31 research outputs found
Fate of the runner in hit-and-run collisions
In similar-sized planetary collisions, a significant part of the impactor
often misses the target and continues downrange. We follow the dynamical
evolution of "runners" from giant impacts to determine their ultimate fate.
Surprisingly, runners re-impact their target planets only about half of the
time, for realistic collisional and dynamical scenarios. Otherwise they remain
in orbit for tens of millions of years (the limit of our N-body calculations)
and longer, or sometimes collide with a different planet than the first one.
When the runner does return to collide again with the same arget planet, its
impact velocity is mainly constrained by the outcome of the prior collision.
Impact angle and orientation, however, are unconstrained by the prior
collision.Comment: 24 pages, 14 figures, 4 tables, accepted for publication in Ap
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
Graze-and-Merge Collisions under External Perturbers
Graze-and-merge collisions (GMCs) are common multi-step mergers occurring in
low-velocity off-axis impacts between similar sized planetary bodies. The first
impact happens at somewhat faster than the mutual escape velocity; for typical
impact angles this does not result in immediate accretion, but the smaller body
is slowed down so that it loops back around and collides again, ultimately
accreting. The scenario changes in the presence of a third major body, i.e.
planets accreting around a star, or satellites around a planet. We find that
when the loop-back orbit remains inside roughly 1/3 of the Hill radius from the
target, then the overall process is not strongly affected. As the loop-back
orbit increases in radius, the return velocity and angle of the second
collision become increasingly random, with no record of the first collision's
orientation. When the loop-back orbit gets to about 3/4 of the Hill radius, the
path of smaller body is disturbed up to the point that it will usually escape
the target.Comment: 19 pages, 16 figures, 1 table, accepted for publication in Ap
Coupling SPH and thermochemical models of planets: Methodology and example of a Mars-sized body
Giant impacts have been suggested to explain various characteristics of
terrestrial planets and their moons. However, so far in most models only the
immediate effects of the collisions have been considered, while the long-term
interior evolution of the impacted planets was not studied. Here we present a
new approach, combining 3-D shock physics collision calculations with 3-D
thermochemical interior evolution models. We apply the combined methods to a
demonstration example of a giant impact on a Mars-sized body, using typical
collisional parameters from previous studies. While the material parameters
(equation of state, rheology model) used in the impact simulations can have
some effect on the long-term evolution, we find that the impact angle is the
most crucial parameter for the resulting spatial distribution of the newly
formed crust. The results indicate that a dichotomous crustal pattern can form
after a head-on collision, while this is not the case when considering a more
likely grazing collision. Our results underline that end-to-end 3-D
calculations of the entire process are required to study in the future the
effects of large-scale impacts on the evolution of planetary interiors.Comment: 29 pages, 10 figures, accepted for publication in Icaru
The Exoplanet Population Observation Simulator. II -- Population Synthesis in the Era of Kepler
The collection of planetary system properties derived from large surveys such
as Kepler provides critical constraints on planet formation and evolution.
These constraints can only be applied to planet formation models, however, if
the observational biases and selection effects are properly accounted for. Here
we show how epos, the Exoplanet Population Observation Simulator, can be used
to constrain planet formation models by comparing the Bern planet population
synthesis models to the Kepler exoplanetary systems. We compile a series of
diagnostics, based on occurrence rates of different classes of planets and the
architectures of multi-planet systems, that can be used as benchmarks for
future and current modeling efforts. Overall, we find that a model with 100
seed planetary cores per protoplanetary disk provides a reasonable match to
most diagnostics. Based on these diagnostics we identify physical properties
and processes that would result in the Bern model more closely matching the
known planetary systems. These are: moving the planet trap at the inner disk
edge outward; increasing the formation efficiency of mini-Neptunes; and
reducing the fraction of stars that form observable planets. We conclude with
an outlook on the composition of planets in the habitable zone, and highlight
that the majority of simulated planets smaller than 1.7 Earth radii have
substantial hydrogen atmospheres.
The software used in this paper is available online for public scrutiny at
https://github.com/GijsMulders/eposComment: Accepted in Ap
The impact of pebble flux regulated planetesimal formation on giant planet formation
Forming gas giant planets by the accretion of 100 km diameter planetesimals,
a typical size that results from self-gravity assisted planetesimal formation,
is often thought to be inefficient. Many models therefore use small km-sized
planetesimals, or invoke the accretion of pebbles. Furthermore, models based on
planetesimal accretion often use the ad hoc assumption of planetesimals
distributed radially in a minimum mass solar nebula fashion. We wish to
investigate the impact of various initial radial density distributions in
planetesimals with a dynamical model for the formation of planetesimals on the
resulting population of planets. In doing so, we highlight the directive role
of the early stages of dust evolution into pebbles and planetesimals in the
circumstellar disk on the following planetary formation. We have implemented a
two population model for solid evolution and a pebble flux regulated model for
planetesimal formation into our global model for planet population synthesis.
This framework is used to study the global effect of planetesimal formation on
planet formation. As reference, we compare our dynamically formed planetesimal
surface densities with ad-hoc set distributions of different radial density
slopes of planetesimals. Even though required, it is not solely the total
planetesimal disk mass, but the planetesimal surface density slope and
subsequently the formation mechanism of planetesimals, that enables planetary
growth via planetesimal accretion. Highly condensed regions of only 100 km
sized planetesimals in the inner regions of circumstellar disks can lead to gas
giant growth. Pebble flux regulated planetesimal formation strongly boosts
planet formation, because it is a highly effective mechanism to create a steep
planetesimal density profile. We find this to lead to the formation of giant
planets inside 1 au by 100 km already by pure planetesimal accretion
Hints for a Turnover at the Snow Line in the Giant Planet Occurrence Rate
The orbital distribution of giant planets is crucial for understanding how
terrestrial planets form and predicting yields of exoplanet surveys. Here, we
derive giant planets occurrence rates as a function of orbital period by taking
into account the detection efficiency of the Kepler and radial velocity (RV)
surveys. The giant planet occurrence rates for Kepler and RV show the same
rising trend with increasing distance from the star. We identify a break in the
RV giant planet distribution between ~2-3 au -- close to the location of the
snow line in the Solar System -- after which the occurrence rate decreases with
distance from the star. Extrapolating a broken power-law distribution to larger
semi-major axes, we find good agreement with the ~ 1% planet occurrence rates
from direct imaging surveys. Assuming a symmetric power law, we also estimate
that the occurrence of giant planets between 0.1-100 au is 26.6 +7.5 -5.4% for
planets with masses 0.1-20MJ and decreases to 6.2 +1.5 -1.2% for planets more
massive than Jupiter. This implies that only a fraction of the structures
detected in disks around young stars can be attributed to giant planets.
Various planet population synthesis models show good agreement with the
observed distribution, and we show how a quantitative comparison between model
and data can be used to constrain planet formation and migration mechanisms.Comment: 16 pages, 10 figure
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Collision Chains among the Terrestrial Planets. II. An Asymmetry between Earth and Venus
During the late stage of terrestrial planet formation, hit-and-run collisions are about as common as accretionary mergers, for expected velocities and angles of giant impacts. Average hit-and-runs leave two major remnants plus debris: the target and impactor, somewhat modified through erosion, escaping at lower relative velocity. Here we continue our study of the dynamical effects of such collisions. We compare the dynamical fates of intact runners that start from hit-and-runs with proto-Venus at 0.7 au and proto-Earth at 1.0 au. We follow the orbital evolutions of the runners, including the other terrestrial planets, Jupiter, and Saturn, in an N-body code. We find that the accretion of these runners can take ≳10 Myr (depending on the egress velocity of the first collision) and can involve successive collisions with the original target planet or with other planets. We treat successive collisions that the runner experiences using surrogate models from machine learning, as in previous work, and evolve subsequent hit-and-runs in a similar fashion. We identify asymmetries in the capture, loss, and interchange of runners in the growth of Venus and Earth. Hit-and-run is a more probable outcome at proto-Venus, being smaller and faster orbiting than proto-Earth. But Venus acts as a sink, eventually accreting most of its runners, assuming typical events, whereas proto-Earth loses about half, many of those continuing to Venus. This leads to a disparity in the style of late-stage accretion that could have led to significant differences in geology, composition, and satellite formation at Earth and Venus