3,526 research outputs found
Building the Terrestrial Planets: Constrained Accretion in the Inner Solar System
To date, no accretion model has succeeded in reproducing all observed
constraints in the inner Solar System. These constraints include 1) the orbits,
in particular the small eccentricities, and 2) the masses of the terrestrial
planets -- Mars' relatively small mass in particular has not been adequately
reproduced in previous simulations; 3) the formation timescales of Earth and
Mars, as interpreted from Hf/W isotopes; 4) the bulk structure of the asteroid
belt, in particular the lack of an imprint of planetary embryo-sized objects;
and 5) Earth's relatively large water content, assuming that it was delivered
in the form of water-rich primitive asteroidal material. Here we present
results of 40 high-resolution (N=1000-2000) dynamical simulations of late-stage
planetary accretion with the goal of reproducing these constraints, although
neglecting the planet Mercury. We assume that Jupiter and Saturn are
fully-formed at the start of each simulation, and test orbital configurations
that are both consistent with and contrary to the "Nice model." We find that a
configuration with Jupiter and Saturn on circular orbits forms low-eccentricity
terrestrial planets and a water-rich Earth on the correct timescale, but Mars'
mass is too large by a factor of 5-10 and embryos are often stranded in the
asteroid belt. A configuration with Jupiter and Saturn in their current
locations but with slightly higher initial eccentricities (e = 0.07-0.1)
produces a small Mars, an embryo-free asteroid belt, and a reasonable Earth
analog but rarely allows water delivery to Earth. None of the configurations we
tested reproduced all the observed constraints. (abridged)Comment: Accepted to Icarus. 21 pages, 12 figures, 5 tables in emulateapj
format. Figures 3 and 4 degraded. For full-resolution see
http://casa.colorado.edu/~raymonsn/ms_emulateapj.pd
Earths in Other Solar Systems N-body simulations: the Role of Orbital Damping in Reproducing the Kepler Planetary Systems
The population of exoplanetary systems detected by Kepler provides
opportunities to refine our understanding of planet formation. Unraveling the
conditions needed to produce the observed exoplanets will sallow us to make
informed predictions as to where habitable worlds exist within the galaxy. In
this paper, we examine using N-body simulations how the properties of planetary
systems are determined during the final stages of assembly. While accretion is
a chaotic process, trends in the ensemble properties of planetary systems
provide a memory of the initial distribution of solid mass around a star prior
to accretion. We also use EPOS, the Exoplanet Population Observation Simulator,
to account for detection biases and show that different accretion scenarios can
be distinguished from observations of the Kepler systems. We show that the
period of the innermost planet, the ratio of orbital periods of adjacent
planets, and masses of the planets are determined by the total mass and radial
distribution of embryos and planetesimals at the beginning of accretion. In
general, some amount of orbital damping, either via planetesimals or gas,
during accretion is needed to match the whole population of exoplanets.
Surprisingly, all simulated planetary systems have planets that are similar in
size, showing that the "peas in a pod" pattern can be consistent with both a
giant impact scenario and a planet migration scenario. The inclusion of
material at distances larger than what Kepler observes has a profound impact on
the observed planetary architectures, and thus on the formation and delivery of
volatiles to possible habitable worlds.Comment: Resubmitted to ApJ. Planet formation models available online at
http://eos-nexus.org/genesis-database
Water Delivery and Giant Impacts in the 'Grand Tack' Scenario
A new model for terrestrial planet formation (Hansen 2009, Walsh et al. 2011)
has explored accretion in a truncated protoplanetary disk, and found that such
a configuration is able to reproduce the distribution of mass among the planets
in the Solar System, especially the Earth/Mars mass ratio, which earlier
simulations have generally not been able to match. Walsh et al. tested a
possible mechanism to truncate the disk--a two-stage, inward-then-outward
migration of Jupiter and Saturn, as found in numerous hydrodynamical
simulations of giant planet formation. In addition to truncating the disk and
producing a more realistic Earth/Mars mass ratio, the migration of the giant
planets also populates the asteroid belt with two distinct populations of
bodies--the inner belt is filled by bodies originating inside of 3 AU, and the
outer belt is filled with bodies originating from between and beyond the giant
planets (which are hereafter referred to as `primitive' bodies).
We find here that the planets will accrete on order 1-2% of their total mass
from primitive planetesimals scattered onto planet-crossing orbits during the
formation of the planets. For an assumed value of 10% for the water mass
fraction of the primitive planetesimals, this model delivers a total amount of
water comparable to that estimated to be on the Earth today. While the radial
distribution of the planetary masses and the dynamical excitation of their
orbits are a good match to the observed system, we find that the last giant
impact is typically earlier than 20 Myr, and a substantial amount of mass is
accreted after that event. However, 5 of the 27 planets larger than half an
Earth mass formed in all simulations do experience large late impacts and
subsequent accretion consistent with the dating of the Moon-forming impact and
the estimated amount of mass accreted by Earth following that event
The Diversity of Extrasolar Terrestrial Planets
Extrasolar planetary host stars are enriched in key planet-building elements.
These enrichments have the potential to drastically alter the building blocks
available for terrestrial planet formation. Here we report on the combination
of dynamical models of late-stage terrestrial planet formation within known
extrasolar planetary systems with chemical equilibrium models of the
composition of solid material within the disk. This allows us to constrain the
bulk elemental composition of extrasolar terrestrial planets. A wide variety of
resulting planetary compositions exist, ranging from those that are essentially
"Earth-like", containing metallic Fe and Mg-silicates, to those that are
dominated by graphite and SiC. This implies that a diverse range of terrestrial
planets are likely to exist within extrasolar planetary systems.Comment: 4 pages, 1 figure. Submitted to the proceedings of IAU symposium 265
Chemical Abundances in the Universe: Connecting First Stars to Planet
Experimental Bayesian Quantum Phase Estimation on a Silicon Photonic Chip
Quantum phase estimation is a fundamental subroutine in many quantum
algorithms, including Shor's factorization algorithm and quantum simulation.
However, so far results have cast doubt on its practicability for near-term,
non-fault tolerant, quantum devices. Here we report experimental results
demonstrating that this intuition need not be true. We implement a recently
proposed adaptive Bayesian approach to quantum phase estimation and use it to
simulate molecular energies on a Silicon quantum photonic device. The approach
is verified to be well suited for pre-threshold quantum processors by
investigating its superior robustness to noise and decoherence compared to the
iterative phase estimation algorithm. This shows a promising route to unlock
the power of quantum phase estimation much sooner than previously believed
Outcomes and Duration of Tidal Evolution in a Star-Planet-Moon System
We formulated tidal decay lifetimes for hypothetical moons orbiting
extrasolar planets with both lunar and stellar tides. Previous work neglected
the effect of lunar tides on planet rotation, and are therefore applicable only
to systems in which the moon's mass is much less than that of the planet. This
work, in contrast, can be applied to the relatively large moons that might be
detected around newly-discovered Neptune-mass and super-Earth planets. We
conclude that moons are more stable when the planet/moon systems are further
from the parent star, the planets are heavier, or the parent stars are lighter.
Inclusion of lunar tides allows for significantly longer lifetimes for a
massive moon relative to prior formulations. We expect that the semi-major axis
of the planet hosting the first detected exomoon around a G-type star is
0.4-0.6 AU and is 0.2-0.4 AU for an M-type star.Comment: Accepted for publication in ApJ, 19 pages, 19 figure
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