193 research outputs found
SPH calculations of asteroid disruptions: The role of pressure dependent failure models
We present recent improvements of the modeling of the disruption of strength
dominated bodies using the Smooth Particle Hydrodynamics (SPH) technique. The
improvements include an updated strength model and a friction model, which are
successfully tested by a comparison with laboratory experiments. In the
modeling of catastrophic disruptions of asteroids, a comparison between old and
new strength models shows no significant deviation in the case of targets which
are initially non-porous, fully intact and have a homogeneous structure (such
as the targets used in the study by Benz&Asphaug (1999). However, for many
cases (e.g. initially partly or fully damaged targets, rubble-pile structures,
etc.) we find that it is crucial that friction is taken into account and the
material has a pressure dependent shear strength. Our investigations of the
catastrophic disruption threshold as a function of target properties
and target sizes up to a few 100 km show that a fully damaged target modeled
without friction has a which is significantly (5-10 times) smaller
than in the case where friction is included. When the effect of the energy
dissipation due to compaction (pore crushing) is taken into account as well,
the targets become even stronger ( is increased by a factor of 2-3).
On the other hand, cohesion is found to have an negligible effect at large
scales and is only important at scales 1km. Our results show the
relative effects of strength, friction and porosity on the outcome of
collisions among small ( 1000 km) bodies. These results will be used
in a future study to improve existing scaling laws for the outcome of
collisions (e.g. Leinhardt&Stewart, 2012).Comment: Accepted for publication in Planetary and Space Scienc
SPH calculations of Mars-scale collisions: the role of the Equation of State, material rheologies, and numerical effects
We model large-scale (2000km) impacts on a Mars-like planet using a
Smoothed Particle Hydrodynamics code. The effects of material strength and of
using different Equations of State on the post-impact material and temperature
distributions are investigated. The properties of the ejected material in terms
of escaping and disc mass are analysed as well. We also study potential
numerical effects in the context of density discontinuities and rigid body
rotation. We find that in the large-scale collision regime considered here
(with impact velocities of 4km/s), the effect of material strength is
substantial for the post-impact distribution of the temperature and the
impactor material, while the influence of the Equation of State is more subtle
and present only at very high temperatures.Comment: 24 pages, 11 figures; accepted for publication in Icaru
Global Scale Impacts
Global scale impacts modify the physical or thermal state of a substantial
fraction of a target asteroid. Specific effects include accretion, family
formation, reshaping, mixing and layering, shock and frictional heating,
fragmentation, material compaction, dilatation, stripping of mantle and crust,
and seismic degradation. Deciphering the complicated record of global scale
impacts, in asteroids and meteorites, will lead us to understand the original
planet-forming process and its resultant populations, and their evolution in
time as collisions became faster and fewer. We provide a brief overview of
these ideas, and an introduction to models.Comment: A chapter for Asteroids IV, a new volume in the Space Science Series,
University of Arizona Press (Patrick Michel, Francesca E. DeMeo, William F.
Bottke, Eds.
Modeling asteroid collisions and impact processes
As a complement to experimental and theoretical approaches, numerical
modeling has become an important component to study asteroid collisions and
impact processes. In the last decade, there have been significant advances in
both computational resources and numerical methods. We discuss the present
state-of-the-art numerical methods and material models used in "shock physics
codes" to simulate impacts and collisions and give some examples of those
codes. Finally, recent modeling studies are presented, focussing on the effects
of various material properties and target structures on the outcome of a
collision.Comment: Chapter to appear in the Space Science Series Book: Asteroids IV.
Includes minor correction
Small-body deflection techniques using spacecraft: techniques in simulating the fate of ejecta
We define a set of procedures to numerically study the fate of ejecta
produced by the impact of an artificial projectile with the aim of deflecting
an asteroid. Here we develop a simplified, idealized model of impact conditions
that can be adapted to fit the details of specific deflection-test scenarios,
such as what is being proposed for the AIDA project. Ongoing studies based upon
the methodology described here can be used to inform observational strategies
and safety conditions for an observing spacecraft. To account for ejecta
evolution, the numerical strategies we are employing are varied and include a
large N-Body component, a smoothed-particle hydrodynamics (SPH) component, and
an application of impactor scaling laws. Simulations that use SPH-derived
initial conditions show high-speed ejecta escaping at low angles of
inclination, and very slowly moving ejecta lofting off the surface at higher
inclination angles, some of which re-impacts the small-body surface. We are
currently investigating the realism of this and other models' behaviors. Next
steps will include the addition of solar perturbations to the model and
applying the protocol developed here directly to specific potential mission
concepts such as the proposed AIDA scenario.Comment: 19 pages, 11 figures, accepted for publication in Advances in Space
Research, Special Issue: Asteroids & Space Debri
Collision and impact simulations including porosity
The Smooth Particle Hydrodynamics (SPH) impact code (Benz & Asphaug 1994) has been developed for the simulation of impacts and collisions involving brittle solids in the strength-and gravity-dominated regime. In the latter regime, the gravitational overburden is used to increase the fracture threshold. In this paper, we extend our numerical approach to include the effect of porosity at a sub-resolution scale by adapting the so-called P -α model (Herrman 1969). Using our extended 3D SPH impact code, we investigated collisions between porous bodies to examine the sensitivity of collisional outcomes to the degree of porosity. Two applications that illustrate the capabilities of our approach are shown: 1) the modeling of a Deep Impact-like impact and 2) the computation of the amount of momentum transferred to an asteroid following the impact of a high velocity projectil
Modification of icy planetesimals by early thermal evolution and collisions: Constraints for formation time and initial size of comets and small KBOs
Comets and small Kuiper belt objects are considered to be among the most
primitive objects in the solar system as comets like C/1995 O1 Hale-Bopp are
rich in highly volatile ices like CO. It has been suggested that early in the
solar system evolution the precursors of both groups, the so-called icy
planetesimals, were modified by both short-lived radiogenic heating and
collisional heating. Here we employ 2D finite-difference numerical models to
study the internal thermal evolution of these objects, where we vary formation
time, radius and rock-to-ice mass fraction. Additionally we perform 3D SPH
collision models with different impact parameters, thus considering both
cratering and catastrophic disruption events. Combining the results of both
numerical models we estimate under which conditions highly volatile ices like
CO, CO2 and NH3 can be retained inside present-day comets and Kuiper belt
objects. Our results indicate that for present-day objects derived from the
largest post-collision remnant the internal thermal evolution controls the
amount of remaining highly volatile ices, while for the objects formed from
unbound post-collision material the impact heating is dominant. Finally we
apply our results to present-day comets and Kuiper belt objects like
67P/Churyumov-Gerasimenko, C/1995 O1 Hale-Bopp and (486958) Arrokoth
Relevance of Tidal Heating on Large TNOs
We examine the relevance of tidal heating for large Trans-Neptunian Objects,
with a focus on its potential to melt and maintain layers of subsurface liquid
water. Depending on their past orbital evolution, tidal heating may be an
important part of the heat budget for a number of discovered and hypothetical
TNO systems and may enable formation of, and increased access to, subsurface
liquid water. Tidal heating induced by the process of despinning is found to be
particularly able to compete with heating due to radionuclide decay in a number
of different scenarios. In cases where radiogenic heating alone may establish
subsurface conditions for liquid water, we focus on the extent by which tidal
activity lifts the depth of such conditions closer to the surface. While it is
common for strong tidal heating and long lived tides to be mutually exclusive,
we find this is not always the case, and highlight when these two traits occur
together.Comment: Submitted to Icaru
Collisional Formation and Modeling of Asteroid Families
In the last decade, thanks to the development of sophisticated numerical
codes, major breakthroughs have been achieved in our understanding of the
formation of asteroid families by catastrophic disruption of large parent
bodies. In this review, we describe numerical simulations of asteroid
collisions that reproduced the main properties of families, accounting for both
the fragmentation of an asteroid at the time of impact and the subsequent
gravitational interactions of the generated fragments. The simulations
demonstrate that the catastrophic disruption of bodies larger than a few
hundred meters in diameter leads to the formation of large aggregates due to
gravitational reaccumulation of smaller fragments, which helps explain the
presence of large members within asteroid families. Thus, for the first time,
numerical simulations successfully reproduced the sizes and ejection velocities
of members of representative families. Moreover, the simulations provide
constraints on the family dynamical histories and on the possible internal
structure of family members and their parent bodies.Comment: Chapter to appear in the (University of Arizona Press) Space Science
Series Book: Asteroids I
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