arXiv subjects

Othon C. Winter

Publications and source records attributed to Othon C. Winter.

13 recordsLinked to original sources

arXiv2026

Dynamical implications of the recently detected feature around Quaoar and constraints on the presence of additional satellites

A recently reported opaque feature in the Quaoar system, detected during the 25 June 2025 stellar occultation, has been interpreted as either a 15 km-radius satellite or a dense, sharp-edged arc orbiting at about 5600-5900 km. Here, we investigate both scenarios through numerical integrations that include Quaoar, its triaxial shape, and Weywot. If the feature is a satellite, stability maps show that it acquires a forced eccentricity of about 0.002 and has only a minor dynamical effect on the Q1R and Q2R rings. Its main effect is to clear a narrow region around its orbit, associated with the overlap of mean-motion resonances, preventing the long-term survival of kilometre-scale moons within approximately one Quaoar radius of the satellite. If instead the feature is an arc, we test confinement around the triangular equilibrium point of an unseen coorbital satellite. While azimuthal confinement is readily obtained for satellites with satellite-to-primary mass ratios up to 0.001, Weywot's secular perturbation induces large radial excursions in the arc particles, preventing reproduction of the observed radial extent. The required radial confinement is achieved only for confiners comparable to or more massive than Weywot, which would likely be detectable by direct imaging. We therefore disfavour triangular-point confinement as an explanation for a long-lived dense arc and argue that the feature is more dynamically consistent with a satellite. We identify broad stable zones where additional undetected moons could reside, including near the rings as possible shepherd moons. Furthermore, Quaoar's ellipticity alone is sufficient to induce non-resonant orbital excitation capable of preventing ring coagulation, an effect that may be enhanced by small moons near the rings.

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arXiv2025

Forming Mercury by a grazing giant collision involving similar mass bodies

The origin of Mercury still remains poorly understood compared to the other rocky planets of the Solar System. One of the most relevant constraints that any formation model has to fulfill refers to its internal structure, with a predominant iron core covered by a thin silicate layer. This led to the idea that it could be the product of a mantle stripping caused by a giant impact. Previous studies in this line focused on binary collisions involving bodies of very different masses. However, such collisions are actually rare in N-body simulations of terrestrial planet formation, whereas collisions involving similar mass bodies appear to be more frequent. Here, we perform smooth particle hydrodynamics simulations to investigate the conditions under which collisions of similar mass bodies are able to form a Mercury-like planet. Our results show that such collisions can fulfill the necessary constraints in terms of mass (0.055 $M_\oplus$) and composition (30/70 silicate-to-iron mass ratio) within less than 5%, as long as the impact angles and velocities are properly adjusted according to well established scaling laws.

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arXiv2024

Accretion of Uranus and Neptune: confronting different giant impact scenarios

The origins of Uranus and Neptune are not fully understood. Their inclined rotation axes -- obliquities -- suggest that they experienced giant impacts during their formation histories. Simulations modeling their accretion from giant impacts among ~5 Earth masses planetary embryos -- with roughly unity impactors' mass ratios -- have been able to broadly match their current masses, final mass ratio, and obliquity. However, due to angular momentum conservation, planets produced in these impacts tend to rotate too fast, compared to Uranus and Neptune. One potential solution for this problem consists of invoking instead collisions of objects with large mass ratios (e.g. a proto-Uranus with 13 Mearth and an embryo of 1 Mearth). Smooth-particle hydrodynamics simulations show that in this scenario final planets tend to have rotation periods more consistent with those of Uranus and Neptune. Here we performed a large suite of N-body numerical simulations modelling the formation of Uranus and Neptune to compare these different dynamical views. Our simulations start with a population of protoplanets and account for the effects of type-I migration, inclination and eccentricity tidal damping. Our results show that although scenarios allowing for large impactors' mass ratio favour slower rotating planets, the probability of occurring collisions in these specific simulations is significantly low. This is because gas tidal damping is relatively less efficient for low-mass embryos (<~1 Merath) and, consequently, such objects are mostly scattered by more massive objects (~13 Mearth) instead of colliding with them. Altogether, our results show that the probability of broadly matching the masses, mass ratio, and rotation periods of Uranus and Neptune in these two competing formation scenarios is broadly similar, within a factor of ~2, with overall probabilities of the order of ~0.1-1%.

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arXiv2023

kinetic impact and gravitational perturbations for asteroid deflection

Asteroids have called the attention of researchers around the world. Its chemical and physical composition can give us important information about the formation of our Solar System. In addition, the hypothesis of mining some of these objects is considered, since they contain precious metals. However, some asteroids have their orbits close to the orbit of the Earth. These nearby objects can pose a danger to our life in the planet, since some of them are large enough to cause catastrophic damage to the Earth. We will pay attention to the theme of deflecting a potentially dangerous asteroid. There are currently two main forms of this deviation: i) the impact of an object at high velocity with the asteroid, which can be a space vehicle or a smaller asteroid; ii) the use of a gravitational "tractor", which consist in placing an object (another asteroid or part of an asteroid), close to the body that is approaching the Earth, such that this gravitational interference can deflect its trajectory. In this work, we will evaluate the influence of gravitational perturbations in the most commonly mentioned asteroid deflection model in the literature, the kinetic impact deflection technique. With the impact, it is intended to change the kinetic energy of the asteroid, changing its orbit enough so that it does not present risks of impacts with the Earth.

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arXiv2023

Assessing the spin-orbit obliquity of low-mass planets in the breaking the chain formation model: A story of misalignment

The spin-orbit obliquity of a planetary system constraints its formation history. A large obliquity may either indicate a primordial misalignment between the star and its gaseous disk or reflect the effect of different mechanisms tilting planetary systems after formation. Observations and statistical analysis suggest that system of planets with sizes between 1 and 4 R$_{\oplus}$ have a wide range of obliquities ($\sim0-30^{\circ}$), and that single- and multi-planet transiting have statistically indistinguishable obliquity distributions. Here, we revisit the ``breaking the chains'' formation model with focus in understanding the origin of spin-orbit obliquities. This model suggests that super-Earths and mini-Neptunes migrate close to their host stars via planet-disk gravitational interactions, forming chain of planets locked in mean-motion resonances. After gas-disk dispersal, about 90-99\% of these planetary systems experience dynamical instabilities, which spread the systems out. Using synthetic transit observations, we show that if planets are born in disks where the disk angular momentum is virtually aligned with the star's rotation spin, their final obliquity distributions peak at about $\sim$5 degrees or less, and the obliquity distributions of single and multi-planet transiting systems are statistically distinct. By treating the star-disk alignment as a free-parameter, we show that the obliquity distributions of single and multi-planet transiting systems only become statistically indistinguishable if planets are assumed to form in primordially misaligned natal disks with a ``tilt'' distribution peaking at $\gtrsim$10-20 deg. We discuss the origin of these misalignments in the context of star formation and potential implications of this scenario for formation models.

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arXiv2021

The "Breaking The Chains" migration model for super-Earths formation: the effect of collisional fragmentation

Planets between 1-4 Earth radii with orbital periods <100 days are strikingly common. The migration model proposes that super-Earths migrate inwards and pile up at the disk inner edge in chains of mean motion resonances. After gas disk dispersal, simulations show that super-Earth's gravitational interactions can naturally break their resonant configuration leading to a late phase of giant impacts. The instability phase is key to matching the orbital spacing of observed systems. Yet, most previous simulations have modelled collisions as perfect accretion events, ignoring fragmentation. In this work, we investigate the impact of imperfect accretion on the breaking the chains scenario. We performed N-body simulations starting from distributions of planetary embryos and modelling the effects of pebble accretion and migration in the gas disk. Our simulations also follow the long-term dynamical evolution of super-Earths after the gas disk dissipation. We compared the results of simulations where collisions are treated as perfect merging events with those where imperfect accretion and fragmentation are allowed. We concluded that the perfect accretion is a suitable approximation in this regime, from a dynamical point of view. Although fragmentation events are common, only ~10% of the system mass is fragmented during a typical "late instability phase", with fragments being mostly reacreted by surviving planets. This limited total mass in fragments proved to be insufficient to alter qualitatively the final system dynamical configuration -- e.g. promote strong dynamical friction or residual migration -- compared to simulations where fragmentation is neglected.

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arXiv2019

The PDS 110 observing campaign - photometric and spectroscopic observations reveal eclipses are aperiodic

PDS 110 is a young disk-hosting star in the Orion OB1A association. Two dimming events of similar depth and duration were seen in 2008 (WASP) and 2011 (KELT), consistent with an object in a closed periodic orbit. In this paper we present data from a ground-based observing campaign designed to measure the star both photometrically and spectroscopically during the time of predicted eclipse in September 2017. Despite high-quality photometry, the predicted eclipse did not occur, although coherent structure is present suggesting variable amounts of stellar flux or dust obscuration. We also searched for RV oscillations caused by any hypothetical companion and can rule out close binaries to 0.1 $M_\odot$. A search of Sonneberg plate archive data also enabled us to extend the photometric baseline of this star back more than 50 years, and similarly does not re-detect any deep eclipses. Taken together, they suggest that the eclipses seen in WASP and KELT photometry were due to aperiodic events. It would seem that PDS 110 undergoes stochastic dimmings that are shallower and shorter-duration than those of UX Ori variables, but may have a similar mechanism.

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arXiv2018

Particles co-orbital to Janus and Epimetheus: a firefly planetary ring

The Cassini spacecraft found a new and unique ring that shares the trajectory of Janus and Epimetheus, co-orbital satellites of Saturn. Performing image analysis, we found this to be a continuous ring. Its width is between 30% and 50% larger than previously announced. We also verified that the ring behaves like a firefly. It can only be seen from time to time, when Cassini, the ring and the Sun are arranged in a particular geometric configuration, in very high phase angles. Otherwise, it remains "in the dark", not visible to Cassini's cameras. Through numerical simulations, we found a very short lifetime for the ring particles, less than a couple of decades. Consequently, the ring needs to be constantly replenished. Using a model of particles production due to micrometeorites impacts on the surfaces of Janus and Epimetheus, we reproduce the ring, explaining its existence and the "firefly" behavior.

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arXiv2016

The Asteroid Belt as a Relic From a Chaotic Early Solar System

The orbital structure of the asteroid belt holds a record of the Solar System's dynamical history. The current belt only contains ${\rm \sim 10^{-3}}$ Earth masses yet the asteroids' orbits are dynamically excited, with a large spread in eccentricity and inclination. In the context of models of terrestrial planet formation, the belt may have been excited by Jupiter's orbital migration. The terrestrial planets can also be reproduced without invoking a migrating Jupiter; however, as it requires a severe mass deficit beyond Earth's orbit, this model systematically under-excites the asteroid belt. Here we show that the orbits of the asteroids may have been excited to their current state if Jupiter and Saturn's early orbits were chaotic. Stochastic variations in the gas giants' orbits cause resonances to continually jump across the main belt and excite the asteroids' orbits on a timescale of tens of millions of years. While hydrodynamical simulations show that the gas giants were likely in mean motion resonance at the end of the gaseous disk phase, small perturbations could have driven them into a chaotic but stable state. The gas giants' current orbits were achieved later, during an instability in the outer Solar System. Although it is well known that the present-day Solar System exhibits chaotic behavior, our results suggest that the early Solar System may also have been chaotic.

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arXiv2015

Formation of Terrestrial Planets in Disks with Different Surface Density Profiles

We present the results of an extensive study of the final stage of terrestrial planet formation in disks with different surface density profiles and for different orbits of Jupiter and Saturn. We carried out simulations for disk densities proportional to r^-0.5, r^-1, and r^-1.5, and also for partially depleted disks as in the recent model of Mars formation by Izidoro et al (2014). The purpose of our study is to determine how the final assembly of planets and their physical properties are affected by the total mass of the disk and its radial profile. Because of the important roles of secular resonances in orbits and properties of the final planets, we studied the effects of these resonances as well. We have divided this study into two parts. In Part 1, we are interested in examining the effects of secular resonances on the formation of Mars and orbital stability of terrestrial planets. In Part 2, our goal is to determine trends that may exist between the disk surface density profile and the final properties of terrestrial planets. In the context of the depleted disk model, results show that the nu_5 resonance does not have a significant effect on the final orbits of terrestrial planets. However, nu_6 and nu_16 resonances play important roles in clearing their affected areas ensuring that no additional mass will be scattered into the accretion zone of Mars so that it can maintain its mass and orbital stability. In Part 2, our results indicate that despite some small correlations, in general, no trend seems to exist between the disk surface density profile and the mean number of the final planets, their masses, time of formation, and distances to the central star. We present the results of our simulations and discuss their implications for the formation of Mars and other terrestrial planets, as well as the physical properties of these objects such as their masses and water contents.

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arXiv2015

On the Erigone family and the $z_2$ secular resonance

The Erigone family is a C-type group in the inner main belt. Its age has been estimated by several researchers to be less then 300 My, so it is a relatively young cluster. Yarko-YORP Monte Carlo methods to study the chronology of the Erigone family confirm results obtained by other groups. The Erigone family, however, is also characterized by its interaction with the $z_2$ secular resonance. While less than 15% of its members are currently in librating states of this resonance, the number of objects, members of the dynamical group, in resonant states is high enough to allow to use the study of dynamics inside the $z_2$ resonance to set constraints on the family age. Like the $ν_{6}$ and $z_1$ secular resonances, the $z_2$ resonance is characterized by one stable equilibrium point at $σ= 180^{\circ}$ in the $z_2$ resonance plane $(σ, \frac{dσ}{dt})$, where $σ$ is the resonant angle of the $z_2$ resonance. Diffusion in this plane occurs on timescales of $\simeq 12$ My, which sets a lower limit on the Erigone family age. Finally, the minimum time needed to reach a steady-state population of $z_2$ librators is about 90 My, which allows to impose another, independent constraint on the group age.

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arXiv2015

Formation of the Janus-Epimetheus system through collisions

Context: Co-orbital systems are bodies that share the same mean orbit. They can be divided into different families according to the relative mass of the co-orbital partners and the particularities of their movement. Janus and Epimetheus are unique in that they are the only known co-orbital pair of comparable masses and thus the only known system in mutual horseshoe orbit. Aims: We aim to establish whether the Janus-Epimetheus system might have formed by disruption of an object in the current orbit of Epimetheus. Methods: We assumed that four large main fragments were formed and neglected smaller fragments. We used numerical integration of the full N-body problem to study the evolution of different fragment arrangements. Collisions were assumed to result in perfectly inelastic merging of bodies. We statistically analysed the outcome of these simulations to infer whether co-orbital systems might have formed from the chosen initial conditions. Results: Depending on the range of initial conditions, up to 9% of the simulations evolve into co-orbital systems. Initial velocities around the escape velocity of Janus yield the highest formation probability. Analysis of the evolution shows that all co-orbital systems are produced via secondary collisions. The velocity of these collisions needs to be low enough that the fragments can merge and not be destroyed. Generally, collisions are found to be faster than an approximate cut-off velocity threshold. However, given a sufficiently low initial velocity, up to 15% of collisions is expected to result in merging. Hence, the results of this study show that the considered formation scenario is viable.

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arXiv2015

Terrestrial Planet Formation Constrained by Mars and the Structure of the Asteroid Belt

Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoplanetary disk between 1 and 3 AU. The Grand Tack model invokes a specific migration history of the giant planets to remove most of the mass initially beyond 1 AU and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas-drag, as has been proposed to explain the formation of close-in super Earths. Here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the Solar System. We performed a series of simulations of terrestrial planet formation and asteroid belt evolution starting from disks of planetesimals and planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Disks with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogs significantly more massive than the real planet. In contrast, a disk with a surface density gradient proportional to $r^{-5.5}$ reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disk profile can simultaneously explain the structure of the terrestrial planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.

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