Collision With a 2 Earth Mass Planet Shaped Uranus' Evolution

Uranus was hit by a massive object roughly twice the size of Earth that caused the planet to tilt and could explain its freezing temperatures, according to new research.

Astronomers at Durham University, UK, led an international team of experts to investigate how Uranus came to be tilted on its side and what consequences a giant impact would have had on the planet's evolution.

The team ran the first high-resolution computer simulations of different massive collisions with the ice giant to try to work out how the planet evolved.

The research confirms a previous study which said that Uranus' tilted position was caused by a collision with a massive object - most likely a young proto-planet made of rock and ice - during the formation of the solar system about 4 billion years ago.

The simulations also suggested that debris from the impactor could form a thin shell near the edge of the planet's ice layer and trap the heat emanating from Uranus' core. The trapping of this internal heat could in part help explain Uranus' extremely cold temperature of the planet's outer atmosphere (-216 degrees Celsius, -357 degrees Fahrenheit), the researchers said.

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paper link.

preprint link.

Did Earth's Carbon Come From a Mercurcy Sized Protoplanetary Impact?

Research by Rice University Earth scientists suggests that virtually all of Earth's life-giving carbon could have come from a collision about 4.4 billion years ago between Earth and an embryonic planet similar to Mercury.

In a new study this week in Nature Geoscience, Rice petrologist Rajdeep Dasgupta and colleagues offer a new answer to a long-debated geological question: How did carbon-based life develop on Earth, given that most of the planet's carbon should have either boiled away in the planet's earliest days or become locked in Earth's core?

"The challenge is to explain the origin of the volatile elements like carbon that remain outside the core in the mantle portion of our planet," said Dasgupta, who co-authored the study with lead author and Rice postdoctoral researcher Yuan Li, Rice research scientist Kyusei Tsuno and Woods Hole Oceanographic Institute colleagues Brian Monteleone and Nobumichi Shimizu.

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When did Mars Form a Crust and Mantle?

Is Planet Nine a Captured Exoplanet?

One of the Biggest Mysteries About Mars: Why is it so Small?

The presence of water isn’t the only Mars mystery scientists are keen to probe. Another centers around a seemingly trivial characteristic of the Red Planet: its size. Classic models of solar system formation predict that the girth of rocky worlds should grow with their distance from the sun. Venus and Earth, for example, should exceed Mercury, which they do. Mars should at least match Earth, which it doesn’t. The diameter of the Red Planet is little more than half that of Earth (1, 2).

“We still don’t understand why Mars is so small,” says astronomer Anders Johansen, who builds computational models of planet formation at Lund University in Sweden. “It’s a really compelling question that drives a lot of new theories.”

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Impact-induced melting during accretion of the Earth

Impact-induced melting during accretion of the Earth

Authors:

de Vries et al

Abstract:

Because of the high energies involved, giant impacts that occur during planetary accretion cause large degrees of melting. The depth of melting in the target body after each collision determines the pressure and temperature conditions of metal-silicate equilibration and thus geochemical fractionation that results from core-mantle differentiation. The accretional collisions involved in forming the terrestrial planets of the inner Solar System have been calculated by previous studies using N-body accretion simulations. Here we use the output from such simulations to determine the volumes of melt produced and thus the pressure and temperature conditions of metal-silicate equilibration, after each impact, as Earth-like planets accrete. For these calculations a parametrised melting model is used that takes impact velocity, impact angle and the respective masses of the impacting bodies into account. The evolution of metal-silicate equilibration pressures (as defined by evolving magma ocean depths) during Earth's accretion depends strongly on the lifetime of impact-generated magma oceans compared to the time interval between large impacts. In addition, such results depend on starting parameters in the N-body simulations, such as the number and initial mass of embryos. Thus, there is the potential for combining the results, such as those presented here, with multistage core formation models to better constrain the accretional history of the Earth.

Could Planet Nine Have Formed in its Current Orbit

Making Planet Nine: Pebble Accretion at 250--750 AU in a Gravitationally Unstable Ring

Authors:

Kenyon et al

Abstract:

We investigate the formation of icy super-Earth mass planets within a gravitationally unstable ring of solids orbiting at 250-750 AU around a 1 solar mass star. Coagulation calculations demonstrate that a system of a few large oligarchs and a swarm of pebbles generates a super-Earth within 100-200 Myr at 250 AU and within 1-2 Gyr at 750 AU. Systems with more than ten oligarchs fail to yield super-Earths over the age of the solar system. As these systems evolve, destructive collisions produce detectable debris disks with luminosities of 10−5 to 10−3 relative to the central star.

Is Planet Nine a Scattered Giant From the Inner Solar System?

Making Planet Nine: A Scattered Giant in the Outer Solar System

Authors:

Bromley et al

Abstract:

Correlations in the orbits of several minor planets in the outer solar system suggest the presence of a remote, massive Planet Nine. With at least ten times the mass of the Earth and a perihelion well beyond 100 AU, Planet Nine poses a challenge to planet formation theory. Here we expand on a scenario in which the planet formed closer to the Sun and was gravitationally scattered by Jupiter or Saturn onto a very eccentric orbit in an extended gaseous disk. Dynamical friction with the gas then allowed the planet to settle in the outer solar system. We explore this possibility with a set of numerical simulations. Depending on how the gas disk evolves, scattered super-Earths or small gas giants settle on a range of orbits, with perihelion distances as large as 300 AU. Massive disks that clear from the inside out on million-year time scales yield orbits that allow a super-Earth or gas giant to shepherd the minor planets as observed. A massive planet can achieve a similar orbit in a persistent, low-mass disk over the lifetime of the solar system.

Is Planet Nine Really a Captured Exoplanet and how Could we Tell?

Is there an exoplanet in the Solar System?

Authors:

Mustill et al

Abstract:

We investigate the prospects for the capture of the proposed Planet 9 from other stars in the Sun's birth cluster. Any capture scenario must satisfy three conditions: the encounter must be more distant than ~150 au to avoid perturbing the Kuiper belt; the other star must have a wide-orbit planet (a>~100au); the planet must be captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit Solar System bodies. Here we use N-body simulations to show that these criteria may be simultaneously satisfied. In a few percent of slow close encounters in a cluster, bodies are captured onto heliocentric, Planet 9-like orbits. During the ~100 Myr cluster phase, many stars are likely to host planets on highly-eccentric orbits with apastron distances beyond 100 au if Neptune-sized planets are common and susceptible to planet--planet scattering. While the existence of Planet 9 remains unproven, we consider capture from one of the Sun's young brethren a plausible route to explain such an object's orbit. Capture appears to predict a large population of Trans-Neptunian Objects (TNOs) whose orbits are aligned with the captured planet, and we propose that different formation mechanisms will be distinguishable based on their imprint on the distribution of TNOs.

Is the Grand Tack Model Compatible with Our Asteroid Belt?

Is the Grand Tack model compatible with the orbital distribution of main belt asteroids?

Authors:

Deienno et al

Abstract:

The Asteroid Belt is characterized by the radial mixing of bodies with different physical properties, a very low mass compared to Minimum Mass Solar Nebula expectations and has an excited orbital distribution, with eccentricities and inclinations covering the entire range of values allowed by the constraints of dynamical stability. Models of the evolution of the Asteroid Belt show that the origin of its structure is strongly linked to the process of terrestrial planet formation. The Grand Tack model presents a possible solution to the conundrum of reconciling the small mass of Mars with the properties of the Asteroid Belt, including the mass depletion, radial mixing and orbital excitation. However, while the inclination distribution produced in the Grand Tack model is in good agreement with the one observed, the eccentricity distribution is skewed towards values larger than those found today. Here, we evaluate the evolution of the orbital properties of the Asteroid Belt from the end of the Grand Tack model (at the end of the gas nebula phase when planets emerge from the dispersing gas disk), throughout the subsequent evolution of the Solar System including an instability of the Giant Planets approximately 400 Myr later. Before the instability, the terrestrial planets were modeled on dynamically cold orbits with Jupiter and Saturn locked in a 3:2 mean motion resonance. The model continues for an additional 4.1 Gyr after the giant planet instability. Our results show that the eccentricity distribution obtained in the Grand Tack model evolves towards one very similar to that currently observed, and the semimajor axis distribution does the same. The inclination distribution remains nearly unchanged with a slight preference for depletion at low inclination; this leads to the conclusion that the inclination distribution at the end of the Grand Tack is a bit over-excited. Also, we constrain the primordial eccentricities of Jupiter and Saturn, which have a major influence on the dynamical evolution of the Asteroid Belt and its final orbital structure.

The Fate of Asteroids in a Migrating Jupiter Scenario

THE EVOLUTION OF ASTEROIDS IN THE JUMPING-JUPITER MIGRATION MODEL

Authors:

Roig et al

Abstract:

In this work, we investigate the evolution of a primordial belt of asteroids, represented by a large number of massless test particles, under the gravitational effect of migrating Jovian planets in the framework of the jumping-Jupiter model. We perform several simulations considering test particles distributed in the Main Belt, as well as in the Hilda and Trojan groups. The simulations start with Jupiter and Saturn locked in the mutual 3:2 mean motion resonance plus three Neptune-mass planets in a compact orbital configuration. Mutual planetary interactions during migration led one of the Neptunes to be ejected in less than 10 Myr of evolution, causing Jupiter to jump by about 0.3 AU in semimajor axis. This introduces a large-scale instability in the studied populations of small bodies. After the migration phase, the simulations are extended over 4 Gyr, and we compare the final orbital structure of the simulated test particles to the current Main Belt of asteroids with absolute magnitude H less than 9.7. The results indicate that, in order to reproduce the present Main Belt, the primordial belt should have had a distribution peaked at ~10° in inclination and at ~0.1 in eccentricity. We discuss the implications of this for the Grand Tack model. The results also indicate that neither primordial Hildas, nor Trojans, survive the instability, confirming the idea that such populations must have been implanted from other sources. In particular, we address the possibility of implantation of Hildas and Trojans from the Main Belt population, but find that this contribution should be minor.

Good Grief: Comets and Asteroids Brought 15N Enriched Ammonia to Earth?!

THE PATH OF REDUCED NITROGEN TOWARD EARLY EARTH: THE COSMIC TRAIL AND ITS SOLAR SHORTCUTS

Authors:

Pizzarello et al

Abstract:

Large isotopic anomalies are found in meteoritic insoluble organic materials (IOMs) and, for nitrogen, show 15N-excesses up to ${\delta }^{15}$N ~ 5000‰. These 15N-enrichments are commonly ascribed to presolar origins, but the attribution seems contradicted by available data on N-isotopes' cosmic distribution. We report here that 15N hotspots in several IOMs are reduced by hydrothermal treatment and their loss correlates with 15N values of ammonia released upon treatment. Because released ammonia's 15N-enrichments also relate with meteorites' mineralogy, i.e., asteroidal processes, and no current models offer plausible explanations for the finding, we account for our data with a novel scenario whereby 15N-enriched ammonia produced in the solar nebula is incorporated by carbonaceous materials and delivered to early Earth by comets and meteorites. The proposal also implies that abundant reduced nitrogen, a required element in origins of life theories, could reach our nascent planet and other planetary systems affecting their habitability.

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.

Earth did NOT get its Water From Comets and Carbonaceous Chondrite Asteroids

In the new study, the researchers report the hydrogen isotope ratios of water trapped in glassy inclusions inside the basalts. The results, published online today in Science, reveal that the inclusions have a much lighter isotopic signature than does the ocean, suggesting that the composition of seawater has indeed evolved over time. Although scientists were aware of processes that could cause an isotopic shift in surface waters, Hallis says, “until we made our measurements, we didn’t know whether that would be a measureable difference or not.”

The new data suggest that the difference is vast. And Hallis suspects that the deepest, most primitive material in the mantle should have an even lighter isotopic composition than the inclusions her team measured. That’s because the rising magma that produced the lavas probably mixed with upper mantle rocks, which have been contaminated with isotopically heavy surface water that got dragged down by subducting slabs of tectonic plates.

So what does all this mean for the origin of Earth’s water? For one, the new data throw a wrench in the conventional story that carbonaceous chondrites—a water-rich variety of asteroid—delivered water to an initially dry Earth after its formation. That scenario has been bolstered by similarities in the isotopic signatures of the asteroids and seawater. But the chondrite signatures are too heavy to explain the deep Earth samples, Hallis says. “The carbonaceous chondrites don’t really work.”

link.

Evidence of Organic Molecules From Another Star System From Carbonaceous Chondrite Asteroid

Multiple Cosmic Sources for Meteorite Macromolecules?

Authors:

Sephton et al

Abstract:

The major organic component in carbonaceous meteorites is an organic macromolecular material. The Murchison macromolecular material comprises aromatic units connected by aliphatic and heteroatom-containing linkages or occluded within the wider structure. The macromolecular material source environment remains elusive. Traditionally, attempts to determine source have strived to identify a single environment. Here, we apply a highly efficient hydrogenolysis method to liberate units from the macromolecular material and use mass spectrometric techniques to determine their chemical structures and individual stable carbon isotope ratios. We confirm that the macromolecular material comprises a labile fraction with small aromatic units enriched in 13C and a refractory fraction made up of large aromatic units depleted in 13C. Our findings suggest that the macromolecular material may be derived from at least two separate environments. Compound-specific carbon isotope trends for aromatic compounds with carbon number may reflect mixing of the two sources. The story of the quantitatively dominant macromolecular material in meteorites appears to be made up of more than one chapter.

Theia Wasn't Alone: Uranus Formed From Two Protoplanets Colliding

Stimulated Radiative Molecular Association in the Early Solar System. II. Orbital Radii of the Planets and Other Satellites of the Sun

Author:

Lombardi

Abstract:

In a previous investigation, the orbital radii of regular satellites of Uranus, Jupiter, Neptune, and Saturn are shown to be directly related to photon energies in the spectra of atomic and molecular hydrogen. To explain these observations a model was developed involving stimulated radiative molecular association (SRMA) reactions among photons and atoms in the protosatellite disks of the planets. In the present investigation, the previously developed model is applied to the planets and important satellites of the Sun. A key component of the model involves resonance associated with SRMA. Through this resonance, thermal energy is extracted from the protosun's protoplanetary disk at specific distances from the protosun wherever there is a match between the local thermal energy of the disk and the energy of photons impinging on the disk. Orbital radii of the planets and satellites are related to photon energies (EP values) in the spectrum of atomic hydrogen. An expression determined previously is used to relate EP values to temperatures in the disk. Results indicate the surface temperature of the protosun at the time when the evolution of the planets begins is higher than the surface temperature of a typical T Tauri star. The present investigation offers an explanation for the existence of the asteroid and classical Kuiper belts and predicts that a primordial belt once existed in the vicinity of Neptune. It also indicates that Uranus is formed from two protoplanets and is thus consistent with the theory that the large tilt of Uranus's axis of rotation was created by the collision of two bodies.

Pluto, the Kupier Belt & the Early Compact Solar System

Earth After Theia

Bounding Theia

I suspect the Grand Tack folks ought to think on this one.  It bounds the wandering jupiter in a big way.

Theia Formed in the Same Region as the Earth

A primordial origin for the composition similarity between the Earth and the Moon

Authors:

Mastrobuono-Battisti et al

Abstract:

Most of the properties of the Earth-Moon system can be explained by a collision between a planetary embryo and the growing Earth late in the accretion process. Simulations show that most of the material that eventually aggregates to form the Moon originates from the impactor. However, analysis of the terrestrial and lunar isotopic composition show them to be highly similar. In contrast, the compositions of other solar system bodies are significantly different than the Earth and Moon. This poses a major challenge to the giant impact scenario since the Moon-forming impactor is then thought to also have differed in composition from the proto-Earth. Here we track the feeding zones of growing planets in a suite of simulations of planetary accretion, in order to measure the composition of Moon-forming impactors. We find that different planets formed in the same simulation have distinct compositions, but the compositions of giant impactors are systematically more similar to the planets they impact. A significant fraction of planet-impactor pairs have virtually identical compositions. Thus, the similarity in composition between the Earth and Moon could be a natural consequence of a late giant impact.