1,721,139 research outputs found
Peculiar Near-Earth Objects
No full textIn this paper we present visible and near-infrared spectroscopy of 7 peculiar NEOs. These objects have been observed within the SINEO (Spectral Investigation of Near-Earth Objects) survey, which have produced more then 100 spectra of NEOs. Among the objects presented here, five of them result to be spectrally peculiar, belonging to the rare V and R classes. The other two have peculiar orbits being comet-like. Their spectroscopy gives a B- and a X-type which is compatible with the scenario of being objects which originated in the outer Solar System
SINEO: Spectroscopic Investigation of Near Earth Objects
No full textIn this paper we present the results obtained until now from our spectroscopic survey in the visible and Near Infrared Region (NIR) of Near Earth Objects (NEO), named SINEO, started in 2000. Up to now we have obtained a data set of about 150 spectra, most of them in the visible range (0.40-0.95 mu m) and about half of them in the whole region 0.40-2.5 mu m. The observations have been performed with the NTT of ESO (Chile) and the Telescopio Nazionale Galileo (TNG) at the Canary Islands. We present the taxonomic classification of the objects, their linkage with meteorites and the influence of space weathering
Mass transfer in the satellite system of Neptune: implications for Triton's crater asymmetry
No full textIn this paper, we shall analyse a promising way to explain the huge crater asymmetry observed on Triton, the largest of Neptune's satellites. Triton shows, as well as many other satellites in the Solar System, a non-symmetric crater distribution on its surface. This fact is principally due to the synchronous rotation of these satellites, as shown by many theoretical works (see Shoemaker and Wolfe, Satellites of Jupiter, University of Arizona Press, Tucson, 1992, p. 277; Horedt and Neukum, Icarus 60 (1984) 710; Zahnle et al., Icarus 136 (1998) 202; Zahnle et al., Icarus 153 (2001) 111). However, on Triton the asymmetry is much more pronounced than on other satellites, and it exceeds what the models, in which the source of the craters are bodies in heliocentric orbits, can account for. For this reason, many authors (Croft et al., Icarus 99 (1992) 94; Schenk and Sobieszczyk, American Astronomical Society, DPS Meeting, Vol. 31, 1999; Zahnle et al., Icarus 153 (2001) 111) proposed that the origin for Triton's asymmetry has to be found in a swarm of bodies having planetocentric orbits, instead of heliocentric ones. Here, we analyse from a dynamical point of view the possibility that such swarm of fragments was generated by a collision between an inner satellite and a third object (a process we call `mass transfer'). Moreover, we discuss the possibility that the observed crater distribution on Triton comes from two populations: heliocentric bodies responsible for a few big craters, plus planetocentric bodies responsible for the big asymmetry.
Finally, we discuss some implications for ground observations
Spectrally Peculiar Objects from SINEO survey
No full textIt is commonly agreed that near-Earth objects (NEOs) can originate from the main asteroid belt, through dynamical resonances, or from the outer Solar System. Spectroscopic observations of NEOs and their taxonomic assessment can in general add useful hints on their origin. We present visible and near-infrared spectroscopy of 7 peculiar NEOs observed within the SINEO (Spectroscopic Investigation of Near-Earth Objects) survey, which have produced more then 100 NEOs spectra. Five of them result to be spectrally peculiar, belonging to the rare V and R classes. We describe their connection with possible parent bodies in the main belt. The other two objects have peculiar orbits being comet-like. Their spectroscopy gives a B- and X-type which is compatible with the scenario of being objects which originated in the outer Solar System
SINEO: Spectroscopic Investigation of Near Earth Objects
No full textIn this paper we present the results obtained until now from our long term spectroscopic survey in the visible and Near Infrared Region (NIR) of Near Earth Objects (NEO), named SINEO, started some years ago. Up to now we have obtained a data set of 107 spectra of which 98 in the visible range (0.40-0.95 mu m) and 63 in the Near Infrared region (0.40-2.5 mu m). The observations have been performed with the NTT of ESO (Chile) and the Telescopio Nazionale Galileo (TNG) at the Canary Islands. We present the results of a taxonomic classification of the objects, their linkage with meteorites and the influence of space weathering
Space weathering and tidal effects among near-Earth objects
No full textThe spectral slope of sunlight reflected by an asteroid surface may change with time due to several physical processes acting on the surface (``space weathering''). We present a general and significant relation between the spectral slope of silicate--rich near-Earth and Main Belt asteroids and the "exposure" to space weathering. We find strong evidences that the Sun-related processes dominate the space weathering. Moreover, by using a large data set of spectroscopic observations of planet--crossing asteroids (near--Earth objects and Mars--crossers), we found a statistically significant correlation between their spectral slope and the perihelion distance. The correlation could be due to tidal effects: during a close encounter with a terrestrial planets tides may partially, or even completely, remove the old and the weathering process. The effects have to be combined to understand the evolution of optical properties of NEAs with time
Discovery of Vesta Analogues among Near-Earth Objects
No full textIt is commonly agreed that most of near--Earth asteroids (NEAs) originate from the main asteroid belt, through a complex dynamical evolution involving the major dynamical resonances. However it is not easy to obtain reliable hints on the origin and following dynamical evolution pertaining to every individual near--Earth body. The evolution within the resonant regions, which is typically chaotic, and the possible close encounters with one or more of the inner planets usually destroy every significant memory of the original orbit. Only in the rare cases in which the spin vector is known, it may be used to evaluate the probability of having the body come from either of the main resonant channels (3:1 or nu6). Thus the most relevant and commonly available information on the possible origin comes out from the spectroscopic observations and taxonomic assessment. In this work we report the observations of four NEAs showing, for the first time, a striking spectroscopic similarity with the main belt (MB) asteroid 4 Vesta, which we can safely identify as their parent body
Towards a general model of space weathering of S-complex asteroids and ordinary chondrites
No full textContext: The effect of the space weathering on the spectral properties of the S-complex asteroids has been widely discussed in recent times, and a systematic reddening due to the exposure to the various influxes has been found. The evolution of spectral properties is also affected by other processes, such as close encounters with planetary bodies.
Aims: In this paper we present our model of asteroidal space weathering, combining the previous analyses and using an increased dataset. We also provide a link with ordinary chondrite meteorites.
Methods: We revise also some age estimates in terms of dynamical and physical considerations.
Results: The present analysis qualitatively confirms the previous results, but a by far more refined and reliable slope-exposure relation is obtained, capable to include in a unique scenario the ordinary chondrite meteorites, NEOs, Mars Crossers and Main Belt asteroids. Moreover, we show that, on the basis of spectroscopic properties, Mars Crossers should be, on the average, significantly younger than Main Belt asteroids of the same size. Finally, we find that the solar ion flux is the most relevant source of the asteroidal space weathering.
Conclusions: . The properties of ordinary chondrite meteorites, NEOs, Mars Crossers and Main Belt asteroids can be included in a unique scenario. This has unveiled the relevant processes - some newly discovered - which play an important role in determining the evolution of the spectral properties of these bodies over time
SINEO: Spectroscopic Investigation of Near Earth Objects
No full textNear-Earth objects (NEOs) represent one of the most intriguing populations of Solar System bodies. These objects appear heterogeneous in all aspects of their physical properties, like shapes, sizes, spin rates, compositions etc. Moreover, as these objects represent also a real threat to the Earth, a good knowledge of their properties and composition is the necessary first step to evaluate mitigation techniques and to understand their origin and evolution. In the last few years we have started a long-term spectroscopic investigation in the visible and near-infrared (NIR) region of NEOs. The observations have been performed with the ESO NTT in La Silla and the TNG in Canary Islands, obtaining about 80 spectra so far. We discuss the taxonomic classification of the observed NEOs, their links with meteorites and possible influences of space weathering
New V-type asteroids in near-Earth space
No full textWe present new visible and near-infrared spectroscopic observations of 4 small, previously unclassified, near-Earth objects (NEOs). They appear to have basaltic surfaces, and hence they can be classified as V-types. Their visible spectra exhibit a closer spectral match with the Main-Belt (MB) Asteroid (4) Vesta than the other, presently known, V-type NEOs and MB asteroids. The near-infrared spectrum of Asteroid 2003 FT3 shows—for the first time among NEOs—a peculiar shape of the 1 μm band, maybe suggesting an overabundance of olivine compared to the other V-types and to (4) Vesta. The presence of V-type objects among NEOs may be a consequence of the delivery processes connecting the inner MB to the near-Earth region. On the basis of the orbital parameters of the NEOs presented here, both the resonances (3:1 and ν), usually considered as the most relevant gateways for the production of near-Earth asteroids, should have been active to transfer the bodies from the MB region
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