1,721,573 research outputs found
Koronis family: Reflectance spectra of 243 Ida, 1442 Corvina and 2226 Cunitza
No full textLow-resolution spectra of the asteroids 243 Ida (target of the Galileo spacecraft on 28 August 1993), 1442 Corvina and 2226 Cunitza (other members of the Koronis family) were obtained. In the frame of a ground-based international campaign to observe Ida before the Galileo encounter, we observed it spectroscopically in the visible at ESO-La Silla (Chile), obtaining four spectra covering the total rotational period (4.63 h). In one of these spectra, we observed a considerable variation in the depth of the absorption feature near 0.9 microns, implying a different content of pyroxene and olivine on the surface of Ida. The spectra obtained for the other two objects are consistent with those of S-type asteroids and similar to that of Ida
Optical Observations of Trans-Neptunian and Centaur Objects
No full textTrans-Neptunian objects are probably primitive remnants from the early accretional phases of the solar system and may contain the most pristine unprocessed material. To investigate the surface properties of these objects we started an observational campaign at the European Southern Observatory (La Silla, Chile) with the 3.6 m telescope and the 3.5 m New Technological Telescope (NTT). We observed U, B, V, R, I colors for six Trans-Neptunian objects (1994 JR1, 1994 TB, 1995 QY9, 1996 TL66, 1996 TO66, and 1996 TP66) and visible spectra for five Centaurs (2060 Chiron, 7066 Nessus, 8405 1995 GO, 1995 DW2, 1997 CU26). The basic result is that the two classes of objects are remarkably similar, even if a great diversity exists among their colors implying a wide range of surface compositions
Low Resolution Reflectance Spectra of 243 Ida
No full textLow Resolution Reflectance Spectra of 243 Ida, target of Galileo spatial missio
Spectroscopic investigation of the Centaurs
No full textThe Centaurs are a peculiar class of objects with chaotic orbits which semimajor axes fall between those of Jupiter and Neptune. It is now believed that they could represent a link between trans neptunian objects and short-period comets. To investigate the nature of these particular objects, we have performed optical spectroscopic observations of 5 Centaurs. The spectral range covered is 0.37-0.75 micron. The spectral slopes are neutral or slightly blue for 2060 Chiron to very red for objects as 7066 Nessus. The investigated objects have not shown any cometary activity. The obtained spectra show a wide types range which implies different surface compositions probably due to evolutionary mechanisms like long-term exposures to cosmic rays and/or solar ultraviolet radiation. These differences are very similar to those obtained also among the Kuiper belt objects. This compositional similarity could confirm that Centaurs are transneptunian objects injected into giant-planet orbits. Even if only Chiron has shown cometary activity until now, the Centaurs are probably transition objects between the trans neptunians, asteroids and cometary nuclei
Visible Spectroscopy of the Rosetta Asteroid Targets: 3840 Mimistrobell and 2530 Shipka
No full textThe asteroids 3840 Mimistrobell and 2530 Shipka, targets of the Rosetta mission, have been spectroscopically investigated in the visible region in order to obtain information on their nature
Visible Spectroscopy of Possible Cometary Candidates
No full textIt is now accepted that comets and asteroids are not two well separated classes of objects. In particular, several peculiar objects have been recognized to resemble comets in several aspects: chemical, dynamical, and/or physical. In this context we spectroscopically observed in the visible region three strong cometary candidates: 944 Hidalgo, 2201 Oljato, and 3200 Phaethon. The spectrum of Hidalgo obtained has a reflectivity slope similar to those of known cometary nuclei. Phaethon shows a spectrum with a negative slope. The spectrum of Oljato shows a strong absorption feature around 0.9 mm which is suggestive of the presence of aqueous altered materials. No clear signs of cometary activity have been found in the spectra of these objects
Water ice in primitive asteroids?
No full textA short review of the literature dealing with possible signatures of ice in some asteroids is presented. The subject is poorly developed, even if in the last decade several authors started a spectroscopic survey of asteroids in the visible and near-infrared wavelengths in order to find ice features on asteroid spectra. Aqueous alteration of the mineral assemblages has been claimed for a number of B-, F- and for more than 50% of the observed C-type asteroids. The compositional and, consequently, the thermal structure of the asteroid belt supports the hypothesis that ices of volatile elements should be more abundant in the external region of the belt, where pristine materials have not undergone drastic modification processes after the accumulation in the planetesimal swarms between those of Mars and of Jupiter. As of today, there is no evidence of any water, water ice or aqueous alteration materials on the D-type asteroids, which are considered the least altered objects
Visible spectroscopy of dark, primitve asteroids
No full textIn the last years we have started a spectroscopic survey in the visible of dark primitive asteroids. These objects, considered the remnants of primordial processes of our solar system, belong essentially to the taxonomical classes C, P, and D. They are thought to contain water ice in their interiors and mineral assemblages derived from aqueous alteration processes of surface materials. In this paper we present the observations of 18 low-albedo asteroids. Only one asteroid, 238 Hypatia, has shown a feature centered around 0.6μm, probably due to charge transfer transition Fe2+→Fe3+ in iron oxides (aqueous alteration products). The results obtained are discussed. The behavior of the reflectance of the objects with the heliocentric distance, with the albedo, and with the reflectivity of the known cometary nuclei will also be analyzed
Asteroid-Comet Relations: Spectroscopic Observations
No full textAsteroid-Comet Relations: Spectroscopic Observation
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