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Scientists Find Extreme Oxygen Isotope Variation In Meteorite

NASA research on a meteorite has provided new evidence that the inner planets formed from materials spread far and wide in the early solar system, and not just from nearby matter.
Oxygen isotopic measurements in the core and outer rim of a calcium-aluminum-rich inclusion contained in the Allende meteorite record the entire range of oxygen isotopic composition previously measured in all solids in the solar system.
The research provides the first measurements to show that early forming solids experienced vastly varying environments during the planet-forming period of our solar system. The study substantiates ideas that the terrestrial planets - Earth, Mars, Mercury and Venus - formed as a result of materials accreting from various sources across the protoplanetary disk rather than from just a nearby region. The findings will be published online March 4 in the journal Science.

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Solar protoplanetary nebula
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Oxygen isotope analysis tells of the wandering life of a dust grain 4.5 billion years ago

Scientists have performed a micro-probe analysis of the core and outer layers of a pea-sized piece of a meteorite some 4.57 billion years old to reconstruct the history of its formation, providing the first evidence that dust particles like this one experienced wildly varying environments during the planet-forming years of our solar system.
The researchers interpret these findings as evidence that dust grains travelled over large distances as the swirling protoplanetary nebula condensed into planets. The single dust grain they studied appears to have formed in the hot environment of the sun, may have been thrown out of the plane of the solar system to fall back into the asteroid belt, and eventually recirculated back to the sun.

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The solar system could be almost two million years older than previously thought, scientists have discovered using evidence from one of the oldest meteorites.
Researchers revised the age after analysing a mineral "relic" buried deep within the meteorite, known as an inclusion, found in the Sahara desert in northwest Africa.
These minerals, from a 1.49-kilo meteorite found in the Moroccan desert in 2004, are among the oldest solid materials formed following the birth of the Sun.

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A New Theory on Why the Sun Never Swallowed the Earth

When the planets in our Solar System first formed, they were swimming through a disk-shaped cloud of gas. Their passage roiled and compressed the gas, and the gravity of the compressed gas in turn pulled on the proto-planets. The original models suggested that the net effect would have been to drag the proto-planets inward - and while the drag would have stopped as the gas eventually dissipated, it would have been too late. They would long since have fallen into the Sun.
But those early models didn't take into account the fact that compressed gas heats up, which limits how dense it can become, and in turn limits how hard its gravity can pull on the proto-planets. Beyond that, the planets' own gravity would fling gas around - the same sort of phenomenon NASA counts on when a spacecraft on its way to Saturn, say, gets a slingshot velocity boost from Jupiter on the way.

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How Earth avoided falling into the sun

As the planets are forming, they are also thought to migrate within the surrounding dust disk. The classic picture of this planet migration suggests that planets like (and including) the Earth should have plummeted into the sun while they were still planetesimals.

"Well, this contradicts basic observational evidence, like We. Are. Here" - astronomer Moredecai-Mark Mac Low of the American Museum of Natural History in New York.

Mac Low and his colleagues investigated this apparent paradox and came up with a new model that explains how planets can migrate as they're forming and still avoid a fiery premature death. He presented these findings here today at the 215th meeting of the American Astronomical Society.


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Planetary migration
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For the last 20 years, the best models of planet formation have contradicted the very existence of Earth. These models assumed locally constant temperatures within a disk, and the planets plunge into the Sun. Now, new simulations from researchers at the American Museum of Natural History and the University of Cambridge show that variations in temperature can lead to regions of outward and inward migration that safely trap planets on orbits.
When the protoplanetary disk begins to dissipate, planets are left behind, safe from impact with their parent star.
The results of this research are being presented at the 2010 meeting of the American Astronomical Society in Washington, D.C.

Source American Museum of Natural History


Title: A torque formula for non-isothermal Type I planetary migration - I. Unsaturated horseshoe drag
Authors: S. Paardekooper, C. Baruteau, A. Crida, W. Kley
(24 Sep 2009)

We study the torque on low-mass planets embedded in protoplanetary discs in the two-dimensional approximation, incorporating non-isothermal effects. We couple linear estimates of the Lindblad (or wave) torque to a simple, but non-linear, model of adiabatic corotation torques (or horseshoe drag), resulting in a simple formula that governs Type I migration in non-isothermal discs. This formula should apply in optically thick regions of the disc, where viscous and thermal diffusion act to keep the horseshoe drag unsaturated. We check this formula against numerical hydrodynamical simulations, using three independent numerical methods, and find good agreement.

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Lead-lead (Pb-Pb) dating is among the most widely used radiometric dating techniques to determine the age of really old things, such as the age of the Earth or the Solar System. However, recent advances in instrumentation now allow scientists to make more precise measurements that promise to revolutionize the way the ages of some samples are calculated with this technique.
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Planetary formation
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Title: Forming Jupiter, Saturn, Uranus and Neptune in Few Million Years by Core Accretion
Authors: Omar G. Benvenuto, Andrea Fortier, Adrian Brunini

Giant planet formation process is still not completely understood. The current most accepted paradigm, the core instability model, explains several observed properties of the solar system's giant planets but, to date, has faced difficulties to account for a formation time shorter than the observational estimates of protoplanetary disks' lifetimes, especially for the cases of Uranus and Neptune. In the context of this model, and considering a recently proposed primordial solar system orbital structure, we performed numerical calculations of giant planet formation. Our results show that if accreted planetesimals follow a size distribution in which most of the mass lies in 30-100 meter sized bodies, Jupiter, Saturn, Uranus and Neptune may have formed according to the nucleated instability scenario. The formation of each planet occurs within the time constraints and they end up with core masses in good agreement with present estimations.

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Craters on Vesta and Ceres could hold key to Jupiter's age
Crater patterns on Vesta and Ceres could help pinpoint when Jupiter began to form during the evolution of the early Solar System. A study modelling the cratering history of the largest two objects in the asteroid belt, which are believed to be among the oldest in the Solar System, indicates that the type and distribution of craters would show marked changes at different stages of Jupiter's development. Results will be presented by Dr Diego Turrini at the European Planetary Science Congress in Potsdam, Germany, on Monday 14 September.
The study, carried out by scientists at the Italian National Institute for Astrophysics in Rome, explored the hypothesis that one or both objects formed during Jupiter's formation by modelling their cratering histories during the birth of the giant planet. Their simulation described Jupiter's formation in three stages: an initial accretion of its core followed by a stage of rapid gas accretion. This is, in turn, followed by a phase where the gas accretion slows down while the giant planet reaches its final mass. During the last two phases Jupiter's gravitational pull starts to affect more and more distant objects. For each of these phases, the team simulated how Jupiter affected the orbits of asteroids and comets from the inner and outer Solar System, and the likelihood of them being moved onto a collision path with Vesta or Ceres.

"We found that the stage of Jupiter's development made a big difference on the speed of impacts and the origin of potential impactors. When Jupiter's core approaches its critical mass, it causes a sharp increase in low-velocity impacts from small, rocky bodies orbiting nearby to Vesta and Ceres which lead to intense and uniform crater distribution patterns. These low-speed collisions may have helped Vesta and Ceres gather mass. Once Jupiter's core has formed and the planet starts to rapidly accrete gas, it deflects more distant objects onto a collision course with Ceres and Vesta and the impacts become more energetic. Although rocky objects from the inner Solar System are the dominant impactors at this stage, the higher energies of collisions with icy bodies from the outer Solar System make the biggest mark" - Dr Diego Turrini.

The third stage of Jupiter's formation is complicated by a period known as the Late Heavy Bombardment, which occurred around 3.8-4.1 billion years ago. During this time a significant number of objects, rich in organic compounds, from the outer Solar System were injected on planet-crossing orbits with the giant planets and may have reached the Asteroid Belt. In addition, Jupiter is thought to have migrated in its orbit around this time, which would have caused an addition flux of impactors on Vesta and Ceres.
The team will have an opportunity to confirm their results when NASA's Dawn space mission reaches Vesta in 2011 and then flies on for a further rendezvous with Ceres in 2015. Dawn will gather information on the structure and the surface morphology of the two asteroids and send back high-resolution images of crater patterns.

"If we can see evidence of an underlying intense, uniform crater pattern, it will support the theory that one or both of these minor planets formed during the final phases of Jupiter accretion, provided that they aren't obliterated by the later heavy bombardment. Dawn will also measure concentrations of organic material, which may give us further information about the collisional history with organic-rich objects from the outer Solar System" - Dr Diego Turrini.

Source: European Planetology Network

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Wadsleyite
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By slamming materials together, scientists have made a mineral that is found naturally only in meteorites and the deep layers of Earth's mantle.
Their successful "shock" experiment reveals new clues about the formation of our early Solar System.
The team report the production of the mineral wadsleyite in the journal PNAS.
Its creation in the lab shows that objects that collided to form the planets may have been far smaller than previously thought.

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