438 research outputs found
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
Collisional Formation and Modeling of Asteroid Families
In the last decade, thanks to the development of sophisticated numerical
codes, major breakthroughs have been achieved in our understanding of the
formation of asteroid families by catastrophic disruption of large parent
bodies. In this review, we describe numerical simulations of asteroid
collisions that reproduced the main properties of families, accounting for both
the fragmentation of an asteroid at the time of impact and the subsequent
gravitational interactions of the generated fragments. The simulations
demonstrate that the catastrophic disruption of bodies larger than a few
hundred meters in diameter leads to the formation of large aggregates due to
gravitational reaccumulation of smaller fragments, which helps explain the
presence of large members within asteroid families. Thus, for the first time,
numerical simulations successfully reproduced the sizes and ejection velocities
of members of representative families. Moreover, the simulations provide
constraints on the family dynamical histories and on the possible internal
structure of family members and their parent bodies.Comment: Chapter to appear in the (University of Arizona Press) Space Science
Series Book: Asteroids I
Global-scale Reshaping and Resurfacing of Asteroids by Small-scale Impacts, with Applications to the DART and Hera Missions
An Impacting Descent Probe for Europa and the other Galilean Moons of Jupiter
We present a study of an impacting descent probe that increases the science
return of spacecraft orbiting or passing an atmosphere-less planetary body of
the solar system, such as the Galilean moons of Jupiter. The descent probe is a
carry-on small spacecraft (< 100 kg), to be deployed by the mother spacecraft,
that brings itself onto a collisional trajectory with the targeted planetary
body in a simple manner. A possible science payload includes instruments for
surface imaging, characterisation of the neutral exosphere, and magnetic field
and plasma measurement near the target body down to very low-altitudes (~1 km),
during the probe's fast (~km/s) descent to the surface until impact. The
science goals and the concept of operation are discussed with particular
reference to Europa, including options for flying through water plumes and
after-impact retrieval of very-low altitude science data. All in all, it is
demonstrated how the descent probe has the potential to provide a high science
return to a mission at a low extra level of complexity, engineering effort, and
risk. This study builds upon earlier studies for a Callisto Descent Probe (CDP)
for the former Europa-Jupiter System Mission (EJSM) of ESA and NASA, and
extends them with a detailed assessment of a descent probe designed to be an
additional science payload for the NASA Europa Mission.Comment: 34 pages, 11 figure
Constraining surface properties of asteroid (162173) Ryugu from numerical simulations of Hayabusa2 mission impact experiment.
The Hayabusa2 mission impact experiment on asteroid Ryugu created an unexpectedly large crater. The associated regime of low-gravity, low-strength cratering remained largely unexplored so far, because these impact conditions cannot be re-created in laboratory experiments on Earth. Here we show that the target cohesion may be very low and the impact probably occurred in the transitional cratering regime, between strength and gravity. For such conditions, our numerical simulations are able to reproduce the outcome of the impact on Ryugu, including the effects of boulders originally located near the impact point. Consistent with most recent analysis of Ryugu and Bennu, cratering scaling-laws derived from our results suggest that surfaces of small asteroids must be very young. However, our results also show that the cratering efficiency can be strongly affected by the presence of a very small amount of cohesion. Consequently, the varying ages of different geological surface units on Ryugu may be due to the influence of cohesion
Reshaping and ejection processes on rubble-pile asteroids from impacts
Context. Most small asteroids (<50 km in diameter) are the result of the breakup of a larger parent body and are often considered to
be rubble-pile objects. Similar structures are expected for the secondaries of small asteroid binaries, including Dimorphos, the smaller
component of the 65 803 Didymos binary system and the target of NASA’s Double Asteroid Redirection Test (DART) and ESA’s Hera
mission. The DART impact will occur on September 26, 2022, and will alter the orbital period of Dimorphos around Didymos.
Aims. In this work we assume Dimorphos-like bodies with a rubble-pile structure and quantify the effects of boulder packing in its
interior on the post-impact morphology, degree of shape change, and material ejection processes.
Methods. We used the Bern smoothed particle hydrodynamics shock physics code to numerically model hypervelocity impacts on
small, 160 m in diameter, rubble-pile asteroids with a variety of boulder distributions.
Results. We find that the post-impact target morphology is most sensitive to the mass fraction of boulders comprising the target, while
the asteroid deflection efficiency depends on both the mass fraction of boulders on the target and on the boulder size distribution close
to the impact point. Our results may also have important implications for the structure of small asteroids
Knowledge and skills related to active optical sensors in the body of knowledge for earth observation and geoinformation (EO4GEO BOK)
Boulder exhumation and segregation by impacts on rubble-pile asteroids
Small asteroids are often considered to be rubble-pile objects, and such asteroids may be the most likely type of Near Earth Objects (NEOs) to pose a threat to Earth. However, impact cratering on such bodies is complex and not yet understood. We perform three low-velocity (≈ 400 m/s) impact experiments in granular targets with and without projectile-size boulders. We conducted SPH simulations that closely reproduced the impact experiments.
Our results suggest that cratering on heterogeneous targets displaces and ejects boulders, rather than fragmenting them, unless directly hit. We also see indications that as long as the energy required to disrupt the boulder is small compared to the kinetic energy of the impact, the disruption of boulders directly hit by the projectile may have minimal effect on the crater size.
The presence of boulders within the target causes ejecta curtains with higher ejection angles compared to homogeneous targets. At the same time, there is a segregation of the fine ejecta from the boulders, resulting in boulders landing at larger distances than the surrounding fine grained material. However, boulders located in the target near the maximum extent of the expanding excavation cavity are merely exhumed and distributed radially around the crater rim, forming ring patterns similar to the ones observed on asteroids Itokawa, Ryugu and Bennu. Altogether, on rubble-pile asteroids this process will redistribute boulders and finer-grained material heterogeneously, both areally around the crater and vertically in the regolith. In the context of a kinetic impactor on a rubble-pile asteroid and the DART mission, our results indicate that the presence of boulders will reduce the momentum transfer compared to a homogeneous, fine-grained target
Momentum Enhancement during Kinetic Impacts in the Low-intermediate-strength Regime: Benchmarking and Validation of Impact Shock Physics Codes
In 2022 September, the DART spacecraft (NASA’s contribution to the Asteroid Impact & Deflection Assessment (AIDA) collaboration) will impact the asteroid Dimorphos, the secondary in the Didymos system. The crater formation and material ejection will affect the orbital period. In 2027, Hera (ESA’s contribution to AIDA) will investigate the system, observe the crater caused by DART, and characterize Dimorphos. Before Hera’s arrival, the target properties will not be well-constrained. The relationships between observed orbital change and specific target properties are not unique, but Hera’s observations will add additional constraints for the analysis of the impact event, which will narrow the range of feasible target properties. In this study, we use three different shock physics codes to simulate momentum transfer from impactor to target and investigate the agreement between the results from the codes for well-defined target materials. In contrast to previous studies, care is taken to use consistent crushing behavior (e.g., distension as a function of pressure) for a given porosity for all codes. First, we validate the codes against impact experiments into a regolith simulant. Second, we benchmark the codes at the DART impact scale for a range of target material parameters (10%–50% porosity, 1.4–100 kPa cohesion). Aligning the crushing behavior improves the consistency of the derived momentum enhancement between the three codes to within +/−5% for most materials used. Based on the derived mass–velocity distributions from all three codes, we derive scaling parameters that can be used for studies of the ejecta curtain
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