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Register a new userThe Formation of Jupiter, the Jovian Early Bombardment and the Delivery of Water to the Asteroid Belt: The Case of (4) Vesta
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The asteroid (4) Vesta, parent body of the Howardite-Eucrite-Diogenite meteorites, is one of the first bodies that formed, mostly from volatile-depleted material, in the Solar System. The Dawn mission recently provided evidence that hydrated material was delivered to Vesta, possibly in a continuous way, over the last 4 Ga, while the study of the eucritic meteorites revealed a few samples that crystallized in presence of water and volatile elements. The formation of Jupiter and probably its migration occurred in the period when eucrites crystallized, and triggered a phase of bombardment that caused icy planetesimals to cross the asteroid belt. In this work, we study the flux of icy planetesimals on Vesta during the Jovian Early Bombardment and, using hydrodynamic simulations, the outcome of their collisions with the asteroid. We explore how the migration of the giant planet would affect the delivery of water and volatile materials to the asteroid and we discuss our results in the context of the geophysical and collisional evolution of Vesta. In particular, we argue that the observational data are best reproduced if the bulk of the impactors was represented by 1-2 km wide planetesimals and if Jupiter underwent a limited (a fraction of au) displacement.
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The asteroid belt is an open window on the history of the Solar System, as it preserves records of both its formation process and its secular evolution. The progenitors of the present-day asteroids formed in the Solar Nebula almost contemporary to the giant planets. The actual process producing the first generation of asteroids is uncertain, strongly depending on the physical characteristics of the Solar Nebula, and the different scenarios produce very diverse initial size-frequency distributions. In this work we investigate the implications of the formation of Jupiter, plausibly the first giant planet to form, on the evolution of the primordial asteroid belt. The formation of Jupiter triggered a short but intense period of primordial bombardment, previously unaccounted for, which caused an early phase of enhanced collisional evolution in the asteroid belt. Our results indicate that this Jovian Early Bombardment caused the erosion or the disruption of bodies smaller than a threshold size, which strongly depends on the size-frequency distribution of the primordial planetesimals. If the asteroid belt was dominated by planetesimals less than 100 km in diameter, the primordial bombardment would have caused the erosion of bodies smaller than 200 km in diameter. If the asteroid belt was instead dominated by larger planetesimals, the bombardment would have resulted in the destruction of bodies as big as 500 km.
We present the results of photometric observations carried out with four small telescopes of the asteroid 4 Vesta in the $B$, $R_{rm C}$, and $z$ bands at a minimum phase angle of 0.1 $timeform{D}$. The magnitudes, reduced to unit distance and zero phase angle, were $M_{B}(1, 1, 0) = 3.83 pm 0.01, M_{R_{rm C}}(1, 1, 0) = 2.67 pm 0.01$, and $M_{z}(1, 1, 0) = 3.03 pm 0.01$ mag. The absolute magnitude obtained from the IAU $H$--$G$ function is $sim$0.1 mag darker than the magnitude at a phase angle of 0$timeform{D}$ determined from the Shevchenko function and Hapke models with the coherent backscattering effect term. Our photometric measurements allowed us to derive geometric albedos of 0.35 in the $B$ band, 0.41 in the $R_{rm C}$ band, and 0.31 in the $z$ bands by using the Hapke model with the coherent backscattering effect term. Using the Hapke model, the porosity of the optically active regolith on Vesta was estimated to be $rho$ = 0.4--0.7, yielding the bluk density of 0.9--2.0 $times$ $10^3$ kg $mathrm{m^{-3}}$. It is evident that the opposition effect for Vesta makes a contribution to not only the shadow-hiding effect, but also the coherent backscattering effect that appears from ca. $1timeform{D}$. The amplitude of the coherent backscatter opposition effect for Vesta increases with a brightening of reflectance. By comparison with other solar system bodies, we suggest that multiple-scattering on an optically active scale may contribute to the amplitude of the coherent backscatter opposition effect ($B_{C0}$).
Several observational works have shown the existence of Jupiter-mass planets covering a wide range of semi-major axes around Sun-like stars. We aim to analyse the planetary formation processes around Sun-like stars that host a Jupiter-mass planet at intermediate distances ranging from $sim$1 au to 2 au. Our study focusses on the formation and evolution of terrestrial-like planets and water delivery in the habitable zone (HZ) of the system. Our goal is also to analyse the long-term dynamical stability of the resulting systems. A semi-analytic model was used to define the properties of a protoplanetary disk that produces a Jupiter-mass planet around the snow line, which is located at $sim$2.7 au for a solar-mass star. Then, it was used to describe the evolution of embryos and planetesimals during the gaseous phase up to the formation of the Jupiter-mass planet, and we used the results as the initial conditions to carry out N-body simulations of planetary accretion. Our simulations produce three different classes of planets in the HZ: water worlds, with masses between 2.75 $M_{oplus}$ and 3.57 $M_{oplus}$ and water contents of 58% and 75% by mass, terrestrial-like planets, with masses ranging from 0.58 $M_{oplus}$ to 3.8 $M_{oplus}$ and water contents less than 1.2% by mass, and dry worlds, simulations of which show no water. A relevant result suggests the efficient coexistence in the HZ of a Jupiter-mass planet and a terrestrial-like planet with a percentage of water by mass comparable to the Earth. Moreover, our study indicates that these planetary systems are dynamically stable for at least 1 Gyr. Systems with a Jupiter-mass planet located at 1.5 au - 2 au around solar-type stars are of astrobiological interest. These systems are likely to harbour terrestrial-like planets in the HZ with a wide diversity of water contents.
The Earth contains between one and ten oceans of water, including water within the mantle, where one ocean is the mass of water on the Earths surface today. With $n$-body simulations we consider how much water could have been delivered from the asteroid belt to the Earth after its formation. Asteroids are delivered from unstable regions near resonances with the giant planets. We compare the relative impact efficiencies from the $ u_6$ resonance, the 2:1 mean motion resonance with Jupiter and the outer asteroid belt. The $ u_6$ resonance provides the largest supply of asteroids to the Earth, with about $2%$ of asteroids from that region colliding with the Earth. Asteroids located in mean motion resonances with Jupiter and in the outer asteroid belt have negligible Earth-collision probabilities. The maximum number of Earth collisions occurs if the asteroids in the primordial asteroid belt are first moved into the $ u_6$ resonance location (through asteroid-asteroid interactions or otherwise) before their eccentricity is excited sufficiently for Earth collision. A maximum of about eight oceans of water may be delivered to the Earth. Thus, if the Earth contains ten or more oceans of water, the Earth likely formed with a significant fraction of this water.
We present the results of snapshot numerical integrations of test particles representing comet-like and asteroid-like objects in the inner solar system aimed at investigating the short-term dynamical evolution of objects close to the dynamical boundary between asteroids and comets as defined by the Tisserand parameter with respect to Jupiter, T_J (i.e., T_J=3). As expected, we find that T_J for individual test particles is not always a reliable indicator of initial orbit types. Furthermore, we find that a few percent of test particles with comet-like starting elements (i.e., similar to Jupiter-family comets) reach main-belt-like orbits (at least temporarily) during our 2 Myr integrations, even without the inclusion of non-gravitational forces, apparently via a combination of gravitational interactions with the terrestrial planets and temporary trapping by mean-motion resonances with Jupiter. We estimate that the fraction of real Jupiter-family comets occasionally reaching main-belt-like orbits on Myr timescales could be on the order of ~0.1-1%, although the fraction that remain on such orbits for appreciable lengths of time is certainly far lower. Thus, the number of JFC-like interlopers in the main-belt population at any given time is likely to be small, but still non-zero, a finding with significant implications for efforts to use main-belt comets to trace the primordial distribution of volatile material in the inner solar system. The test particles with comet-like starting orbital elements that transition onto main-belt-like orbits in our integrations appear to be largely prevented from reaching low eccentricity, low inclination orbits. We therefore find that low-eccentricity, low-inclination main-belt comets may provide a more reliable means for tracing the primordial ice content of the main asteroid belt than the main-belt comet population as a whole.
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