Neptune Resonance Research Articles

Uranus’s Influence on Neptune’s Exterior Mean-motion Resonances

Neptune’s external mean-motion resonances play an important role in sculpting the observed population of trans-Neptunian objects (TNOs). The population of scattering TNOs is known to “stick” to Neptune's resonances while evolving in semimajor axis (a), though simulations show that resonance sticking is less prevalent at a ≳ 200–250 au. Here we present an extensive numerical exploration of the strengths of Neptune's resonances for scattering TNOs with perihelion distances q = 33 au. We show that the drop-off in resonance sticking for the large a scattering TNOs is not a generic feature of scattering dynamics but can instead be attributed to the specific configuration of Neptune and Uranus in our solar system. In simulations with just Uranus removed from the giant planet system, Neptune's resonances are strong in the scattering population out to at least ∼300 au. Uranus and Neptune are near a 2:1 period ratio, and the variations in Neptune's orbit resulting from this near-resonance are responsible for destabilizing Neptune's resonances for high-e TNO orbits beyond the ∼20:1 resonance at a ≈ 220 au. Direct interactions between Uranus and the scattering population are responsible for slightly weakening Neptune's closer-in resonances. In simulations where Neptune and Uranus are placed in their mutual 2:1 resonance, we see almost no stable libration of scattering particles in Neptune's external resonances. Our results have important implications for how the strengths of Neptune's distant resonances varied during the epoch of planet migration when the Neptune–Uranus period ratio was evolving. These strength variations likely affected the distant scattering, resonant, and detached TNO populations.

Col-OSSOS: The Distribution of Surface Classes in Neptune's Resonances

The distribution of surface classes of resonant trans-Neptunian objects (TNOs) provides constraints on the protoplanetesimal disk and giant planet migration. To better understand the surfaces of TNOs, the Colours of the Outer Solar System Origins Survey acquired multiband photometry of 102 TNOs and found that the surfaces of TNOs can be well described by two surface classifications: BrightIR and FaintIR. These classifications both include optically red members and are differentiated predominantly based on whether their near-infrared spectral slope is similar to their optical spectral slope. The vast majority of cold classical TNOs, with dynamically quiescent orbits, have the FaintIR surface classification, and we infer that TNOs in other dynamical classifications with FaintIR surfaces share a common origin with the cold classical TNOs. Comparison between the resonant populations and the possible parent populations of cold classical and dynamically excited TNOs reveal that the 3:2 has minimal contributions from the FaintIR class, which could be explained by the ν 8 secular resonance clearing the region near the 3:2 before any sweeping capture occurred. Conversely, the fraction of FaintIR objects in the 4:3 resonance, 2:1 resonance, and the resonances within the cold classical belt suggest that the FaintIR surface formed in the protoplanetary disk between ≳34.6 and ≲47 au, though the outer bound depends on the degree of resonance sweeping during migration. The presence and absence of the FaintIR surfaces in Neptune’s resonances provides critical constraints for the history of Neptune’s migration, the evolution of the ν 8, and the surface class distribution in the initial planetesimal disk.

Loss of a satellite could explain Saturn's obliquity and young rings.

The origin of Saturn's ~26.7° obliquity and ~100-million-year-old rings is unknown. The observed rapid outward migration of Saturn's largest satellite, Titan, could have raised Saturn's obliquity through a spin-orbit precession resonance with Neptune. We use Cassini data to refine estimates of Saturn's moment of inertia, finding that it is just outside the range required for the resonance. We propose that Saturn previously had an additional satellite, which we name Chrysalis, that caused Saturn's obliquity to increase through the Neptune resonance. Destabilization of Chrysalis's orbit ~100 million years ago can then explain the proximity of the system to the resonance and the formation of the rings through a grazing encounter with Saturn.

Lightcurves and Rotations of Trans-Neptunian Objects in the 2:1 Mean Motion Resonance with Neptune

We report the rotational lightcurves of 21 trans-Neptunian objects (TNOs) in Neptune’s 2:1 mean motion resonance obtained with the 6.5 m Magellan-Baade telescope and the 4.3 m Lowell Discovery Telescope. The main survey’s goal is to find objects displaying a large lightcurve amplitude that is indicative of contact binaries or highly elongated objects. In our sample, two 2:1 resonant TNOs showed a significant short-term lightcurve amplitude: 2002 VD130 and (531074) 2012 DX98. The full lightcurve of 2012 DX98 infers a periodicity of 20.80 ± 0.06 hr and amplitude of 0.56 ± 0.03 mag, whereas 2002 VD130 rotates in 9.85 ± 0.07 hr with a 0.31 ± 0.04 mag lightcurve amplitude. Based on lightcurve morphology, we classify (531074) 2012 DX98 as a likely contact binary but 2002 VD130 as a likely single elongated object. Based on our sample and the lightcurves reported in the literature, we estimate the lower percentage of nearly equal-sized contact binaries at only 7%–14% in the 2:1 resonance, which is comparable to the low fraction reported for the dynamically cold classical TNOs. This low contact binary fraction in the 2:1 Neptune resonance is consistent with the lower estimate of the recent numerical modeling. We report the Sloan g′, r′, and i′ surface colors of 2002 VD130, which is an ultra-red TNO whereas 2012 DX98 is a very red object based on published surface colors.

Resonance libration and width at arbitrary inclination

ABSTRACTWe apply the analytical disturbing function for arbitrary inclination derived in our previous work to characterize resonant width and libration of mean motion resonances at arbitrary inclination obtained from direct numerical simulations of the three-body problem. We examine the 2:1 and 3:1 inner Jupiter and 1:2 and 1:3 outer Neptune resonances and their possible asymmetric librations using a new analytical pendulum model of resonance that includes the simultaneous libration of multiple arguments and their second harmonics. The numerically derived resonance separatrices are obtained using the mean exponential growth factor of nearby orbits (megno chaos indicator). We find that the analytical and numerical estimates are in agreement and that resonance width is determined by the first few fundamental resonance modes that librate simultaneously on the resonant time-scale. Our results demonstrate that the new pendulum model may be used to ascertain resonance width analytically, and more generally, that the disturbing function for arbitrary inclination is a powerful analytical tool that describes resonance dynamics of low as well as high inclination asteroids in the Solar system.

The Structure of the Distant Kuiper Belt in a Nice Model Scenario

Abstract This work explores the orbital distribution of minor bodies in the outer Solar System emplaced as a result of a Nice model migration from the simulations of Brasser and Morbidelli. This planetary migration scatters a planetesimal disk from between 29 and 34 au and emplaces a population of objects into the Kuiper Belt region. From the 2:1 Neptune resonance and outward, the test particles analyzed populate the outer resonances with orbital distributions consistent with trans-Neptunian object (TNO) detections in semimajor axis, inclination, and eccentricity, while capture into the closest resonances is too efficient. The relative populations of the simulated scattering objects and resonant objects in the 3:1 and 4:1 resonances are also consistent with observed populations based on debiased TNO surveys, but the 5:1 resonance is severely underpopulated compared to population estimates from survey results. Scattering emplacement results in the expected orbital distribution for the majority of the TNO populations; however, the origin of the large observed population in the 5:1 resonance remains unexplained.

BEYOND THE KUIPER BELT EDGE: NEW HIGH PERIHELION TRANS-NEPTUNIAN OBJECTS WITH MODERATE SEMIMAJOR AXES AND ECCENTRICITIES

ABSTRACT We are conducting a survey for distant solar system objects beyond the Kuiper Belt edge (∼50 au) with new wide-field cameras on the Subaru and CTIO telescopes. We are interested in the orbits of objects that are decoupled from the giant planet region to understand the structure of the outer solar system, including whether a massive planet exists beyond a few hundred astronomical units as first reported in 2014 by Trujillo & Sheppard. In addition to discovering extreme trans-Neptunian objects detailed elsewhere, we found several objects with high perihelia (q > 40 au) that differ from the extreme and inner Oort cloud objects due to their moderate semimajor axes (50 < a < 100 au) and eccentricities (e ≲ 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have the third and fourth highest perihelia known after Sedna and 2012 VP113, yet their orbits are not nearly as eccentric or distant. We found several of these high-perihelion but moderate orbit objects and observe that they are mostly near Neptune mean motion resonances (MMRs) and have significant inclinations (i > 20°). These moderate objects likely obtained their unusual orbits through combined interactions with Neptune’s MMRs and the Kozai resonance, similar to the origin scenarios for 2004 XR190. We also find the distant 2008 ST291 has likely been modified by the MMR+KR mechanism through the 6:1 Neptune resonance. We discuss these moderately eccentric distant objects along with some other interesting low inclination outer classical belt objects like 2012 FH84 discovered in our ongoing survey.

A SOUTHERN SKY AND GALACTIC PLANE SURVEY FOR BRIGHT KUIPER BELT OBJECTS

About 2500 square degrees of sky south of declination -25 degrees and/or near the galactic plane were surveyed for bright outer solar system objects. This survey is one of the first large scale southern sky and galactic plane surveys to detect dwarf planets and other bright Kuiper Belt objects in the trans-Neptunian region. The survey was able to obtain a limiting R-band magnitude of 21.6. In all, 18 outer solar system objects were detected, including Pluto which was detected near the galactic center using optimal image subtraction techniques to remove the high stellar density background. Fourteen of the detections were previously unknown trans-Neptunian objects, demonstrating that the southern sky had not been well-searched to date for bright outer solar system objects. Assuming moderate albedos, several of the new discoveries from this survey could be in hydrostatic equilibrium and thus be considered dwarf planets. Combining this survey with previous surveys from the northern hemisphere suggests that the Kuiper Belt is nearly complete to around 21st magnitude in the R-band. All the main dynamical classes in the Kuiper Belt are occupied by at least one dwarf planet sized object. The 3:2 Neptune resonance, which is the innermost well-populated Neptune resonance, has several large objects while the main outer Neptune resonances such as the 5:3, 7:4, 2:1, and 5:2 do not appear have any large objects. This indicates that the outer resonances are either significantly depleted in objects relative to the 3:2 resonance or have a significantly different assortment of objects than the 3:2 resonance. For the largest objects (H<4.5 mag), the scattered disk population appears to have a few times more objects than the main Kuiper Belt population, while the Sedna population could be several times more than that of the main Kuiper Belt.

Impactor flux and cratering on the Pluto-Charon system

We study the impactor flux and cratering on Pluto and Charon due to the collisional evolution of Plutinos. Plutinos are those trans-Neptunian objects located at 39.5 AU, in the 3:2 mean motion resonance with Neptune. To do this, we develop a statistical code that includes catastrophic collisions and cratering events, and takes into account the stability and instability zones of the 3:2 mean motion resonance with Neptune. We proposes different initial populations that account for the uncertainty in the size distribution of Plutinos at small sizes. Depending on the initial population, our results indicate the following. The number of D > 1 km Plutinos streaking Pluto over 3.5 Gyr is between 1271 and 5552. For Charon, the number of D > 1 km Plutino impactors is between 354 and 1545. The number of D > 1 km craters on Pluto produced by Plutinos during the last 3.5 Gyr is between 43076 and 113879. For Charon, the number of D > 1 km craters is between 20351 and 50688.The largest Plutino impactor onto Pluto has a diameter between 17 and 23 km, which produces a craterwith a diameter of 31 - 39 km. The largest Plutino impactor onto Charon has a diameter between 10 and 15 km, which produces a crater with a diameter of 24 - 33 km. We test if 2 Pluto-sized objects are assumed in the 3:2 Neptune resonance, then the total number of Plutino impactors both onto Pluto as Charon with diameters D > 1 km is a factor of 1.6 - 1.8 larger if considering 1 Pluto-sized object. Given the dynamical structure of the trans-Neptunian region, it is necessary to study in detail the contribution of all the potential sources of impactors on the Pluto-Charon system, to obtain the main contributor and the whole production of craters. Then, we will be able to contrast those studies with observations which will help us to understand the geological processes and history of the surface of those worlds.

Impactor Flux on the Pluto-Charon System

AbstractIn this work, we study the impactor flux on Pluto and Charon due to the collisional evolution of Plutinos.To do this, we develop a statistical code that includes catastrophic collisions and cratering events, and takes into account the stability and instability zones of the 3:2 mean motion resonance with Neptune. Our results suggest that if 1 Pluto-sized object is in this resonance, the flux of D = 2 km Plutinos on Pluto is ~4–24 percent of the flux of D = 2 km Kuiper Belt projectiles on Pluto. However, with 5 Pluto-sized objects in the resonance, the contribution of the Plutino population to the impactor flux on Pluto may be comparable to that of the Kuiper Belt. As for Charon, if 1 Pluto-sized object is in the 3:2 resonance, the flux of D = 2 km Plutinos is ~10–63 percent of the flux of D = 2 km impactors coming from the Kuiper Belt. However, with 5 Pluto-sized objects, the Plutino population may be a primary source of the impactor flux on Charon. We conclude that it is necessary to specify the Plutino size distribution and the number of Pluto-sized objects in the 3:2 Neptune resonance in order to determine if the Plutino population is a primary source of impactors on the Pluto-Charon system.

Collisional and dynamical evolution of Plutinos

Aims. In this paper, we analyze the collisional and dynamical evolution of the population of Plutinos. Methods. To do this, we test different collisional parameters and include a dynamical treatment that takes into account the stability and instability zones of the 3:2 mean motion resonance with Neptune. This procedure allows us to estimate the size distribution of Plutinos, to study their mean collisional lifetimes, to analyze the formation of families, to obtain ejection rates of fragments from the resonance and to discuss their possible contribution to the ecliptic comet population. Our simulations are developed assuming the existence of one Pluto-sized object in the 3:2 Neptune resonance. Results. The Plutino population larger than a few kilometers in diameter is not significantly altered by catastrophic collisions over the age of the Solar System. Thus, we infer that the break suggested by previous works at a diameter D near 40−80 km in the Plutino cumulative size distribution should be primordial and not a result of the collisional evolution. The existence of such a break is still a matter of debate. On the other hand, our analysis indicates that one large family was formed in the 3:2 Neptune resonance over the Solar System history. Concerning Plutino removal, we find that one object with a diameter D > 1 km is ejected from the 3:2 resonance with Neptune every ∼300−1200 yr. Then, we study the sensitivity of our results to the number of Pluto-sized objects in the 3:2 Neptune resonance. Our simulations suggest that the larger the number of Pluto-sized bodies, the higher the ejection rate of fragments from that resonant region and the number of families formed over 4.5 Gyr. Thus, if a maximum of 5 Pluto-sized objects are assumed to be in the 3:2 Neptune resonance, one body with a diameter D > 1 km is ejected every tens of years while ∼30 large families are formed over the Solar System history. From these estimates, we conclude that it is necessary to specify the number of Pluto-sized objects present in the 3:2 Neptune resonance to determine if this region can be considered an important source of ecliptic comets. Finally, we find that the current orbital distribution of the Plutinos does not offer a strong constraint on the dynamical origin of this population.

Neptune's Migration into a Stirred-Up Kuiper Belt: A Detailed Comparison of Simulations to Observations

We use N-body simulations to examine the consequences of Neptune's outward migration into the Kuiper Belt, with the simulated end states being compared rigorously and quantitatively to the observations. These simulations confirm the 2003 findings of Chiang and coworkers, who showed that Neptune's migration into a previously stirred-up Kuiper Belt can account for the Kuiper Belt objects (KBOs) known to librate at Neptune's 5 : 2 resonance. We also find that capture is possible at many other weak, high-order mean-motion resonances, such as 11 : 6, 13 : 7, 13 : 6, 9 : 4, 7 : 3, 12 : 5, 8 : 3, 3 : 1, 7 : 2, and 4 : 1. The more distant of these resonances, such as the 9 : 4, 7 : 3, 5 : 2, and 3 : 1, can also capture particles in stable, eccentric orbits beyond 50 AU, in the region of phase space conventionally known as the "Scattered Disk." Indeed, 90% of the simulated particles that persist over the age of the solar system in the Scattered-Disk zone never had a close encounter with Neptune but instead were promoted into these eccentric orbits by Neptune's resonances during the migration epoch. This indicates that the observed Scattered Disk might not be so scattered. This model also produced only a handful of Centaurs, all of which originated at Neptune's mean-motion resonances in the Kuiper Belt. However, a noteworthy deficiency of the migration model considered here is that it does not account for the observed abundance of Main Belt KBOs having inclinations higher than 15°. In order to rigorously compare the model end state with the observed Kuiper Belt in a manner that accounts for telescopic selection effects, Monte Carlo methods are used to assign sizes and magnitudes to the simulated particles that survive over the age of the solar system. If the model considered here is indeed representative of the outer solar system's early history, then the following conclusions are obtained: (1) The observed 3 : 2 and 2 : 1 resonant populations are both depleted by a factor of ∼20 relative to model expectations; this depletion is likely due to unmodeled effects, possibly perturbations by other large planetesimals. (2) The size distribution of those KBOs inhabiting the 3 : 2 resonance is significantly shallower than the Main Belt's size distribution. (3) The total number of KBOs having radii R > 50 km and orbiting interior to Neptune's 2 : 1 resonance is N ∼ 1.7 × 105; these bodies have a total mass of M ∼ 0.08(ρ/1 g cm-3)(p/0.04)-3/2 M⊕, assuming they have a material density ρ and an albedo p. We also report estimates of the abundances and masses of the Belt's various subpopulations (e.g., the resonant KBOs, the Main Belt, and the so-called Scattered Disk) and provide upper limits on the abundance of Centaurs and Neptune's Trojans, as well as upper limits on the sizes and abundances of hypothetical KBOs that might inhabit the a > 50 AU zone.

The characteristics of orbital distribution of Kuiper belt objects

A statistical analysis of the orbital semi-major axes of Kuiper belt objects (KBOs) shows that the mass weighted mean of the heliocentric distances of 528 trans-Neptunian objects (TNOs) is 43.3 AU, and that except the Plutinos (i.e., “Little Plutos”) in the 3:2 Neptune resonance region their radial distribution is approximately a normal distribution with maximum at about 43 AU. This distribution cannot be interpreted with resonant capture mechanism. But it is similar to the radial distribution of particles in a protoplanetary nebula computed with the author's simulative quantum theory. Comparing with the normal distribution, we find that there is an absence of objects in the range between the 3:2 Neptune resonance and 43 AU. The distribution of eccentricities of the TNOs suggests that the absent objects might have been removed into the resonance region.

Mean Motion Resonances in the Transneptunian Region: Part II: The 1 : 2, 3 : 4, and Weaker Resonances

The stability of orbits in the transneptunian region is numerically computed. It is found that, in analogy to the asteroid belt, there exist many chaotic layers associated with thin mean-motion resonances. These are either moderate- and high-order resonances with Neptune or three-body resonances with Neptune and Uranus. The orbital eccentricity chaotically increases at the thin resonances, allowing some Kuiper Belt objects to be slowly transferred to Neptune-crossing orbits. The stability of two large mean-motion resonances with Neptune, the 1 : 2 and 3 : 4, is systematically explored. It is shown that orbits in both resonances, with small resonant amplitudes are stable over the age of the Solar System. The possible role of collisions and dynamical scattering in clearing the resonances is discussed. It is inferred from orbital angles of 1997 SZ10 and 1996 TR66 that these bodies are most probably on stable tadpole orbits in the 1 : 2 Neptune resonance.

Close Approaches of Trans-Neptunian Objects to Pluto Have Left Observable Signatures on Their Orbital Distribution

It is shown that in addition to four outer planets (Jupiter to Neptune) Pluto should be also taken into account in studies of the orbital dynamics in the trans-Neptunian region. Pluto's effect is particularly large on the orbits in the 2:3 Neptune mean motion resonance. The trajectories found stable over the age of the solar system when only the gravitational effect of four outer planets is considered are often destabilized there in the effect of close Pluto approaches. We estimate that many dynamically primordial bodies moving initially with low to moderate amplitudes in the 2:3 Neptune resonance (semimajor axis 39.45 AU) have been removed from their respective, otherwise stable, locations, when their resonant amplitudes increased in the course of close encounters with Pluto. At large libration amplitude, the orbits became exposed to chaotic changes, and objects were ejected from the 2:3 resonance to Neptune-crossing trajectories. The process of the resonant amplitude excitation was especially efficient for orbits with moderate and large inclinations (i > 8°), where more than 50% of the population has been removed in 4 × 109 yr. We estimate that the remaining part of the primordial resonant population at these inclinations should have had its resonant amplitude excited to about 80°. The effect of Pluto on low-inclination orbits is smaller. We have examined the distribution of 33 objects observed on the 2:3 resonant orbits (Plutinos) and found that there could actually exist indications of the above mechanism. The resonant amplitudes of Plutinos are unusually high for 0.15 < e < 0.3 when compared with randomly generated distribution, and, also, there is only one object (1997 QJ4) on an orbit similar to that of Pluto. In fact, a certain gap may be noticed in the distribution of Plutinos at Pluto's inclination and eccentricity, which, if confirmed by future observations, may be the consequence of Pluto's sweeping effect.

The Dynamics of Plutinos

Plutinos are Kuiper-belt objects that share the 3:2 Neptune resonance with Pluto. The long-term stability of Plutino orbits depends on their eccentricity. Plutinos with eccentricities close to Pluto (fractional eccentricity difference |e-e_p|/e_p =0.3 can also be stable; the longitude difference circulates and close encounters are possible, but the effects of Pluto are weak because the encounter velocity is high. Orbits with intermediate eccentricity differences are likely to be unstable over the age of the solar system, in the sense that encounters with Pluto drive them out of the 3:2 Neptune resonance and thus into close encounters with Neptune. This mechanism may be a source of Jupiter-family comets.

The Phase Space Structure Near Neptune Resonances in the Kuiper Belt

The Solar system beyond Neptune is believed to house a population of small primordial bodies left over from the planet formation process. The region up to heliocentric distance -50 AU (a.k.a. the Kuiper Belt) may be the source of the observed short-period comets. In this region, the phase space structure near orbital resonances with Neptune is of special interest for the long-term stability of orbits. There is reason to believe that a significant fraction (perhaps most) of the Kuiper Belt objects reside preferentially in these resonance locations. This paper describes the dynamics of small objects near the major orbital resonances with Neptune. Estimates of the widths of stable resonance zones as well as the properties of resonant orbits are obtained from the circular, planar restricted three-body model. Although this model does not contain the full complexity of the long-term orbital dynamics of Kuiper Belt objects subject to the full N-body perturbations of all the planets, it does provide a baseline for the phase space structure and properties of resonant orbits in the trans-Neptunian Solar system.