arXiv subjects

Kathryn Volk

Publications and source records attributed to Kathryn Volk.

At least 37 records · Page 2Linked to original sources

arXiv2023

OSSOS. XXIX. The Population and Perihelion Distribution of the Detached Kuiper Belt

The detached transneptunian objects (TNOs) are those with semimajor axes beyond the 2:1 resonance with Neptune, which are neither resonant nor scattering. Using the detached sample from the OSSOS telescopic survey, we produce the first studies of their orbital distribution based on matching the orbits and numbers of the known TNOs after accounting for survey biases. We show that the detached TNO perihelion ($q$) distribution cannot be uniform, but is instead better matched by two uniform components with a break near $q\approx40$ au. We produce parametric two-component models that are not rejectable by the OSSOS data set, and estimate that there are $36,\!000^{+12,000}_{-9,000}$ detached TNOs with absolute magnitudes $H_r < 8.66$ ($D \gtrsim 100$ km) and semimajor axes $48 < a < 250$ au (95% confidence limits). Although we believe these heuristic two-parameter models yield a correct population estimate, we then use the same methods to show that the perihelion distribution of a detached disk created by a simulated rogue planet matches the $q$ distribution even better, suggesting that the temporary presence of other planets in the early Solar System is a promising model to create today's large semimajor axis TNO population. This numerical model results in a detached TNO population estimate of $48,\!000^{+15,000}_{-12,000}$. Because this illustrates how difficult-to-detect $q>50$ au objects are likely present, we conclude that there are $(5 \pm 2)\times10^4$ dynamically detached TNOs, which are thus roughly twice as numerous as the entire transneptunian hot main belt.

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arXiv2023

Tuning the Legacy Survey of Space and Time (LSST) Observing Strategy for Solar System Science

The Vera C. Rubin Observatory is expected to start the Legacy Survey of Space and Time (LSST) in early to mid-2025. This multi-band wide-field synoptic survey will transform our view of the solar system, with the discovery and monitoring of over 5 million small bodies.The final survey strategy chosen for LSST has direct implications on the discoverability and characterization of solar system minor planets and passing interstellar objects. Creating an inventory of the solar system is one of the four main LSST science drivers. The LSST observing cadence is a complex optimization problem that must balance the priorities and needs of all the key LSST science areas. To design the best LSST survey strategy, a series of operation simulations using the Rubin Observatory scheduler have been generated to explore the various options for tuning observing parameters and prioritizations. We explore the impact of the various simulated LSST observing strategies on studying the solar system's small body reservoirs. We examine what are the best observing scenarios and review what are the important considerations for maximizing LSST solar system science. In general, most of the LSST cadence simulations produce +/-5% or less variations in our chosen key metrics, but a subset of the simulations significantly hinder science returns with much larger losses in the discovery and light curve metrics.

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arXiv2022

The Transition from the Kuiper Belt to the Jupiter-Family (Comets)

Kuiper Belt Objects, or more generally Trans-Neptunian Objects (TNOs), are planetesimals found beyond the orbit of Neptune. Some TNOs evolve onto Neptune-crossing orbits and become Centaurs. Many Centaurs, in turn, reach Jupiter-crossing orbits and become Jupiter-family comets (JFCs). TNOs are the main source of the JFCs. TNOs offer a different window than the JFCs, of more primordial bodies and over a different size and temperature range. It is in that context that this chapter is written. Here we discuss the dynamical pathways taken from the trans-Neptunian region to the JFCs, and the most important properties of TNOs that relate to the JFC population, including considerations of their origins, compositions, morphologies, and size distributions. We relate these properties to the JFCs whenever possible. We reflect on a few key outstanding issues regarding our incomplete knowledge of TNOs as they pertain to the Centaurs and JFC populations. We finish with a short discussion of notable new and upcoming facilities and the impacts they will have regarding these outstanding questions.

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arXiv2022

Orbital dynamics landscape near the most distant known trans-Neptunian objects

The most distant known trans-Neptunian objects (perihelion distance above 38 au and semimajor axis above 150 au) are of interest for their potential to reveal past, external, or present but unseen perturbers. Realizing this potential requires understanding how the known planets influence their orbital dynamics. We use a recently-developed Poincare mapping approach for orbital phase space studies of the circular planar restricted three body problem, which we have extended to the case of the three-dimensional restricted problem with $N$ planetary perturbers. With this approach, we explore the dynamical landscape of the 23 most distant TNOs under the perturbations of the known giant planets. We find that, counter to common expectations, almost none of these TNOs are far removed from Neptune's resonances. Nearly half (11) of these TNOs have orbits consistent with stable libration in Neptune's resonances; in particular, the orbits of TNOs 148209 and 474640 overlap with Neptune's 20:1 and 36:1 resonances, respectively. Five objects can be ruled currently non-resonant, despite their large orbital uncertainties, because our mapping approach determines the resonance boundaries in angular phase space in addition to semimajor axis. Only three objects are in orbital regions not appreciably affected by resonances: Sedna, 2012 VP113 and 2015 KG163. Our analysis also demonstrates that Neptune's resonances impart a modest (few percent) non-uniformity in the longitude of perihelion distribution of the currently observable distant TNOs. While not large enough to explain the observed clustering, this small dynamical sculpting of the perihelion longitudes could become relevant for future, larger TNO datasets.

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arXiv2022

Col-OSSOS: The Two Types of Kuiper Belt Surfaces

The Colours of the Outer Solar System Origins Survey (Col-OSSOS) has gathered high quality, near-simultaneous (g-r) and (r-J) colours of 92 Kuiper Belt Objects (KBOs) with (u-g) and (r-z) gathered for some. We present the current state of the survey and data analysis. Recognizing that the optical colours of most icy bodies broadly follow the reddening curve, we present a new projection of the optical-NIR colours, which rectifies the main non-linear features in the optical-NIR along the ordinates. We find evidence for a bifurcation in the projected colours which presents itself as a diagonal empty region in the optical-NIR. A reanalysis of past colour surveys reveals the same bifurcation. We interpret this as evidence for two separate surface classes: the BrightIR class spans the full range of optical colours and broadly follows the reddening curve, while the FaintIR objects are limited in optical colour, and are less bright in the NIR than the BrightIR objects. We present a two class model. Objects in each class consist of a mix of separate blue and red materials, and span a broad range in colour. Spectra are modelled as linear optical and NIR spectra with different slopes, that intersect at some transition wavelength. The underlying spectral properties of the two classes fully reproduce the observed structures in the UV-optical-NIR colour space ($0.4\lesssimλ\lesssim1.4 \mbox{ $μ$m}$), including the bifurcation observed in the Col-OSSOS and H/WTSOSS datasets, the tendency for cold classical KBOs to have lower (r-z) colours than excited objects, and the well known bimodal optical colour distribution.

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arXiv2022

Dynamical Population of Comet Reservoirs

The Oort cloud and the scattered disk are the two primary reservoirs for long-period and short-period comets, respectively. In this review, we assess the known observational constraints on these reservoirs' properties and their formation. In addition, we discuss how the early orbital evolution of the giant planets generated the modern scattered disk from the early, massive planetesimal disk and how $\sim$5\% of this material was captured into the Oort cloud. We review how the Sun's birth environment and dynamical history within the Milky Way alters the formation and modern structure of the Oort cloud. Finally, we assess how the coming decade's anticipated observing campaigns may provide new insights into the formation and properties of the Oort cloud and scattered disk.

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arXiv2022

Free Inclinations for Transneptunian Objects in the Main Kuiper Belt

There is a complex inclination structure present in the transneptunian object (TNO) orbital distribution in the main classical belt region (between orbital semimajor axes of 39 and 48 au). The long-term gravitational effects of the giant planets make TNO orbits precess, but non-resonant objects maintain a nearly constant 'free' inclination ($I_\text{free}$) with respect to a local forced precession pole. Because of the likely cosmogonic importance of the distribution of this quantity, we tabulate free inclinations for all main-belt TNOs, each individually computed using barycentric orbital elements with respect to each object's local forcing pole. We show that the simplest method, based on the Laplace-Lagrange secular theory, is unable to give correct forcing poles for objects near the $ν_{18}$ secular resonance, resulting in poorly conserved $I_\text{free}$ values in much of the main belt. We thus instead implemented an averaged Hamiltonian to obtain the expected nodal precession for each TNO, yielding significantly more accurate free inclinations for non-resonant objects. For the vast majority (96\%) of classical belt TNOs, these $I_\text{free}$ values are conserved to $<1^\circ$ over 4 Gyr numerical simulations, demonstrating the advantage of using this well-conserved quantity in studies of the TNO population and its primordial inclination profile; our computed distributions only reinforce the idea of a very co-planar surviving 'cold' primordial population, overlain by a large $I$-width implanted 'hot' population.

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arXiv2021

Col-OSSOS: Probing Ice Line/Color Transitions within the Kuiper Belt's Progenitor Populations

Dynamically excited objects within the Kuiper belt show a bimodal distribution in their surface colors, and these differing surface colors may be a tracer of where these objects formed. In this work we explore radial color distributions in the primordial planetesimal disk and implications for the positions of ice line/color transitions within the Kuiper belt's progenitor populations. We combine a full dynamical model of the Kuiper belt's evolution due to Neptune's migration with precise surface colors measured by the Colours of the Outer Solar System Origins Survey in order to examine the true color ratios within the Kuiper belt and the ice lines within the primordial disk. We investigate the position of a dominant, surface color changing ice-line, with two possible surface color layouts within the initial disk; (1) inner neutral surfaces and outer red, and (2) inner red surfaces and outer neutral. We performed simulations with a primordial disk that truncates at 30 au. By radially stepping the color transition out through 0.5 au intervals we show that both disk configurations are consistent with the observed color fraction. For an inner neutral, outer red primordial disk we find that the color transition can be at $28^{+2}_{-3}$ au at a 95% confidence level. For an inner red, outer neutral primordial disk the color transition can be at $27^{+3}_{-3}$ au at a 95% confidence level.

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arXiv2021

OSSOS. XXIII. 2013 VZ70 and the Temporary Coorbitals of the Giant Planet

We present the discovery of 2013 VZ70, the first known horseshoe coorbital companion of Saturn. Observed by the Outer Solar System Origins Survey (OSSOS) for 4.5 years, the orbit of 2013 VZ70 is determined to high precision, revealing that it currently is in `horseshoe' libration with the planet. This coorbital motion will last at least thousands of years but ends ~10 kyr from now; 2013 VZ70 is thus another example of the already-known `transient coorbital' populations of the giant planets, with this being the first known prograde example for Saturn (temporary retrograde coorbitals are known for Jupiter and Saturn). We present a theoretical steady state model of the scattering population of trans-Neptunian origin in the giant planet region (2--34 au), including the temporary coorbital populations of the four giant planets. We expose this model to observational biases using survey simulations in order to compare the model to the real detections made by a set of well-characterized outer Solar System surveys. While the observed number of coorbitals relative to the scattering population is higher than predicted, we show that the number of observed transient coorbitals of each giant planet relative to each other is consistent with a transneptunian source.

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arXiv2021

OSSOS finds an Exponential Cutoff in the Size Distribution of the Cold Classical Kuiper belt

The cold main classical Kuiper Belt consists of those non-resonant small solar system bodies with low orbital inclinations and orbital semi-major axes between 42.4 and 47.7 au. These objects likely formed \textit{in situ} and the population has experienced minimal collisional modification since formation. Using the Outer Solar System Origins Survey (OSSOS) ensemble sample and characterization, combined with constraints from deeper surveys and supported by evidence from the Minor Planet Center catalog and the Deep Ecliptic Survey, we determine the absolute magnitude $H_r$ distribution of the cold classical belt from $H_r\simeq5$ to 12 (roughly diameters of 400 km to 20 km). We conclude that the cold population's $H_r$ distribution exhibits an exponential cutoff at large sizes. Exponential cutoffs at large sizes are not a natural outcome of pair-wise particle accretion but exponentially tapered power-law size distributions are a feature of numerical simulations of planetesimal formation via a streaming instability. Our observation of an exponential cutoff agrees with previous observational inferences that no large objects ($D \gtrsim 400$ km) exist in the cold population. We note that the asymptotic slope of the $H_r$ distribution is consistent with $α\sim 0.4$ and this asymptotic slope is also found in streaming instability modelling of planetesimal formation and is thus not necessarily associated with achieving collisional equilibrium. Studies of the transneptunian region are providing the parameters that will enable future streaming-instability studies to determine the initial conditions of planetesimal formation in the $\approx$45 au region of the Sun's protoplanetary disk.

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arXiv2021

Collision Probabilities in the Edgeworth-Kuiper belt

Here, we present results on the intrinsic collision probabilities, $ P_I$, and range of collision speeds, $V_I$, as a function of the heliocentric distance, $r$, in the trans-Neptunian region. The collision speed is one of the parameters, that serves as a proxy to a collisional outcome e.g., complete disruption and scattering of fragments, or formation of crater, where both processes are directly related to the impact energy. We utilize an improved and de-biased model of the trans-Neptunian object (TNO) region from the "Outer Solar System Origins Survey" (OSSOS). It provides a well-defined orbital distribution model of TNOs, based on multiple opposition observations of more than 1000 bodies. In this work we compute collisional probabilities for the OSSOS models of the main classical, resonant, detached+outer and scattering TNO populations. The intrinsic collision probabilities and collision speeds are computed using the Öpik's approach, as revised and modified by Wetherill for non-circular and inclined orbits. The calculations are carried out for each of the dynamical TNO groups, allowing for inter-population collisions as well as collisions within each TNO population, resulting in 28 combinations in total. Our results indicate that collisions in the trans-Neptunian region are possible over a wide range in ($r, V_I$) phase space. Although collisions are calculated to happen within $r\sim 20 - 200$~AU and $V_I \sim 0.1$~km/s to as high as $V_I\sim9$~km/s, most of the collisions are likely to happen at low relative velocities $V_I<1$~km/s and are dominated by the main classical belt.

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arXiv2021

Col-OSSOS: The Distinct Colour Distribution of Single and Binary Cold Classical KBOs

The cold classical Kuiper Belt Objects (KBOs) possess a high, $\gtrsim30\%$ binary fraction. Widely separated and dynamically fragile, these binary systems have been useful in tracing the origins of KBOs. A new class of binaries was recently identified by their colours. The so-called blue binaries are unanimously members of the less red compositional class, and exhibit a 100% binary fraction. They appear to be push-out survivors, emplaced in the classical region during Neptune's phases of outward migration. The presence of these binary systems implies that the majority of objects that formed near the cold classical region formed as binaries. Here we present new optical colour measurements of cold classical KBOs from the Colours of the Outer Solar System Origins Survey, including colours of a blue binary discovered by the Solar System Origins Legacy Survey -- 2015 RJ277. The increased size of the colours sample has resulted in order-of-magnitude decrease in the probability that the binaries and singles sample share the same colour distribution. From the Anderson-Darling statistic, this probability is only a 0.3%, while it is only 0.002% when utilizing the difference of means statistic. We find a hint that the blue binaries have inflated free inclinations compared to their red counterparts, consistent with the push-out origin for these bodies.

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arXiv2021

K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System

$K2$ greatly extended $Kepler$'s ability to find new planets, but it was typically limited to identifying transiting planets with orbital periods below 40 days. While analyzing $K2$ data through the Exoplanet Explorers project, citizen scientists helped discover one super-Earth and four sub-Neptune sized planets in the relatively bright ($V=12.21$, $K=10.3$) K2-138 system, all which orbit near 3:2 mean motion resonances. The $K2$ light curve showed two additional transit events consistent with a sixth planet. Using $Spitzer$ photometry, we validate the sixth planet's orbital period of $41.966\pm0.006$ days and measure a radius of $3.44^{+0.32}_{-0.31}\,R_{\oplus}$, solidifying K2-138 as the $K2$ system with the most currently known planets. There is a sizeable gap between the outer two planets, since the fifth planet in the system, K2-138 f, orbits at 12.76 days. We explore the possibility of additional non-transiting planets in the gap between f and g. Due to the relative brightness of the K2-138 host star, and the near resonance of the inner planets, K2-138 could be a key benchmark system for both radial velocity and transit timing variation mass measurements, and indeed radial velocity masses for the inner four planets have already been obtained. With its five sub-Neptunes and one super-Earth, the K2-138 system provides a unique test bed for comparative atmospheric studies of warm to temperate planets of similar size, dynamical studies of near resonant planets, and models of planet formation and migration.

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arXiv2021

OSSOS: The Eccentricity and Inclination Distributions of the Stable Neptunian Trojans

The minor planets on orbits that are dynamically stable in Neptune's 1:1 resonance on Gyr timescales were likely emplaced by Neptune's outward migration. We explore the intrinsic libration amplitude, eccentricity, and inclination distribution of Neptune's stable Trojans, using the detections and survey efficiency of the Outer Solar System Origins Survey (OSSOS) and Pan-STARRS1. We find that the libration amplitude of the stable Neptunian Trojan population can be well modeled as a Rayleigh distribution with a libration amplitude width $σ_{A_phi}$ of 15$^\circ$. When taken as a whole, the Neptune Trojan population can be acceptably modeled with a Rayleigh eccentricity distribution of width $σ_e$ of 0.045 and a typical sin(i) x Gaussian inclination distribution with a width $σ_i$ of 14 +/- 2 degrees. However, these distributions are only marginally acceptable. This is likely because, even after accounting for survey detection biases, the known large Hr < 8 and small Hr >= 8 Neptune Trojans appear to have markedly different eccentricities and inclinations. We propose that like the classical Kuiper belt, the stable intrinsic Neptunian Trojan population have dynamically `hot' and dynamically `cold' components to its eccentricity/inclination distribution, with $σ_{e-cold}$ ~ 0.02 / $σ_{i-cold}$ ~ 6$^\circ$ and $σ_{e-hot}$~ 0.05 / $σ_{i-hot}$ ~ 18$^\circ$. In this scenario, the `cold' L4 Neptunian Trojan population lacks the Hr >= 8 members and has 13 +11/-6 `cold' Trojans with Hr < 8. On the other hand, the `hot' L4 Neptunian Trojan population has 136 +57/-48 Trojans with Hr < 10 -- a population 2.4 times greater than that of the L4 Jovian Trojans in the same luminosity range.

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arXiv2021

Contemporaneous Multi-Wavelength and Precovery Observations of Active Centaur P/2019 LD2 (ATLAS

Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) (Sarid et al. 2019) provides the first opportunity to observe the migration of a Solar System small body from a Centaur orbit to a Jupiter Family Comet (JFC) four decades from now (Kareta et al., 2020; Hsieh et al. 2020). The Gateway transition region is beyond where water ice can power cometary activity, and coma production there is as poorly understood as in all Centaurs. We present contemporaneous multi-wavelength observations of LD2 from 2020 July 2-4: Gemini-North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO SMT millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleu's effective radius to <=1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has g'-r'=0.70+/-0.07, r'-i'=0.26+/-0.07, a dust production rate of ~10-20 kg/s, and an outflow velocity between v~0.6-3.3 m/s. We did not detect CO towards LD2 on 2020 July 2-3, with a 3-sigma upper limit of Q(CO) < 4.4 * 10^27 mol/s (<200 kg/s). Near-infrared spectra show evidence for water ice at the 1-10% level depending on grain size. Spatial profiles and archival data are consistent with sustained activity. The evidence supports the hypothesis that LD2 is a typical small Centaur that will become a typical JFC, and thus it is critical to understanding the transition between these two populations. Finally, we discuss potential strategies for a community-wide, long baseline monitoring effort.

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arXiv2020

P/2019 LD2 (ATLAS): An Active Centaur in Imminent Transition to the Jupiter Family

The recently discovered object P/2019 LD2 (ATLAS) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 years. We find that 2019 LD2 is currently in the vicinity of a dynamical "Gateway" that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population; Sarid et al. 2019). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ~3 years to less than once every 70 years, if 2019 LD2's nucleus is ~1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition.

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arXiv2020

Machine Learning Classification of Kuiper Belt Populations

In the outer solar system, the Kuiper Belt contains dynamical sub-populations sculpted by a combination of planet formation and migration and gravitational perturbations from the present-day giant planet configuration. The subdivision of observed Kuiper Belt objects (KBOs) into different dynamical classes is based on their current orbital evolution in numerical integrations of their orbits. Here we demonstrate that machine learning algorithms are a promising tool for reducing both the computational time and human effort required for this classification. Using a Gradient Boosting Classifier, a type of machine learning regression tree classifier trained on features derived from short numerical simulations, we sort observed KBOs into four broad, dynamically distinct populations - classical, resonant, detached, and scattering - with a >97 per cent accuracy for the testing set of 542 securely classified KBOs. Over 80 per cent of these objects have a $>3σ$ probability of class membership, indicating that the machine learning method is classifying based on the fundamental dynamical features of each population. We also demonstrate how, by using computational savings over traditional methods, we can quickly derive a distribution of class membership by examining an ensemble of object clones drawn from the observational errors. We find two major reasons for misclassification: inherent ambiguity in the orbit of the object - for instance, an object that is on the edge of resonance - and a lack of representative examples in the training set. This work provides a promising avenue to explore for fast and accurate classification of the thousands of new KBOs expected to be found by surveys in the coming decade.

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arXiv2020

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 $\sim20\%$ of the cases on a wide range of timescales (up to $5\times10^9$ 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 $\sim80\%$ of Kepler-102 simulations. Kepler-102 b likely has a mass $>\sim0.1M_{\oplus}$, 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 ($\sim5\times10^6$ orbits). We find that small spectral fractions ($\lesssim0.01$) are strongly associated with dynamical stability on long timescales ($5\times10^9$ 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.

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