* Astronomy

Giant planet ejected from the solar system
 
The solar system may have given up a giant planet and spared the Earth, according to an article recently published in The Astrophysical Journal Letters.
Clues suggest that the orbits of giant planets were affected by a dynamical instability when the solar system was only about 600 million years old. As a result, the giant planets and smaller bodies scattered away from each other.
Some small bodies moved into the Kuiper Belt and others travelled inward, producing impacts on the terrestrial planets and the Moon. The giant planets moved as well. Jupiter, for example, scattered most small bodies outward and moved inward.
Read more

Title: A Hot Gap Around Jupiter's Orbit in the Solar Nebula
Authors: N. J. Turner, M. Choukroun, J. Castillo-Rogez, G. Bryden

The Sun was an order of magnitude more luminous during the first few hundred thousand years of its existence, due in part to the gravitational energy released by material accreting from the Solar nebula. If Jupiter was already near its present mass, the planet's tides opened an optically-thin gap in the nebula. We show using Monte Carlo radiative transfer calculations that sunlight absorbed by the nebula and re-radiated into the gap raised temperatures well above the sublimation threshold for water ice, with potentially drastic consequences for the icy bodies in Jupiter's feeding zone. Bodies up to a meter in size were vaporized within a single orbit if the planet was near its present location during this early epoch. Dust particles lost their ice mantles, and planetesimals were partially to fully devolatilized, depending on their size. Scenarios in which Jupiter formed promptly, such as those involving a gravitational instability of the massive early nebula, must cope with the high temperatures. Enriching Jupiter in the noble gases through delivery trapped in clathrate hydrates will be more difficult, but might be achieved by either forming the planet much further from the star, or capturing planetesimals at later epochs. The hot gap resulting from an early origin for Jupiter also would affect the surface compositions of any primordial Trojan asteroids.

Read more (1654kb, PDF)

Title: Young Solar System's Fifth Giant Planet?
Authors: David Nesvorny

Recent studies of solar system formation suggest that the solar system's giant planets formed and migrated in the protoplanetary disk to reach resonant orbits with all planets inside 15 AU from the Sun. After the gas disk's dispersal, Uranus and Neptune were likely scattered by gas giants, and approached their current orbits while dispersing the transplanetary disk of planetesimals, whose remains survived to this time in the region known as the Kuiper belt. Here we performed N-body integrations of the scattering phase between giant planets in an attempt to determine which initial states are plausible. We found that the dynamical simulations starting with a resonant system of four giant planets have a low success rate in matching the present orbits of giant planets, and various other constraints (e.g., survival of the terrestrial planets). The dynamical evolution is typically too violent, if Jupiter and Saturn start in the 3:2 resonance, and leads to final systems with fewer than four planets. Several initial states stand out in that they show a relatively large likelihood of success in matching the constraints. Some of the statistically best results were obtained when assuming that the solar system initially had five giant planets and one ice giant, with the mass comparable to that of Uranus and Neptune, was ejected to interstellar space by Jupiter. This possibility appears to be conceivable in view of the recent discovery of a large number free-floating planets in interstellar space, which indicates that planet ejection should be common.

Read more  (65kb, PDF)

From candy floss to rock: study provides new evidence about beginnings of the Solar System

The earliest rocks in our Solar System were more like candy floss than the hard rock that we know today, according to research published in the journal Nature Geoscience.
The work, by researchers from Imperial College London and other international institutions, provides the first geological evidence to support previous theories, based on computer models and lab experiments, about how the earliest rocks were formed. The study adds weight to the idea that the first solid material in the Solar System was fragile and extremely porous - much like candy floss - and that it was compacted during periods of extreme turbulence into harder rock, forming the building blocks that paved the way for planets like Earth.
Read more