216 research outputs found
Three-Body Capture of Irregular Satellites: Application to Jupiter
We investigate a new theory of the origin of the irregular satellites of the
giant planets: capture of one member of a ~100-km binary asteroid after tidal
disruption. The energy loss from disruption is sufficient for capture, but it
cannot deliver the bodies directly to the observed orbits of the irregular
satellites. Instead, the long-lived capture orbits subsequently evolve inward
due to interactions with a tenuous circumplanetary gas disk.
We focus on the capture by Jupiter, which, due to its large mass, provides
the most stringent test of our model. We investigate the possible fates of
disrupted bodies, the differences between prograde and retrograde captures, and
the effects of Callisto on captured objects. We make an impulse approximation
and discuss how it allows us to generalize capture results from equal-mass
binaries to binaries with arbitrary mass ratios.
We find that at Jupiter, binaries offer an increase of a factor of ~10 in the
capture rate of 100-km objects as compared to single bodies, for objects
separated by tens of radii that approach the planet on relatively low-energy
trajectories. These bodies are at risk of collision with Callisto, but may be
preserved by gas drag if their pericenters are raised quickly enough. We
conclude that our mechanism is as capable of producing large irregular
satellites as previous suggestions, and it avoids several problems faced by
alternative models.Comment: 39 pages, 12 figures, 1 table, submitted to Icaru
A Tale of Two Cases
Professor Agnor here traces the development of what he suggests is a bad rule of law which originated in a poor decision of a jurisdiction highly respected for its decisions on the law of future interests. The author\u27s demonstration of how the case has been blindly followed by both bench and bar underscores his message that members of the legal profession must not rely on encyclopedic statements of the law without an examination into the policies and problems involved
On the Migration of Jupiter and Saturn: Constraints from Linear Models of Secular Resonant Coupling with the Terrestrial Planets
We examine how the late divergent migration of Jupiter and Saturn may have
perturbed the terrestrial planets. We identify six secular resonances between
the nu_5 apsidal eigenfrequency of Jupiter and Saturn and the four
eigenfrequencies of the terrestrial planets (g_{1-4}). We derive analytic upper
limits on the eccentricity and orbital migration timescale of Jupiter and
Saturn when these resonances were encountered to avoid perturbing the
eccentricities of the terrestrial planets to values larger than the observed
ones. If Jupiter and Saturn migrated with eccentricities comparable to their
present day values, smooth migration with exponential timescales characteristic
of planetesimal-driven migration (\tau~5-10 Myr) would have perturbed the
eccentricities of the terrestrial planets to values greatly exceeding the
observed ones. This excitation may be mitigated if the eccentricity of Jupiter
was small during the migration epoch, migration was very rapid (e.g. \tau<~ 0.5
Myr perhaps via planet-planet scattering or instability-driven migration) or
the observed small eccentricity amplitudes of the j=2,3 terrestrial modes
result from low probability cancellation of several large amplitude
contributions. Further, results of orbital integrations show that very short
migration timescales (\tau<0.5 Myr), characteristic of instability-driven
migration, may also perturb the terrestrial planets' eccentricities by amounts
comparable to their observed values. We discuss the implications of these
constraints for the relative timing of terrestrial planet formation, giant
planet migration, and the origin of the so-called Late Heavy Bombardment of the
Moon 3.9+/-0.1 Ga ago. We suggest that the simplest way to satisfy these
dynamical constraints may be for the bulk of any giant planet migration to be
complete in the first 30-100 Myr of solar system history.Comment: Accepted for publication in The Astrophysical Journa
Christian and Non-Religious Sociopaths Compared: Self-Concept, Locus of Control, Guilt, and Quality of Religious Experience
Criminal sociopaths frequently claim commitment to Christianity, a religion which philosophically is counter to a sociopath\u27s world view. Ascertaining whether or not religious commitment is a variable relevant to corrections is confusing in light of a lack of research which addresses this problem. In this study 25 non-religious and 27 orthodox Christian male sociopaths, inmates from Oregon State Penitentiary, were administered the Tennessee Self-Concept Scale, the Rotter Internal/External Locus of Control Scale, and the Mosher Forced Choice Guilt Scales. To gather data on the religious experience of the sociopath, the Spiritual Well-Being Scale, the Intrinsic/Extrinsic Religious Orientation Scale, and the God Concept Semantic Differential Scale were also given. Christian sociopaths had significantly higher guilt and had significantly more internal locus of control than non-religious sociopaths. There were no self-esteem differences, but Christian sociopaths had higher behavior self-concept. It was concluded that the Christian and non-religious sociopaths were distinct populations, and since higher guilt and more internal locus of control are signs in the direction of psychological health, Christian sociopaths were better positioned than non-religious sociopaths. The Christian sociopaths were possibly better prospects for rehabilitation, an idea deserving further consideration in longitudinal research
Constraints on the Orbital Evolution of Triton
We present simulations of Triton's post-capture orbit that confirm the
importance of Kozai-type oscillations in its orbital elements. In the context
of the tidal orbital evolution model, these variations require average
pericenter distances much higher than previously published, and the timescale
for the tidal orbital evolution of Triton becomes longer than the age of the
Solar System. Recently-discovered irregular satellites present a new constraint
on Triton's orbital history. Our numerical integrations of test particles
indicate a timescale for Triton's orbital evolution to be less than yrs
for a reasonable number of distant satellites to survive Triton's passage. This
timescale is inconsistent with the exclusively tidal evolution (time scale of
yrs), but consistent with the interestion with the debris from
satellite-satellite collisions. Any major regular satellites will quickly
collide among themselves after being perturbed by Triton, and the resulting
debris disk would eventually be swept up by Triton; given that the total mass
of the Uranian satellite system is 40% of that of Triton, large scale evolution
is possible. This scenario could have followed either collisional or the
recently-discussed three-body-interaction-based capture.Comment: 10 pages, 4 figures, accepted for ApJ
Minimum Radii of Super-Earths: Constraints from Giant Impacts
The detailed interior structure models of super-Earth planets show that there
is degeneracy in the possible bulk compositions of a super-Earth at a given
mass and radius, determined via radial velocity and transit measurements,
respectively. In addition, the upper and lower envelopes in the mass--radius
relationship, corresponding to pure ice planets and pure iron planets,
respectively, are not astrophysically well motivated with regard to the
physical processes involved in planet formation. Here we apply the results of
numerical simulations of giant impacts to constrain the lower bound in the
mass--radius diagram that could arise from collisional mantle stripping of
differentiated rocky/iron planets. We provide a very conservative estimate for
the minimum radius boundary for the entire mass range of large terrestrial
planets. This envelope is a readily testable prediction for the population of
planets to be discovered by the Kepler mission.Comment: 8 pages, 4 figures, Accepted for publication in ApJ Letter
Embryo impacts and gas giant mergers II: Diversity of Hot Jupiters' internal structure
We consider the origin of compact, short-period, Jupiter-mass planets. We
propose that their diverse structure is caused by giant impacts of embryos and
super-Earths or mergers with other gas giants during the formation and
evolution of these hot Jupiters. Through a series of numerical simulations, we
show that typical head-on collisions generally lead to total coalescence of
impinging gas giants. Although extremely energetic collisions can disintegrate
the envelope of gas giants, these events seldom occur. During oblique and
moderately energetic collisions, the merger products retain higher fraction of
the colliders' cores than their envelopes. They can also deposit considerable
amount of spin angular momentum to the gas giants and desynchronize their spins
from their orbital mean motion. We find that the oblateness of gas giants can
be used to infer the impact history. Subsequent dissipation of stellar tide
inside the planets' envelope can lead to runaway inflation and potentially a
substantial loss of gas through Roche-lobe overflow. The impact of super-Earths
on parabolic orbits can also enlarge gas giant planets' envelope and elevates
their tidal dissipation rate over 100 Myr time scale. Since giant
impacts occur stochastically with a range of impactor sizes and energies, their
diverse outcomes may account for the dispersion in the mass-radius relationship
of hot Jupiters.Comment: 19 pages, 7 figures, 7 tables. Accepted for publication in MNRA
Water/Icy Super-Earths: Giant Impacts and Maximum Water Content
Water-rich super-Earth exoplanets are expected to be common. We explore the
effect of late giant impacts on the final bulk abundance of water in such
planets. We present the results from smoothed particle hydrodynamics
simulations of impacts between differentiated water(ice)-rock planets with
masses between 0.5 and 5 M_Earth and projectile to target mass ratios from 1:1
to 1:4. We find that giant impacts between bodies of similar composition never
decrease the bulk density of the target planet. If the commonly assumed maximum
water fraction of 75wt% for bodies forming beyond the snow line is correct,
giant impacts between similar composition bodies cannot serve as a mechanism
for increasing the water fraction. Target planets either accrete materials in
the same proportion, leaving the water fraction unchanged, or lose material
from the water mantle, decreasing the water fraction. The criteria for
catastrophic disruption of water-rock planets are similar to those found in
previous work on super-Earths of terrestrial composition. Changes in bulk
composition for giant impacts onto differentiated bodies of any composition
(water-rock or rock-iron) are described by the same equations. These general
laws can be incorporated into future N-body calculations of planet formation to
track changes in composition from giant impacts.Comment: 9 pages, 4 figures, Accepted for publication in ApJ Letter
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