The production of craters on the mid-sized saturnian satelites by Centaur objects

Context. The Saturnian satellite system has been observed in detail by the Cassini-Huygens mission. These satellites present different surface features, including impact craters caused by small objects probably coming from the trans-Neptunian region. Aims. In this paper we calculate the production of craters on the mid-sized Saturnian satellites produced by Centaurs from the scattered disk (SD) and plutinos in order to determine this contribution, and we compare our estimations with the Cassini observations. Methods. We used a method developed in a previous paper that uses a numerical investigation of the dynamical evolution of Centaur objects to calculate the production of craters. We used a size-frequency distribution (SFD) of scattered disk objects (SDOs) as a power law with a break at diameters d = 60 km considering two cases for the differential power-law index: s2 = 2.5 and s2 = 3.5 for d < 60 km. Results. We calculated the number of craters, the greatest crater produced by Centaurs from the SD and plutinos, and the present cratering rate on each of the mid-sized satellites, for both cases of the SFD of SDOs considered. The contribution of plutinos is negligible compared to SDOs. From our calculations and the comparison with observations we note that the calculated number of craters for s2 = 3.5 is in general nearer the observed number. However, in general for smaller craters, the observed number is less than the calculated one. This trend can be explained by at least two mechanisms. On the one hand, this could be caused by an erasing process that gradually buries the craters, which does not affect large craters. On the other hand, the comparison of the calculated and observed crater size-frequency distribution for different size ranges implies that for d < 60 km, the SFD of SDOs is consistent with the assumed index s2 = 3.5, for d ≳ 0.2−1.4 km and for d ≲ 0.2−1.4 km, it is consistent with s2 = 2.5. Then in the range d ~ 0.2−1.4 km, the SFD of SDOs could have a new break. This change of slope could explain the reduction of small craters, at least for some cases. Conclusions. We found a good agreement when comparing our results with observations. However, independent determination of surface ages and geological processes are needed to determine if there is a new break on the SFD of SDOs, if there is a planetocentric source of craters in the Saturnian system, and which craters are primordial.Fil: Di Sisto, Romina Paula. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Astrofísica de la Plata; ArgentinaFil: Zanardi, M.. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

The production of craters on the mid-sized Saturnian satellites by Centaur objects

Context. The Saturnian satellite system has been observed in detail by the Cassini-Huygens mission. These satellites present different surface features, including impact craters caused by small objects probably coming from the trans-Neptunian region. Aims. In this paper we calculate the production of craters on the mid-sized Saturnian satellites produced by Centaurs from the scattered disk (SD) and plutinos in order to determine this contribution, and we compare our estimations with the Cassini observations. Methods. We used a method developed in a previous paper that uses a numerical investigation of the dynamical evolution of Centaur objects to calculate the production of craters. We used a size-frequency distribution (SFD) of scattered disk objects (SDOs) as a power law with a break at diameters d = 60 km considering two cases for the differential power-law index: s2 = 2.5 and s2 = 3.5 for d < 60 km. Results. We calculated the number of craters, the greatest crater produced by Centaurs from the SD and plutinos, and the present cratering rate on each of the mid-sized satellites, for both cases of the SFD of SDOs considered. The contribution of plutinos is negligible compared to SDOs. From our calculations and the comparison with observations we note that the calculated number of craters for s2 = 3.5 is in general nearer the observed number. However, in general for smaller craters, the observed number is less than the calculated one. This trend can be explained by at least two mechanisms. On the one hand, this could be caused by an erasing process that gradually buries the craters, which does not affect large craters. On the other hand, the comparison of the calculated and observed crater size-frequency distribution for different size ranges implies that for d < 60 km, the SFD of SDOs is consistent with the assumed index s2 = 3.5, for d ≥ 0.2-1.4 kmand for d ≤ 0.2-1.4 km, it is consistent with s2 = 2.5. Then in the range d ~ 0.2-1.4 km, the SFD of SDOs could have a new break. This change of slope could explain the reduction of small craters, at least for some cases. Conclusions. We found a good agreement when comparing our results with observations. However, independent determination of surface ages and geological processes are needed to determine if there is a new break on the SFD of SDOs, if there is a planetocentric source of craters in the Saturnian system, and which craters are primordial.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Origin of craters on Phoebe: Comparison with Cassini's data

Context. Phoebe is one of the irregular satellites of Saturn. The images taken by the Cassini-Huygens spacecraft have allowed us to analyze its surface and the craters on it. Aims. We study the craters on Phoebe produced by both Centaur objects from the scattered disk (SD) and plutinos that have escaped from the 3:2 mean motion resonance with Neptune and compare our results with the observations by Cassini. Methods. We use previously developed simulations of trans-Neptunian objects and a method that allows us to derive the number of craters and the cratering rate on Phoebe. Results. We determine the number of craters and the largest crater on Phoebe produced by Centaurs in the present configuration of the solar system. We obtain a present normalized rate of encounters of Centaurs with Saturn of F = 7.1 × 10-11 per year, from which we can infer the current cratering rate on Phoebe for each crater diameter. Conclusions. Our study and comparison with observations suggest that the main crater features on Phoebe are unlikely to have been produced in the present configuration of the solar system but that they must have been created instead when the SD were depleted in the early solar system. If this is indeed what happened and the craters were produced when Phoebe was a satellite of Saturn, then it must have been captured, very early on in the evolution of the solar system.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Surface ages of mid-size Saturnian satellites

The observations of the surfaces of the mid-sized saturnian satellites made by Cassini–Huygens mission have shown a variety of features that allows study of the processes that took place and are taking place on those worlds. Research of the saturnian satellite surfaces has clear implications not only for Saturn’s history and Saturn’s surroundings, but also for the Solar System. Crater counting from high definition images is very important and could serve for the determination of the age of the surfaces. In a recent paper, we have calculated the production of craters on the mid-sized saturnian satellites by Centaur objects considering the current configuration of the Solar System. Also, we have compared our results with crater counts from Cassini images by other authors and we have noted that the number of observed small craters is less than our calculated theoretical number. In this paper we estimate the age of the surface for each observed terrain on each mid-sized satellite of Saturn. All the surfaces analyzed appear to be old with the exception of Enceladus. However, we have noticed that since there are less observed small craters than calculated (except on Iapetus), this results in younger ages than expected. This could be the result of efficient endogenous or exogenous process(es) for erasing small craters and/or crater saturation at those sizes. The size limit from which the observed number of smaller craters is less than the calculated is different for each satellite, possibly indicating processes that are unique to each, but other potential common explanations for this paucity of small craters would be crater saturation and/or deposition of E-ring particles. These processes are also suggested by the findings that the smaller craters are being preferentially removed, and the erasure process is gradual. On Enceladus, only mid and high latitude plains have remnants of old terrains; the other regions could be young. In particular, the regions near the South Polar Terrain could be as young as 50 Myr old. On the contrary for Iapetus, all the surface is old and it notably registers a primordial source of craters. As the crater size is decreased, it would be perceived to approach saturation until DK 2 km-craters, where saturation is complete.Instituto de Astrofísica de La Plat

The production of craters on the mid-sized Saturnian satellites by Centaur objects

Context. The Saturnian satellite system has been observed in detail by the Cassini-Huygens mission. These satellites present different surface features, including impact craters caused by small objects probably coming from the trans-Neptunian region. Aims. In this paper we calculate the production of craters on the mid-sized Saturnian satellites produced by Centaurs from the scattered disk (SD) and plutinos in order to determine this contribution, and we compare our estimations with the Cassini observations. Methods. We used a method developed in a previous paper that uses a numerical investigation of the dynamical evolution of Centaur objects to calculate the production of craters. We used a size-frequency distribution (SFD) of scattered disk objects (SDOs) as a power law with a break at diameters d = 60 km considering two cases for the differential power-law index: s2 = 2.5 and s2 = 3.5 for d < 60 km. Results. We calculated the number of craters, the greatest crater produced by Centaurs from the SD and plutinos, and the present cratering rate on each of the mid-sized satellites, for both cases of the SFD of SDOs considered. The contribution of plutinos is negligible compared to SDOs. From our calculations and the comparison with observations we note that the calculated number of craters for s2 = 3.5 is in general nearer the observed number. However, in general for smaller craters, the observed number is less than the calculated one. This trend can be explained by at least two mechanisms. On the one hand, this could be caused by an erasing process that gradually buries the craters, which does not affect large craters. On the other hand, the comparison of the calculated and observed crater size-frequency distribution for different size ranges implies that for d < 60 km, the SFD of SDOs is consistent with the assumed index s2 = 3.5, for d ≥ 0.2-1.4 kmand for d ≤ 0.2-1.4 km, it is consistent with s2 = 2.5. Then in the range d ~ 0.2-1.4 km, the SFD of SDOs could have a new break. This change of slope could explain the reduction of small craters, at least for some cases. Conclusions. We found a good agreement when comparing our results with observations. However, independent determination of surface ages and geological processes are needed to determine if there is a new break on the SFD of SDOs, if there is a planetocentric source of craters in the Saturnian system, and which craters are primordial.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Surface ages of mid-size Saturnian satellites

The observations of the surfaces of the mid-sized saturnian satellites made by Cassini–Huygens mission have shown a variety of features that allows study of the processes that took place and are taking place on those worlds. Research of the saturnian satellite surfaces has clear implications not only for Saturn’s history and Saturn’s surroundings, but also for the Solar System. Crater counting from high definition images is very important and could serve for the determination of the age of the surfaces. In a recent paper, we have calculated the production of craters on the mid-sized saturnian satellites by Centaur objects considering the current configuration of the Solar System. Also, we have compared our results with crater counts from Cassini images by other authors and we have noted that the number of observed small craters is less than our calculated theoretical number. In this paper we estimate the age of the surface for each observed terrain on each mid-sized satellite of Saturn. All the surfaces analyzed appear to be old with the exception of Enceladus. However, we have noticed that since there are less observed small craters than calculated (except on Iapetus), this results in younger ages than expected. This could be the result of efficient endogenous or exogenous process(es) for erasing small craters and/or crater saturation at those sizes. The size limit from which the observed number of smaller craters is less than the calculated is different for each satellite, possibly indicating processes that are unique to each, but other potential common explanations for this paucity of small craters would be crater saturation and/or deposition of E-ring particles. These processes are also suggested by the findings that the smaller craters are being preferentially removed, and the erasure process is gradual. On Enceladus, only mid and high latitude plains have remnants of old terrains; the other regions could be young. In particular, the regions near the South Polar Terrain could be as young as 50 Myr old. On the contrary for Iapetus, all the surface is old and it notably registers a primordial source of craters. As the crater size is decreased, it would be perceived to approach saturation until DK 2 km-craters, where saturation is complete.Instituto de Astrofísica de La Plat

Evolución dinámica post escape de los asteroides Hildas

El cinturón de asteroides entre Marte y Júpiter constituye un ejemplo a menor escala del gradiente de elementos observados en los planetas del Sistema Solar. Preservan el registro de la composición y mecánica del origen del Sistema Solar. Los asteroides Hildas en resonancia 3:2 con Júpiter (∼ 4 UA), tienen alto porcentaje de materiales volátiles, son una población dinámicamente muy estable aunque colisionalmente activa, y por tanto tienen una cierta tasa de despoblación. En esta tesis estudiamos la evolución dinámica de esta población mediante simulaciones numéricas con un código simpléctico híbrido realizado por el Dr. Adrián Brunini y colaboradores y realizamos una pseudo evolución colisional. El objetivo de este trabajo es estudiar las rutas que siguen los Hildas que escapan de la resonancia y su contribución a diferentes poblaciones y procesos en el Sistema Solar.Facultad de Ciencias Astronómicas y Geofísica

Evolución dinámica post escape de los asteroides Hildas

El cinturón de asteroides entre Marte y Júpiter constituye un ejemplo a menor escala del gradiente de elementos observados en los planetas del Sistema Solar. Preservan el registro de la composición y mecánica del origen del Sistema Solar. Los asteroides Hildas en resonancia 3:2 con Júpiter (∼ 4 UA), tienen alto porcentaje de materiales volátiles, son una población dinámicamente muy estable aunque colisionalmente activa, y por tanto tienen una cierta tasa de despoblación. En esta tesis estudiamos la evolución dinámica de esta población mediante simulaciones numéricas con un código simpléctico híbrido realizado por el Dr. Adrián Brunini y colaboradores y realizamos una pseudo evolución colisional. El objetivo de este trabajo es estudiar las rutas que siguen los Hildas que escapan de la resonancia y su contribución a diferentes poblaciones y procesos en el Sistema Solar.Facultad de Ciencias Astronómicas y Geofísica

Realización, análisis y aplicaciones del archivo de placas astrométricas del Observatorio Astronómico de La Plata

La observación fotográfica de asteroides y cometas se ha llevado a cabo en el Observatorio de La Plata desde la adquisición, y puesta en funcionamiento del telescopio Astrográfico en el año 1913. Este telescopio funcionó en forma ininterrumpida hasta el año 1986, proporcionando un gran número de placas fotográficas. Durante estos años de observación el Observatorio de La Plata, ha contribuido de forma significativa en la determinación precisa de las posiciones y efemérides de asteroides y cometas. Es interesante recordar, además que se han descubierto varios asteroides en este período, como por ejemplo: (965) Angélica, (1029) La Plata, (1254) Erfodia. El telescopio dejó de utilizarse en el año 1986, debido a las malas condiciones existentes para la observación, como la luz de la ciudad de La Plata y la polución y luminosidad provocada por la planta petroquímica ubicada al Norte del Observatorio en la Localidad de Ensenada. Por otro lado las placas fotográficas se habían dejado de fabricar dando paso a las modernas técnicas de fotografía astronómica, con detectores digitales (CCD). Sin embargo, durante los más de 80 años de observación con este telescopio se obtuvo una gran cantidad de placas fotográficas de asteroides y cometas que cubren gran parte del cielo del hemisferio sur, el cual es considerablemente menos fotografiado que el norte. La importancia de este material que forma parte de la historia y trayectoria del Observatorio de La Plata motivó la realización de una clasificación del mismo, en base a las placas y cuadernos donde era registrada la información. Esta clasificación permitió realizar una base de datos con acceso por computadora y realizar un análisis a fin de obtener algunas características de nuestro archivo de placas. A partir de esta base de datos fue posible encontrar un grupo de placas cuyas posiciones no habían sido reducidas. Se redujeron estas placas con el Catálogo SAO y se publicaron los resultados. Por otro lado se seleccionó otro grupo de placas que fue reducido por primera vez con el Catálogo Hipparcos. Este mismo grupo se redujo también con el catálogo SAO 2000.0, obteniéndose además una comparación de los resultados obtenidos con ambos catálogos.Facultad de Ciencias Astronómicas y Geofísica

Las poblaciones distantes de cuerpos pequeños del Sistema Solar

In recent years, the great advance in astronomical observation and space exploration has changed our knowledge about planetary systems and particularly about our Solar System. The nding of objects of similar orlarger sizes than Pluto, beyond Neptune's orbit, asteroids and binary objects, planets and disks around other stars, are examples of these changes. The theoretical development has also advanced and there are new theories about the formation and distribution of objects in our Solar System. It has been observed that the transneptunian region has a structure that contains dynamic and physical traces of the gestation, formation and evolution processes of the Solar System. The complex interactions of these objects with the Centaur objects, typical of the giant planet zone, and with comets are crucial. In this article, we will present what we know about the populations of distant small bodies of our Solar System, the proposed models to explain the current observed distribution and their link with the comets and Centarus.En los últimos años, el gran avance en la observación astronómica y la exploración espacial ha cambiado lo que conocemos sobre los sistemas planetarios y particularmente sobre nuestro Sistema Solar. El hallazgo de objetos de dimensiones similares o más grandes que Plutón más allá de la órbita de Neptuno, asteroides y objetos binarios, planetas y discos en torno a otras estrellas, son ejemplos de estos cambios. El desarrollo teórico también ha avanzado y se cuenta con nuevas teor´ıas sobre la formación y distribución de los objetos en nuestro Sistema Solar. Se ha logrado observar que la región transneptuniana tiene una estructura que contiene en s´ı misma rastros dinámicos y f´ısicos del proceso de gestación, formación y evolución del Sistema Solar. Las complejas interacciones de estos objetos con los objetos Centauros, t´ıpicos de la zona de los planetas gigantes, y con los cometas son cruciales. En este art´ıculo, presentaremos lo que conocemos sobre las poblaciones de cuerpos peque˜nos más distantes de nuestro Sistema Solar, los modelos propuestos para explicar la distribución actual observada y su v´ınculo con los cometas y Centauros.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; Argentina61ª Reunión Anual de la Asociación Argentina de AstronomíaViedmaArgentinaUniversidad Nacional de Río NegroInstituto Argentino de Radioastronomí