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Context. Previously known as 2003 EL61, (136108) Haumea, is the largest member of a group of trans-Neptunian objects (TNOs) with similar orbits and “unique” spectral characteristics in the form of a neutral slope in the visible and the deepest water ice absorption bands observed in the trans-Neptunian belt (TNb). Studying the surface of 2003 EL61provides useful constraints of the origin of this particular group of TNOs and about the outer Solar System's history.

Context. The recent discovery of a group of trans-neptunian objects (TNOs) in a narrow region of the orbital parameter space and with surfaces composed of almost pure water ice, being 2003 EL61its largest member, promises new and interesting results about the formation and evolution of the TNb and the outer Solar System.

Aims. In this paper we analyze the spectra of a sample of asteroids in cometary orbits (ACOs) in order to understand the relationship between them, the Jupiter family comets (JFCs), and the outer main belt populations, such as Hilda, Trojan and Cybele asteroids.

Context.Recent results suggest that there is a group of trans-Neptunian objects (TNOs) (2003 EL61being the biggest member), with surfaces composed of almost pure water ice and with very similar orbital elements. These objects provide exciting laboratories for the study of the processes that prevent the formation of an evolved mantle of organics on the surfaces of the bodies in the trans-Neptunian belt (TNb).

Context.The study of asteroids that present sporadic cometary activity is of fundamental importance to address several astronomical problems including the end states of comet nuclei, the abundance of water in main belt asteroids, and its role as a possible source of terrestial water.

Context.The recent discovery of two large trans-Neptunian objects (TNOs) 2003 UB313and 2005 FY9, with surface properties similar to those of Pluto, provides an exciting new laboratory for the study of processes considered for Pluto and Triton: volatile mixing and transport; atmospheric freeze-out and escape, ice chemistry, and nitrogen phase transitions.

Context.The knowledge of the physical properties of the population of known large trans-Neptunian objects (TNOs) is a key issue in understanding the origin and evolution of the Solar System. In particular, the knowledge of their surface composition helps to understand the original composition of the TNOs and the processes that affect their surfaces during their life.

Context.The population of known large trans-neptunian objects (TNOs) is growing very fast and the knowledge of their physical properties is a key issue to understand the origin and evolution of the Solar System.

Aims. The aim of this work is to estimate the size distribution of small Trans-Neptunian objects.Methods. We simulate the irradiation and collisional processes affecting the surface of a Trans-Neptunian object for the first time using as a constraint the peculiar crystalline to amorphous water ice ratio observed on (136108) 2003 EL61.Results. We find that the size distribution changes its exponent from q0=4.2 at larger sizes to q1=2.40?0.3 at the smaller ones, with a break radius of r1=35?15?km. If this size distribution is applied to studying the collisional surface evolution of (136108) 2003 EL61, we find that the object must be covered by a thin ice crust of ?0.12?cm, while the original composition of the object is still present at 1.61?cm or more below the surface. This result is not affected by a collision with a large projectile that occurred by chance more than 109?yr ago since after a short time the mean value obtained for the crystalline to amorphous water ice ratio is indistinguishable from the one obtained without a collision with a large projectile. Since the simulations are not sensitive to the effects of very small projectiles (rp<10-30?m), it is possible that the exponent of the size distribution for these very small objects changes again, approaching a Donhanyi's size distribution.

Aims.The objective of this work is to summarize the discussion of a workshop aimed at investigating the properties, origins, and evolution of the materials that are responsible for the red coloration of the small objects in the outer parts of the solar system. Because of limitations or inconsistencies in the observations and, until recently, the limited availability of laboratory data, there are still many questions on the subject. Our goal is to approach two of the main questions in a systematic way:

Context.X-Shooter is the first second-generation instrument for the ESO-Very Large Telescope. It is a spectrograph covering the entire 300−2480 nm spectral range at once with a high resolving power. These properties enticed us to observe the well-known trans-Neptunian object (136199) Eris during the science verification of the instrument. The target has numerous absorption features in the optical and near-infrared domain that have been observed by different authors, showing differences in these features’ positions and strengths.

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).

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.

Context.(65) Cybele is the most representative member of a population of primitive asteroids in the outer edge of the main belt, the Cybele asteroids. Recent dynamical models suggest that a significant fraction of them originated in the primordial transneptunian disk, so the study of the physical properties of these asteroids is potentially a useful test of these models.