Dynamical aspects of jovian irregular satellites

Growth and evolution of satellites in a Jovian massive disc

The formation of satellite systems in circum-planetary discs is considered to be similar to the formation of rocky planets in a proto-planetary disc, especially Super-Earths. Thus, it is possible to use systems with large satellites to test formation theories that are also applicable to extrasolar planets. Furthermore, a better understanding of the origin of satellites might yield important information about the environment near the growing planet during the last stages of planet formation. In this work we investigate the formation and migration of the Jovian satellites through N-body simulati…

Secular resonances between bodies on close orbits: a case study of the Himalia prograde group of jovian irregular satellites

The gravitational interaction between two objects on similar orbits can effect noticeable changes in the orbital evolution even if the ratio of their masses to that of the central body is vanishingly small. Christou (2005) observed an occasional resonant lock in the differential node $ΔΩ$ between two members in the Himalia irregular satellite group of Jupiter in the $N$-body simulations (corresponding mass ratio $\sim 10^{-9}$). Using a semianalytical approach, we have reproduced this phenomenon. We also demonstrate the existence of two additional types of resonance, involving angle difference…

巨行星不规则卫星与特洛伊小行星之间的光谱联系

Spectroscopic Links Among Giant Planet Irregular Satellites and Trojans

本文通过对比木星、天王星不规则卫星与海王星特洛伊小行星的可见光及近红外光谱，发现其与木星特洛伊及柯伊伯带天体的相似性，并检测到水合特征，提出挥发分升华导致的风化层差异可解释光谱变化，为含水陨石起源提供线索。

Astrometric observations of outer Jovian satellites with the `Saturn' telescope. First results

The one-meter telescope-reflector `Saturn' (D=1 m, F = 4 m) was partially renovated at the Pulkovo observatory at the end of 2014. The telescope was equipped by CCD camera S2C with 14x14 arcmin field of view and 824 mas per pix scale. The observations of outer Jovian satellites have been performed in a test mode since January 2015. The exposure time of 30 seconds allows us to obtain images of stars up to magnitude 19.5 with the present state of the mirror and the equipment. The observations of outer Jovian satellites have been performed during testing period. These objects are interesting targ…

Photoevaporation of the Jovian circumplanetary disk I. Explaining the orbit of Callisto and the lack of outer regular satellites

Context: The Galilean satellites are thought to have formed from a circumplanetary disk (CPD) surrounding Jupiter. When it reached a critical mass, Jupiter opened an annular gap in the solar protoplanetary disk (PPD) that might have exposed the CPD to radiation from the young Sun or from the stellar cluster in which the Solar System formed. Aims: We investigate the radiation field to which the Jovian CPD was exposed during the process of satellite formation. The resulting photoevaporation of the CPD is studied in this context to constrain possible formation scenarios for the Galilean satellite…

JWST揭示木星不规则卫星的不同起源

JWST Reveals Varied Origins Between Jupiter's Irregular Satellites

JWST观测八颗木星不规则卫星，发现Himalia家族含氨化硅酸盐及复杂CO2，揭示母体异质，部分卫星经历水蚀变，表明木星捕获了不同起源的天体。

Colors of Irregular Satellites of Saturn with DECam

We report g-r and r-i new colors for 21 Saturn Irregular Satellites, among them, 4 previously unreported. This is the highest number of Saturn Irregular satellites reported in a single survey. These satellites were measured by "stacking" their observations to increase their signal without trailing. This work describes a novel processing algorithm that enables the detection of faint sources under significant background noise and in front of a severely crowded field. Our survey shows these new color measurements of Saturn Irregular Satellites are consistent with other Irregular Satellites popula…

Dynamics and distribution of Jovian dust ejected from the Galilean satellites

In this paper, the dynamical analysis of the Jovian dust originating from the four Galilean moons is presented. High accuracy orbital integrations of dust particles are used to determine their dynamical evolution. A variety of forces are taken into account, including the Lorentz force, solar radiation pressure, Poynting-Robertson drag, solar gravity, the satellites' gravity, plasma drag, and gravitational effects due to non-sphericity of Jupiter. More than 20,000 dust particles from each source moon in the size range from 0.05 micron to 1 cm are simulated over 8,000 (Earth) years until each du…

Capture of Irregular Satellites at Jupiter

The irregular satellites of outer planets are thought to have been captured from heliocentric orbits. The exact nature of the capture process, however, remains uncertain. We examine the possibility that irregular satellites were captured from the planetesimal disk during the early Solar System instability when encounters between the outer planets occurred (Nesvorny, Vokrouhlicky & Morbidelli 2007, AJ 133; hereafter NVM07). NVM07 already showed that the irregular satellites of Saturn, Uranus and Neptune were plausibly captured during planetary encounters. Here we find that the current instabili…

The 2014-2015 Brazilian Mutual Phenomena campaign for the Jovian satellites and improved results for the 2009 events

Progress in astrometry and orbital modelling of planetary moons in the last decade enabled better determinations of their orbits. These studies need accurate positions spread over extended periods. We present the results of the 2014-2015 Brazilian campaign for 40 mutual events from 47 observed light curves by the Galilean satellites plus one eclipse of Amalthea by Ganymede. We also reanalysed and updated results for 25 mutual events observed in the 2009 campaign. All telescopes were equipped with narrow-band filters centred at 889 nm with a width of 15 nm to eliminate the scattered light from …

Properties of the irregular satellite system around Uranus inferred from K2, Herschel and Spitzer observations

In this paper we present visible range light curves of the irregular Uranian satellites Sycorax, Caliban, Prospero, Ferdinand and Setebos taken with Kepler Space Telescope in the course of the K2 mission. Thermal emission measurements obtained with the Herschel/PACS and Spitzer/MIPS instruments of Sycorax and Caliban were also analysed and used to determine size, albedo and surface characteristics of these bodies. We compare these properties with the rotational and surface characteristics of irregular satellites in other giant planet systems and also with those of main belt and Trojan asteroid…

Colors and Shapes of the Irregular Planetary Satellites

It is widely recognized that the irregular satellites of the giant planets were captured from initially heliocentric orbits. However, the mechanism of capture and the source region from which they were captured both remain unknown. We present an optical color survey of 43 irregular satellites of the outer planets conducted using the LRIS camera on the 10-meter telescope at the Keck Observatory in Hawaii. The measured colors are compared to other planetary bodies in search for similarities and differences that may reflect upon the origin of the satellites. We find that ultrared matter (with col…

On collisional capture rates of irregular satellites around the gas-giant planets and the minimum mass of the solar nebula

We investigated the probability that an inelastic collision of planetesimals within the Hill sphere of the Jovian planets could explain the presence and orbits of observed irregular satellites. Capture of satellites via this mechanism is highly dependent on not only the mass of the protoplanetary disk, but also the shape of the planetesimal size distribution. We performed 2000 simulations for integrated time intervals $\sim 2$ Myr and found that, given the currently accepted value for the minimum mass solar nebula and planetesimal number density based upon the \citet{Nesvorny2003} and \citet{C…

Capture of Irregular Satellites via Binary Planetesimal Exchange Reactions in Migrating Planetary Systems

By logging encounters between planetesimals and planets we compute the distribution of encounters in a numerically integrated two planet system that is migrating due to interactions with an exterior planetesimal belt. Capture of an irregular satellite in orbit about a planet through an exchange reaction with a binary planetesimal is only likely when the binary planetesimal undergoes a slow and close encounter with the planet. In our simulations we find that close and slow encounters between planetesimals and a planet primarily occur with the outermost and not innermost planet. Taking care to c…

The 3 $μ$m Spectrum of Jupiter's Irregular Satellite Himalia

We present a medium resolution spectrum of Jupiter's irregular satellite Himalia covering the critical 3 $μ$m spectral region. The spectrum shows no evidence for aqueously altered phyllosilicates, as had been suggested from the tentative detection of a 0.7 $μ$m absorption, but instead shows a spectrum strikingly similar to the C/CF type asteroid 52 Europa. 52 Europa is the prototype of a class of asteroids generally situated in the outer asteroid belt between less distant asteroids which show evidence for aqueous alteration and more distant asteroids which show evidence for water ice. The spec…

New orbits of irregular satellites designed for the predictions of stellar occultations up to 2020, based on thousands of new observations

Gomes-Júnior et al. (2015) published 3613 positions for the 8 largest irregular satellites of Jupiter and 1787 positions for the largest irregular satellite of Saturn, Phoebe. These observations were made between 1995 and 2014 and have an estimated error of about 60 to 80 mas. Based on this set of positions, we derived new orbits for the eight largest irregular satellites of Jupiter: Himalia, Elara, Pasiphae, Carme, Lysithea, Sinope, Ananke and Leda. For Phoebe we updated the ephemeris from Desmars et al. (2013) using 75% more positions than the previous one. Due to their orbital characteristi…

木星不规则卫星尘埃的“生命”

"Life" of dust originating from the irregular satellites of Jupiter

本文通过数值模拟与解析理论，研究了木星不规则卫星尘埃的动力学、寿命与归宿，并提出了木卫四轨道外由2-25微米尘埃主导的环及其光学深度。

论木星卫星木卫五（Amalthea）的起源与动力学演化

On the origin and dynamical evolution of Jupiter's moon Amalthea

本文提出木卫五与伽利略卫星共同形成于外侧卫星星子储库，并被木卫一通过共振俘获、牧羊迁移至内侧轨道，从而约束木卫形成期环木盘纵横比至少约0.08。

布朗哈密顿量的扩展Ⅲ。巨行星不规则卫星的应用

Extensions of Brown Hamiltonian-III. Applications to irregular satellites of giant planets

本文基于扩展的布朗哈密顿量框架，引入修改后的利多夫积分作为诊断指数，识别不规则卫星在ZLK共振中的捕获状态，并通过N体模拟验证了26个候选体，其中S/2019 S1的偏差归因于其接近分隔线。

Composition of Jupiter irregular satellites sheds light on their origin

Irregular satellites of Jupiter with their highly eccentric, inclined and distant orbits suggest that their capture took place just before the giant planet migration. We aim to improve our understanding of the surface composition of irregular satellites of Jupiter to gain insight into a narrow time window when our Solar System was forming. We observed three Jovian irregular satellites, Himalia, Elara, and Carme, using a medium-resolution 0.8-5.5 micro m spectrograph on the National Aeronautics and Space Administration (NASA) Infrared Telescope Facility (IRTF). Using a linear spectral unmixing …

Three-Body Capture of Irregular Satellites: Application to Jupiter

We investigate a new theory of the origin of the irregular satellites of the giant planets: capture of one member of a ~100-km binary asteroid after tidal disruption. The energy loss from disruption is sufficient for capture, but it cannot deliver the bodies directly to the observed orbits of the irregular satellites. Instead, the long-lived capture orbits subsequently evolve inward due to interactions with a tenuous circumplanetary gas disk. We focus on the capture by Jupiter, which, due to its large mass, provides the most stringent test of our model. We investigate the possible fates of dis…

Probability of Collisional Capture of Irregular Satellites Around the Gas Giant Planets and Mass Constraints for the Solar Nebula

We investigated the probability that an inelastic collision of planetesimals within the Hill sphere of the Jovian planets could explain the presence and orbits of observed irregular satellites. Capture of these satellites via this mechanism is highly dependent on not only the mass of the protoplanetary disk, but also the shape of the planetesimal size distribution. We performed 2000 simulations for integrated time intervals $\sim 2$ Myr and found that given the currently accepted value for the minimum mass solar nebula and planetesimal number density based upon the \citet{Bottke2010b} size dis…

土星不规则卫星作为柯伊伯带表面演化的探针

Saturnian Irregular Satellites as a Probe of Kuiper Belt Surface Evolution

本研究利用JWST光谱分析土星三颗最大不规则卫星，发现菲比富含水冰而较小卫星缺乏，提出碰撞升华与后期CO2形成机制，揭示柯伊伯带表面演化。

A new perspective on the irregular satellites of Saturn - II Dynamical and physical origin

The origin of the irregular satellites of the giant planets has been long debated since their discovery. Their dynamical features argue against an in-situ formation suggesting they are captured bodies, yet there is no global consensus on the physical process at the basis of their capture. In this paper we explore the collisional capture scenario, where the actual satellites originated from impacts occurred within Saturn's influence sphere. By modeling the inverse capture problem, we estimated the families of orbits of the possible parent bodies and the specific impulse needed for their capture…

A new perspective on the irregular satellites of Saturn - I Dynamical and collisional history

The dynamical features of the irregular satellites of the giant planets argue against an in-situ formation and are strongly suggestive of a capture origin. Since the last detailed investigations of their dynamics, the total number of satellites have doubled, increasing from 50 to 109, and almost tripled in the case of Saturn system. We have performed a new dynamical exploration of Saturn system to test whether the larger sample of bodies could improve our understanding of which dynamical features are primordial and which are the outcome of the secular evolution of the system. We have performed…

来自太阳系外不规则卫星的碎屑环

Debris Rings from Extrasolar Irregular Satellites

本文模拟系外巨行星不规则卫星碰撞产生尘埃并在辐射压作用下形成环恒星碎屑环的过程，解释薄而方位对称的窄环观测特征。

On the existence of regular and irregular outer moons orbiting the Pluto-Charon system

The dwarf planet Pluto is known to host an extended system of five co-planar satellites. Previous studies have explored the formation and evolution of the system in isolation, neglecting perturbative effects by the Sun. Here we show that secular evolution due to the Sun can strongly affect the evolution of outer satellites and rings in the system, if such exist. Although precession due to extended gravitational potential from the inner Pluto-Charon binary quench such secular evolution up to $a_{crit}\sim0.0035$ AU ($\sim0.09$ $R_{Hill}$ the Hill radius; including all of the currently known sat…

Mapping the $ν_\odot$ Secular Resonance for Retrograde Irregular Satellites

Constructing dynamical maps from the filtered output of numerical integrations, we analyze the structure of the $ν_\odot$ secular resonance for fictitious irregular satellites in retrograde orbits. This commensurability is associated to the secular angle $θ= \varpi - \varpi_\odot$, where $\varpi$ is the longitude of pericenter of the satellite and $\varpi_\odot$ corresponds to the (fixed) planetocentric orbit of the Sun. Our study is performed in the restricted three-body problem, where the satellites are considered as massless particles around a massive planet and perturbed by the Sun. Depend…

Direct Imaging of Irregular Satellite Disks in Scattered Light

Direct imaging surveys have found that long-period super-Jupiters are rare. By contrast, recent modeling of the widespread gaps in protoplanetary disks revealed by ALMA suggests an abundant population of smaller Neptune to Jupiter-mass planets at large separations. The thermal emission from such lower-mass planets is negligible at optical and near-infrared wavelengths, leaving only their weak signals in reflected light. Planets do not scatter enough light at these large orbital distances, but there is a natural way to enhance their reflecting area. Each of the four giant planets in our solar s…

Red material on the large moons of Uranus: Dust from irregular satellites?

The large and tidally-locked classical moons of Uranus display longitudinal and planetocentric trends in their surface compositions. Spectrally red material has been detected primarily on the leading hemispheres of the outer moons, Titania and Oberon. Furthermore, detected H2O ice bands are stronger on the leading hemispheres of the classical satellites, and the leading/trailing asymmetry in H2O ice band strengths decreases with distance from Uranus. We hypothesize that the observed distribution of red material and trends in H2O ice band strengths results from infalling dust from Uranian irreg…

相互逼近的解析框架——推导及其在木星卫星上的应用

Analytical framework for mutual approximations -- Derivation and application to Jovian satellites

本文提出一种将相互逼近的中心时刻作为直接观测量的解析方法，以木星卫星为案例验证其能使状态估计形式误差改善10-20%，确保充分利用观测信息。

Secular resonances between bodies on close orbits II: prograde and retrograde orbits for irregular satellites

In extending the analysis of the four secular resonances between close orbits in Li and Christou (Celest Mech Dyn Astron 125:133-160, 2016) (Paper I), we generalise the semianalytical model so that it applies to both prograde and retrograde orbits with a one to one map between the resonances in the two regimes. We propose the general form of the critical angle to be a linear combination of apsidal and nodal differences between the two orbits $ b_1 Δ\varpi + b_2 ΔΩ$, forming a collection of secular resonances in which the ones studied in Paper I are among the strongest. Test of the model in the…

Searching for Saturn's Dust Swarm: Limits on the size distribution of Irregular Satellites from km to micron sizes

We describe a search for dust created in collisions between the Saturnian irregular satellites using archival \emph{Spitzer} MIPS observations. Although we detected a degree scale Saturn-centric excess that might be attributed to an irregular satellite dust cloud, we attribute it to the far-field wings of the PSF due to nearby Saturn. The Spitzer PSF is poorly characterised at such radial distances, and we expect PSF characterisation to be the main issue for future observations that aim to detect such dust. The observations place an upper limit on the level of dust in the outer reaches of the …

Collisional Cascade Caclulations for Irregular Satellite Swarms in Fomalhaut b

We describe an extensive suite of numerical calculations for the collisional evolution of irregular satellite swarms around 1--300 M-earth planets orbiting at 120 AU in the Fomalhaut system. For 10--100 M-earth planets, swarms with initial masses of roughly 1% of the planet mass have cross-sectional areas comparable to the observed cross-sectional area of Fomalhaut b. Among 30--300 M-earth planets, our calculations yield optically thick swarms of satellites for ages of 1-10 Myr. Observations with HST and ground-based AO instruments can constrain the frequency of these systems around stars in t…

Multicolor Photometry of the Neptune Irregular Satellite Neso

We report on time series photometry of the faint Neptune irregular satellite Neso. Observations in the V, R, and I pass-bands were performed in photometric conditions at the Cerro Paranal observatory using the instrument FORS2, in the night of July 15th, 2010. Astrometry and photometry derived from these observations are presented here. The time coverage of about six hours does not allow to construct a light curve and derive a meaningful rotational period. However, we could derive new estimates of apparent magnitudes obtaining R=25.2 pm 0.2 mag in agreement with Brozovic, Jacobson, Sheppard (2…

Capturing Trojans and Irregular Satellites - the key required to unlock planetary migration

It is now accepted that the Solar system's youth was a dynamic and chaotic time. The giant planets migrated significant distances to reach their current locations, and evidence of that migration's influence on the Solar system abounds. That migration's pace, and the distance over which it occurred, is still heavily debated. Some models feature systems in which the giant planets were initially in an extremely compact configuration, in which Uranus and Neptune are chaotically scattered into the outer Solar system. Others feature architectures that were initially more relaxed, and smoother, more …

为潜在的JUICE飞行动作表征千米级木卫

Kilometre-scale Jovian moon characterized for a potential JUICE flyby

该研究通过多仪器观测表征了适合JUICE飞掠的千米级木卫卡里科雷，降低了其轨道不确定性，确定了形状、尺寸等参数，为JUICE飞掠提供了可行条件。

Finding the trigger to Iapetus' odd global albedo pattern: Dynamics of dust from Saturn's irregular satellites

The leading face of Saturn's moon Iapetus, Cassini Regio, has an albedo only one tenth that on its trailing side. The origin of this enigmatic dichotomy has been debated for over forty years, but with new data, a clearer picture is emerging. Motivated by Cassini radar and imaging observations, we investigate Soter's model of dark exogenous dust striking an originally brighter Iapetus by modeling the dynamics of the dark dust from the ring of the exterior retrograde satellite Phoebe under the relevant perturbations. In particular, we study the particles' probabilities of striking Iapetus, as we…

Evidence for sulfur-bearing species on Callisto's leading hemisphere: Sourced from Jupiter's irregular satellites or Io?

We investigated whether sulfur-bearing species are present on the icy Galilean moon Callisto by analyzing eight near-infrared reflectance spectra collected over a wide range of sub-observer longitudes. We measured the band areas and depths of a 4-micron feature in these spectra, which has been attributed to sulfur dioxide (SO2), as well as carbonates, in previously collected datasets of this moon. All eight spectra we collected display the 4-micron band. The four spectra collected over Callisto's leading hemisphere display significantly stronger 4-micron bands compared to the four trailing hem…

Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations

The irregular satellites of the giant planets are believed to have been captured during the evolution of the solar system. Knowing their physical parameters, such as size, density, and albedo is important for constraining where they came from and how they were captured. The best way to obtain these parameters are observations in situ by spacecrafts or from stellar occultations by the objects. Both techniques demand that the orbits are well known. We aimed to obtain good astrometric positions of irregular satellites to improve their orbits and ephemeris. We identified and reduced observations o…

Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar Planets

Since the 1980's it has been becoming increasingly clear that the Solar System's irregular satellites are collisionally evolved. We derive a general model for the collisional evolution of an irregular satellite swarm and apply it to the Solar System and extrasolar planets. Our model reproduces the Solar System's complement of observed irregulars well, and suggests that the competition between grain-grain collisions and Poynting-Robertson (PR) drag helps set the fate of the dust. Because swarm collision rates decrease over time the main dust sink can change with time, and may help unravel the a…

The origin of Neptune's unusual satellites from a planetary encounter

The Neptunian satellite system is unusual, comprising Triton, a large ($\sim2700$ km) moon on a close-in, circular, yet retrograde orbit, flanked by Nereid, the largest irregular satellite ($\sim$300 km) on a highly eccentric orbit. Capture origins have been previously suggested for both moons. Here we explore an alternative in-situ formation model where the two satellites accreted in the circum-Neptunian disk and are imparted irregular and eccentric orbits by a deep planetary encounter with an ice giant (IG), like that predicted in the Nice scenario of early solar system development. We use $…

不规则卫星的固定轨道 II：不规则卫星的轨道

Irregular Fixation II: The orbits of irregular satellites

本研究利用布朗哈密顿量新形式体系描述不规则卫星轨道，构建半解析判据预测平动轨道，并通过 N 体积分验证，发现 13 颗平动卫星，其中 5 颗为首次发现。

Irregular satellites of Jupiter: Capture configurations of binary-asteroids

The origins of irregular satellites of the giant planets are an important piece of the giant "puzzle" that is the theory of Solar System formation. It is well established that they are not "in situ" formation objects, around the planet, as are believed to be the regular ones. Then, the most plausible hypothesis to explain their origins is that they formed elsewhere and were captured by the planet. However, captures under restricted three-body problem dynamics have temporary feature, which makes necessary the action of an auxiliary capture mechanism. Nevertheless, there not exist one well estab…

The first observed stellar occultations by the irregular satellite (Saturn IX) Phoebe and improved rotational period

We report six stellar occultations by (Saturn IX) Phoebe, an irregular satellite of Saturn, obtained between mid-2017 and mid-2019. The 2017 July 06 event is the first stellar occultation by an irregular satellite ever observed. The occultation chords were compared to a 3D shape model of the satellite obtained from Cassini observations. The rotation period available in the literature led to a sub-observer point at the moment of the observed occultations where the chords could not fit the 3D model. A procedure was developed to identify the correct sub-observer longitude. It allowed us to obtain…

Chaotic dust dynamics and implications for the hemispherical color asymmetries of the Uranian satellites

Dust grains generated by the Uranian irregular satellites will undergo chaotic large-amplitude eccentricity oscillations under the simultaneous action of radiation forces and the highly misaligned quadrupole potentials of the oblate planet and distant Sun. From a suite of orbital histories, we estimate collision proba- bilities of dust particles with the regular satellites and argue that this process may explain the observed hemispherical color asymmetries of the outermost four regular satellites of Uranus.

木星伽利略卫星上的莱斯-瑟林效应

The Lense-Thirring effect on the Galilean moons of Jupiter

研究木星角动量引起的莱斯-瑟林效应对伽利略卫星轨道的影响，数值积分显示木卫一效应达数十角秒，木卫四约0.2角秒，未来任务或可探测。

Nereid 作为海王星的规则卫星

Nereid as a Regular Satellite of Neptune

通过 JWST 近红外光谱和轨道动力学模拟，证明 Nereid 不是捕获的柯伊伯带天体，而是海王星唯一的幸存规则卫星。

Dynamical history of the Galilean satellites for a fast migration of Callisto

The dynamics of the innermost Galilean satellites (Io, Europa and Ganymede) is characterised by a chain of mean motion resonances, called Laplace resonance, and by a strong tidal dissipation that causes wide variations of their semi-major axes over large timescales. The precise history of energy dissipation in the Jovian system is not known, but several theories have been proposed. Tidal resonance locking states that big outer moons can also migrate fast. If this is the case for Callisto, then it should have crossed the 2:1 mean motion resonance with Ganymede in the past, affecting the motion …

原生动动力学对木星卫星忒拜密度的约束

A constraint on the density of Jupiter's moon Thebe from primordial dynamics

本研究通过模拟艾奥迁移对阿马尔塞和忒拜的共振牧羊效应，推导出忒拜密度下限，为木星内卫星演化模型提供可检验的约束。

High-Precision Measurements of Brightness Variation of Nereid

Nereid, a satellite of Neptune, has a highly eccentric prograde orbit with a semi-major axis larger than 200 Neptune radius and is classified as an irregular satellite. Although the capture origin of irregular satellites has been widely accepted, several previous studies suggest that Nereid was formed in the circumplanetary disk of Neptune and was ejected outward to the present location by Triton. Our time-series photometric observations confirm that the spin is stable and non-chaotic with a period of 11.5 hr as indicated by Grav et al. (2003). The optical colors of Nereid are indistinguishabl…

Capture in restricted four body problem

A number of irregular moons of the Jovian planets have recently been discovered. Most adequate way of their origin is capture, but detailed mechanism is unknown. A few possibilities are discussed: collisions, gas drag, tidal destruction of a binary asteroid. In this paper the capture process in restricted four body problem (RFBP) is researched. The interaction with regular satellite can be studied by this way as well as binary asteroid destruction in Hill sphere of planet. The energetic criteria of ballistic capture are studied and some numerical experiments are developed. It is confirmed, tha…

Preliminary results of CCD observations of Himalia at Yunnan Observatories in 2015

In order to study the potential in high precision CCD astrometry of irregular satellites, we have made experimental observations for Himalia, the sixth and irregular satellite of Jupiter. A total of 185 CCD observations were obtained by using the 2.4 m telescope and 1 m telescope at Yunnan Observatories over ten nights. Preliminary analysis for the observations were made, including the geometric distortion, the atmospheric refraction, and also the phase effect. All positions of Himalia are measured relative to the reference stars from the catalogue UCAC4 in each CCD field of view. The theoreti…

Asteroid 2014 OL339: yet another Earth quasi-satellite

Our planet has one permanently bound satellite -the Moon-, a likely large number of mini-moons or transient irregular natural satellites, and three temporary natural retrograde satellites or quasi-satellites. These quasi-moons -(164207) 2004 GU9, (277810) 2006 FV35 and 2013 LX28- are unbound companions to the Earth. The orbital evolution of quasi-satellites may transform them into temporarily bound satellites of our planet. Here, we study the dynamical evolution of the recently discovered Aten asteroid 2014 OL339 to show that it is currently following a quasi-satellite orbit with respect to th…