J. de León

Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the Early Solar System

A spacecraft flyby of an asteroid reveals a high-density body that is more like a planetesimal than a rubble pile. Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which is seen to flow in major landslides associated with albedo variation. Its geologically complex surface, ancient surface age, and high density suggest that Lutetia is most likely a primordial planetesimal. This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles.

Origin of the near-Earth asteroid Phaethon and the Geminids meteor shower

Aims. In this paper we establish a compositional and dynamical connection between two B-type objects: main belt asteroid (2) Pallas and near-Earth asteroid (3200) Phaethon. The final purpose is to help understand the origin of this very interesting object. Methods. We first compare visible and near-infrared spectra of asteroids Phaethon and Pallas. We then compare the reflectance spectra of Phaethon with all the available visible spectra of B-type asteroids belonging to the Pallas family. One last spectral comparison is then performed to search for any correspondence between Phaethon and any B-type asteroid in the main belt. Numerical simulations are also carried out to explore the dynamical connection between the orbital neighborhoods of Pallas and Phaethon. Results. Main differences between Phaethon and Pallas lie in the visible wavelength part of their reflectance spectra. We have also found that the nine asteroids belonging to the Pallas family have visible spectra that are different from that of Pallas and strikingly similar to that of Phaethon. Spectral comparison excludes any other B-type asteroid in the main belt as a possible parent body of Phaethon. Numerical simulations establish a dynamical pathway that connects Phaethon with Pallas and its family members. Conclusions. The spectral similarities between Phaethon and Pallas family members, together with their established dynamical connection, supports Pallas as the most likely parent body of Phaethon and therefore, the associated Geminids meteor stream. We suggest that differences in asteroid sizes are the most likely explanation for the differences in the visible reflectance spectra between Phaethon and Pallas.

Testing the comet nature of main belt comets. The spectra of 133P/Elst-Pizarro and 176P/LINEAR

Context. Dynamically, 133P/Elst-Pizarro and 176P/LINEAR are main belt asteroids, likely members of the Themis collisional family, and unlikely of cometary origin. They have been observed with cometary-like tails, which may be produced by water-ice sublimation. They are part of a small group of objects called Main Belt Comets (MBCs, Hsieh & Jewitt 2006). Aims. We attempt to determine if these MBCs have spectral properties compatible with those of comet nuclei or with other Themis family asteroids. Methods. We present the visible spectrum of MBCs 133P and 176P, as well as three Themis family asteroids: (62) Erato, (379) Huenna and (383) Janina, obtained in 2007 using three telescopes at “El Roque de los Muchachos” Observatory, in La Palma, Spain, and the 8 m Kueyen (UT2) VLT telescope at Cerro Paranal, Chile. The spectra of the MBCs are compared with those of the Themis family asteroids, comets, likely “dormant” comets and asteroids with past cometary-like activity in the near-Earth (NEA) population. As 133P was observed active, we also look for the prominent CN emission around 0.38 μm typically observed in comets, to test if the activity is produced by the sublimation of volatiles. Results. The spectra of 133P and 176P resemble best those of B-type asteroid and are very similar to those of Themis family members and another activated asteroid in the near-Earth asteroid population, (3200) Phaethon. On the other hand, these spectra are significantly different from the spectrum of comet 162P/Siding-Spring and most of the observed cometary nuclei. CN gas emission is not detected in the spectrum of 133P. We determine an upper limit for the CN production rate Q(CN) = 1.3 × 10 21 mol/s, three orders of magnitude lower than the Q(CN) of Jupiter family comets observed at similar heliocentric distances. Conclusions. The spectra of 133P/Elst-Pizarro and 176P/LINEAR confirm that they are likely members of the Themis family of asteroids, fragments that probably retained volatiles, and unlikely have a cometary origin in the trans-Neptunian belt or the Oort Cloud. They have similar surface properties to activated asteroids in the NEA population, which supports the hypothesis that these NEAs are scattered MBCs. The low Q(CN) of 133P means that, if water-ice sublimation is the activation mechanism, the gas production rate is very low and/or the parent molecules of CN present in the nuclei of normal comets are much less abundant in this MBC.

THE DUST ENVIRONMENT OF MAIN-BELT COMET P/2010 R2 (LA SAGRA)

We present a model of the dust environment of Main-Belt Comet P/2010 R2 (La Sagra) from images acquired during the period 2010 October-2011 January. The tails are best simulated by anisotropic ejection models, with emission concentrated near the nucleus south pole, the spin axis having an obliquity near 90{sup 0}, indicative of a possible seasonally driven behavior. The dust mass loss rate increases rapidly shortly before perihelion, reaching a maximum value of {approx}4 kg s{sup -1}, and maintaining a sustained, cometary-like, activity of about 3-4 kg s{sup -1} up to at least 200 days after perihelion, the date of the latest observation. The size distribution function is characterized by particles in the 5 x 10{sup -4} cm to 1 cm radius range, assuming a time-constant power-law distribution with an index of -3.5. The ejection velocities are compatible with water-ice sublimation activity at the heliocentric distance of 2.7 AU, with values of 10-20 cm s{sup -1} for particle radius of 1 cm, and inverse square root dependence on particle size, typical of hydrodynamical gas drag.

Exploring the nature of new main-belt comets with the 10.4 m GTC telescope: (300163) 2006 VW139

Aims. We aim to study the dust ejected by main-belt comet (MBC) (300163) 2006 VW139 to obtain information on the ejection mechanism and the spectral properties of the object. This will help to see if they are compatible with those of “normal” comets. Methods. Broad-band images in the g and r band as well as a low-resolution spectrum in the 0.35–0.9 μm region were obtained with the GTC telescope (Roque de los Muchachos Observatory, La Palma, Spain). Images were analyzed to produce a color map and derive a lower limit of the absolute magnitude H. A Monte Carlo scattering model was used to derive dust properties such as mass loss rates and ejection velocities as a function of time. The reflectance spectrum was compared to that of the well-studied MBC 133P/ Elst-Pizarro. The spectrum was also used to search for CN emission and to determine the upper limit of the CN production rate. Results. The reflectance spectrum of 2006 VW139 is typical of a C-class asteroid, with a spectral slope S � = 0.5 ± 1.0%/1000 A. It is similar to the spectrum of 133P and other MBCs. No CN emission is detected in the spectrum. A CN production rate upper limit of 3.76 × 10 23 s −1 is derived. Images show that the MBC present a narrow almost linear tail that extends up to 40 000 km in the anti-solar direction and more than 80 000 km in the direction of the object’s orbital plane. The color of the tail is slightly redder than

New observations of asteroid (175706) 1996 FG3, primary target of the ESA Marco Polo-R mission

Context. Near-Earth asteroid (175706) 1996 FG3 is the primary target of the ESA Marco Polo-R mission, which was selected for the assessment study phase of ESA M3 missions. This is a primitive (C-type), binary asteroid that will allow new research to be performed. The primary is a rapidly rotating (3.6 h) small asteroid (1.4 km diameter) that is almost spherical and has a satellite of ∼400 m. Aims. We analyse new ground-based spectroscopic data of 1996 FG3 to help us characterise its surface composition and prepare for the mission. Methods. We obtained a near-infrared spectrum covering the range 0.8–2.5 μm, using the camera-spectrograph NICS at the 3.6 m telescope TNG (Telescopio Nazionale Galileo), located at “El Roque de los Muchachos” Observatory on La Palma, Spain. We combine our near-infrared spectrum with previously published data, and compare all the available spectra of this asteroid with the spectra of meteorites to constrain the mineralogy of the asteroid. Results. Our spectrum of FG3 differs remarkably from previously published ones. Spectral classification performed using the complete visible and near-infrared range yields more than one result, varying from C to Xk types. However, all the possible spectral types indicate that this asteroid is a primitive object. The comparison with meteorites behaves in the same way, providing several good matches to our new near-infrared spectrum (CM2 carbonaceous chondrite, and L6 and H4 ordinary chondrites), and only one match in the case of the previously published spectra (weakly shocked H4 ordinary chondrite, dark vein). The albedo of the asteroid (∼0.04), is typical of a primitive object, and is consistent with the reflectance value at 0.55 μm of the CM2 carbonaceous chondrite. Further observations will be essential to help us characterise more clearly the mineralogy of this asteroid.

Geometric aspects of nonholonomic field theories

A geometric model for nonholonomic Lagrangian field theory is studied. The multisymplectic approach to such a theory as well as the corresponding Cauchy formalism are discussed. It is shown that in both formulations the relevant equations for the constrained system can be recovered by a suitable projection of the equations for the underlying free (i.e. unconstrained) Lagrangian system.

Physical properties of B-type asteroids from WISE data

Aims: Our aim is to obtain more information about the physical nature of B-type asteroids and extend on the previous work by studying their physical properties derived from fitting an asteroid thermal model to their NASAs Wide-field Infrared Survey Explorer (WISE) data. We also examine the Pallas collisional family, a B-type family with a moderately high albedo in contrast to the large majority of B-types. Methods: We apply a combination of the NEATM and a model of the reflected sunlight to WISE asteroid data in order to derive effective diameter (D), the so-called infrared beaming parameter (\eta), ratio of infrared to visible albedo (R_p = p_{IR}/p_V) and visible geometric albedo (p_V). Results: We obtained parameter values for

Near-infrared spectroscopy of 1999 JU3, the target of the Hayabusa 2 mission

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Basaltic asteroids in the Near-Earth Objects population: a mineralogical analysis

100 B-types asteroids and plotted the value distributions of p_V, R_p and \eta (p_V = 0.07 +- 0.03