Constraining the cometary flux through the asteroid belt during the late heavy bombardment (original) (raw)
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The Planetary Science Journal, 2021
Jupiter-family comets (JFCs) contribute a significant amount of debris to near-Earth space. However, telescopic observations of these objects seem to suggest that they have short physical lifetimes. If this is true, the material generated will also be short-lived, but fireball observation networks still detect material on cometary orbits. This study examines centimeter-to-meter-scale sporadic meteoroids detected by the Desert Fireball Network from 2014 to 2020 originating from JFC-like orbits. Analyzing each event’s dynamic history and physical characteristics, we confidently determined whether they originated from the main asteroid belt or the trans-Neptunian region. Our results indicate that <4% of sporadic meteoroids on JFC-like orbits are genetically cometary. This observation is statistically significant and shows that cometary material is too friable to survive in near-Earth space. Even when considering shower contributions, meteoroids on JFC-like orbits are primarily from ...
Disruption of fragmented parent bodies as the origin of asteroid families
Nature, 2003
Asteroid families are groups of small bodies that share certain orbit 1 and spectral properties 2 . More than 20 families have now been identified, each believed to have resulted from the collisional break-up of a large parent body 3 in a regime where gravity controls the outcome of the collision more than the material strength of the rock. The size and velocity distributions of the family members provide important constraints for testing our understanding of the break-up process, but erosion and dynamical diffusion of the orbits over time can erase the original signature of the collision 4,5 . The recently identified young Karin family 6 provides a unique opportunity to study a collisional outcome almost unaffected by orbit evolution. Here we report numerical simulations modelling classes of collisions that reproduce the main characteristics of the Karin family. The sensitivity of the outcome of the collision to the internal structure of the parent body allows us to show that the family must have originated from the break-up of a pre-fragmented parent body, and that all large family members formed by the gravitational reaccumulation of smaller bodies. We argue that most of the identified asteroid families are likely to have had a similar history.
Asteroid families: Current situation
Planetary and Space Science, 2009
Being the products of energetic collisional events, asteroid families provide a fundamental body of evidence to test the predictions of theoretical and numerical models of catastrophic disruption phenomena. The goal is to obtain, from current physical and dynamical data, reliable inferences on the original disruption events that produced the observed families. The main problem in doing this is recognizing, and quantitatively assessing, the importance of evolutionary phenomena that have progressively changed the observable properties of families, due to physical processes unrelated to the original disruption events. Since the early 1990s, there has been a significant evolution in our interpretation of family properties. New ideas have been conceived, primarily as a consequence of the development of refined models of catastrophic disruption processes, and of the discovery of evolutionary processes that had not been accounted for in previous studies. The latter include primarily the Yarkovsky and Yarkovsky-O'Keefe-Radzvieski-Paddack (YORP) effects-radiation phenomena that can secularly change the semi-major axis and the rotation state. We present a brief review of the current state of the art in our understanding of asteroid families, point out some open problems, and discuss a few likely directions for future developments.
P/2006 VW139: a main-belt comet born in an asteroid collision?
Monthly Notices of the Royal Astronomical Society, 2012
In this paper, we apply different methods to examine the possibility that a small group of 24 asteroids dynamically linked to a main-belt comet P/2006 VW 139 , recently discovered by the Pan-STARRS1 survey telescope, shares a common physical origin. By applying the hierarchical clustering and backward integration methods, we find strong evidence that 11 of these asteroids form a subgroup which likely originated in a recent collision event, and that this group includes P/2006 VW 139. The objects not found to be part of the 11-member subgroup , which we designate as the P/2006 VW 139 family, were either found to be dynamically unstable or are likely interlopers which should be expected due to the close proximity of the Themis family. As we demonstrated, statistical significance of the P/2006 VW 139 family is >99 per cent. We determine the age of the family to be 7.5 ± 0.3 Myr, and estimate the diameter of the parent body to be ∼11 km. Results show that the family is produced by an impact which can be best characterized as a transition from the catastrophic to the cratering regime. The dynamical environment of this family is studied as well, including the identification of the most influential mean motion and secular resonances in the region. Our findings now make P/2006 VW 139 the second main-belt comet to be dynamically associated with a young asteroid family, a fact with important implications for the origin and activation mechanism of such objects.
Collisional and Rotational Disruption of Asteroids
Advanced Science Letters, 2011
Asteroids are leftover pieces from the era of planet formation that help us understand conditions in the early Solar System. Unlike larger planetary bodies that were subject to global thermal modification during and subsequent to their formation, these small bodies have kept at least some unmodified primordial material from the solar nebula. However, the structural properties of asteroids have been modified considerably since their formation. Thus, we can find among them a great variety of physical configurations and dynamical histories. In fact, with only a few possible exceptions, all asteroids have been modified or completely disrupted many times during the age of the Solar System. This picture is supported by data from space mission encounters with asteroids that show much diversity of shape, bulk density, surface morphology, and other features. Moreover, the gravitational attraction of these bodies is so small that some physical processes occur in a manner far removed from our common experience on Earth. Thus, each visit to a small body has generated as many questions as it has answered. In this review we discuss the current state of research into asteroid disruption processes, focusing on collisional and rotational mechanisms. We find that recent advances in modeling catastrophic disruption by collisions have provided important insights into asteroid internal structures and a deeper understanding of asteroid families. Rotational disruption, by tidal encounters or thermal effects, is responsible for altering many smaller asteroids, and is at the origin of many binary asteroids and oddly shaped bodies.
Dynamical and physical properties of comet--asteroid transition objects
Astronomy and Astrophysics
In the last few years it has been pointed out that, from both physical and dynamical point of view, it is becoming more and more difficult to distinguish comets from asteroids and indeed there are some examples of small bodies first designated as comets which had, later, to be reclassified as asteroids and vice versa . In order to investigate the evolutionary path of comets and asteroids in terms of both dynamical and physical properties, we performed spectroscopic observations of three objects discovered between 1990 and 1995 -(6042) 1990 WW 2 , (6144) 1994 EQ 3 , and 1995 QY 2 -and analyzed their orbital evolution. Obtained spectra show the typical trend of low-albedo, "primitive" objects, similar to those of outer-belt asteroids and comet nuclei. The dynamical analysis shows that (6042) 1990 WW 2 is on a stable orbit with a typical asteroidal behavior; (6144) 1994 EQ 3 is on a Jupitercrossing chaotic orbit and in the past could have spent some time in a Jupiter's horsehoe orbit; 1995 QY 2 is a Mars crosser and librates about the 15/7 resonance with Jupiter and has a 40% chance to make a transition from asteroid to comet orbit over a timescale of about 3-5×10 5 yr.
Icarus, 1999
An extensive analysis of the size-ejection velocity relationship for members of several of the most important asteroid families identified in the Main Belt is presented. We have found a well defined behavior, with smaller fragments having on the average higher ejection velocities. The results provide useful constraints to current models of catastrophic breakup processes and lead also to a new estimate of the transition limit in largest remnant/parent body mass ratio, distinguishing cratering, and shattering regimes. Moreover, we have now available a practical method for estimating fragment ejection velocities in interasteroid collisional events. This can be easily implemented in numerical models of the collisional evolution of the asteroid belt. In particular, it should be possible to undertake a more quantitative assessment of the efficiency of collisional events in the Main Belt as the sources of near Earth asteroids of different sizes.
Assessing the physical nature of near-Earth asteroids through their dynamical histories
Icarus, 2014
We analyze a sample of 139 near-Earth asteroids (NEAs), defined as those that reach perihelion distances q < 1.3 au, and that also fulfill the conditions of approaching or crossing Jupiter's orbit (aphelion distances Q > 4.8 au), having Tisserand parameters 2 < T < 3 and orbital periods P < 20 yr. In order to compare the dynamics, we also analyze a sample of 42 Jupiter family comets (JFCs) in near-Earth orbits, i.e. with q < 1.3 au. We integrated the orbits of these two samples for 10 4 yr in the past and in the future. We find that the great majority of the NEAs move on stable orbits during the considered period, and that a large proportion of them are in one of the main mean motion resonances with Jupiter, in particular the 2:1. We find a strong coupling between the perihelion distance and the inclination in the motion of most NEAs, due to Kozai mechanism, that generates many sungrazers. On the other hand, most JFCs are found to move on very unstable orbits, showing large variations in their perihelion distances in the last few 10 2 − 10 3 yr, which suggests a rather recent capture in their current near-Earth orbits. Even though most NEAs of our sample move in typical 'asteroidal' orbits, we detect a small group of NEAs whose orbits are highly unstable, resembling those of the JFCs.
Dynamical Evolution of Ecliptic Comets
Comets II, 2004
In this chapter, we review the enormous progress that has been made in our understanding of the dynamical evolution of these bodies. We begin by reviewing the evidence that Jupiter-family comets (JFCs; those with 2 < T < 3) form a dynamically distinct class of comets that originate in a flattened disk beyond Neptune. We present a model for the distribution of comets throughout the JFC and Centaur regions that is consistent with current observations, although further observations and numerical simulations in the Centaur region are called for. We then discuss dynamical results (since confirmed by observations) that a significant amount of material that was scattered by Neptune during the early stages of planet formation could persist today in the form of a "scattered disk" of bodies with highly eccentric orbits beyond Neptune. We describe the dynamical mechanisms believed responsible for the longevity of the surviving bodies and argue that if objects in the Kuiper belt and scattered disk have similar size distributions, then the scattered disk is likely to be the primary source of JFCs and Centaurs. Finally, we describe the importance of understanding the ecliptic comet population for the purposes of determining impact rates on the satellites of the giant planets and of age determinations of the satellite surfaces. We present tables of impact rates based on the best currently available analyses. Further refinements of these rates and age determinations await better observations of the Centaur population (including its size distribution), as well as a better understanding of the formation and early dynamical evolution of the outer solar system.
Comet and asteroid hazard to the terrestrial planets
Advances in Space Research, 2004
We estimated the rate of comet and asteroid collisions with the terrestrial planets by calculating the orbits of 13000 Jupiter-crossing objects (JCOs) and 1300 resonant asteroids and computing the probabilities of collisions based on random-phase approximations and the orbital elements sampled with a 500 yr step. The Bulirsh-Stoer and a symplectic orbit integrator gave similar results for orbital evolution, but may give different collision probabilities with the Sun. A small fraction of former JCOs reached orbits with aphelia inside Jupiter's orbit, and some reached Apollo orbits with semi-major axes less than 2 AU, Aten orbits, and inner-Earth orbits (with aphelia less than 0.983 AU) and remained there for millions of years. Though less than 0.1% of the total, these objects were responsible for most of the collision probability of former JCOs with Earth and Venus. We conclude that a significant fraction of near-Earth objects could be extinct comets that came from the trans-Neptunian region.