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Up to now, 17 Neptune Trojan asteroids have been detected with their orbits being well determined by continuous observations. This paper analyzes systematically their orbital dynamics. Our results show that except for two temporary members with relatively short lifespans on Trojan orbits, the vast majority of Neptune Trojans located within their orbital uncertainties may survive in the solar system age. The escaping probability of Neptune Trojans, through slow diffusion in the orbital element space in 4.5 billion years, is estimated to be ∼50%. The asteroid 2012 UW177 classified as a Centaur asteroid by the IAU Minor Planet Center currently is in fact a Neptune Trojan. Numerical simulations indicate that it is librating on the tadpole-shaped orbit around the Neptune's L4 point. It was captured into the current orbit approximately 0.23 million years ago, and will stay there for at least another 1.3 million years in the future. Its high inclination of i ≈ 54∘ not only makes it the most inclined Neptune Trojan, but also makes it exhibit the complicated and interesting co-orbital transitions between the leading and trailing Trojans via the quasi-satellite orbit phase.

Centaurs, minor planets with a semi-major axis between the orbits of Jupiter and Neptune (5–30 AU), are thought to be among the most diverse small bodies in the solar system. These important targets for future missions may have recently been Kuiper Belt Objects (KBOs), which are thought to be chemically and physically primitive remnants of the early solar system. While the Kuiper Belt spans distances of 30–50 AU, making direct observations difficult, Centaurs' proximity to the Earth and Sun make them more accessible targets for robotic missions. Thus, we outline a mission concept designed to reconnoiter 10199 Chariklo, the largest Centaur and smallest ringed body yet discovered. Named for a legendary Centaur tamer, the conceptual Camilla mission is designed to fit under the cost cap of the National Aeronautics and Space Administration (NASA) New Frontiers program, leveraging a conservative payload to support a foundational scientific investigation to these primitive bodies. Specifically, the single flyby encounter utilizes a combined high-resolution camera/VIS-IR mapping spectrometer, a sub-mm point spectrometer, and a UV mapping spectrometer. In addition, the mission concept utilizes a kinetic impactor, which would provide the first opportunity to sample the composition of potentially primitive subsurface material beyond Saturn, thus providing key insights into solar system origins. Such a flyby of the Chariklo system would provide a linchpin in the understanding of small body composition, evolution, and transport of materials in the solar system.

The quasi-Hilda asteroid (457175) 2008 GO98 was found in a previous study as a good candidate to show cometary activity since it seems to come from the Centaurs region. The object was observed in the post-perihelion arc of its orbit during several runs between September 2016 and June 2017 with the 2.15 m telescope at Complejo Astronomico El Leoncito (CASLEO) in San Juan, Argentina. The images obtained were analyzed and the object was observed active with a small coma that grew in size and brightness as the object moved away from the perihelion of the orbit, while in June 2017 it also showed a small tail. In order to get an estimation of the diameter of the nucleus the coma contribution has been calculated and subtracted to find values of 15.5 ± 4.0 k m and 20.1 ± 5.4 k m for albedos of p R = 0.13 and p R = 0.069 , respectively. To understand the recent dynamical evolution of (457175) 2008 GO98, the orbit of the object and those of 100 clones were numerically integrated backward and forward in time for 30000 y r . The dynamical evolution confirms that this object is a recent incomer from the outer region of the solar system but it will return to this region in a short period of time indicating that its present dynamical state is rather transient.

We numerically study the dynamical evolution of observed samples of active and inactive Centaurs and clones that reach the Jupiter-Saturn region. Our aim is to compare the evolution between active and inactive Centaurs, their end states and their transfer to Jupiter family comets and Halley-type comets. We find that the median lifetime of inactive Centaurs is about twice longer than that for active Centaurs, suggesting that activity is related to the residence time in the region. This view is strengthened by the observation that high-inclination and retrograde Centaurs (Tisserand parameters with respect to Jupiter $T_J < 2$) which have the longest median dynamical lifetime ($=1.37 \times 10^6$ yr) are all inactive. We also find that the perihelion distances of some active, comet-like Centaurs have experienced drastic drops of a few au in the recent past ($\sim 10^2-10^3$ yr), while such drops are not found among inactive Centaurs. Inactive Centaurs with $T_J \lsim 2.5$ usually evolve to Halley-type comets, whereas inactive Centaurs with $T_J \gsim 2.5$ and active Centaurs (that also have $T_J \gsim 2.5$) evolve almost always to Jupiter family comets and very seldom to Halley type comets. Inactive Centaurs are also more prone to end up as sungrazers, and both inactive and active Centaurs transit through different mean motion resonances (generally with Jupiter) during their evolution., Paper presented at the Asteroids, Comets, Meteors meeting held in Montevideo, Uruguay, 2017

We present a concept study for a distinctive robotic spacecraft mission that combines both the exploration of a never-before-visited class of planetary bodies and cutting-edge astrophysical investigations. The planetary targets are a class of objects called Centaurs that have relatively recently escaped from the Kuiper Belt and currently orbit closer to the Sun among the giant planets. We developed a trajectory that would visit several Centaurs, including the second largest known Centaur, 2060 Chiron, which displays enigmatic coma activity at large heliocentric distances and orbiting ring or dust structures. This concept takes advantage of the cruise times between planetary encounters to conduct nearly continuous astrophysical observations at wavelengths that are not accessible by ground-based facilities. Additionally, ride-along cubesats included aboard can be deployed at different points in the mission to perform various experiments or observations. This mission concept achieves its objectives with solar power (MegaFlex arrays), no new technology development, and within the approximate budget of a NASA New Frontiers class mission. The mission design accomplishes its objectives using solar electric propulsion and the recently developed NASA Evolutionary Xenon Thruster (NEXT) ion engines.

We study the contribution of JFC (Jupiter family comet) and Centaur regions to the NEA (near Earth asteroid) population having Tisserand parameters for Jupiter between 2 and 3. We define a region for JFCs (aphelion distance ( Q ) > 4.61 au, perihelion distance ( q ) 4.95 au, > 1.3 au) and we check the contributions of selected bodies (JFCs, Centaurs, Halley-type comets (HTCs), some elliptic comets, and some outer main belt asteroids) from various regions to the NEA region. Additionally, we integrated NEAs with Tisserand parameters for Jupiter ( T J ) between 2 and 3 and their clones backward in time to see whether there was a strong dynamical path between those NEAs and the defined JFC region. As a result, 35.1% of the orbits from the defined JFC region turned out to be Earth-crossing orbits for forward integrations, while 66.7% of NEAs ( 2 T J 3 ) reached the JFC region for backward integrations. Considering these probabilities, 304 orbits of today’s JFC regional bodies can contribute the Earth-crossing asteroids in 0.55 Myr. Almost 254 NEA regional bodies look like they came from the defined region in a comparable time interval (0.80 Myr).

Pre-dawn sightings of a fireball over Spain on November 3, 2015, and the subsequent discovery of three composite overwrap pressure vessel (COPV) spheres and other suspected space debris, pointed to a re-entry as the cause. The resource of record for re-entries is the USSTRATCOM (U.S. Strategic Command); however, its Space Track web site reported neither predictions nor historical data that correlated with the events in Spain. The mystery was solved by estimating the orbital elements from the fireball sightings and positions of the debris, and finding a matching object in the orbital data of independent sources. The re-entering object was the Centaur upper stage with the international designation 2008-010B, and the USSTRATCOM catalogue number 32707.

We present an analysis of the colors available for seven trans-neptunian objects (TNOs) and three centaurs among the reddest known, aimed at characterizing their surface chemical properties. In particular we seek to obtain evidence in support of the proposed correlation between the visible coloration of the surface of TNOs and their surface compositions (Brown, M.E., Schaller, E.L., Fraser, W.C. [2011]. Astrophys. J. 739, L60). The analysis focuses on nine available colors in the visible–near IR (0.3–4.5 μm) spectral range scaled to the V albedo to provide a proxy for the spectral shape of the objects. The colors include Spitzer IRAC data never published before, key in providing an effective constraint in the discrimination of ices contributing to the surface composition of the objects. Compositions are obtained by comparing the data to a grid of radiative transfer models convolved by the filter response functions of the colors adopted in the spectrum-proxies to match the resolution of the observations. We find evidence suggesting the presence of hydrocarbons and/or methanol on the surfaces of most objects in our sample, supporting the hypothesis by Brown et al. (Brown, M.E., Schaller, E.L., Fraser, W.C. [2011]. Astrophys. J. 739, L60) that the coloration of red TNOs could be linked to their methanol content. From our finding of methanol/hydrocarbon ices on the surfaces of the objects in our sample of very red TNOs and centaurs we infer that ultra-red objects in general might contain these ices and therefore might have formed in the outer part of the Solar System. We also deduce that the surfaces of most of the very red TNOs in our dataset are probably still quite pristine, and that their organic materials could have been produced by irradiation of the volatile ices whose traces are still present on their surface. Although our sample is small, we infer that the irradiation process is still in progress, as hinted by the centaurs’ slightly elevated organic amounts at smaller perihelion distances. However, considering the relatively similar amounts of organics found in our data at a wide variety of perihelion distances, we also infer that it could have started before Neptune’s migration. The technique used to constrain the composition described as part of this study introduces a new approach at investigating the surface chemistry of the very small and numerous objects that constitute the bulk of the TNO and centaur populations. This innovative method has the potential to provide constraints for irradiation theories and for models of dynamical and chemical evolution of the Solar System.

On 29 November 2011 UT, 2060 Chiron occulted a R = 14.9-mag star; data were successfully obtained at the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea and 2-m Las Cumbres Observatory Global Telescope Network (LCOGT) Faulkes Telescope North (FTN) at Haleakala. The MORIS lightcurve shows a solid-body detection of Chiron’s nucleus with a chord duration of 16.0±1.4 s, corresponding to a chord length of 158±14 km. Symmetric, dual extinction features in the FTN light curve indicate the presence of optically thick material roughly 300 km from the body midpoint. The duration of the features indicates a 3±2 km feature separated by 10–14 km from a second 7±2 km feature. The symmetry, optical thickness, and narrow size of these features allow for the intriguing possibility of a near-circular arc or shell of material.

The Centaurs are a population of small, planet-crossing objects in the outer solar system. They are dynamically short-lived and represent the transition population between the Kuiper belt and the Jupiter family short-period comets. Dynamical models and observations of the physical properties of the Centaurs indicate that they may have multiple source populations in the trans-Neptunian region. It has been suggested that the inclination distribution of the Centaurs may be useful in distinguishing amongst these source regions. The Centaurs, however, undergo many close encounters with the giant planets during their orbital evolution; here we show that these encounters can substantially determine the inclination distribution of the Centaurs. Almost any plausible initial inclination distribution of a Kuiper belt source results in Centaurs having inclinations peaked near 10-20 degrees. Our studies also find that the Kuiper belt is an extremely unlikely source of the retrograde Centaur that has been observed., 21 pages, 9 figures, accepted for publication in Icarus

During the last 10 years, the FORS instrument of the ESO very large telescope was regularly used to obtain broadband linear polarization measurements of small bodies of the solar system. In particular, FORS was the first (and so far unique) instrument that allowed us to explore polarimetrically objects of the solar system other than planets, moons, asteroids, and active comets. From 2002 to 2010, more than 150 h of telescope time were allocated for the observations of Centaurs, trans-Neptunian objects, and cometary nuclei. With a R magnitude between 16 and 21, these targets are probably the faintest objects of the solar system ever observed in polarimetric mode. In addition to these objects, polarimetric measurements were obtained for asteroids, active comets, Mars, the Saturn moon Iapetus, and the Moon earthshine. Here we present a review of these measurements, from the strategies adopted for the observations to the observational results.

In order to study the statistical characters and physical significance of the color indexes and orbital parameters of Centaurs, we have analyzed the color and orbit parameter correlations by using statistical methods according to the known color indexes of 39 Centaurs and their respective orbital parameters. We find that all the correlations of B − V vs. V − R , V − R vs. R − I , B − V vs. R − I and B − R vs. R − I are strong. The Centaurs exhibit obvious redblue double-color property, and the point of demarcation is close to B − R = 1.4. The distributions of the various color indexes of Centaurs exhibit the normal distribution. For the correlations between colors and orbital parameters, except for the weak correlations between B − V and the orbital inclination i as well as between V − R and the orbital semi-major axis a , no evident correlation has been found between color indexes and orbital parameters.

We observed Phoebe for 13 nights over a period of 55 days before, during, and after the 2005 Saturn opposition with the New Mexico State University (NMSU) 1-m telescope at Apache Point Observatory (APO) in Sunspot, NM and characterized the width and magnitude of Phoebe’s opposition surge in BVRI filters. Our observations cover a phase angle range of 4.87° to 0.0509°. We use a Hapke reflectance model incorporating shadow hiding and coherent backscatter to investigate the wavelength dependence of Phoebe’s opposition surge. We find a significant opposition surge magnitude of 55–58% between phase angles of 5° and 0°. We find the strongest opposition surge for phase angles less than 2° in the I-band. The coherent backscatter angular width is on the order of 0.50°. We find Phoebe’s albedo to be spectrally flat within our error limits, with a B-band albedo of 0.0855 ± 0.0031, a V-band albedo of 0.0856 ± 0.0023, an R-band albedo of 0.0843 ± 0.0020, and an I-band albedo of 0.0839 ± 0.0023. We compare Phoebe’s albedo, color, and opposition surge magnitudes and slopes with those of other outer solar system bodies and find similarities to Centaurs, Nereid, Puck, and Comets 19P/Borrelly, 9P/Tempel 1, and 81P/Wild 2. We find that this comparison supports the idea that Phoebe originated in the Kuiper Belt. We also discuss the caveats of using results from a Hapke reflectance model to derive specific surface particle properties.

The mythology of the Greeks and Romans is full of monsters of fiction: giants, cyclops, centaurs, hydras, Gorgons… The accounts of travelers, reproduced in the Natural History of Pline l'Ancien reported the existence, in distant countries, of men with a dog's head (baboons), of men with a single tall foot (sciapode), beings whose face is embedded in the chest (or acephala blemmyes), to which must be added a wide variety of men with no mouth, no nose, or equipped with giant ears or feet turned backwards, as well as hermaphrodites. Teratology reports on monstrous births, which have constituted the factual basis from which the imagination conceived adults whose morphology corresponds to the monsters of legend. Newborns sirenomelia were behind the legend of sciapode and sirens. Cyclopia have inspired the legend of the cyclops. Anencephaly probably explains the description of headless or blemmyes. The genesis of the legend of baboons may have multiple origins: firstly the existence of people suffering from congenital hypertrichosis, on the other hand, the influence of Egyptian mythology where the god Anubis has a dog's head. The acardiac fetus may explain some monstrous forms, features the work of Hieronymus Bosch. The significance of the monsters of legend, their genesis, their persistence through the ages is complex. By approaching teratology, we added a new field of exploration of real monsters of antiquity and Middle Ages.

The Eurybates family is a compact core inside the Menelaus clan, located in the L4 swarm of Jupiter Trojans. Fornasier et al. (2007) found that this family exhibits a peculiar abundance of spectrally flat objects, similar to Chiron-like Centaurs and C-type main belt asteroids. On the basis of the visible spectra available in literature, Eurybates family's members seemed to be good candidates for having on their surfaces water/water ice or aqueous altered materials. To improve our knowledge of the surface composition of this peculiar family, we carried out an observational campaign at the Telescopio Nazionale Galileo (TNG), obtaining near-infrared spectra of 7 members. Our data show a surprisingly absence of any spectral feature referable to the presence of water, ices or aqueous altered materials on the surface of the observed objects. Models of the surface composition are attempted, evidencing that amorphous carbon seems to dominate the surface composition of the observed bodies and some amount of silicates (olivine) could be present., 23 pages, 2 figures, paper accepted for publication in Icarus

We study the origin of the Jupiter-family comets. We focus our attention on the part of the scattered disk where the perihelion distance is in the interval from 35 to 40 AU, considering this region as a source, from which the comets start their migration to the Jupiter family. To be more specific, we perform a numerical simulation of the dynamical evolution of 5179 massless test particles, which represent the objects in the scattered disk. The simulation maps the routes of the transit from the orbital phase-space of the scattered disk to that of the Jupiter-family comets. We predict the dynamical structure of this population. Some predicted dynamical properties of the group are compared with the observed Jupiter-family comets.

The history of “comet families”, in particular the Jupiter comet family, is reviewed, together with ways in which the Jupiter family has been defined. New criteria are proposed, particularly with regard to distinguishing Jupiter-family comets (JFCs) from centaurs. The effect of nongravitational forces on JFCs is also discussed.

Our current understanding of split, Jupiter-family comets is reviewed. The focus is on what recent studies of comets have told us about the nature of the splitting phenomenon. The goal is to not repeat the information given in recent reviews of split comets, but to build upon it. In particular, we discuss comets that have suffered splitting or fragmentation events in the past few years. These include comets (a) 57P/du Toit-Neujmin-Delporte, observed with a long train of fragments in 2002; (b) 73P/Schwassmann-Wachmann 3, which split in 1995 and was extensively studied during its relatively close passage to Earth in 2006, during which dozens of fragments were discovered and studied; and (c) 174P/Echeclus, a Centaur and potentially future JFC, which split in late 2005 and was the first such Centaur observed to do so. We also discuss recent observations by SOHO of split comets that are likely of short-period. The Spitzer Space Telescope has observed many JFCs and provided us with unprecedented detailed views of cometary debris trails, which may be thought of as a middle ground between "normal" ejection of micron-sized dust grains and the cleaving off of meter-to-kilometer sized fragments. We will also discuss potential breakthroughs in studying splitting JFCs that may come from future surveys., 29 pages, 6 figures, to be published in Planetary and Space Science

International audience; We present in this work the observations performed with SINFONI in the framework of a new ESO-Large Program (2006-2008) on Trans-Neptunian Objects (TNOs) and Centaurs. We obtained 21 near-infrared (1.49 to 2.4 microns) spectra of high quality, including 4 spectra of objects never observed before. We search for the presence of features due to ices, particularly water ice. Eris is the only object showing deep methane ice absorption bands. The spectra of 4 objects are featureless, and 6 others show clearly the presence of water ice. For 7 objects, the detections are more ambiguous, but absorption bands could be embedded in the noise. The 3 remaining spectra are too noisy to draw any reliable conclusion. The possible amount of water ice on each object's surface has been computed. The analysis shows that some objects present strong compositional heterogeneities over the surface (e.g. Chariklo), while some others are completely homogeneous (e.g. Quaoar).

The extremely red colors of some transneptunian objects and Centaurs are not seen among the Jupiter family comets which supposedly derive from them. Could this mismatch result from sublimation loss of colorless ice? Radiative transfer models show that mixtures of volatile ice and nonvolatile organics could be extremely red, but become progressively darker and less red as the ice sublimates away., Comment: 10 pages, 2 figures, accepted for publication in Icarus

We analyze the Centaur population as a group of objects with perihelion distances (q) of less than 30 AU and heliocentric distances outside the orbit of Jupiter, formed by objects entering this region from the Scattered Disk (SD). We perform a numerical integration of 95 real Scattered Disk Objects (SDOs) extracted from the Minor Planet Center database and of 905 synthetic SDOs compensating for observational biases. SDOs have in the Centaur zone a mean lifetime of 72 Myr, though this number falls with a decrease of q. After this incursion, 30% of them enter the zone interior to Jupiter's orbit. We find that the contribution to the Centaur population from the SD gives a total of ∼ 2.8 × 108 Centaurs with a radius R > 1 km. We also propose a model for the intrinsic distribution of orbital elements of Centaurs and their distance and apparent magnitude distribution. © 2007 Elsevier Inc. All rights reserved. Fil: Di Sisto, Romina Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina Fil: Brunini, Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina

The orbital structure of trans-neptunian objects (TNOs) in the trans-neptunian belt (Edgeworth–Kuiper belt) and scattered disk provides important clues to understand the origin and evolution of the Solar System. To better characterize these populations, we performed computer simulations of currently observed objects using long-arc orbits and several thousands of clones. Our preliminary analysis identified 622 TNOs, and 65 non-resonant objects whose orbits penetrate that of at least one of the giant planets within 1 Myr (the centaurs). In addition, we identified 196 TNOs locked in resonances with Neptune, which, sorted by distance from the Sun, are 1:1 (Neptune trojans), 5:4, 4:3, 11:8, 3:2, 18:11, 5:3, 12:7, 19:11, 7:4, 9:5, 11:6, 2:1, 9:4, 16:7, 7:3, 12:5, 5:2, 8:3, 3:1, 4:1, 11:2, and 27:4. Kozai resonant TNOs are found inside the 3:2, 5:3, 7:4, and 2:1 resonances. We present detailed general features for the resonant populations (i.e., libration amplitude angles, libration centers, Kozai libration amplitudes, etc.). Taking together the simulations of Lykawka and Mukai [Lykawka, P.S., Mukai, T., 2007. Icarus 186, 331–341], an improved classification scheme is presented revealing five main classes: centaurs, resonant, scattered, detached and classical TNOs. Scattered and detached TNOs (non-resonant) have q (perihelion distance) q > 40 AU , respectively. TNOs with 37 AU q 40 AU occupy an intermediate region where both classes coexist. Thus, there are no clear boundaries between the scattered and detached regions. We also securely identified a total of 9 detached TNOs by using 4–5 Gyr orbital integrations. Classical objects are non-resonant TNOs usually divided into cold and hot populations. Their boundaries are as follows: cold classical TNOs ( i ⩽ 5 ° ) are located at 37 AU a 40 AU ( q > 37 AU ) and 42 AU a 47.5 AU ( q > 38 AU ), and hot classical TNOs ( i > 5 ° ) occupy orbits with 37 AU a 47.5 AU ( q > 37 AU ). However, a more firm classification is found with i > 10 ° for hot classical TNOs. Lastly, we discuss some implications of our classification scheme comparing all TNOs with our model and other past models.

Here we estimate the regions of stability, fragmentation, and destruction for cometary bodies versus rotational breakup in the radius–rotational period plane. By testing different plausible physical models of the cometary nucleus equation of state, we show that the plane is divided into 3 segments: the allowed, damaged, and forbidden regions. We then compare the location of well-observed comets with respect to the separation lines. The range of constituent material parameters from the literature for cometary nuclei are used to show that all the observed comets lie in the allowed region, except for Comet C/1995 O1 (Hale–Bopp), which resides in the damaged region (where the body is fractured and only held together gravitationally). We speculate that the extremely high activity demonstrated by Comet Hale–Bopp during the 1997 apparition may have been due to its highly fractured state. Comet Hyakutake, observed to emit fragments at perigee in 1996, may be near the boundary of the damaged region. Comet C/1999 S4 (LINEAR) was solidly in the rotationally allowed region, making its disintegration in July 2000 due to centrifugal forces unlikely. In contrast to the comets, the centaurs do not cluster in the allowed region, with the majority falling instead into the rotationally damaged and forbidden regions. The centaurs are only stable against breakup assuming much stronger solid water ice properties, strongly suggesting that on the whole, these bodies have different bulk physical properties than cometary nuclei.

Accurate absolute optical magnitude values ( H V and H R ) for Kuiper belt objects (KBOs) and Centaurs are becoming increasingly important as observations in other wavelengths, particularly SIRTF thermal infrared measurements, become available for large samples of objects. We present accurate H V and H R values for 90 KBOs and Centaurs, based on our published optical photometry. We find that our H V values are in good agreement with those available from the European photometric survey of minor bodies in the outer Solar System. Comparison with H V values from the JPL Horizons database and the Minor Planet Center database shows that these sources are systematically brighter than ours by about 0.3 mag.

We present optical photometry of the Centaur 5145 Pholus during 2003 May and 2004 April using the facility CCD camera on the 1.8-m Vatican Advanced Technology Telescope on Mt. Graham, Arizona. We derive a double-peaked lightcurve and a rotation period of 9.980 ± 0.002 h for Pholus, consistent with periods of 9.9825 ± 0.004 and 9.9823 ± 0.0012 h by Buie and Bus (1992, Icarus 100, 288–294) and Farnham (2001, Icarus 152, 238–245). We find a lightcurve peak-to-peak amplitude of 0.60 mag, significantly larger than peak-to-peak amplitude determinations of 0.15 and 0.39 mag by Buie and Bus and Farnham. We use the three observed amplitudes and an amplitude-aspect model to derive four possible rotational pole positions as well as axial ratios of a / b = 1.9 and c / b = 0.9 . If we assume an albedo of 0.04, we find Pholus has dimensions of 310 × 160 × 150 km . If we assume Pholus is a strengthless rubble-pile and its non-spherical shape is due to rotational distortion, our axial ratios and period measurements indicate Pholus has a density of 0.5 g cm−3, suggestive of an ice-rich, porous interior. By combining B-band and R-band lightcurves, we find B − R = 1.94 ± 0.01 and any B − R color variation over the surface of Pholus must be smaller than 0.06 mag (i.e., much smaller than the 1.0 B − R 2.0 range seen among the Centaur and Kuiper belt object populations). By combining our V − R measurements with values in the literature, we find no evidence for any color variegation between the northern and southern hemispheres of Pholus. Observations of the Kuiper belt object 2004 DW (90482) over a time interval of seven hours show no color variation Our observations add to the growing body of evidence that individual Centaurs and KBOs exhibit homogeneous surface colors and hence gray impact craters on radiation reddened crusts are probably not responsible for the surprising range of colors seen among the Centaur and Kuiper belt object populations.

We present here the latest B − V , V − R , and R − I color measurements obtained with the CFH12K mosaic camera of the 3.6-m Canada–France–Hawaii Telescope (CFHT). This work is the latest extension of the Meudon Multicolor Survey (2MS) and extends the total number of Centaurs and trans-neptunian objects (TNOs) in the dataset to 71. With this large and homogeneous dataset, we performed relevant statistical analyses to search for correlations with physical and orbital parameters and interrelations with related populations (cometary nuclei and irregular satellites). With a larger dataset, we confirm the correlations found for the Classical TNOs in our previous survey: some colors are significantly correlated with perihelion distance and inclination. The only exception is with the eccentricity. However, results strongly depend on which objects are considered Classicals, and with a dynamically more restricted definition these correlations are no longer present. We also find that strongly significant trends with orbital parameters are not detected for Centaurs, Plutinos or scattered disk objects (SDOs). We also make for the first time reliable statistical comparison between TNOs and related populations (e.g., Centaurs, irregular satellites, short period comets—i.e., SPCs). We find that (1) the colors of SPCs do not match either their TNO or Centaur precursors, and this suggests that some process modifies the surface of SPCs at entry into the inner Solar System. The only exception concerns colors of SDOs from which we could statistically assess that SPCs and SDOs could be drawn from a same single parent distribution. (2) Not surprisingly, Centaurs are compatible with each of the Edgeworth–Kuiper belt dynamical groups at a highly significant level except with the SDOs. (3) Centaurs' colors still present a strong dichotomy between a neutral/slightly red group (e.g., Chiron) and a very red group (e.g., Pholus). (4) The irregular satellite population is not compatible with any of the Centaur, Plutino or Classical populations; however, the similarity of their color properties with SDOs suggests that both groups can be extracted from the same parent distribution. However, due to the small number of Centaurs and SDOs these conclusions cannot be taken as definitive.

The programs of observations of Solar System bodies conducted in the first year of the operation of the Spitzer Space Telescope as part of the Guaranteed Observing Time allocations are described. Initial results include the determination of the albedos of a number of Kuiper Belt objects and Centaurs from observations of their flux densities at 24 and 70 microns, and the detection of emission bands in the spectra of several distant asteroids (Trojans) around 10 and 25 microns. The 10 Kuiper Belt objects observed to date have albedos in the range 0.08 - 0.15, significantly higher than the earlier estimated 0.04. An additional KBO [(55565) 2002 AW(sub l97)] has an albedo of 0.17 plus or minus 0.03. The emission bands in the asteroid spectra are indicative of silicates, but specific minerals have not yet been identified. The Centaur/comet 29P/Schwassmann-Wachmann 1 has a nucleus surface albedo of 0.025 plus or minus 0.01, and its dust production rate was calculated from the properties of the coma. Several other investigations are in progress as the incoming data are processed and analyzed.

International audience; We report 43 new visible colors of Centaurs and TNOs, obtained at NTT and VLT telescopes under the "ESO large program on physical properties of Centaurs and TNOs." Merging these new measurements with those obtained during the first part of the program (Boehnhardt et al., 2002, Astron. Astrophys. 395, 297-303) and the "Meudon Multicolor Survey" (Doressoundiram et al., 2002, Astron. J. 124, 2279-2296) we have a unique dataset of 109 objects. We checked for correlations and trends between colors, physical and orbital parameters, carrying out an analysis based on Monte Carlo simulation to account for observational error bars. Centaurs show no evidence for correlation between V- R vs. R- I colors which raises the hypothesis that more than one single coloring process might be acting on their surfaces. Classical objects seem to be composed of two different color populations: objects with i4.5° display the whole range of colors from blue to very red. The possibility that the low inclined population is misguiding global conclusions is analyzed. Classical objects also show a stronger color-perihelion correlation for intrinsically brighter objects, corresponding to critical estimated sizes of different formation/evolutionary histories. Scattered disk objects show color resemblances with the classical objects at i>12°, hence surface reflectivities resemblances, pointing to a common origin. No color-aphelion trend is found for SDOs, as expected from the intense irradiation by galactic cosmic-rays beyond the solar wind termination shock. Plutinos show a color-absolute magnitude trend, in which all the intrinsically faintest objects are blue. We see many red Plutinos in highly inclined and highly eccentric orbits, that should have originated in a primordial inner disk under Gomes (2003, Icarus 161, 404-418) migration scenario. This seems to invalidate the assumption that objects originated in this inner disk are mainly blue. Finally, we also find six candidates for light-curve studies: four objects (1998 WU 31, 1999 OE 4, 1999 OX 3, and 2001 KP 77) present significant short term R-magnitude variability, and two objects (1999 XX 143 and 2000 GP 183) evidence possible color variations with rotation.

Reflectance spectroscopy of Solar System bodies provides a rich source of information on their compositions (minerals, ices, metals, and macromolecular carbon-bearing materials). Models calculated with radiative transfer theories for the spectral distribution of diffusely scattered sunlight from planetary surfaces yield information on the compositions, abundances, physical states, layering, and particle microstructure of those surfaces. We discuss and evaluate the scattering theories of Hapke and Shkuratov that are widely used for modeling the reflectance spectra and color data for Kuiper Belt objects, Centaur objects, and other airless bodies in the Solar System. Both theories yield good models of the reflectance spectrum of Centaur 5145 Pholus using five components (ices, carbon, a silicate mineral, and a complex organic material), although the derived abundances differ widely. To cite this article: D.P. Cruikshank et al., C. R. Physique 4 (2003).

Trans-Neptunian Objects (TNOs) and Centaurs display the widest colour range among solar system objects. Moreover, recent observational results revealed: (1) the existence of a family of classical TNOs (also called Cubewanos) with very red colours in dynamically ‘cold’ orbits beyond about 40 AU from the Sun; and (2) a few correlations among the dynamically ‘hot’ Cubewanos. Other TNO populations and the Centaurs show no obvious and systematic trends. The article describes the observations and reduction techniques applied for the photometry of these distant and faint solar system objects and provides a brief overview on the results and their links with formation and evolution scenarios of these primitive bodies in the outer solar system. To cite this article: A. Doressoundiram, H. Boehnhardt, C. R. Physique 4 (2003).

We present observations of the Centaur (32532) 2001 PT13 taken between September 2000 and December 2000. A multi-wavelength lightcurve was assembled from V-, R- and J-band photometry measurements. Analysis of the lightcurve indicates that there are two peaks of slightly different brightness, a rotation period of 0 .34741 ± 0.00005 day, and a maximum photometric range of 0.18 mag. We obtained VRJHK colors (V–R = 0.50 ± 0.01, V–J = 1.69 ± 0.02, V–H = 2.19 ± 0.04, and V–K = 2.30 ± 0.04) that are consistent with the grey KBO/Centaur population. The V–R color shows no variation as a function of rotational phase; however, we cannot exclude the possibility that rotational variations are present in the R–J color. Assuming a 4% albedo, we estimate that 2001 PT13 has an effective diameter of 90 km and a minimum axial ratio a/b of 1.18. We find no evidence of a coma and place an upper limit of 15 g s −1 on the dust production rate.

From the basic laws of physics one can deduce the Jeans empirical rule, which should preferably be called the Jeans rule. Its representations in velocity, height and energy are completely equivalent and may be arbitrarily chosen. This rule is most easily interpreted in terms of energy. The Jeans rule merely provides a necessary condition for the particles to be the main atmospheric constituent of a planet or satellite with a dense atmosphere. Its range of applicability can be expressed by equations or figures, or by a nomogram. It is applicable to planets, satellites, asteroids and meteoric bodies in the solar system, as well as to some objects in the outer solar system, such as the objects in the Kuiper belt and the Centaurs. This rule still possesses a general and realistic significance even at present day.

The results of photometric observations of Centaur object Chiron carried out at the Observatorio do Pico dos Dias (OPD, Brazil), the Estacion Astrofisica de Bosque Alegre (EABA, Argentina), and Complejo Astronomico El Leoncito (CASLEO, Argentina) from 1997 to 2001 are presented here. The analysis of the photometric data shows that the brightness of Chiron reached a minimum value in 1999 and began increasing again in 2000. The absolute magnitude, HV, varied from 7.26 in June 1999 to 5.78 in April 2001. The data tend to indicate that Chiron is starting a new outburst of activity which is compatible with a sporadic cometary behavior not related to heliocentric distance.

2060 Chiron (95P/Chiron) is the first known object of the entire class called Centaurs. Since the day of the discovery many papers have discussed its past and future fates. Up to now, Centaurs were perceived as a evolutionary stage between Kuiper Belt Objects and the Jupiter Family comets. Other types of dynamical evolution were not widely discussed in previous works. This paper shows there is a possibility that Chiron's and other Centaurs present orbits can evolve into Halley Type comets orbits and this type of dynamical evolution is significant.

We are continuing our photometric survey of the trans-neptunian and Centaur populations started in 1997. We report multicolor photometry for 17 objects. With these results combined with previous data (M. A. Barucci, A. Doressoundiram, M. Fulchignoni, D. Tholen, and M. Lazzarin 1999. Icarus 142 , 476–481; M. A. Barucci, J. Romon, A. Doressoundiram, and D. Tholen 2000. Astron. J. 120 , 496–500), we have at our disposal a homogeneous and high-quality set of color indices for 29 objects, numerous enough to make significant studies. The color–color diagrams confirm the wide and continuous spread of colors in the trans-neptunian object population. This diversity may be explained by the combined action of space weathering and collisional resurfacing. We do not find any correlation of colors with size or heliocentric distance, but we note an excess of red objects for perihelion distance greater than 40 AU. Furthermore, our results suggest also that highly inclined (e.g., i >17°) and eccentric objects are preferentially neutral. These objects may have suffered more collisional resurfacing than others.

We present observations of the Centaur 5145 Pholus from January 2000 to August 2000. A rotational lightcurve was assembled from both V and R measurements, confirming previous period determinations of 0.416 day but exhibiting an amplitude over twice as high as previously measured. This lightcurve was then used in conjunction with previously published lightcurves to solve for a north pole position of λ0=149°, β0=+26° (prograde rotation), and a sidereal period of 0.4159256±0.0000016 day. As part of this analysis, the axial ratios of Pholus were found to be a/b=1.8 and b/c=1.0. Color analyses of the data give an average V−R color of 0.71±0.03, which is slightly lower than the 0.75–0.84 range previously seen. This difference, combined with the fact that we see color variations as a function of rotation, suggest that Pholus' northern hemisphere contains bluer features than are seen in its southern hemisphere.

The detection and observation of satellites of the small bodies orbiting the Sun in the outer Solar System is extremely important in order to determine the orbit and masses of the components in the binary system as well as to know their sizes to derive their mean bulk density. This note provides a formal estimation of the possible separation distances, orbital periods, and apparent brightnesses of possible satellites of the objects in the inner region of the Edgeworth–Kuiper Belt.

A near-infrared spectrum of Neptune's satellite Nereid was obtained at the Keck Observatory on 1997 May 1. The spectrum shows two absorptions near 1.54 and 2.03 μm and is well matched by a synthetic spectrum of an intimate mix of low-temperature, particulate water ice and dark, blue-colored material. Comparisons of Nereid's spectrum with those of other objects such as the Centaurs 1997 CU 26 and 5145 Pholus, and Neptune's largest regular satellite Proteus, admit the possibility that Nereid is a primordial satellite of Neptune (and perhaps its only remaining one) rather than a captured object, but more data are needed to rule out one scenario or the other.

The cometary activity of Chiron inspires us to investigate observable lifetimes of hypothetical dust particles around large, distant Centaur and Kuiper Belt objects (KBOs). Our model computes dust particle trajectories assuming comet nucleus gravity, solar gravity, and solar radiation pressure. We find that particle lifetimes are extremely sensitive to the magnitude of the initial velocity. Long-lived orbits require an exact combination of nucleus size, heliocentric distance, particle size, and initial velocity. Estimating ejection velocities due to CO sublimation, we find that particles escape >50,000 km from Centaurs in ≲6 days and from KBOs in ≲10 days. Assuming optimal ejection velocities

We present visible and near-infrared broadband photometry of the Centaur objects 1995 GO and 5145 Pholus. Our data confirm the extremely redV−Jcolor and nearly solarJ−HandH−Kcolors of 5145 Pholus. OurV−Jdata reveal that 1995 GO is as red as the reddest D-type asteroid, 1748 Mauderli, but not nearly as red as 5145 Pholus. We suggest that the red color of 1995 GO is probably due to the presence of organic-rich materials produced by eons of particle bombardment and ultraviolet irradiation of surface grains, a process that may be widespread among the Centaur and trans-neptunian object populations. We show that theV−Jdata for the Centaurs suggest thatV−Jincreases with increasing semimajor axis. If this correlation is correct, then the red colors of the Centaurs 5145 Pholus and 1993 HA2may be typical of fairly pristine Centaur objects. In contrast, the progressively less red colors of 1995 GO and 2060 Chiron may be the result of an increased rate of resurfacing of these objects as they migrate progressively closer to the Sun.

Spacewatch was the first large-scale astronomical survey program employing automated and real-time software for moving object detection. The search has resulted in the discovery of three new Centaurs and a serendipitous detection of (2060) Chiron. We have determined the efficiency of the Spacewatch system as a function of an object's apparent visual magnitude and rate of motion. Convolving these efficiencies with the scanning pattern of the telescope and a theoretically motivated orbital distribution for the Centaurs allows us to determine the system's efficiency as a function of their absolute magnitude. The efficiency is nonzero in the range −4

We present new CCD photometry of the Centaur object 1995 GO obtained in April 1996, including a lightcurve, a V − R color, and a surface brightness profile. The apparent brightness implies a circular effective radius of 53.5 km, assuming a 4% albedo. The shape of the lightcurve is compatible with an aspherical rotating body, with a rotation period of 8.870 ± 0.020 hr. No evidence of cometary activity was found in the observations, allowing us to place an upper limit of 3 kg sec −1 on the mass loss rate in 1995 GO. We measure the colors V − R = 0.73 ± 0.04 and B − V = 0.78 ± 0.05, which fall within the previously reported color range for Centaurs and Kuiper Belt objects.

We model the collisional evolution of Trojan asteroids using a numerical code which combines recent calculations of the intrinsic collision probabilities and impact speeds in the Trojan swarms (Marzariet al.1996) with our current understanding of the outcomes of high-velocity collisions between asteroid-sized bodies. Using plausible collision parameters and energy scaling of impact strength with size, we obtain a good match to the present Trojan population, as inferred by Shoemakeret al.(1989). The steep slope of the current Trojan size distribution at diameters larger than about 50–100 km is essentially unaltered by the collisional process and must reflect the formative processes of these bodies. At smaller sizes, collisions have produced a power law size distribution having a slope characteristic of collisionally relaxed populations. Hence, we cannot distinguish whether the small-size end of the distribution was formed before or after the disruptive collisional regime characteristic of the present Trojan environment was established. The formation of prominent dynamical families in the Trojan swarms is a natural outcome of the collisional process; their number may allow us to constrain the degree of collisional evolution that has occurred in the Trojans. Finally, we find that Trojan collisional debris escaping from the libration regions and ending up into cometary orbits could supply ≈10% of the current population of short-period comets and Centaur asteroids. Whether this occurs depends on the dynamical lifetime of such bodies and whether they contain enough volatiles to become active comets.

The Cassini mission to Saturn will start a second phase in the exploration of the Saturnian system, after the historical Voyager flybys of Saturn in 1980 and 1981. The Cassini primary mission is scheduled to be launched in October 1997 by the Titan IV/Centaur. Cassini uses four planetary gravity-assist flybys to gain the energy necessary to reach Saturn in July 2004. This arrival date at Saturn provides a unique opportunity for a flyby of Saturn's outer satellite Phoebe on the final approach. This paper provides an overview of the processes involved in the interplanetary trajectory design and analysis of the Cassini mission to Saturn.

The Pastoral Symphony episode in Disney’s Fantasia depicts scenes from domestic life as realized by various mythological creatures: child-rearing and play, courtship, wine-making and celebration, mutual aid and protection, and sleep. Gods are ‘played’ by human-form characters one of which, Bacchus, is central to the episode. Humans are played both by animal-human hybrids (centaurs and fauns) and by animal hybrids (flying horses, unicorns). Bacchus is accompanied by a Disney-invented hybrid, a unicorn donkey. Patterns of oral and sexual imagery are arranged in ring-form structure that runs in counterpoint to a typical cumulative dramatic structure, which is built on a contrast between the Dionysian mode of the central Bacchanal and the more Apollonian conclusion, where all’s right with the world and everything is in it’s place. The poetic function, as described by Roman Jakobson, governs various transformations and displacements that structure the visual and sonic materials in such a way that the episode has something of a ‘meta’ quality of being art about art, with Bacchus as a figure for the artist.

Two NASA-sponsored cost-constrained mission implementations for the exploration of Pluto are described. One is the Pluto Fast Flyby (PFF) mission, which utilizes an 83 kg spacecraft to be launched in 1998 aboard a Titan IV (Solid Rocket Motor Upgrade)/Centaur) for an about 7-year-long direct trajectory to Pluto, which will carry an integrated CCD-imaging/UV spectrometer, with a possible integrated IR spectrometer. The other is the Pluto-350 spacecraft, weighing about 316 kg, which will carry a broader instrument set, greater redundancy, and which will require greater than 11 year flight time. Pluto-350 will be launched in 2001 aboard a Delta or Atlas, toward earth and Jupiter swingbys to provide the energy to reach Pluto.

We present a reflectance spectrum of 2060 Chiron over the wavelength range 1.6–2.2 μm. The 2-μm water ice absorption feature seen in several other Centaurs at λ=2.03 μm is identified at the 5% level below the continuum.

"I swear by Apollo the physician, by Aesculapius, Hygeia, and Panacea, and I take to witness all the gods, all the goddesses...." Thus begins the Hippocratic oath, taken by all physicians; Apollo was the chief god of healing in the Greek Pantheon. His far-reaching arrows inflicted plagues and epidemics on humankind. Arrows shot at mortals symbolized sudden death not only in Greece but also in other civilizations. Apollo was the most revered and influential of all the Greek gods. His father was Zeus, and his mother was Leto. Apollo apparently was of foreign origin, coming either from somewhere north ofGreece or from Asia. Traditionally, however, Apollo and his twin sister, Artemis, were born on the isle ofDelos (a small island in the south Aegean Sea). From there, Apollo went to Pytho (Delphi), where he slew Python, the female dragon who guarded the region. At Delphi, Apollo established his greatest oracular shrine. Other shrines of Apollo existed on the Greek mainland, at Delos, and in Anatolia (the part of Turkey that is the peninsula of Asia Minor). As Homer relates, Apollo was physician to the Olympian gods, whose wounds or diseases he cured by means of the root of the peony. This cure inspired the name "Paean" and the epithet "sons ofPaean" that has been applied to physicians. In time, Apollo became identified as the god ofhealing and as the father (by Coronis) of Aesculapius, the god of medicine. According to legend, a knowledge of medicine was communicated by Apollo and his sister Artemis to the centaur Chiron. As one skilled in music and surgery and especially versed in ancient lore, Chiron was entrusted with the rearing and education of the Greek heroes Jason, Hercules, Achilles, and Aesculapius. When Zeus had Aesculapius killed by thunderbolts for restoring Hippolytus (son of Theseus, legendary king of Athens) to life, Apollo in retaliation killed the Cyclopes (a race of giants in Greek mythology who had a single eye in the middle of their foreheads) for forging the thunderbolts. Zeus then banished Apollo from Olympus and compelled him to spend a year on earth as a mortal. During that year, he was a herdsman of cattle and horses for Admetus, king of Pherae in Thessaly (a region in eastern Greece). In the Trojan War, Apollo sided with Troy (an ancient city in northwest Asia Minor). Apollo has been featured on many Greek stamps, one of which, issued in 1959, shows a coin depicting the portrait of Apollo on one side.

In ancient mythology, not all centaurs were violent and lustful. Although their general character was that of wild, lawless, and inhospitable beings, one-Chiron-was wise and just. Chiron, the wisest of all centaurs, was the teacher of the Greek heroes Jason, Hercules, Asklepios, and Achilles. Chiron was well versed in medicine, music, prophecy, and hunting, having been raised and educated by Apollo and his wife, Artemis. Chiron was the son of the god Cronus and the sea nymph Philyra. He lived in a cave at the foot of Mount Pelion in Thessaly (a region in eastern Greece). Centaurs were a race of beings that were part horse and part man: the head, neck, and arms of a man and the body, legs, and tail of a horse. They lived in the mountains of Thessaly and Arcadia (a region in southern Greece). Traditionally, they were the offspring of Ixion, the king of the Lapiths, a Thessalian people. The centaurs were best known for their fight with the Lapiths. They lost the battle and were driven from Mount Pelion. When Chiron was accidentally pierced by a poisoned arrow shot by Hercules, he renounced his immortality in favor ofPrometheus (god offire) and was placed among the stars in the constellation Sagittarius-a southern constellation that has the form of a centaur shooting an arrow. Chiron and the centaurs have been depicted on many stamps. Chiron is shown on this stamp issued by Spain in 1956.