Are There Trans Neptunian Objects in the Asteroid Belt?

CAPTURE OF TRANS-NEPTUNIAN PLANETESIMALS IN THE MAIN ASTEROID BELT

Authors:

Vokrouhlický et al

Abstract:

The orbital evolution of the giant planets after nebular gas was eliminated from the Solar System but before the planets reached their final configuration was driven by interactions with a vast sea of leftover planetesimals. Several variants of planetary migration with this kind of system architecture have been proposed. Here, we focus on a highly successful case, which assumes that there were once five planets in the outer Solar System in a stable configuration: Jupiter, Saturn, Uranus, Neptune, and a Neptune-like body. Beyond these planets existed a primordial disk containing thousands of Pluto-sized bodies, ~50 million D > 100 km bodies, and a multitude of smaller bodies. This system eventually went through a dynamical instability that scattered the planetesimals and allowed the planets to encounter one another. The extra Neptune-like body was ejected via a Jupiter encounter, but not before it helped to populate stable niches with disk planetesimals across the Solar System. Here, we investigate how interactions between the fifth giant planet, Jupiter, and disk planetesimals helped to capture disk planetesimals into both the asteroid belt and first-order mean-motion resonances with Jupiter. Using numerical simulations, we find that our model produces the right proportion of P- and D-type asteroids in the inner, central, and outer main belt, while also populating the Hilda and Thule regions in Jupiter's 3/2 and 4/3 resonances. Moreover, the largest observed P/D types in each sub-population are an excellent fit to our captured population results (within uncertainties). The model produces a factor of ~10 overabundance of diameter D > 10 km P/D types in the main belt, but this mismatch can likely be explained by various removal mechanisms (e.g., collision evolution over 4 Gyr, dynamical losses via Yarkovsky thermal forces over 4 Gyr, thermal destruction of the planetesimals en route to the inner solar system). Overall, our instability model provides a more satisfying match to constraints than that of Levison et al., and it provides us with strong supporting evidence that the five giant planet instability model is reasonable. Our results lead us to predict that D-type asteroids found in the near-Earth object population on low delta-V orbits with Earth are the surviving relics from the same source population that now make up the Kuiper Belt, the irregular satellites, and the Jupiter Trojans. The singular Tagish Lake meteorite, a primitive sample unlike other carbonaceous chondrite meteorites, is likely a fragment from a D-type asteroid implanted into the inner main belt. This would effectively make it the first known hand sample with the same composition as Kuiper Belt objects.

Crustal Failure on Icy Moons and Satellites from a Strong Tidal Encounter

Crustal Failure on Icy Moons and Satellites from a Strong Tidal Encounter

Authors:

Quillen et al

Abstract:

Close tidal encounters among large planetesimals and satellites should have been more common than grazing or normal impacts. Using a mass spring model within an N-body simulation, we simulate the deformation of the surface of an elastic spherical body caused by a close parabolic tidal encounter with a body that has similar mass as that of the primary body. Such an encounter can induce sufficient stress on the surface to cause brittle failure of an icy crust and simulated fractures can extend a large fraction of the radius of body. Strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy moons and satellites such as Dione, Tethys, Ariel and Charon.

Solar System Asteroid Belt Best Explained as Remnants of Planetary Formation Collisions, not Pristine, Remnant Planetesimals

Erosive Hit-and-Run Impact Events: Debris Unbound

Authors:

Sarid et al

Abstract:

Erosive collisions among planetary embryos in the inner solar system can lead to multiple remnant bodies, varied in mass, composition and residual velocity. Some of the smaller, unbound debris may become available to seed the main asteroid belt. The makeup of these collisionally produced bodies is different from the canonical chondritic composition, in terms of rock/iron ratio and may contain further shock-processed material. Having some of the material in the asteroid belt owe its origin from collisions of larger planetary bodies may help in explaining some of the diversity and oddities in composition of different asteroid groups.

Impacts Induced Martian Surface Heating?

Impact inducted surface heating by planetesimals on early Mars

Authors:

Maindl et al

Abstract:

We investigate the influence of impacts of large planetesimals and small planetary embryos on the early Martian surface on the hydrodynamic escape of an early steam atmosphere that is exposed to the high soft X-ray and EUV flux of the young Sun. Impact statistics in terms of number, masses, velocities, and angles of asteroid impacts onto the early Mars are determined via n-body integrations. Based on these statistics, smoothed particle hydrodynamics (SPH) simulations result in estimates of energy transfer into the planetary surface material and according surface heating. For the estimation of the atmospheric escape rates we applied a soft X-ray and EUV absorption model and a 1-D upper atmosphere hydrodynamic model to a magma ocean-related catastrophically outgassed steam atmosphere with surface pressure values of 52 bar H2O and 11 bar CO2. The estimated impact rates and energy deposition onto an early Martian surface can account for substantial heating. The energy influx and conversion rate into internal energy is most likely sufficient to keep a shallow magma ocean liquid for an extended period of time. Higher surface temperatures keep the outgassed steam atmosphere longer in vapor form and therefore enhance its escape to space within about 0.6 Myr after its formation.