Bibcode
Lucas, Michael P.; Emery, Joshua P.; Pinilla-Alonso, Noemi; Lindsay, Sean S.; Lorenzi, V.
Bibliographical reference
Icarus, Volume 291, p. 268-287.
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7
2017
Journal
Citations
19
Refereed citations
18
Description
The Hungaria asteroids remain as survivors of late giant planet
migration that destabilized a now extinct inner portion of the
primordial asteroid belt and left in its wake the current resonance
structure of the Main Belt. In this scenario, the Hungaria region
represents a ;purgatory; for the closest, preserved samples of the
asteroidal material from which the terrestrial planets accreted.
Deciphering the surface composition of these unique samples may provide
constraints on the nature of the primordial building blocks of the
terrestrial planets. We have undertaken an observational campaign
entitled the Hungaria Asteroid Region Telescopic Spectral Survey
(HARTSS) to record near-infrared (NIR) reflectance spectra in order to
characterize their taxonomy, surface mineralogy, and potential meteorite
analogs. The overall objective of HARTSS is to evaluate the
compositional diversity of asteroids located throughout the Hungaria
region. This region harbors a collisional family of Xe-type asteroids,
which are situated among a background (i.e., non-family) of
predominantly S-complex asteroids. In order to assess the compositional
diversity of the Hungaria region, we have targeted background objects
during Phase I of HARTSS. Collisional family members likely reflect the
composition of one original homogeneous parent body, so we have largely
avoided them in this phase. We have employed NIR instruments at two
ground-based telescope facilities: the NASA Infrared Telescope Facility
(IRTF), and the Telescopio Nazionale Galileo (TNG). Our data set
includes the NIR spectra of 42 Hungaria asteroids (36 background; 6
family). We find that stony S-complex asteroids dominate the Hungaria
background population (29/36 objects; ∼80%). C-complex asteroids are
uncommon (2/42; ∼5%) within the Hungaria region. Background
S-complex objects exhibit considerable spectral diversity as band
parameter measurements of diagnostic absorption features near 1- and
2-μm indicate that several different S-subtypes are represented
therein, which translates to a variety of surface compositions. We
identify the Gaffey S-subtype (Gaffey et al. [1993]. Icarus 106,
573-602) and potential meteorite analogs for 24 of these S-complex
background asteroids. Additionally, we estimate the olivine and
orthopyroxene mineralogy for 18 of these objects using spectral band
parameter analysis established from laboratory-based studies of ordinary
chondrite meteorites. Nine of the asteroids have band parameters that
are not consistent with ordinary chondrites. We compared these to the
band parameters measured from laboratory VIS+NIR spectra of six
primitive achondrite (acapulcoite-lodranite) meteorites. These
comparisons suggest that two main meteorite groups are represented among
the Hungaria background asteroids: unmelted, nebular L- (and possibly
LL-ordinary chondrites), and partially-melted primitive achondrites of
the acapulcoite-lodranite meteorite clan. Our results suggest a source
region for L chondrite like material from within the Hungarias, with
delivery to Earth via leakage from the inner boundary of the Hungaria
region. H chondrite like mineralogies appear to be absent from the
Hungaria background asteroids. We therefore conclude that the Hungaria
region is not a source for H chondrite meteorites. Seven Hungaria
background asteroids have spectral band parameters consistent with
partially-melted primitive achondrites, but the probable source region
of the acapulcoite-lodranite parent body remains inconclusive. If the
proposed connection with the Hungaria family to fully-melted enstatite
achondrite meteorites (i.e., aubrites) is accurate (Gaffey et al.
[1992]. Icarus 100, 95-109; Kelley and Gaffey [2002]. Meteorit. Planet.
Sci. 37, 1815-1827), then asteroids in the Hungaria region exhibit a
full range of petrologic evolution: from nebular, unmelted ordinary
chondrites, through partially-melted primitive achondrites, to
fully-melted igneous aubrite meteorites.