Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userForming Mercury by Giant Impacts
122
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The origin of Mercurys high iron-to-rock ratio is still unknown. In this work we investigate Mercurys formation via giant impacts and consider the possibilities of a single giant impact, a hit-and-run, and multiple collisions in one theoretical framework. We study the standard collision parameters (impact velocity, mass ratio, impact parameter), along with the impactors composition and the cooling of the target. It is found that the impactors composition affects the iron distribution within the planet and the final mass of the target by up to 15%, although the resulting mean iron fraction is similar. We suggest that an efficient giant impact requires to be head-on with high velocities, while in the hit-and-run case the impact can occur closer to the most probable collision angle (45$^{circ}$). It is also shown that Mercurys current iron-to-rock ratio can be a result of multiple-collisions, with their exact number depending on the collision parameters. Mass loss is found to be more significant when the collisions are tight in time.
rate research
Read More
In our solar system, Mars-sized protoplanets frequently collided with each other during the last stage of terrestrial planet formation called the giant impact stage. Giant impacts eject a large amount of material from the colliding protoplanets into the terrestrial planet region, which may form debris disks with observable infrared excesses. Indeed, tens of warm debris disks around young solar-type stars have been observed. Here, we quantitatively estimate the total mass of ejected materials during the giant impact stages. We found that $sim$0.4 times the Earths mass is ejected in total throughout the giant impact stage. Ejected materials are ground down by collisional cascade until micron-sized grains are blown out by radiation pressure. The depletion timescale of these ejected materials is determined primarily by the mass of the largest body among them. We conducted high-resolution simulations of giant impacts to accurately obtain the mass of the largest ejected body. We then calculated the evolution of the debris disks produced by a series of giant impacts and depleted by collisional cascades to obtain the infrared excess evolution of the debris disks. We found that the infrared excess is almost always higher than the stellar infrared flux throughout the giant impact stage ($sim$100 Myr) and is sometimes $sim$10 times higher immediately after a giant impact. Therefore, giant impact stages would explain the infrared excess from most observed warm debris disks. The observed fraction of stars with warm debris disks indicates that the formation probability of our solar system-like terrestrial planets is approximately 10%.
The detectability of planetesimal impacts on imaged exoplanets can be measured using Jupiter during the 1994 comet Shoemaker-Levy 9 events as a proxy. By integrating the whole planet flux with and without impact spots, the effect of the impacts at wavelengths from 2 - 4 microns is revealed. Jupiters reflected light spectrum in the near-infrared is dominated by its methane opacity including a deep band at 2.3 microns. After the impact, sunlight that would have normally been absorbed by the large amount of methane in Jupiters atmosphere was instead reflected by the cometary material from the impacts. As a result, at 2.3 microns, where the planet would normally have low reflectivity, it brightened substantially and stayed brighter for at least a month.
The giant impact hypothesis for Moon formation successfully explains the dynamic properties of the Earth-Moon system but remains challenged by the similarity of isotopic fingerprints of the terrestrial and lunar mantles. Moreover, recent geochemical evidence suggests that the Earths mantle preserves ancient (or primordial) heterogeneity that predates the Moon-forming giant impact. Using a new hydrodynamical method, we here show that Moon-forming giant impacts lead to a stratified starting condition for the evolution of the terrestrial mantle. The upper layer of the Earth is compositionally similar to the disk, out of which the Moon evolves, whereas the lower layer preserves proto-Earth characteristics. As long as this predicted compositional stratification can at least partially be preserved over the subsequent billions of years of Earth mantle convection, the compositional similarity between the Moon and the accessible Earths mantle is a natural outcome of realistic and high-probability Moon-forming impact scenarios. The preservation of primordial heterogeneity in the modern Earth not only reconciles geochemical constraints but is also consistent with recent geophysical observations. Furthermore, for significant preservation of a proto-Earth reservoir, the bulk composition of the Earth-Moon system may be systematically shifted towards chondritic values.
Voyager 2 observations revealed that the internal luminosity of Neptune is an order of magnitude higher than that of Uranus. If the two planets have similar interior structures and cooling histories, the luminosity of Neptune can only be explained by invoking some energy source beyond gravitational contraction. This paper investigates whether Centaur impacts could provide the energy necessary to produce the luminosity of Neptune. The major findings are (1) that impacts on both Uranus and Neptune are too infrequent to provide luminosities of order the observed value for Neptune, even for optimistic impact-rate estimates, and (2) that Uranus and Neptune rarely have significantly different impact-generated luminosities at any given time. Uranus and Neptune most likely have structural differences that force them to cool and contract at different rates.
Recent work has shown that sulfur hazes may arise in the atmospheres of some giant exoplanets due to the photolysis of H$_{2}$S. We investigate the impact such a haze would have on an exoplanets geometric albedo spectrum and how it may affect the direct imaging results of WFIRST, a planned NASA space telescope. For temperate (250 K $<$ T$_{rm eq}$ $<$ 700 K) Jupiter--mass planets, photochemical destruction of H$_{2}$S results in the production of $sim$1 ppmv of seight between 100 and 0.1 mbar, which, if cool enough, will condense to form a haze. Nominal haze masses are found to drastically alter a planets geometric albedo spectrum: whereas a clear atmosphere is dark at wavelengths between 0.5 and 1 $mu$m due to molecular absorption, the addition of a sulfur haze boosts the albedo there to $sim$0.7 due to scattering. Strong absorption by the haze shortward of 0.4 $mu$m results in albedos $<$0.1, in contrast to the high albedos produced by Rayleigh scattering in a clear atmosphere. As a result, the color of the planet shifts from blue to orange. The existence of a sulfur haze masks the molecular signatures of methane and water, thereby complicating the characterization of atmospheric composition. Detection of such a haze by WFIRST is possible, though discriminating between a sulfur haze and any other highly reflective, high altitude scatterer will require observations shortward of 0.4 $mu$m, which is currently beyond WFIRSTs design.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
