170 research outputs found
The curiously warped mean plane of the Kuiper belt
We measured the mean plane of the Kuiper belt as a function of semi-major
axis. For the classical Kuiper belt as a whole (the non-resonant objects in the
semi-major axis range 42--48~au), we find a mean plane of inclination
and longitude of ascending
node (in the J2000
ecliptic-equinox coordinate system), in accord with theoretical expectations of
the secular effects of the known planets. With finer semi-major axis bins, we
detect a statistically significant warp in the mean plane near semi-major axes
40--42~au. Linear secular theory predicts a warp near this location due to the
nodal secular resonance, however the measured mean plane for the
40.3-42~au semi-major axis bin (just outside the ) is inclined
to the predicted plane, a nearly 3- discrepancy. For
the more distant Kuiper belt objects of semi-major axes in the range 50--80~au,
the expected mean plane is close to the invariable plane of the solar system,
but the measured mean plane deviates greatly from this: it has inclination
and longitude of ascending
node . We estimate this
deviation from the expected mean plane to be statistically significant at the
confidence level. We discuss several possible explanations for
this deviation, including the possibility that a relatively close-in
(~au), unseen small planetary-mass object in the outer solar
system is responsible for the warping.Comment: This version corrects an error in Figure 7 and typographical errors
in some equations in Appendix D (changes accepted as an erratum in AJ
Dynamical instabilities in systems of multiple short-period planets are likely driven by secular chaos: a case study of Kepler-102
We investigated the dynamical stability of high-multiplicity Kepler and K2
planetary systems. Our numerical simulations find instabilities in
of the cases on a wide range of timescales (up to orbits) and
over an unexpectedly wide range of initial dynamical spacings. To identify the
triggers of long-term instability in multi-planet systems, we investigated in
detail the five-planet Kepler-102 system. Despite having several near-resonant
period ratios, we find that mean motion resonances are unlikely to directly
cause instability for plausible planet masses in this system. Instead, we find
strong evidence that slow inward transfer of angular momentum deficit (AMD) via
secular chaos excites the eccentricity of the innermost planet, Kepler-102 b,
eventually leading to planet-planet collisions in of Kepler-102
simulations. Kepler-102 b likely has a mass , hence a bulk
density exceeding about half Earth's, in order to avoid dynamical instability.
To investigate the role of secular chaos in our wider set of simulations, we
characterize each planetary system's AMD evolution with a "spectral fraction"
calculated from the power spectrum of short integrations (
orbits). We find that small spectral fractions () are strongly
associated with dynamical stability on long timescales ( orbits)
and that the median time to instability decreases with increasing spectral
fraction. Our results support the hypothesis that secular chaos is the driver
of instabilities in many non-resonant multi-planet systems, and also
demonstrate that the spectral analysis method is an efficient numerical tool to
diagnose long term (in)stability of multi-planet systems from short
simulations.Comment: accepted for publication in A
Not a Simple Relationship between Neptune’s Migration Speed and Kuiper Belt Inclination Excitation
We present numerical simulations of giant planet migration in our solar system and examine how the speed of planetary migration affects inclinations in the resulting population of small bodies (test particles) scattered outward and subsequently captured into Neptune's 3:2 mean motion resonance (the Plutinos), as well as the hot classical Kuiper Belt population. We do not find a consistent relationship between the degree of test particle inclination excitation and e-folding planet migration timescales in the range 5-50 Myr. Our results present a counterexample to Nesvorny's finding that the Plutino and hot classical inclinations showed a marked increase with increasing e-folding timescales for Neptune's migration. We argue that these differing results are likely due to differing secular architectures of the giant planets during and after migration. Small changes in the planets' initial conditions and differences in the numerical implementation of planet migration can result in different amplitudes of the planets' inclination secular modes, and this can lead to different final inclination distributions for test particles in the simulations. We conclude that the observed large inclination dispersion of Kuiper Belt objects does not require Neptune's migration to be slow; planetary migration with e-folding timescales of 5, 10, 30, and 50 Myr can all yield inclination dispersions similar to the observed Plutino and hot classical populations, with no correlation between the degree of inclination excitation and migration speed.NASA [NNX14AG93G, 80NSSC19K0785]; NSF [AST-1312498, AST-1824869]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
The Scattered Disk as the source of the Jupiter Family comets
The short period Jupiter family comets (JFCs) are thought to originate in the
Kuiper Belt; specifically, a dynamical subclass of the Kuiper Belt known as the
`scattered disk' is argued to be the dominant source of JFCs. However, the best
estimates from observational surveys indicate that this source may fall short
by more than two orders of magnitude the estimates obtained from theoretical
models of the dynamical evolution of Kuiper belt objects into JFCs. We
re-examine the scattered disk as a source of the JFCs and make a rigorous
estimate of the discrepancy. We find that the uncertainties in the dynamical
models combined with a change in the size distribution function of the
scattered disk at faint magnitudes (small sizes) beyond the current
observational limit offer a possible but problematic resolution to the
discrepancy. We discuss several other possibilities: that the present
population of JFCs is a large fluctuation above their long term average, that
larger scattered disk objects tidally break-up into multiple fragments during
close planetary encounters as their orbits evolve from the trans-Neptune zone
to near Jupiter, or that there are alternative source populations that
contribute significantly to the JFCs. Well-characterized observational
investigations of the Centaurs, objects that are transitioning between the
trans-Neptune Kuiper belt region and the inner solar system, can test the
predictions of the non-steady state and the tidal break-up hypotheses. The
classical and resonant classes of the Kuiper belt are worth re-consideration as
significant additional or alternate sources of the JFCs.Comment: 33 pages, 6 figures. Revised Content. To be published in The
Astrophysical Journa
Exoplanets Torqued by the Combined Tides of a Moon and Parent Star
In recent years, there has been interest in Earth-like exoplanets in the
habitable zones of low mass stars (). Furthermore, it has
been argued that a large moon may be important for stabilizing conditions on a
planet for life. If these two features are combined, then an exoplanet can feel
a similar tidal influence from both its moon and parent star, leading to
potentially interesting dynamics. The moon's orbital evolution depends on the
exoplanet's initial spin period . When is small, transfer of the
exoplanet's angular momentum to the moon's orbit can cause the moon to migrate
outward sufficiently to be stripped by the star. When is large, the moon
migrates less and the star's tidal torques spin down the exoplanet. Tidal
interactions then cause the moon to migrate inward until it is likely tidally
disrupted by the exoplanet and potentially produces rings. While one may think
that these findings preclude the presence of moons for the exoplanets of low
mass stars, in fact a wide range of timescales are found for the loss or
destruction of the moon; it can take depending on
the system parameters. When the moon is still present, the combined tidal
torques force the exoplanet to spin asynchronously with respect to both its
moon and parent star, which tidally heats the exoplanet. This can produce heat
fluxes comparable to those currently coming through the Earth, arguing that
combined tides may be a method for driving tectonic activity in exoplanets.Comment: 10 pages, 9 figures, updated with minor changes to match version
accepted for publication in A
Trans-Neptunian Objects Transiently Stuck in Neptune's Mean Motion Resonances: Numerical simulations of the current population
A substantial fraction of our solar system's trans-Neptunian objects (TNOs)
are in mean motion resonance with Neptune. Many of these objects were likely
caught into resonances by planetary migration---either smooth or
stochastic---approximately 4 Gyr ago. Some, however, gravitationally scattered
off of Neptune and became transiently stuck in more recent events. Here, we use
numerical simulations to predict the number of transiently-stuck objects,
captured from the current actively scattering population, that occupy 111
resonances at semimajor axes 30--100 au. Our source population is an
observationally constrained model of the currently-scattering TNOs. We predict
that, integrated across all resonances at these distances, the current
transient sticking population comprises 40\% of total
transiently-stuck+scattering TNOs, suggesting that these objects should be
treated as a single population. We compute the relative distribution of
transiently-stuck objects across all : resonances with ,
, and , providing predictions for the population of transient
objects with in each resonance. We find that the relative
populations are approximately proportional to each resonance's libration period
and confirm that the importance of transient sticking increases with semimajor
axis in the studied range. We calculate the expected distribution of libration
amplitudes for stuck objects and demonstrate that observational constraints
indicate that both the total number and the amplitude-distribution of 5:2
resonant TNOs are inconsistent with a population dominated by transient
sticking from the current scattering disk. The 5:2 resonance hence poses a
challenge for leading theories of Kuiper belt sculpting
The effect of orbital evolution on the Haumea (2003 EL61) collisional family
The Haumea family is currently the only identified collisional family in the
Kuiper belt. We numerically simulate the long-term dynamical evolution of the
family to estimate a lower limit of the family's age and to assess how the
population of the family and its dynamical clustering are preserved over Gyr
timescales. We find that the family is not younger than 100 Myr, and its age is
at least 1 Gyr with 95% confidence. We find that for initial velocity
dispersions of 50-400 m/s, approximately 20-45% of the family members are lost
to close encounters with Neptune after 3.5 Gyr of orbital evolution. We apply
these loss rates to two proposed models for the formation of the Haumea family,
a graze-and-merge type collision between two similarly sized, differentiated
KBOs or the collisional disruption of a satellite orbiting Haumea. For the
graze-and-merge collision model, we calculate that >85% of the expected mass in
surviving family members within 150 m/s of the collision has been identified,
but that one to two times the mass of the known family members remains to be
identified at larger velocities. For the satellite-break-up model, we estimate
that the currently identified family members account for ~50% of the expected
mass of the family. Taking observational incompleteness into account, the
observed number of Haumea family members is consistent with either formation
scenario at the 1 sigma level, however both models predict more objects at
larger relative velocities (>150 m/s) than have been identified.Comment: 25 pages, accepted to Icaru
- …