118 research outputs found
Origin and evolution of the Saturn system
A review is provided of current concepts concerning the formation of the Saturn system and the subsequent history of the planet, its satellites, and rings. Emphasis is placed upon numerical models of Saturn's evolution and interior models of its satellites. Alternative theories are presented and assessed for the origins of the Saturn system, the rings of Saturn, and the atmosphere of Titan
The late accretion and erosion of Vesta's crust recorded by eucrites and diogenites as an astrochemical window into the formation of Jupiter and the early evolution of the Solar System
For decades the limited thickness of Vesta's basaltic crust, revealed by the
link between the asteroid and the howardite-eucrite-diogenite family of
meteorites, and its survival to collisional erosion offered an important
constraint for the study of the early evolution of the Solar System. Some
results of the Dawn mission, however, cast doubts on our understanding of
Vesta's interior composition and of the characteristics of its basaltic crust,
weakening this classical constraint. In this work we investigate the late
accretion and erosion experienced by Vesta's crust after its differentiation
and recorded in the composition of eucrites and diogenites and show that it
offers an astrochemical window into the earliest evolution of the Solar System.
In our proof-of-concept case study focusing on the late accretion and erosion
of Vesta's crust during the growth and migration of Jupiter, the water
enrichment of eucrites appears to be a sensitive function of Jupiter's
migration while the enrichment in highly-siderophile elements of diogenites
appears to be particularly sensitive to the size-frequency distribution of the
planetesimals. The picture depicted by the enrichments created by late
accretion in eucrites and diogenites is not qualitatively affected by the
uncertainty on the primordial mass of Vesta. Crustal erosion, instead, is more
significantly affected by said uncertainty and Vesta's crust survival appears
to be mainly useful to study violent collisional scenarios where highly
energetic impacts can strip significant amounts of vestan material while
limitedly contributing to Vesta's late accretion. Our results suggest that the
astrochemical record of the late accretion and erosion of Vesta's crust
provided by eucrites and diogenites can be used as a tool to investigate any
process or scenario associated to the evolution of primordial Vesta and of the
early Solar System.Comment: 21 pages, 15 figures, accepted for publication on Icaru
Olivine on Vesta as exogenous contaminants brought by impacts: Constraints from modeling Vesta's collisional history and from impact simulations
The survival of asteroid Vesta during the violent early history of the Solar
System is a pivotal constraint on theories of planetary formation. Particularly
important from this perspective is the amount of olivine excavated from the
vestan mantle by impacts, as this constrains both the interior structure of
Vesta and the number of major impacts the asteroid suffered during its life.
The NASA Dawn mission revealed that olivine is present on Vesta's surface in
limited quantities, concentrated in small patches at a handful of sites and
interpreted as the result of the excavation of endogenous olivine. Later works
raised the possibility that the olivine had an exogenous origin, based on the
geologic and spectral features of the deposits. In this work we quantitatively
explore the proposed scenario of a exogenous origin for the detected olivine to
investigate whether its presence on Vesta can be explained as a natural outcome
of the collisional history of the asteroid. We took advantage of the impact
contamination model previously developed to study the origin and amount of dark
and hydrated materials observed by Dawn on Vesta, which we updated by
performing dedicated hydrocode impact simulations. We show that the exogenous
delivery of olivine by impacts can offer a viable explanation for the currently
identified olivine-rich sites without violating the constraint posed by the
lack of global olivine signatures on Vesta. Our results indicate that no mantle
excavation is in principle required to explain the observations of the Dawn
mission and support the idea that the vestan crust could be thicker than
indicated by simple geochemical models based on the Howardite-Eucrite-Diogenite
family of meteorites.Comment: 24 pages, 6 figures, accepted for publication on the journal Icaru
Color patterns in the Kuiper Belt: A possible primordial origin
As a result of our continuing photometric survey, we report here optical colors for 36 Kuiper Belt objects, increasing our sample size to 91 objects. We find that certain dynamical classes of objects exhibit distinctive colors—21 out of 21 objects on small-inclination and small-eccentricity orbits with perihelion distances larger than 40 AU exhibit red surface colors (B-R > 1.5), while 17 out of 20 objects on large-inclination and large-eccentricity orbits with aphelion distances larger than 70 AU exhibit gray surface colors (B-R < 1.5). Our observations are consistent with a primordial origin for Kuiper Belt surface colors, if we assume that gray objects formed closer to the Sun than red objects, and as Neptune migrated outward it scattered gray objects onto dynamically hot orbits. By this model, the contrasting dynamically cold and red objects beyond 40 AU remained far enough away from Neptune that they were never perturbed by the planet
Colors of Inner Disk Classical Kuiper Belt Objects
We present new optical broadband colors, obtained with the Keck 1 and Vatican
Advanced Technology telescopes, for six objects in the inner classical Kuiper
Belt. Objects in the inner classical Kuiper Belt are of interest as they may
represent the surviving members of the primordial Kuiper Belt that formed
interior to the current position of the 3:2 resonance with Neptune, the current
position of the plutinos, or, alternatively, they may be objects formed at a
different heliocentric distance that were then moved to their present
locations. The six new colors, combined with four previously published, show
that the 10 inner belt objects with known colors form a neutral clump and a
reddish clump in B-R color. Nonparametric statistical tests show no significant
difference between the B-R color distribution of the inner disk objects
compared to the color distributions of Centaurs, plutinos, or scattered disk
objects. However, the B-R color distribution of the inner classical Kuiper belt
objects does differ significantly from the distribution of colors in the cold
(low inclination) main classical Kuiper belt. The cold main classical objects
are predominately red, while the inner classical belt objects are a mixture of
neutral and red. The color difference may reveal the existence of a gradient in
the composition and /or surface processing history in the primordial Kuiper
Belt, or indicate that the inner disk objects are not dynamically analogous to
the cold main classical belt objects.Comment: Accepted for publication in A
Internal structure and physical properties of the Asteroid 2008 TC3 inferred from a study of the Almahata Sitta meteorites
Peer reviewe
The contamination of the surface of Vesta by impacts and the delivery of the dark material
The Dawn spacecraft observed the presence of dark material, which in turn
proved to be associated with OH and H-rich material, on the surface of Vesta.
The source of this dark material has been identified with the low albedo
asteroids, but it is still a matter of debate whether the delivery of the dark
material is associated with a few large impact events, to micrometeorites or to
the continuous, secular flux of impactors on Vesta. The continuous flux
scenario predicts that a significant fraction of the exogenous material
accreted by Vesta should be due to non-dark impactors likely analogous to
ordinary chondrites, which instead represent only a minor contaminant in the
HED meteorites. We explored the continuous flux scenario and its implications
for the composition of the vestan regolith, taking advantage of the data from
the Dawn mission and the HED meteorites. We used our model to show that the
stochastic events scenario and the micrometeoritic flux scenario are natural
consequences of the continuous flux scenario. We then used the model to
estimate the amounts of dark and hydroxylate materials delivered on Vesta since
the LHB and we showed how our results match well with the values estimated by
the Dawn mission. We used our model to assess the amount of Fe and siderophile
elements that the continuous flux of impactors would mix in the vestan
regolith: concerning the siderophile elements, we focused our attention on the
role of Ni. The results are in agreement with the data available on the Fe and
Ni content of the HED meteorites and can be used as a reference frame in future
studies of the data from the Dawn mission and of the HED meteorites. Our model
cannot yet provide an answer to the fate of the missing non-carbonaceous
contaminants, but we discuss possible reasons for this discrepancy.Comment: 31 pages, 7 figures, 4 tables. Accepted for publication on the
journal ICARUS, "Dark and Bright Materials on Vesta" special issu
Hazardous near Earth asteroid mitigation campaign planning based on uncertain information on fundamental asteroid characteristics
Given a limited warning time, an asteroid impact mitigation campaign would hinge on uncertainty-based information consisting of remote observational data of the identified Earth-threatening object, general knowledge of near-Earth asteroids (NEAs), and engineering judgment. Due to these ambiguities, the campaign credibility could be profoundly compromised. It is therefore imperative to comprehensively evaluate the inherent uncertainty in deflection and plan the campaign accordingly to ensure successful mitigation. This research demonstrates dual-deflection mitigation campaigns consisting of primary (instantaneous/quasi-instantaneous) and secondary (slow-push) deflection missions, where both deflection efficiency and campaign credibility are taken into account. The results of the dual-deflection campaign analysis show that there are trade-offs between the competing aspects: the launch cost, mission duration, deflection distance, and the confidence in successful deflection. The design approach is found to be useful for multi-deflection campaign planning, allowing us to select the best possible combination of missions from a catalogue of campaign options, without compromising the campaign credibility
Optical spectroscopy of the large Kuiper Belt objects 136472 (2005 FY9) and 136108 (2003 EL61).
We present high signal precision optical reflectance spectra of the large Kuiper Belt objects 2005 FY9 and 2003 EL61. The spectrum of 2005 FY9 exhibits strong CH4 ice bands. A comparison between the spectrum and a Hapke model indicates that the CH4 bands are shifted 3.25 ± 2.25 Å relative to pure CH4 ice, suggesting the presence of another ice component on the surface of 2005 FY9, possibly N2 ice, CO ice, or Ar. The spectrum of 2003 EL61 is remarkably featureless. There is a hint of an O2 ice band at 5773 Å; however, this feature needs to be confirmed by future spectroscopic observations of 2003 EL61 with a higher continuum signal precision sufficient to detect a second, weaker O2 ice band at 6275 Å. [on SciFinder(R)
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