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Bits of dust and gas gathered into clumps, and boulder-size bodies careened into each other, forming asteroids and ultimately planets. A lot went on in the infant solar system, and new research suggests that some of it happened in a hurry.
A study published supports theoretical models in which some planetesimals--asteroids and other building blocks of planets--had already formed, heated up, and partially cooled a mere 5 million years after the birth of the solar system. The analysis identifies the radioactive isotope aluminum-26 as the heat source that melted these primitive rocks.

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A University of Toronto-led study has uncovered tiny zircon crystals in a meteorite originating from Vesta (a large asteroid between Mars and Jupiter) shedding light on the formation of planetesimals, small astronomical objects that form the basis of planets.
To date, studying zircons in eucrites meteorites formed by volcanic activity has been difficult due to impact- induced fracturing and their small size, typically less than five microns. Most eucrites are formed within the asteroid belt that orbits Mars and Jupiter, a heap of astronomical debris from the earliest epoch of the solar system. In a study published in the recent issue of Science, researchers collected samples from eucrites found in Antarctica believed to have originated from Vesta. The researchers used new technology to reveal that asteroids boiling rock turned solid and crystallised within less than 10 million years of solar system formation.

Until now we have not been able to determine this time frame unambiguously. By pinpointing the timeframe were able to add one more piece to the geological and historical map of our solar system -  Professor Gopalan Srinivasan, lead author, University of Torontos Department of Geology.

Scientists believe that at some point Vesta was quickly heated and then melted into a metallic and silicate core, a similar process that happened on the Earth. The energy for this process was released from the radioactive decay that was present in abundance in the early solar system. What has been unclear is when this process occurred. Equipped with the ion microprobe at the Swedish National Museum, Srinivasan and colleagues from four institutions set to analyse the zircons in the eucrites, which formed when a radioactive element hafnium-182 was still alive. Radioactive hafnium-182 decays to another element tungsten-182 with a nearly 9 million year half-life span. By studying zircons for their 182 tungsten abundance, the researchers were able to determine the crystallisation ages of eucrites occurred within that timeframe.

Zircons on Earth and in space have basically the same characteristics. They occur when boiling rock crystallises and turns into solid form primary crystallisation products or they could be secondary products caused by heating from impacts. We know Vesta became inactive within first 10 million years of solar system formation which is nearly 4.5 billion years ago. This provides a snapshot of the early solar system and clues to the early evolution of Earths mantle and core  - Gopalan Srinivasan.


From Dust to Planetesimals: Implications for the Solar Protoplanetary Disk from Short-lived Radionuclides

Since the publication of the Protostars and Planets IV volume in 2000, there have been significant advances in our understanding of the potential sources and distributions of short-lived, now extinct, radionuclides in the early Solar System.

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 Scientists have used meteorites from Mars and other planetary bodies to help resolve how the Earth's core formed.
Comparing meteorites provided by the Natural History Museum, with terrestrial rocks, scientists discovered that the Earth's metallic iron core, the area that gives the Earth its magnetic field, is very likely to contain small amounts of silicon.
Silicon is the major constituent of the silicate minerals and rocks that build the Earth's crust and underlying mantle. However, there has been no direct evidence that light elements, such as silicon, exist in the Earth's core since the idea was proposed by Harvard geophysicist Francis Birch in 1952.

The international team, lead by Alex Halliday from Oxford University, applied novel analytical techniques and compared the abundance of isotopes of the element silicon in meteorites with those in rocks from Earth.
Isotopes are atoms of the same element that differ slightly in mass. These small mass differences can be analysed using sophisticated mass-spectrometers and allow the scientists to make conclusions as to how rocks formed.
The team looked for silicon's three stable isotopes with the masses 28, 29 and 30, and found that meteorites from Mars and a large asteroid known as Vesta have higher proportions of light silicon with the mass 28, when compared with rocks from the Earth and the Moon.
The team concluded that this small mass difference of silicon was caused during core formation, when silicon was incorporated into the core.

To the team's surprise they found no evidence for such processes on Mars and Vesta, even though they both also have iron cores.
This difference could be explained because the Earth is eight times larger than Mars and would have experienced much higher temperatures and pressures during core formation. Such high pressures and temperatures are required for silicon to be present in the metallic core.
These findings provide new evidence that the Earth's core formed under different conditions from those on Mars and Vesta.

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These Hubble Space Telescope images of Vesta and Ceres show two of the most massive asteroids in the asteroid belt, a region between Mars and Jupiter. The images are helping astronomers plan for the Dawn spacecrafts tour of these hefty asteroids.
These Hubble Space Telescope images of Vesta and Ceres show two of the most massive asteroids in the asteroid belt, a region between Mars and Jupiter. The images are helping astronomers plan for the Dawn spacecraft's tour of these hefty asteroids.

On July 7, NASA is scheduled to launch the spacecraft on a four-year journey to the asteroid belt. Once there, Dawn will do some asteroid-hopping, going into orbit around Vesta in 2011 and Ceres in 2015. Dawn will be the first spacecraft to orbit two targets. At least 100,000 asteroids inhabit the asteroid belt, a reservoir of leftover material from the formation of our solar-system planets 4.6 billion years ago.
Dawn also will be the first satellite to tour a dwarf planet. The International Astronomical Union named Ceres one of three dwarf planets in 2006. Ceres is round like planets in our solar system, but it does not clear debris out of its orbit as our planets do.
To prepare for the Dawn spacecraft's visit to Vesta, astronomers used Hubble's Wide Field Planetary Camera 2 to snap new images of the asteroid. The image at right was taken on May 14 and 16, 2007. Using Hubble, astronomers mapped Vesta's southern hemisphere, a region dominated by a giant impact crater formed by a collision billions of years ago. The crater is 456 kilometers across, which is nearly equal to Vesta's 530-kilometer diameter. If Earth had a crater of proportional size, it would fill the Pacific Ocean basin. The impact broke off chunks of rock, producing more than 50 smaller asteroids that astronomers have nicknamed "vestoids." The collision also may have blasted through Vesta's crust.

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Hubble space telescope image of Vesta.


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Credit NASA

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Tatahouine
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In the 1970s, an army of extraterrestrials invaded the desert of Tunisia: R2-D2, C-3PO, Darth Vader, and a whole bunch of storm troopers. They were filming scenes for the original "Star Wars" movie, set on the planet Tatooine.

Latitude: 32 55' 60N - Longitude: 10 26' 60E

But almost a half-century earlier, the real Tatahouine -- a small Tunisian village that inspired the fictional planet's name -- received a real cosmic visitor: a meteor that exploded in the atmosphere, showering tiny fragments of rock across the desert.

The explosion took place 75 years ago tonight. Villagers headed into the desert to examine the site, and picked up more than 25 pounds of fragments -- most of them the size of pebbles. In the 1990s, scientists found about three pounds more.
Today, meteorite collectors call these olive-green fragments the "little green stones from space." They contain large mineral crystals that formed in a pool of molten rock that cooled slowly.
Astronomers say the rocks may have formed on Vesta, one of the largest asteroids. It orbits the Sun between Mars and Jupiter.
Sometime in the distant past, another asteroid slammed into Vesta, blasting pieces into space. Many of these pieces have found their way to Earth -- including the parent body of the Tatahouine meteorites. As it plunged into Earth's atmosphere, the sudden deceleration caused it to explode. Pieces of rock rained across the desert -- forming Tunisia's second-most famous extraterrestrial visitors.

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Since 30 years, Vesta, one of the three largest main belt bodies, poses a problem to the scientists: "Given that its basaltic surface is roughly similar to the lunar surface, which is intensely space weathered, why is Vesta not?" Astronomers from the Paris Observatory (LESIA), the Observatory of Catania and from the CEREGE laboratory brought for the first time a plausible explanation to this question, suggesting the presence of a magnetic field on this asteroid!

The Solar Wind (ions and electrons) affects Solar System bodies that are not protected by an atmosphere or a magnetosphere (e.g. the Moon and asteroids), altering the optical properties of their soil. This alteration changes the spectral properties of silicate-rich objects, inducing progressive darkening and reddening of the solar reflectance spectra in the UV-Vis-NIR range .

The surface of the asteroid Vesta, one of the three largest main belt bodies (D = 529 ± 10 km), is surprisingly pristine. Recent ion irradiation experiments on pyroxenes have shown significant reddening and darkening of the collected spectra with progressive irradiation. Since pyroxene is a major surface component of Vesta as determined by spectroscopy, a team from the Paris Observatory led by Pierre Vernazza aimed to test whether the solar wind irradiation alters significantly the optical properties of the surface of Vesta.



Consequently, an ion irradiation experiment has been performed (at the Observatory of Catania) on a eucrite meteorite (basalt) called Bereba, which characterises well the surface of Vesta, in order to simulate the solar wind irradiation on this asteroid.

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