Mineralogical investigation of severalQ_pasteroids and their relation to the Vesta family

Abstract

Context. To take advantage of the large dataset provided by the SDSS data, recently a new taxonomic scheme was proposed designed to be compatible with previous taxonomies. One interesting feature in this distribution is the large number of Q p asteroids scattered all around the main belt with a marked concentration in the Vesta region, where the V p are found most frequently. Since the mineralogy and thermal evolution traditionally related to the classical Q-and V-type taxonomic classes (and by construction the Q p and V p ), this finding was quite surprising. Aims. We aim to observationally determine the mineralogy of a sample of Q p asteroids of and outside the Vesta family to test whether the Q p of the Vesta family are indeed basaltic, and whether the difference in band depth implied by the SDSS spectra relates to diffences in mineralogy with respect to the V p . Moreover, we aim to determine whether the Q p outside Vesta family have an ordinary chondrite (OC) mineralogy and whether their spectra indeed correspond to Q-class asteroids. Methods. We observed a sample of asteroids classified as Q p -type in the literature, mainly located in the Vesta family and neighborhood, to confirm their mineralogy. Spectroscopic observations of 11 asteroids were obtained at the SOAR and IRTF telescopes in the visible and near-infrared region. Thermal observations of three objects were also carried out at the Gemini South telescope in order to determine the albedo of the asteroids. Results. The analysis indicated that all observed asteroids in the Vesta vicinity have a basalt-rich mineralogy, with no clear difference from other Vesta family members in terms of silicate composition. From our study it is not clear why these particular basaltic asteroids have a relatively suppressed band I so that they are classified as Q p . Two asteroids with an OC-compatible mineralogy were identified in the external part of the main belt, at around 2.8−2.9 AU. This discovery suggests new dynamical routes for the transport of Q-type asteroids to the near-Earth region and of OC meteorites to the Earth.

Basalt or Not? Near-infrared Spectra, Surface Mineralogical Estimates, and Meteorite Analogs for 33 Vp-type Asteroids

“…Those asteroids that lie above the olivine-orthopyroxene trend line in Figure 4, with the exception of (36118) 1999 RE 135 , have relatively large amounts of olivine or clinopyroxene present on their surfaces, which excludes them from classification as likely basaltic asteroids. Jasmin et al (2013) reported an NIR spectrum for (7302) 1993 CQ that is very similar to our spectrum in Figure 2. Their reported band parameters (Band I: 0.958 μm; Band II: 1.914 μm; BAR: 0.566) are broadly consistent with our results, although our reported band centers and BAR values are marginally larger.…”

“…(26417) Michaelgord displays a much shallower increase in reflectance across the same spectral range but is also spectrally featureless. However, Jasmin et al (2013) report an NIR spectrum and analysis for (11699) 1998 FL 105 that are consistent with a basaltic surface composition. Verification of the basaltic nature of (11699) 1998 FL 105 will require additional observations, but our results should be taken as provisional, pending verification of the presence of rotational variations in the asteroid's NIR spectra.…”

“…Their reported band parameters (Band I: 0.958 μm; Band II: 1.914 μm; BAR: 0.566) are broadly consistent with our results, although our reported band centers and BAR values are marginally larger. Jasmin et al (2013) suggested an ordinary chondrite meteorite analog for (7302) 1993 CQ. Our two results are consistent in that (7302) 1993 CQ is inconsistent with a basaltic surface composition.…”

Shape and solar phase angle effects on the taxonomic classification of asteroids

“…1 is clear that there is an excess of observations classified as Q p at low phase angles and a deficit of observations with this classification at higher phase angles, with the reverse occurring for the S p and V p classes. This effect was originally noted by Jasmim et al (2013) when analyzing Q p asteroids in the Vesta family. Considering the classes without band, the observations classified as C p are also more frequent at low phase angles and missing at higher phase angles, while the opposite is true for the observations with D p class, and the distribution of observations with X p class more closely reproduces the distribution of all observations.…”

“…While analyzing the distribution of SDSS-based taxonomies (Carvano et al 2010;Hasselmann et al 2011) in the Vesta family, Jasmim et al (2013) recently noted a considerable number of asteroids classified as Q p , along with the dominant V p class. Mineralogy inferred from near-infrared (NIR) spectra of a sample of V p and Q p in the family showed that although the Q p asteroids presented a shallower 1 µm band than the V p asteroids, their silicate mineralogy was essentially the same.…”