different models have been proposed to explain the high inclination of the Trojans and to interpret their relation with the Trans-Neptunian objects, but none of these models can also satisfactorily explain the asymmetry ratio between the number of asteroids in the two swarms. It has recently been found that the asymmetry ratio can arise if Jupiter has migrated inwards through the protoplanetary disc by at least a few astronomical units during its growth. The more numerous population of the leading swarm and the dark photometric colours of the Trojans are natural outcomes of this new model, but simulations with massless unperturbed disc particles led to a flat distribution of the Trojan inclinations and a final total mass of the Trojans that was 3–4 orders of magnitude larger than the current mass. We here investigate the possible origin of the peculiar inclination distribution of the Trojans in the scenario where Jupiter migrates inwards. We analyse different possibilities: (a) the secular evolution of an initially flat Trojan population, (b) the presence of planetary embryos among the Trojans, and (c) capture of the Trojans from a pre-stirred planetesimal population in which Jupiter grows and migrates. We find that the secular evolution of the Trojans and secular perturbations from Saturn do not affect the inclination distribution of the Trojans appreciably, nor is there any significant mass depletion over the age of the Solar System. Embryos embedded in the Trojan swarms, in contrast, can stir the Trojans to their current degree of excitation and can also deplete the swarms efficiently, but it is very difficult to remove all of the massive bodies in 4.5 Gyr of evolution. We propose that the disc where Jupiter’s core was forming was already stirred to high inclination values by other planetary embryos competing in the feeding zone of Jupiter’s core. We show that the trapped Trojans preserve their high inclination through the gas phase of the protoplanetary disc and that Saturn’s perturbations are more effective on highly inclined Trojans, leading to a lower capture efficiency and to a substantial depletion of the swarms during 4.5 Gyr of evolution.

Impacts into rotating targets: angular momentum draining and efficient formation of synthetic families

About 10% of the observed asteroids have rotational periods lower thanP= 3 h and seem to be relatively close to the spin barrier. Yet, the rotation has often been neglected in simulations of asteroid collisions. To determine the effect of rotation, we performed a large number of impact simulations with rotating targets. We developed a new unified smoothed particle hydrodynamics and N-body code with self-gravity, suitable for simulations of both fragmentation phase and gravitational reaccumulation. The code has been verified against previous ones, but we also tested new features, such as rotational stability, tensile stability, etc. Using the new code, we ran simulations withDpb= 10 and 100 km monolithic targets and compared synthetic asteroid families created by these impacts with families corresponding to non-rotating targets. The rotation affects mostly cratering events at oblique impact angles. The total mass ejected by these collisions can be up to five times larger for rotating targets. We further computed the transfer of the angular momentum and determined conditions under which impacts accelerate or decelerate the target. While individual cratering collisions can cause both acceleration and deceleration, the deceleration prevails on average. Collisions thus cause a systematic spin-down of the asteroid population.

Near-Earth asteroids spectroscopic survey atIsaac NewtonTelescope

Context.The population of near-Earth asteroids (NEAs) shows a large variety of objects in terms of physical and dynamical properties. They are subject to planetary encounters and to strong solar wind and radiation effects. Their study is also motivated by practical reasons regarding space exploration and long-term probability of impact with the Earth.Aims.We aim to spectrally characterize a significant sample of NEAs with sizes in the range of ~0.25–5.5 km (categorized as large), and search for connections between their spectral types and the orbital parameters.Methods.Optical spectra of NEAs were obtained using theIsaac NewtonTelescope (INT) equipped with the IDS spectrograph. These observations are analyzed using taxonomic classification and by comparison with laboratory spectra of meteorites.Results.A total number of 76 NEAs were observed. We spectrally classified 44 of them as Q/S-complex, 16 as B/C-complex, eight as V-types, and another eight belong to the remaining taxonomic classes. Our sample contains 27 asteroids categorized as potentially hazardous and 31 possible targets for space missions including (459872) 2014 EK24, (436724) 2011 UW158, and (67367) 2000 LY27. The spectral data corresponding to (276049) 2002 CE26 and (385186) 1994 AW1 shows the 0.7μm feature which indicates the presence of hydrated minerals on their surface. We report that Q-types have the lowest perihelia (a median value and absolute deviation of 0.797 ± 0.244 AU) and are systematically larger than the S-type asteroids observed in our sample. We explain these observational evidences by thermal fatigue fragmentation as the main process for the rejuvenation of NEA surfaces.Conclusions.In general terms, the taxonomic distribution of our sample is similar to the previous studies and matches the broad groups of the inner main belt asteroids. Nevertheless, we found a wide diversity of spectra compared to the standard taxonomic types.

Kinematic Approximation of Position Accuracy Achieved Using Optical Observations of Distant Asteroids

NASA’s Deep Space 1 mission demonstrated that a spacecraft can be navigated autonomously during deep-space cruise operations using only optical navigation measurements. A methodology is developed to evaluate the feasibility and accuracy of the Deep Space 1 orbit determination approach throughout the solar system as a function of a spacecraft’s imaging capabilities. Feasibility can be addressed by comparing the apparent magnitudes of the known population of asteroids against the imaging system capabilities. An upper limit on the accuracy of the spacecraft position estimate at a given location can be formulated by assuming observations of at least two asteroids simultaneously. Example results are presented for three camera implementations that span the range of capabilities flown in deep space to date using orbit and absolute magnitude data for 50,129 of the brightest known asteroids. Broadly speaking, achievable accuracies range from approximately 200 to 12,000 km () interior to the main asteroid belt and from 50 to 2000 km within the main belt, depending strongly on the chosen camera implementation. Between the main belt and Jupiter, only a current state-of-the-art imaging system is consistently capable of kinematic positioning using only asteroids. Beyond Jupiter, there are insufficient known asteroids to support this approach without including images of planets and moons. Although these levels of accuracy are far inferior to those achievable with radiometric navigation, they may yet be sufficient to satisfy cruise-phase requirements for many deep-space missions.

The Case for a Large-scale Occultation Network

Abstract We discuss the feasibility of and present initial designs and approximate cost estimates for a large (N ∼ 2000) network of small photometric telescopes that is purpose-built to monitor V ≲ 15 Gaia mission program stars for occultations by minor solar system bodies. The implementation of this network would permit measurement of the solar system’s tidal gravity field to high precision, thereby revealing the existence of distant trans-Neptunian objects such as the proposed “Planet Nine.” As a detailed example of the network capabilities, we investigate how occultations by Jovian Trojans can be monitored to track the accumulation of gravitational perturbations, thereby constraining the presence of undetected massive solar system bodies. We also show that the tidal influence of Planet Nine can be discerned from that of smaller, nearer objects in the Kuiper Belt. Moreover, ephemerides for all small solar system bodies observed in occultation could be significantly improved using this network, thereby improving spacecraft navigation and refining solar system modeling. Finally, occultation monitoring would generate direct measurements of size distributions for asteroid populations, permitting a better understanding of their origins.

A common origin for dynamically associated near-Earth asteroid pairs

Though pairs of dynamically associated asteroids in the Main Belt have been identified and studied for over a decade, very few pair systems have been identified in the near-Earth asteroid population. We present data and analysis that supports the existence of two genetically related pairs in near-Earth space. The members of the individual systems, 2015 EE7 – 2015 FP124 and 2017 SN16 – 2018 RY7, are found to be of the same spectral taxonomic class, and both pairs are interpreted to have volatile-poor compositions. In conjunction with dynamical arguments, this suggests that these two systems formed via YORP spin-up and/or dissociation of a binary precursor. Backwards orbital integrations suggest a separation age of <10 kyr for the pair 2017 SN16 – 2018 RY7, making these objects amongst the youngest multiple asteroid systems known to date. A unique separation age was not realized for 2015 EE7 – 2015 FP124 due to large uncertainties associated with these objects' orbits. Determining the ages of such young pairs is of great value for testing models of space weathering and asteroid spin-state evolution. As the NEO catalog continues to grow with current and future discovery surveys, it is expected that more NEO pairs will be found, thus providing an ideal laboratory for studying time dependent evolutionary processes that are relevant to asteroids throughout the Solar System.

Influence of the YORP Effect on the Rotation of Small Main-Belt Asteroids

The distribution of rotation rates of small (D = 3–15 km) main-belt asteroids is analyzed in the context of the probable influence of solar radiation on the rotation of asteroids (YORP effect). It is demonstrated that the evolution of this distribution with heliocentric distance (i.e., the presence of well-marked slow and fast rotation excesses in the inner part of the belt, which become less noticeable in the middle part and are almost indistinguishable in the outer part) is well accounted for by the YORP effect. The influence of this effect on the studied asteroid population is rather weak compared to its influence on near-Earth asteroids, which are 3–4 times smaller on average and with ~3 times more intense solar irradiation; however, it is still sufficiently significant to be identified reliably in the available observational data.

Time and Phase Resolved Optical Spectra of Potentially Hazardous Asteroid 2014 JO25

Abstract The asteroid 2014 JO25, considered to be potentially hazardous by the Minor Planet Center, was spectroscopically followed during its close-Earth encounter on 2017 April 19 and 20. The spectra of the asteroid were taken with the low-resolution spectrograph (LISA), mounted on the 1.2 m telescope at the Mount Abu Infrared Observatory, India. Coming from a region close to the Hungaria population of asteroids, this asteroid follows a comet-like orbit with a relatively high inclination and large eccentricity. Hence, we carried out optical spectroscopic observations of the asteroid to look for comet-like molecular emissions or outbursts. However, the asteroid showed a featureless spectrum, devoid of any comet-like features. The light curve of the asteroid was analyzed using V-band magnitudes derived from the spectra and the most likely solution for the rotation of the asteroid was obtained. The absolute magnitude H and the slope parameter G were determined for the asteroid in the V filter band using the IAU accepted standard two-parameter H–G model. A peculiar, rarely found result from these observations is its phase bluing trend. The relative B–V color index seems to decrease with increasing phase angle, which indicates a phase bluing trend. Such trends have seldom been reported in the literature. However, phase reddening in asteroids is very common. The asymmetry parameter g and the single-scattering albedo w were estimated for the asteroid by fitting the Hapke phase function to the observed data. The asteroid shows a relatively large value for the single-scattering albedo and a highly back-scattering surface.

Effect of Different Angular Momentum Transport Mechanisms on the Distribution of Water in Protoplanetary Disks

Abstract The snow line in a protoplanetary disk demarcates regions with H2O ice from regions with H2O vapor. Where a planet forms relative to this location determines how much water and other volatiles it forms with. Giant-planet formation may be triggered at the water–snow line if vapor diffuses outward and is cold-trapped beyond the snow line faster than icy particles can drift inward. In this study, we investigate the distribution of water across the snow line, considering three different radial profiles of the turbulence parameter α(r), corresponding to three different angular momentum transport mechanisms. We consider the radial transport of water vapor and icy particles by diffusion, advection, and drift. We show that even for similar values of α, the gradient of α(r) across the snow line significantly changes the snow line location, the sharpness of the volatile gradient across the snow line, and the final water/rock ratio in planetary bodies. A profile of radially decreasing α, consistent with transport by hydrodynamic instabilities plus magnetic disk winds, appears consistent with the distribution of water in the solar nebula, with monotonically increasing radial water content and a diverse population of asteroids with different water content. We argue that Σ(r) and water abundance are likely a diagnostic of α(r) and thus of the mechanism for angular momentum transport in inner disks.

Ancient and primordial collisional families as the main sources of X-type asteroids of the inner main belt

Aims. The near-Earth asteroid population suggests the existence of an inner main belt source of asteroids that belongs to the spectroscopic X complex and has moderate albedos. The identification of such a source has been lacking so far. We argue that the most probable source is one or more collisional asteroid families that have escaped discovery up to now. Methods. We apply a novel method to search for asteroid families in the inner main-belt population of asteroids belonging to the X complex with moderate albedo. Instead of searching for asteroid clusters in orbital element space, which could be severely dispersed when older than some billions of years, our method looks for correlations between the orbital semimajor axis and the inverse size of asteroids. This correlation is the signature of members of collisional families that have drifted from a common centre under the effect of the Yarkovsky thermal effect. Results. We identify two previously unknown families in the inner main belt among the moderate-albedo X-complex asteroids. One of them, whose lowest numbered asteroid is (161) Athor, is ~3 Gyr old, whereas the second one, whose lowest numbered object is (689) Zita, could be as old as the solar system. Members of this latter family have orbital eccentricities and inclinations that spread them over the entire inner main belt, which is an indication that this family could be primordial, that is, it formed before the giant planet orbital instability. Conclusions. The vast majority of moderate-albedo X-complex asteroids of the inner main belt are genetically related, as they can be included into a few asteroid families. Only nine X-complex asteroids with moderate albedo of the inner main belt cannot be included in asteroid families. We suggest that these bodies formed by direct accretion of the solids in the protoplanetary disc, and are thus surviving planetesimals.

The latest spectral analysis on asteroids at NAO Rozhen

AbstractBy virtue of the physical, chemical and dynamical characteristics of asteroids, researchers gain insight into the formation and evolution of our Solar system. Since these objects do not undergo any changes, or the changes during the Solar system evolution are insignificant, we are certain they carry important information regarding the formation of our planetary system and its evolution. Knowing the spectral class of an asteroid is crucial for determining its chemical properties. In our work the spectral classification was done on several asteroids by comparing their spectra with laboratory spectra. We determined spectral types of the asteroids by the overall shapes of the spectra between 450 nm and 700 nm. Increasing the number of asteroids with known rotation period, shapes and spectra enriches the asteroid database of physical and dynamical characteristics of asteroid population.

Dust properties of double-tailed active asteroid (6478) Gault

Context. Asteroid (6478) Gault was discovered to exhibit a comet-like tail in observations from December 2018, becoming a new member of the so-called active asteroid population in the main asteroid belt. Aims. We seek to investigate the grain properties of the dust ejected from asteroid (6478) Gault and to give insight into the activity mechanism(s). Methods. We use a Monte Carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. The code takes into account the brightness contribution of the asteroid itself. The model is applied to a large data set of images spanning the period from 2019 January 11 to 2019 March 13. In addition, we carried out both short- and long-term photometric measurements of the asteroid. Results. It is shown that, to date, asteroid (6478) Gault has experienced two episodes of impulsive dust ejection, which took place around 2018 November 5 and 2019 January 2. These two episodes released at least 1.4 × 107 kg and 1.6 × 106 kg of dust, respectively, at escape speeds. The size distribution, consisting of particles in the 1 μm–1 cm radius range, follows a broken power law with bending points near 15 μm and 870 μm. On the other hand, the photometric series indicate a nearly constant magnitude over several 5–7.3 h periods, which is a possible effect of the masking of a rotational light curve by the dust. Conclusions. The dust particles forming Gault’s tails were released from the asteroid at escape speeds, but the specific ejection mechanism is unclear until photometry of the dust-free asteroid are conducted to assess whether this was related to rotational disruption or to other possible causes.

Oort cloud asteroids: collisional evolution, the Nice Model, and the Grand Tack

If the Solar system had a history of planet migration, the signature of that migration may be imprinted on the populations of asteroids and comets that were scattered in the planets' wake. Here, we consider the dynamical and collisional evolution of inner Solar system asteroids which join the Oort cloud. We compare the Oort cloud asteroid populations produced by migration scenarios based on the `Nice' and `Grand Tack' scenarios, as well as a null hypothesis where the planets have not migrated, to the detection of one such object, C/2014 S3 (PANSTARRS). Our simulations find that the discovery of C/2014 S3 (PANSTARRS) only has a greater than one percent chance of occurring if the Oort cloud asteroids evolved on to Oort cloud orbits when the Solar system was not more than about one million years old, as this early transfer to the Oort cloud is necessary to keep the amount of collisional evolution low. We argue this only occurs when a giant (greater than thirty Earth masses) planet orbits at 1 ~ 2 au, and thus our results strongly favour a `Grand Tack'-like migration having occurred early in the Solar system's history.

Co-orbital Asteroids as the Source of Venus's Zodiacal Dust Ring

Abstract Photometry from the Helios and STEREO spacecraft revealed regions of enhanced sky surface-brightness suggesting a narrow circumsolar ring of dust associated with Venus’s orbit. We model this phenomenon by integrating the orbits of 10,000,000+ dust particles subject to gravitational and non-gravitational forces, considering several different kinds of plausible dust sources. We find that only particles from a hypothetical population of Venus co-orbital asteroids can produce enough signal in a narrow ring to match the observations. Previous works had suggested such objects would be dynamically unstable. However, we re-examined the stability of asteroids in 1:1 resonance with Venus and found that ∼8% should survive for the age of the solar system, enough to supply the observed ring.

Systematic Structure and Sinks in the YORP Effect

Abstract There is a correlation between the components of the YORP effect of most asteroids, which drives the obliquity and spin rate of the affected bodies in a consistent pattern. This allows for a clear and unambiguous picture for how the spin rates and poles of asteroids affected by YORP will evolve and simplifies the overall picture for how populations will migrate on average. The YORP effect can also lead to a previously unexplored equilibrium state for affected bodies. This equilibrium state is a function of the usual normal YORP effect (which arises due to the global shape asymmetry of the asteroid) and the tangential YORP effect (which arises due the transport of thermal energy through rocky surface features). Estimates from current shape models show that 10%–20% of asteroids have the proper condition to be captured in this equilibrium state, indicating that the occurrence of this state may be significant. The existence of this attractor for the asteroid population means that objects affected by YORP may leave their usual YORP cycles and maintain a constant spin rate over long time periods—this has significant implications for our interpretation of asteroid spin rate evolution and related theories for their physical evolution.

Solar Radiation Pressure–Compatible Trajectories in the Vicinity of a Binary Asteroid

Asteroid missions are now an important component of space exploration, and binary asteroids compose approximately 16% of the near Earth asteroids (NEA) population. This fact, combined with the planned mission to binary asteroid 65803 Didymos, makes them a subject of interest for the study of spacecraft dynamics. Binary asteroid systems are composed of two bodies orbiting their barycenter. The presence of two sources of gravitational potential and the rotation of the system makes the study of the dynamics of a spacecraft in their vicinity more challenging than in the vicinity of a single asteroid. The present study is presenting an advanced dynamical model of the motion of a spacecraft in the vicinity of a binary asteroid that includes a fourth-order gravitational potential model and the solar radiation pressure (SRP). Based on this model, trajectories under the form of periodic orbits compatible with the SRP are designed and presented. The stability of the different orbits is then compared. This study is novel by the inclusion of the SRP early in the design of the trajectories.

Indirect methods for fuel-minimal rendezvous with a large population of temporarily captured orbiters

A main objective of this work is to assess the feasibility of space missions to a new population of near Earth asteroids which temporarily orbit Earth, called temporarily captured orbiter. We design rendezvous missions to a large random sample from a database of over 16,000 simulated temporarily captured orbiters using an indirect method based on the maximum principle. The main contribution of this paper is the development of techniques to overcome the difficulty in initializing the algorithm with the construction of the so-called cloud of extremals.

The influence of Ceres on the dynamical evolution of the Zdenekhorsky/Nemesis asteroid family

The Nemesis family, also identified as the Zdenekhorsky family by some authors, is an “incomplete” asteroid family in the central main belt, characterized by an asymmetric distribution between its left and right side, with most of its members located in the left part of the family. It has been suggested that this asymmetry, as well as the shape of its left slope, could have been significantly affected by Ceres, either though close encounters or because of the effect of the nodal linear resonance ν1C. Several age estimates were also found for this family, ranging from a minimum of 150 ± 80 Myr to a maximum of 440 ± 20 Myr. Here we study the effect that Ceres may have had on the dynamical evolution of this family. For this purpose, we performed several numerical simulations that include the Yarkovsky effect and either consider or neglect Ceres as a massive body. We found that the asymmetric shape of this family does not seem to be a product of the local dynamics, but may be an intrinsic feature of the original ejection velocity field by which this family was created. If we assume that the current population of asteroids in librating states of the ν1C secular resonance is currently in a steady-state and originates from the Nemesis family, this population will no longer be sustainable on timescales of 200 Myr since the group formation, which sets an upper limit on the maximum possible family age.

Dancing with Venus in the shadow of the Earth: a pair of genetically related near-Earth asteroids trapped in a mean-motion resonance

ABSTRACT YORP-induced fission events may form dynamically coherent pairs or even families of asteroids. The outcome of this process is well documented among members of the main asteroid belt, but not in the case of the near-Earth asteroid (NEA) population because their paths randomize very efficiently in a short time-scale. Mean-motion resonances (MMRs) may stabilize the orbits of small bodies by making them avoid close encounters with planets. In theory, YORP-induced fission of asteroids trapped in MMRs can preserve evidence of this process even in near-Earth space. Here, we show that two NEAs, 2017 SN16 and 2018 RY7, are currently following an orbital evolution in which their relative mean longitude does not exhibit any secular increase due to the stabilizing action of the 3:5 MMR with Venus. The mechanism that makes this configuration possible may be at work both in the Solar system and elsewhere. Our analysis suggests that the pair 2017 SN16–2018 RY7 may have had its origin in one out of two mechanisms: YORP-induced splitting or binary dissociation.

The dynamical evolution of escaped Jupiter Trojan asteroids, link to other minor body populations

The Jupiter Trojans constitute an important asteroidal population both in number and also in relation to their dynamical and physical properties. They are asteroids located around L4 and L5 Lagrangian points on relatively stable orbits, in 1: 1 mean motion resonance with Jupiter. However, not all of them lie in orbits that remain stable over the age of the Solar System. Unstable zones allow some Trojans to escape in time scales shorter than the Solar System age. This may contribute to populate other small body populations. In this paper, we study this process by performing long-term numerical simulations of the observed Trojans, focusing on the trajectories of those that leave the resonance. The orbits of current Trojan asteroids are taken as initial conditions and their evolution is followed under the gravitational action of the Sun and the planets. We built “occupancy maps” that represent the zones in the Solar System where escaped Trojans should be found. We find the rate of escape of Trojans from L5, ∼ 1.1 times greater than from L4. The majority of escaped Trojans have encounters with Jupiter although they have encounters with the other planets too. The median lifetime of escaped Trojans in the Solar System is ∼ 264, 000 years for L4 and ∼ 249, 000 years for L5. Almost all escaped Trojans reach the comet zone, ∼ 90% cross the Centaur zone and only L4 Trojans reach the transneptunian zone. Considering the real asymmetry between L4 and L5, we show that 18 L4 Trojans and 14 L5 Trojans with diameter D > 1 km are ejected from the resonance every Myr. The contribution of the escaped Trojans to other minor body populations would be negligible, being the contribution from L4 and L5 to Jupiter-family comets (JFCs) and no-JFCs almost the same, and the L4 contribution to Centaurs and TNOs, orders of magnitude greater than that of L5. Considering the collisional removal, besides the dynamical one, and assuming that Trojans that escape due to collisions follow the same dynamical behavior that the ones removed by dynamics, we would have a minor contribution of Trojans to comets and Centaurs. However, there would be some specific regions were escaped Trojans could be important such as Asteroids in Cometary Orbits (ACOs), Encke-type comets, Shoemaker-Levy 9-type impacts on Jupiter and Near-Earth objects (NEOs).