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Post Info TOPIC: Basaltic Asteroids
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Basaltic asteroids
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Title: V-type candidates and Vesta family asteroids in the Moving Objects VISTA (MOVIS) Catalogue
Author: J. Licandro, M. Popescu, J. de Leon, D. Morate

Basaltic asteroids (V-types) are believed to be fragments of large differentiated bodies. The majority of them are found in the inner part of the asteroid belt, and are current or past members of the Vesta family. Recently, some V-type asteroids have been discovered far from the Vesta family supporting the hypothesis of the presence of multiple basaltic asteroids in the early solar system. The discovery of basaltic asteroids in the outer belt challenged the models of the radial extent and the variability of the temperature distribution in the early solar system. We aim to identify new basaltic V-type asteroids using near-infrared colours of ~40000 asteroids observed by the VHS-VISTA survey and compiled in the MOVIS-C catalogue. We also want to study their near-infrared colours and to study the near-infrared colour distribution of the Vesta dynamical family. We performed a search in the MOVIS-C catalogue of all the asteroids with (Y-J) and (J-Ks) in the range (Y-J) > 0.5 and (J-Ks) < 0.3, associated with V-type asteroids, and studied their colour distribution. We have also analysed the near-infrared colour distribution of 273 asteroid members of the Vesta family and compared them with the albedo and visible colours from WISE and SDSS data. We determined the fraction of V-type asteroids in the family. We found 477 V-type candidates in MOVIS-C, 244 of them outside the Vesta dynamical family. We identified 19 V-type asteroids beyond the 3:1 mean motion resonance, 6 of them in the outer main belt, and 16 V-types in the inner main belt with proper inclination i_p < 3.0deg, well below the inclination of the Vesta family. We computed that ~85% of the members of the Vesta dynamical family are V-type asteroids, and only 1-2% are primitive class asteroids and unlikely members of the family. This work almost doubles the sample of basaltic asteroid candidates in regions outside the Vesta family.

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Blobrana


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Posts: 131433
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V-type Asteroids
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Title: Lightcurve Survey of V-type Asteroids. I. Observations until Spring 2004
Authors: Sunao Hasegawa, Seidai Miyasaka, Chiaki Yoshizumi, Tomohiko Sekiguchi, Yuki Sarugaku, Setsuko Nishihara, Kouhei Kitazato, Masanao Abe, Hiroyuki Mito

To examine the distribution of rotational rates for chips of asteroid 4 Vesta, lightcurve observation of seven V-type asteroids (2511 Patterson, 2640 Hallstorm, 2653 Principia, 2795 Lapage, 3307 Athabasca, 4147 Lennon, and 4977 Rauthgundis) were performed from fall 2003 to spring 2004. Distribution of spin rates of V-type main-belt asteroids from the past and our observations have three peaks. This result implies that age of catastrophic impact making Vesta family may be not as young as Karin and Iannini families but as old as Eos and Koronis families.

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Blobrana


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Posts: 131433
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Basaltic Asteroids
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Title: The Distribution of Basaltic Asteroids in the Main Belt
Authors: Nicholas A. Moskovitz (1), Robert Jedicke (1), Eric Gaidos (2 and 3), Mark Willman (1), David Nesvorny (4), Ronald Fevig (5), Zeljko Ivezic (6) ((1) Institute for Astronomy, Univ. of Hawaii, (2) Dept. of Geology & Geophysics, Univ. of Hawaii, (3) NASA Astrobiology Institute, (4) Southwest Research Institute, (5) LPL, Univ. of Arizona, (6) Univ. of Washington)

We present the observational results of a survey designed to target and detect asteroids whose colours are similar to those of Vesta family members and thus may be considered as candidates for having a basaltic composition. Fifty basaltic candidates were selected with orbital elements that lie outside of the Vesta dynamical family. Optical and near-infrared spectra were used to assign a taxonomic type to 11 of the 50 candidates. Ten of these were spectroscopically confirmed as V-type asteroids, suggesting that most of the candidates are basaltic and can be used to constrain the distribution of basaltic material in the Main Belt.
Using our catalogue of V-type candidates and the success rate of the survey, we calculate unbiased size-frequency and semi-major axis distributions of V-type asteroids. These distributions, in addition to an estimate for the total mass of basaltic material, suggest that Vesta was the predominant contributor to the basaltic asteroid inventory of the Main Belt, however scattered planetesimals from the inner Solar System (a < 2.0 AU) and other partially/fully differentiated bodies likely contributed to this inventory. In particular, we infer the presence of basaltic fragments in the vicinity of asteroid 15 Eunomia, which may be derived from a differentiated parent body in the middle Main Belt (2.5 < a < 2.8). We find no asteroidal evidence for a large number of previously undiscovered basaltic asteroids, which agrees with previous theories suggesting that basaltic fragments from the ~100 differentiated parent bodies represented in meteorite collections have been "battered to bits" [Burbine, T.H., Meibom, A., Binzel, R.P., 1996. Mantle material in the Main Belt: Battered to bits? Met. & Planet. Sci. 31, 607].

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Blobrana


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Title: Two new basaltic asteroids in the Outer Main Belt?
Authors: R. Duffard and F. Roig

Aims. The identification of other basaltic objects in  the asteroid belt is mandatory to explain the diversity in the collection of basaltic meteorites. This diversity requires more than one differentiated parent body, a fact that is consistent with the diversity of differentiated parent bodies implied by the iron meteorites.
Methods. Based on a list of previously identified candidate basaltic (V-type) asteroids, two asteroids in the outer main belt, (7472) Kumakiri and (10537) 1991 RY16, were spectroscopically observed during an observational run in Calar Alto Observatory, Spain.
Results. We confirm the V-type character of these two asteroids that, together with (1459) Magnya, become the only known traces of basaltic found in the outer main belt up to now. We also demonstrate that the searching for candidate V-type asteroids using a photometric survey, like the Sloan Digital Sky Survey, produces reliable results.

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Blobrana


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Analysis of the chemical make up of two asteroids in the outer asteroid belt has thrown the classification system for these small bodies, which orbit between Mars and Jupiter, into disorder.

We appear to have detected basalt on the surface of these asteroids, which is very unusual for this part of the asteroid belt. We do not know whether we have discovered two basaltic asteroids with a very particular and previously unseen mineralogical composition or two objects of non basaltic nature that have to be included in a totally new taxonomic class - Dr Rene Duffard, who is presenting results at the European Planetary Science Congress in Potsdam on Wednesday 22nd August.

The presence of basalt means that the asteroid must have melted partially at some time in the past, which implies that it was once part of a larger body which had internal heating processes. However, there do not appear to be other basaltic fragments in the region and, from spectral analysis, it is not clear whether the two are fragments of the same parent body or not.
Until recently, most of the known basaltic asteroids, which are classified as V-type, were thought to be fragments of Vesta, the second largest object in the asteroid belt. Since 2001, several V-type asteroids have been identified as not belonging to this Vesta family, including (1459) Magnya, the first basaltic object to be detected in the outer asteroid belt.
Dr Duffard, of the Instituto de Astrofisica de Andalucia in Spain, and his colleague, Dr Fernando Roig, from the Observatorio Nacional in Rio de Janeiro, Brazil, selected the two asteroids, (7472) Kumakiri and (10537) 1991 RY16, for investigation by from a group of six candidate V-type asteroids identified using photometric data from the Sloan Digital Sky Survey (SDSS).
The reflectance spectra of the two bodies seem to show the characteristics of a V-type asteroid. However, there is a shallow absorption band around the wavelength of red visible light, which has never been observed before in other V-type spectra. This means that these objects have a slightly different chemical composition and do not fit into any existing category of asteroid. The unexpected dip in the spectra could have two sources: it could be due to impacts with other asteroids or comets shocking iron-rich compounds into a oxidized state, or it could indicate the presence of olivine, a green mineral that is also known as the semi-precious gemstone.

We need now to observe both objects in the near-infrared range to confirm whether they have a basaltic surface. If they do, we will need to try and work out where they came from and the fate of their parent objects. If they do not, we will have to come up with a new class of asteroid  - Dr Rene Duffard.

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