The Rings of Chariklo under Close Encounters with the Giant Planets

Araujo, R. A. N.; Sfair, R.; Winter, O. C.

The Astrophysical Journal

[ Abstract ] [ PDF ]

The Centaur population is composed of minor bodies wandering between the giant planets that frequently perform close gravitational encounters with these planets, leading to a chaotic orbital evolution. Recently, the discovery of two well-defined narrow rings was announced around the Centaur 10199 Chariklo. The rings are assumed to be in the equatorial plane of Chariklo and to have circular orbits. The existence of a well-defined system of rings around a body in such a perturbed orbital region poses an interesting new problem. Are the rings of Chariklo stable when perturbed by close gravitational encounters with the giant planets? Our approach to address this question consisted of forward and backward numerical simulations of 729 clones of Chariklo, with similar initial orbits, for a period of 100 Myr. We found, on average, that each clone experiences during its lifetime more than 150 close encounters with the giant planets within one Hill radius of the planet in question. We identified some extreme close encounters that were able to significantly disrupt or disturb the rings of Chariklo. About 3% of the clones lose their rings and about 4% of the clones have their rings significantly disturbed. Therefore, our results show that in most cases (more than 90%), the close encounters with the giant planets do not affect the stability of the rings in Chariklo-like systems. Thus, if there is an efficient mechanism that creates the rings, then these structures may be common among these kinds of Centaurs.

The sailboat island and the New Horizons trajectory

Giuliatti Winter, S. M.; Winter, O, C.; Vieira Neto, E.; Sfair, R.

Icarus

[ Abstract ] [ PDF ]

In previous works we have studied the location of stable regions in the Pluto-Charon system. Among the findings, we discovered an island of stability, named sailboat island. One of the main goals of the New Horizons mission, launched in 2006, is to have a flyby close to the Pluto-Charon system in order to explore it. In the present work we analyze the relevance of the sailboat island for the New Horizons mission. Firstly, we identify the location and extent of these stable trajectories in the physical space around Pluto. They go beyond the trajectory of Charon in a way that Charon never crosses such trajectories. We verify that the nominal trajectory of the New Horizons spacecraft passes near the region of the sailboat island trajectories, reaching the closest distance at about 1650 km. Analyzing an alternative trajectory for the spacecraft, known as Deep Inner SHBOT, we found that it is not as safe as the nominal trajectory, because it crosses a region of highly inclined trajectories located at the sailboat island. We also estimate the density of particles from the sailboat island in the physical space around Pluto in comparison with the density of particles from a well-known stable region of near circular trajectories close to Pluto. Finally, we identified the location of the densest regions, which corresponds to the highest probable location of particles of the sailboat island. Such locations can be considered as spots for search and new detections of bodies by the New Horizons cameras along the flyby close to the Pluto-Charon system.

doi: http://dx.doi.org/10.1016/j.icarus.2014.04.003

A ring system detected around the Centaur (10199) Chariklo

Braga-Ribas, F.; Sicardy, B.; Ortiz, J. L.; Snodgrass, C.; Roques, F.; Vieira-Martins, R.; Camargo, J. I. B.; Assafin, M.; Duffard, R.; Jehin, E.; Pollock, J.; Leiva, R.; Emilio, M.; Machado, D. I.; Colazo, C.; Lellouch, E.; Skottfelt, J.; Gillon, M.; Ligier, N.; Maquet, L. Benedetti-Rossi, G.; Gomes, A. Ramos; Kervella, P.; Monteiro, H.; Sfair, R.; et al.

Nature

[ Abstract ] [ PDF ]

Hitherto, rings have been found exclusively around the four giant planets in the Solar System. Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur--that is, one of a class of small objects orbiting primarily between Jupiter and Neptune--with an equivalent radius of 124 9 kilometres (ref. 2). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period. This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites.

A peculiar stable region around Pluto

Giuliatti Winter, S. M.; Winter, O. C.; Vieira Neto, E.; Sfair, R.

Monthly Notices of the Royal Astronomical Society

[ Abstract ] [ PDF ]

Giuliatti Winter et al. found several stable regions for a sample of test particles located between the orbits of Pluto and Charon. One peculiar stable region in the space of the initial orbital elements is located at a = (0.5d, 0.7d) and e = (0.2, 0.9), where a and e are the initial semimajor axis and eccentricity of the particles, respectively, and d is the Pluto-Charon distance. This peculiar region (hereafter called the sailboat region) is associated with a family of periodic orbits derived from the planar, circular, restricted three-body problem (Pluto-Charon-particle). In this work, we study the origin of this stable region by analysing the evolution of such family of periodic orbits. We show that they are not in resonances with Charon. The period of the periodic orbit varies along the family, decreasing with the increase of the Jacobi constant. We also explore the extent of the sailboat region by adopting different initial values of the orbital inclination (I) and argument of the pericentre (ω) of the particles. The sailboat region is present for I = [0°, 90°] and for two intervals of ω, ω = [-10°, 10°] and (160°, 200°). A crude estimative of the size of the hypothetical bodies located at the sailboat region can be derived by computing the tidal damping in their eccentricities. If we neglect the orbital evolution of Pluto and Charon, the time-scale for circularization of their orbits is longer than the age of the Solar system for bodies smaller than 500 m in radius.

doi: http://dx.doi.org/10.1093/mnras/stu147

Analysis of 25 mutual eclipses and occultations between the Galilean satellites observed from Brazil in 2009

Dias-Oliveira, A.; Vieira-Martins, R.; Assafin, M.; Camargo, J. I. B.; Braga-Ribas, F.; da Silva Neto, D. N.; Gaspar, H. S.; Pires dos Santos, P. M.; Domingos, R. C.; Boldrin, L. A. G.; Izidoro, A.; Carvalho, J. P. S.; Sfair, R.; Sampaio, J. C.; Winter, O. C.

Monthly Notices of the Royal Astronomical Society

[ Abstract ] [ PDF ]

The light curves of mutual eclipses and occultations between the natural satellites of a planet allow us to obtain high-precision position and relative motion from differential photometry, enough to detect weak orbital disturbing forces, such as tidal forces. The observations are made during the equinoxes of the planet.We studied 25 light curves observed in Brazil during the 2009 campaign of the Galilean satellites' mutual phenomena. A narrow-band filter centred at 890 nm was used, strongly attenuating the Jupiter's scattered light. We fitted the occultation and eclipse light curves using semi-analytical models that take into account the gradual decrease of light over the shadow, the solar limb darkening and the solar phase angle. The Oren-Nayar reflexive model was used to map the inhomogeneous light scattering on the surface of the satellites. For the first time it is used in a work about mutual events. Here, we include the study that made us decide for this model.We measured the impact parameter, relative velocity and central instant with average precisions of 7.46 km (2.2 mas), 0.08 km s-1 (0.02 mas s-1) and 0.42 s (6.13 km), respectively. The fit precision of the normalized light-curve fluxes ranged between 0.4 and 4.4 per cent.

doi: http://dx.doi.org/10.1093/mnras/stt447

Small particles in Pluto's environment: effects of the solar radiation pressure

Pires dos Santos, P. M.; Giuliatti Winter, S. M.; Sfair, R.; Mourão, D. C.

Monthly Notices of the Royal Astronomical Society

[ Abstract ] [ PDF ]

Impacts of micrometeoroids on the surfaces of the plutonian small satellites Nix and Hydra can generate dust particles. Even in this region so far from the Sun these tiny ejected particles are under the effects of the solar radiation pressure.In this work, we investigate the orbital evolution of the escaping ejecta from both the small satellites under the effects of the radiation pressure combined with the gravitational effects of Pluto, Charon, Nix and Hydra. The mass production rate of micron-sized dust particles generated by micrometeoroids hitting the satellites is obtained, and numerical simulations are performed to derive the lifetime of the ejecta. These pieces of information allow us to estimate the optical depth of a putative ring, which extends from the orbits of Nix to Hydra.The ejected particles, between the orbits of Nix and Hydra, form a wide ring of about 16 000 km. Collisions with the massive bodies and escape from the system are mainly determined by the effects of the solar radiation pressure. This is an important loss mechanism, removing 30 per cent of the initial set of 1 μm-sized particles in 1 yr. The surviving particles form a ring too faint to be detectable with the derived maximum optical depth of 4 × 10-11.

doi: 10.1093/mnras/stt076

Stable regions around Pluto

Giuliatti Winter, S. M.; Winter, O. C.; Vieira Neto, E.; Sfair, R.

Monthly Notices of the Royal Astronomical Society

[ Abstract ] [ PDF ]

In a previous work, Giuliatti Winter et al. found several stable regions for test particles in orbit around Pluto associated with families of periodic orbits obtained in the circular, restricted three-body problem. They have shown that a possible eccentricity of the Pluto-Charon binary slightly reduces but does not destroy any of these stable regions. In this work, we extended their results by analysing the cases with the orbital inclination (I) equal to zero and considering the argument of pericentre (ω) equal to 90°, 180° and 270°. We explore the influence of the orbital inclination of the particles in these stable regions. In this case, the initial inclination varies from 10° to 170° in steps of 10°. We also present a sample of results for the longitude of the ascending node Ω = 90°, considering the cases I = 20°, 50°, 130° and 180°. Our results show that stable regions are present in all of the inclined cases, except when the initial inclination of the particles is equal to 110°. A sample of 3D trajectories of quasi-periodic orbits were found related to the periodic orbits obtained in the planar case by Giuliatti Winter et al.

doi: 10.1093/mnras/stt015

Small particles in Pluto's environment: effects of the solar radiation pressure

Pires dos Santos, P. M.; Giuliatti Winter, S. M.; Sfair, R.; Mourão, D. C.

Monthly Notices of the Royal Astronomical Society

[ Abstract ] [ PDF ]

Impacts of micrometeoroids on the surfaces of the plutonian small satellites Nix and Hydra can generate dust particles. Even in this region so far from the Sun these tiny ejected particles are under the effects of the solar radiation pressure.In this work, we investigate the orbital evolution of the escaping ejecta from both the small satellites under the effects of the radiation pressure combined with the gravitational effects of Pluto, Charon, Nix and Hydra. The mass production rate of micron-sized dust particles generated by micrometeoroids hitting the satellites is obtained, and numerical simulations are performed to derive the lifetime of the ejecta. These pieces of information allow us to estimate the optical depth of a putative ring, which extends from the orbits of Nix to Hydra.The ejected particles, between the orbits of Nix and Hydra, form a wide ring of about 16 000 km. Collisions with the massive bodies and escape from the system are mainly determined by the effects of the solar radiation pressure. This is an important loss mechanism, removing 30 per cent of the initial set of 1 μm-sized particles in 1 yr. The surviving particles form a ring too faint to be detectable with the derived maximum optical depth of 4 × 10<sup>-11</sup>.

doi: 10.1093/mnras/stt076

The brightening of Saturn's F ring

French, Robert S.; Showalter, Mark R.; Sfair, Rafael; Argüelles, Carlos A.; Pajuelo, Myriam; Becerra, Patricio; Hedman, Matthew M.; Nicholson, Philip D.

Icarus

[ Abstract ] [ PDF ]

Image photometry reveals that the F ring is approximately twice as bright during the Cassini tour as it was during the Voyager flybys of 1980 and 1981. It is also three times as wide and has a higher integrated optical depth. We have performed photometric measurements of more than 4800 images of Saturn's F ring taken over a 5-year period with Cassini's Narrow Angle Camera. We show that the ring is not optically thin in many observing geometries and apply a photometric model based on single-scattering in the presence of shadowing and obscuration, deriving a mean effective optical depth τ ≈ 0.033. Stellar occultation data from Voyager PPS and Cassini VIMS validate both the optical depth and the width measurements. In contrast to this decades-scale change, the baseline properties of the F ring have not changed significantly from 2004 to 2009. However, we have investigated one major, bright feature that appeared in the ring in late 2006. This transient feature increased the ring's overall mean brightness by 84% and decayed with a half-life of 91 days.

doi: 10.1016/j.icarus.2012.02.020

The role of Mab as a source for the μ ring of Uranus

Sfair, R.; Giuliatti Winter, S. M.

Astronomy & Astrophysics

[ Abstract ] [ PDF ]

Context. We previously analysed how the solar radiation force combined with the planetary oblateness changes the orbital evolution of a sample of dust particles located at the secondary ring system of Uranus. Both effects combined with the gravitational perturbations of the close satellites lead to the depletion of these dust particles through collisions on the surfaces of these satellites on a timescale of hundreds of years. Aims: In this work we investigate if the impacts of interplanetary dust particles (IDPs) onto Mab's surface can produce sufficient particles to replenish the μ ring population. Methods: We first analysed through numerical simulations the evolution of a sample of particles ejected from the surface of Mab and computed the lifetime of the grains when the effects of the solar radiation pressure and the planetary oblateness are taken into account. Then we estimated the mass production rate due to the impacts of IDPs following a previously established algorithm, and used this value to determine the time necessary to accumulate an amount of particles comparable with the mass of the μ ring. Results: Based on an estimate of the flux of interplanetary particles and on the surface properties of Mab it is expected that the satellite supplies material to the ring at a rate of ~3 g/s. Meanwhile, our numerical model showed that the ejected particles are removed from the system through collisions with the satellite, and the mean lifetime of the grains may vary from 320 to 1500 years, depending on the radius of the particle. Conclusions: The time necessary to accumulate the mass of the μ ring via ejection from Mab is much shorter than the mean lifetime of the particles, and a stationary regime is not reached. If the ring is kept in a steady state, other effects such as the electromagnetic force and/or the existence of additional bodies may play a significant role in the dust balance, but the current lack of information about the environment renders modelling these effects unfeasible.

doi: 10.1051/0004-6361/201117346

Gravitational effects of Nix and Hydra in the external region of the Pluto-Charon system Show affiliations

Pires Dos Santos, P. M.; Giuliatti Winter, S. M.; Sfair, R.

Monthly Notices of the Royal Astronomical Society

[ Abstract ] [ PDF ]

Two new companions to the Pluto-Charon binary system have been detected in 2005 by Weaver et al. These small satellites, named Nix and Hydra, are located beyond Charon's orbit. Although they are small when compared to Charon, their gravitational perturbations can decrease the stability of the external region (beyond Charon's orbit). The dynamical structure of this external region is analysed by numerically simulating a sample of particles under the gravitational effects of Pluto, Charon, Nix and Hydra. As expected the effects of Nix and Hydra decrease the external stable region. Agglomerates of particles can survive even after 105 orbital periods of the binary in some regions, such as coorbital to Nix and Hydra and between their orbits. We also analysed the effects of hypothetical satellites on the orbital evolution of Nix and Hydra in order to constrain an upper limit size. Some hypothetical satellites can be coorbital to Nix or Hydra without provoking any significant gravitational effects on them.

doi: 10.1111/j.1365-2966.2010.17437.x

Dinâmica dos anéis de poeira e satélites de Urano e do anel F de Saturno

Sfair, R.

PhD Thesis

[ Abstract ] [ PDF ]

Os anéis μ and ν de Urano compõem um segundo sistema de anéis juntamente com os satélites Puck, Mab, Portia e Rosalind. Estes anéis são tênues e compostos por partı́culas micrométricas, as quais podem ser bastante perturbadas por forças não gravitacionais, como por exemplo a força de radiação solar. Simulações numéricas foram utilizadas para analisar a evolução orbital de um conjunto de partı́culas deste sistema com raios de 1, 3, 5 e 10 μm sob influência da força de radiação e também do achatamento do planeta, combinados com a perturbação gravitacional dos satélites próximos. Como esperado, a componente do arrasto de Poynting-Robertson causa o colapso da órbita, enquando um aumento na excentricidade é verificado devido à componente da radiação solar. A inclusão do achatamento do planeta evita este aumento da excentricidade e confina as partı́culas na região dos anéis. Encontros com os satélites causam variações no semi-eixo maior das partı́culas, que podem permanecer na região dos anéis ou colidir com os satélites. Para estas colisões, o resultado mais provável é a deposição na superfı́cie. Como este mecanismo causa a remoção de material do anel, foram investigadas fontes adicionais de partı́culas. Adotando um valor aproximado para o fluxo de micrometeoritos na órbita de Urano, foi calculada a quantidade de material que pode ser ejetado devido à colisões com projéteis interplanetários. Verificou-se que as ejeções de Mab seriam suficientes para produzir um anel com profundidade óptica comparavável às observações.

Uma análise semelhante dos efeitos da radiação solar foi conduzida para a região de poeira que existe ao redor do anel F de Saturno. O amortecimento causado pelo achatamento do planeta evita as grandes variações da excentricidade, aumentando assim o tempo de vida das partı́culas de poeira. Além disso, um estudo da fotometria do anel utilizando imagens da sonda Cassini revelou que houve um aumento do brilho do anel nos últimos 25 anos. A forma da curva de fase obtida é semelhante aos dados da Voyager, indicando que, apesar do número de partı́culas ter aumentado, a distribuição de tamanho dos grãos permanece inalterada. As regiões de poeira dos anéis de Urano foram observadas no final de 2007 durante o equinócio, quando Sol cruzou o plano dos anéis. Os dados obtidos com o VLT (Very Large Telescope) durante quatro noites consecutivas foram tratados e combinados, resultando em imagens com longo tempo de exposição. Para cada imagem, foram extraı́dos os perfis radiais. Estes perfis serão utilizados para desenvolver um modelo fotométrico.

Dynamical evolution of Saturn's F ring dust particles

Sfair, R.; Winter, S. M. Giuliatti; Mourão, D. C.; Winter, O. C.

Monthly Notices of the Royal Astronomical Society

[ Abstract ] [ PDF ]

Saturn's F ring has been the subject of study due to its peculiar structure and the proximity to two satellites, named Prometheus (interior) and Pandora (exterior to the ring), which cause perturbations to the ring particles. Early results from Voyager data have proposed that the ring is populated with centimetre- and micrometre-sized particles. The Cassini spacecraft also detected a less dense part in the ring with width of 700km. Small particles suffer the effects of solar radiation. Burns et al. showed that due to effects of one component of the solar radiation, the Poynting-Robertson drag, a ring particle will decay in the direction of the planet in a time much shorter than the age of the Solar system. In this work, we have analysed a sample of dust particles (1, 3, 5 and 10μm) under the effects of solar radiation, the Poynting-Robertson drag and the radiation pressure components and the gravitational effects of the satellites Prometheus and Pandora. In this case, the high increase of the eccentricity of the particles leads almost all of them to collide with the outer edge of the A ring. The inclusion of the oblateness of Saturn in this system significantly changes the outcome, since the large variation of the eccentricity is reduced by the oblateness effect. As a result, there is an increase in the lifetime of the particle in the envelope region. Our results show that even the small dust particles, which are very sensitive to the effects of solar radiation, have an orbital evolution similar to larger particles located in the F ring. The fate of all particles is a collision with Prometheus or Pandora in less than 30 years. On the other hand, collisions of these particles with moonlets/clumps present in the F ring could change this scenario.

doi: 10.1111/j.1365-2966.2009.14666.x

Orbital evolution of the μ and ν dust ring particles of Uranus

Sfair, R.; Giuliatti Winter, S. M.

Astronomy & Astrophysics

[ Abstract ] [ PDF ]

The μ and ν rings of Uranus form a secondary ring-moon system with the satellites Puck, Mab, Portia, and Rosalind. These rings are tenuous and dominated by micrometric particles, which can be strongly disturbed by dissipative forces, such as the solar radiation pressure. In the region of these rings, the solar radiation force and the planetary oblateness change the orbital evolution of these dust particles significantly. In this work, we performed a numerical analysis of the orbital evolution of a sample of particles with radii of 1, 3, 5, and 10~μm under the influence of these perturbations, combined with the gravitational interaction with the close satellites. As expected, the Poynting-Robertson component of the solar radiation force causes the collapse of the orbits on a timescale between 3.1×105 and 3.6×106 years, while the radiation pressure causes an increase in the eccentricity of the particles. The inclusion of Uranus's oblateness prevents a large variation in the eccentricity, confining the particles in the region of the rings. The encounters with the close satellites produce variations in the semimajor axis of the particles, leading them to move inward and outward within the ring region. These particles can either remain within the region of the rings or collide with a neighbouring satellite. The number of collisions depends on the size of both the particles and the satellites, and the radial width of the ring. For the time span analysed, the percentage of particles that collide with a satellite varies from 43% to 94% for the ν ring, and from 12% to 62% for the μ ring. Our study shows that all collisions with Portia and Rosalind have the value of impact velocity comparable to the escape velocity, which could result in the deposition of material onto the surface of the satellite. Collisions between Puck and particles larger than 1~μm also occur at an impact velocity comparable to the value of the escape velocity. The exception is Mab, which is hit by particles with velocities several times larger than the escape velocity. These collisions are energetic enough to eject material and supply material to the μ ring. However, only a few particles (3%) collide with the surface of the satellite Mab at such a velocity.

doi: 10.1051/0004-6361/200911886

Analysing the New Saturnian Rings, R/2004 S1 and R/2004 S2

Winter, S. M. Giuliatti; Sfair, R.; Mourão, D. C.; Bastos, T. A.

Earth, Moon, and Planets

[ Abstract ] [ PDF ]

The Cassini-Huygens arrival into the Saturnian system brought a large amount of data about the satellites and rings. Two diffuse rings were found in the region between the A ring and Prometheus. R/2004 S1 is coorbital to Atlas and R/2004 S2 is close to Prometheus. In this work we analysed the closest approach between Prometheus and both rings. As a result we found that the satellite removes particles from R/2004 S2 ring. Long-term numerical simulations showed that some particles can cross the F ring region . The well known region of the F ring, where small satellites are present and particles are being taking from the ring, gains a new insight with the presence of particles from R/2004 S2 ring. The computation of the Lyapunov Characteristic Exponent reveled that the R/2004 S2 ring lies in a chaotic region while R/2004 S1 ring and Atlas are in a stable region. Atlas is responsible for the formation of three regimes in the R/2004 S1 ring, as expected for a satellite embedded in a ring.

doi: 10.1007/s11038-006-9082-x