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Irregular Satellites

Title: Outer irregular satellites of the planets and their relationship with asteroids, comets and Kuiper Belt objects
Authors: Scott S. Sheppard (Carnegie Institution of Washington)

Outer satellites of the planets have distant, eccentric orbits that can be highly inclined or even retrograde relative to the equatorial planes of their planets. These irregular orbits cannot have formed by circumplanetary accretion and are likely products of early capture from heliocentric orbit.
The irregular satellites may be the only small bodies remaining which are still relatively near their formation locations within the giant planet region. The study of the irregular satellites provides a unique window on processes operating in the young solar system and allows us to probe possible planet formation mechanisms and the composition of the solar nebula between the rocky objects in the main asteroid belt and the very volatile rich objects in the Kuiper Belt.
The gas and ice giant planets all appear to have very similar irregular satellite systems irrespective of their mass or formation timescales and mechanisms. Water ice has been detected on some of the outer satellites of Saturn and Neptune whereas none has been observed on Jupiter's outer satellites.

All 96 Known irregular satellites of the giant planets. The horizontal axis is the ratio of the satellites semi-major axis to the respective planet’s Hill radius. The vertical axis is the orbital eccentricity. The size of the symbol represents the radius of the object: Large symbol r > 25 km, medium symbol 25 > r > 10 km, and small symbol r < 10 km. Again, all 53 known regular satellites would fall near the origin of this plot, where Triton and Mars’ satellites are located.

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Scientists have developed a novel approach to extract organic and inorganic compounds from meteoric materials. It’s called hydropyrolysis.

The new technology uses high hydrogen gas pressures, extreme temperature, and water as a non-destructive means for extracting organic and inorganic compounds.

It had been thought that meteoric material originated from a molecular cloud that collapsed to form the Solar System, however the results of the study contradict that theory.
It was also discovered that meteorites contain high amounts of carbon and nitrogen- elements and several never-before-seen organic molecules.

Hydropyrolysis: A new technique for the analysis of macromolecular material in meteorites
Authors: Sephton, Mark A.; Love, Gordon D.; Meredith, Will; Snape, Colin E.; Sun, Cheng-Gong; Watson, Jonathan S.

The carbonaceous chondrite meteorites are fragments of asteroids that have remained relatively unprocessed since the formation of the Solar System 4.56 billion years ago. The major organic component in these meteorites is a macromolecular phase that is resistant to solvent extraction. The information contained within macromolecular material can be accessed by degradative techniques such as pyrolysis. Hydropyrolysis refers to pyrolysis assisted by high hydrogen gas pressures and a dispersed sulphided molybdenum catalyst.
Hydropyrolysis of the Murchison macromolecular material successfully releases much greater quantities of hydrocarbons than traditional pyrolysis techniques (twofold greater than hydrous pyrolysis) including significant amounts of high molecular weight polyaromatic hydrocarbons (PAH) such as phenanthrene, carbazole, fluoranthene, pyrene, chrysene, perylene, benzoperylene and coronene units with varying degrees of alkylation.
When hydropyrolysis products are collected using a silica trap immersed in liquid nitrogen, the technique enables the solubilisation and retention of compounds with a wide range of volatilities (i.e. benzene to coronene). This report describes the hydropyrolysis method and the information it can provide about meteorite macromolecular material constitution.


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Enstatite chondrite

Important clues to the environment in which the early Earth formed may be emerging from Purdue University scientists' recent study of a particular class of meteorites.
By examining the chemistry of 29 chunks of rock that formed billions of years ago, probably in close proximity to our planet, two Purdue researchers, Michael E. Lipschutz and Ming-Sheng Wang, have clarified our understanding of the conditions present in the vicinity of the ancient Earth's orbit.
Because direct evidence for these conditions is lacking in terrestrial samples, the scientists believe that the composition of these so-called enstatite chondrite (EC) meteorites could offer a window into the planet's distant past.

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"What happened to these rocks most likely happened to the Earth in its early stages – with one great exception. Shortly after the early Earth formed, an object the size of Mars smashed into it, and the heat from the cataclysm irrevocably altered the geochemical makeup of our entire planet. These EC meteorites, however, are likely formed of matter similar to that which formed the early Earth, but they were not involved in this great collision and so were not chemically altered. They might be the last remaining pristine bits of the material that became the planet beneath our feet" - Michael E. Lipschutz, professor of chemistry in Purdue's College of Science.

The research appeared in the Sept. 27 edition of a new journal, Environmental Chemistry, which solicited the paper. Lipschutz said the journal's editorial board includes F. Sherwood Rowland and Mario Molina, who received the Nobel prize for their discovery that Earth's protective ozone layer was threatened by human activity.
Lipschutz and Wang initially set out to increase our knowledge of EC meteorites, one of many different meteorite classes.
Meteorites come from many different parts of the solar system, and a scientist can link one with its parent object by determining the different isotopes of oxygen in a meteorite's minerals.
Chunks of the moon, the Earth and EC meteorites, for example, have very similar isotopic "signatures," quite different from those of Mars and other objects formed in the asteroid belt. The variations occurred because different materials condensed in different regions of the disk of gas and dust that formed the sun and planets.
Bits of these materials orbit the sun, occasionally falling to earth as meteorites. But there is one place on our planet that meteorites accumulate and are preserved in a pristine fashion – the ice sheet of Antarctica.

"Over the millennia, many thousands of meteorites have struck the Antarctic ice sheet, which both preserves them and slowly concentrates them near mountains sticking through the ice, much as ocean waves wash pebbles to the shore. These stones have come from many different parts of the solar system and have given us a better picture of the overall properties of their parent objects" - Michael E. Lipschutz.

By examining their mineralogy, scientists have determined that about 200 of these Antarctic stones are EC meteorites that formed from the same local batch of material as the Earth did more than 4.5 billion years ago.
But there is additional information that the chemistry of these ECs can offer on the temperatures at which they formed. To obtain this information, however, required Lipschutz to analyze chemicals in the meteorites called volatiles – rare elements such as indium, thallium and cadmium.

"Volatiles in meteorites can give unique information on their temperature histories, but only 14 of them had ever been analyzed for these elements. Naturally, we want to know the story behind the formation of objects in our own neighbourhood, so we set out to increase that number" - Michael E. Lipschutz.

In this study, the researchers gathered samples taken from another 15 EC meteorites that had, for the most part, landed in Antarctica tens of thousands of years ago. Using a unique method involving bombardment of the samples with neutrons, chemically separating the radioactive species and counting them, the researchers were able to determine the amounts of 15 volatiles that together offered clues to each rock's heating history.

"Volatiles can act like thermometers. They can tell you whether the temperature was high or low when the rock formed. We tested two different kinds of ECs, and the oldest, most primitive examples of each kind had very similar volatile contents – which means their temperature at formation was similar. These rocks have essentially recorded the temperature at which the early Earth formed, and we now know that this was much lower than 500 degrees Celsius" - Michael E. Lipschutz.

The two different kinds of EC meteorites, known as ELs and EHs, were found in the Purdue study to have condensed at low temperatures like the Earth.
However, the two groups are controversial because scientists have not been able to agree on whether they originated from a single parent object or two different ones. Unfortunately, the data from the 29 ECs they analyzed were insufficient to settle the issue.

"There are still quite a few unanswered questions about the earliest periods of the Earth's history, and this study only provides one piece of the puzzle. But aspects of this study also show that ECs differ substantially from other meteorite types that came from much farther out in the disk, in the region of the asteroid belt" - Michael E. Lipschutz.

For Lipschutz, who had an asteroid named for him on his 50th birthday in honour of his many studies of meteorites, their parent bodies and the early history of the solar system, deeper answers may lie farther away than Antarctica.

"If we understand how our solar system formed, we might be better able to understand the processes at work in other solar systems, which we are just beginning to discover. Probing the asteroid belt could give us clues to these processes" - Michael E. Lipschutz.




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Tagish Lake meteorite

An unusual meteorite that fell on a frozen lake in Canada five years ago has led a Florida State University geochemist to a breakthrough in understanding the origin of the chemical elements that make up our solar system.

Professor Munir Humayun of the National High Magnetic Field Laboratory and the geological sciences department at FSU and Alan Brandon of NASA discovered an isotopic anomaly in the rare element osmium in primitive meteorites.
The anomalous osmium was derived from small stars with a higher neutron density than that which formed our solar system. The findings of the researchers, who also included colleagues from the University of Maryland and Bern University in Switzerland, were recently published in the journal Science.

"Our new data enabled us to catch a glimpse of the different star types that contributed elements to the solar system, the parental stars of our chemical matter. It opens a treasure trove of prospects for exploring the formation of the elements"- Professor Munir Humayun.

The asteroid initially was about 4 meters in diameter with a mass of about 56 metric tons. The meteorite fragmented several times between 50 and 30 kilometres altitude while entering the Earths atmosphere, and heavily ablated until terminal velocity was reached at an altitude of about 28 km.
It was estimated that at this point, only about 1.3 metric tons of rock remained -- 97% of the rock had simply burned-up in the atmosphere, releasing about 1.7 kilotons of energy.
Only about 0.1% of the estimated 1.3 metric tons of surviving rock was ever recovered. This is only 0.002% of the estimated mass of rock that entered the atmosphere.

The largest Tagish Lake stone, originally massing 159 grams, has been broken open to show the gross texture of the meteorite. The right side of the stone shows the fusion crust formed by melting of the surface by friction with the atmosphere as it fell. The cube is 1 cm across.

For about 50 years, scientists have known that all the elements beyond iron in the periodic table were made in stars by up to three nuclear processes. Osmium is mainly formed by two of those processes, the so-called s-process in which neutrons are slowly added to nuclei over a period of perhaps thousands of years in aging, medium-size stars and the r-process that occurs in supernovae in which neutrons are pumped into nuclei at a rate of hundreds of neutrons in a few seconds.

The new data gathered by Humayun's team not only shows the different star types that contribute elements to the solar system, it also will be used to test astrophysical models of production of the chemical elements at a more sophisticated level than previously possible, he said.

Humayun and colleagues studied samples from an extremely fragile meteorite that fell on Tagish Lake on Jan. 18, 2000. Unlike iron meteorites, primitive meteorites like this one are not preserved long on the Earth's surface because they disintegrate and form mud when exposed to water.
This one was retrieved within 48 hours of its fall in the dead of an Arctic winter.

This sequence of pictures was captured by Ewald Lemke on January 18, 2000. It shows the expanding smoke train of the Yukon meteor over a 14-minute period. The first frame shows a smoky red vapour trail just 1 minute and 30 seconds after the initial flash.

Most meteorites have a uniform osmium isotopic distribution, but Humayun's team found that osmium extracted from the Tagish Lake meteorite was deficient in s-process osmium. They are the first to report an anomaly in the isotopic makeup of the element osmium from meteorites.
Other researchers have found isotope anomalies in several other elements in some primitive meteorites, but not in others. Because of the disparity, scientists believed that the ashes of stars that preceded the solar system must have been sprinkled in a non-uniform way into the solar nebula, the disk of gas and dust that formed the sun, planets and meteorites.
Scientists had hypothesized that some of the dust could have been created by an active nearby star.

Humayun's findings challenge that explanation.
He believes that the anomaly is an expression of presolar stardust that survived the homogenization that affected nearly all other meteorites. Typically, stardust accretes to form meteorites and is then heated by radioactivity - a process that destroys the silicon carbide grains that are the carriers of the anomaly. But in the case of the meteorites with osmium isotopic anomalies, the heat was not significant enough to destroy the silicon carbide.

"The previous interpretation of incomplete mixing of different sources of dust at the scale of the solar nebula no longer seems tenable. We now interpret those anomalies as incomplete dissolution of silicon carbide grains that carried traces of molybdenum, ruthenium and osmium. These anomalies reveal that the raw materials from which our solar system was built are preserved in a few exceptional meteorites, from which we can now recover the prehistory of our solar system" - Munir Humayun.




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Earliest meteorites

Earliest meteorites provide new piece in planetary formation puzzle

Researchers trying to work out how the planets formed have uncovered a new clue by analysing meteorites that are older than the Earth.

The research shows that the process which depleted planets and meteorites of so-called volatile elements such as zinc, lead and sodium (in their gaseous form) must have been one of the first things to happen in our nebula. The implication is that 'volatile depletion' may be an inevitable part of planet formation - a feature not just of our Solar System, but of many other planetary systems too.

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Renazzo Meteorite
The Renazzo meteorite fell in Italy in 1824. It's a carbonaceous chondrite of the CR class (Renazzo is the type-specimen). It has been analysed a lot because many researchers believe it is one of the most primitive meteorites - in particular, its organic chemistry appears to be extremely primitive, with a similar set of organic compounds to what we think are present in the interstellar medium.

The researchers at Imperial College London, who are funded by the Particle Physics and Astronomy Research Council (PPARC), reached their conclusions after analysing the composition of primitive meteorites, stony objects that are older than the Earth and which have barely changed since the Solar System was made up of fine dust and gas.

Their analysis, published today in the Proceedings of the National Academy of Sciences, shows that all the components that make up these rocks are depleted of volatile elements. This means that volatile element depletion must have occurred before the earliest solids had formed.
All of the terrestrial planets in the Solar System as far out as Jupiter, including Earth, are depleted of volatile elements. Researchers have long known that this depletion must have been an early process, but it was unknown whether it occurred at the beginning of the formation of the Solar System, or a few million years later.
It might be that volatile depletion is necessary to make terrestrial planets as we know them -as without it our inner solar system would look more like the outer solar system with Mars and Earth looking more like Neptune and Uranus with much thicker atmospheres.

"Studying meteorites helps us to understand the initial evolution of the early Solar System, its environment, and what the material between stars is made of. Our results answer one of a huge number of questions we have about the processes that converted a nebula of fine dust and gas into planets" - Dr Phil Bland, from Imperial's Department of Earth Science and Engineering, who led the research.

"This research shows how looking at the tiniest of fragments of material can help us answer one of the biggest questions asked: 'How did the Solar System form?'. It is fascinating to see how processes that took place over 4.5 billion years ago can be traced in such detail in laboratories on Earth today" - Professor Monica Grady, a planetary scientist from the Open University and member of PPARC's Science Committee.

For planetary scientists, the most valuable meteorites are those that are found immediately after falling to earth, and so are only minimally contaminated by the terrestrial environment. The researchers analysed around half of the approximately 45 primitive meteorite falls in existence around the world, including the Renazzo meteorite which was found in Italy in 1824.
Dr Phil Bland is a member of the Impacts and Astromaterials Research Centre (IARC), which combines planetary science researchers from Imperial College London and the Natural History Museum.




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RE: Oldest meteorite

A new paper on the Fassaite Achondrite, Angrite SAH99555 (Sahara 99555, a 2710g single stone with black fusion crust found in May 1999) was published in the last issue of the scientific journal Nature.

The latest ultra-precise measurement techniques have been used to obtain lead isotope ages for two examples of a rare type of meteorite, called basaltic angrites. These 'differentiated' meteorites are from parent bodies that were once molten and had solidified as a metal core and silicate mantle. Their absolute age is about 4.6 billion years, only a million years younger than the currently accepted minimum age of the Solar System. An excess of magnesium-26 in the angrite samples suggests that aluminium-26 decay triggered melting of the planetesimal that was the parent body.

In the words of co-authors Joel Baker, Director of Geology School of Earth Sciences, University of Wellington, New Zealand, and Martin Bizarro, Leader, MC-ICP-MS Laboratory, University of Copenhagen, Denmark : "Your angrite meteorite find SAH9955 is now the oldest absolutely dated igneous rock in the Solar System, has clear evidence for the former presence of short-lived 26Al in it (which caused planetesimal melting), and very likely will become the "Rosetta Stone" for early Solar System chronology"

Baker and Bizzarro are now able to show that achondrite planetesimals formed before chondrite planetesimals.




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RE: Solar Formation

A Victoria University scientist who has found the key to dating the very beginnings of our Solar System will have his work published in the prestigious scientific journal Nature on the 25th August 2005.
Dr Joel Baker, Senior Lecturer in the School of Earth Sciences, is the lead author of a report that shows it is possible to date the formation of our Solar System’s oldest rocks with unprecedented resolution, using cutting-edge geochemical analytical techniques. The results indicate the Solar System is at least three million years older than previously thought. (Ed - !)

Dr Baker, who completed a Master of Science at Victoria before undertaking a PhD and ten years of research in Europe, says compressing his results onto a more meaningful timeframe can make the significance of his work clearer.

"If the 4.56 billion year history of the Earth is compressed into one day, then Homo Sapiens appeared just a few seconds before the end of the day. In contrast, my colleagues and I are building a picture of the very first seconds of the Solar System to see why and how it formed."

Dr Baker’s analysis of isotopes in an extremely small quantity of lead (one billionth of a gram) from a meteorite found in the Sahara Desert has shown this meteorite is 4.5662 billion years old – just one million years younger than the conventionally accepted age of the Solar System and at least 500 million years older than Earth’s oldest rocks.
This meteorite is an igneous rock, like those erupted from volcanoes on Earth, and is now, thanks to Dr Baker’s research, confirmed as the oldest and most precisely-dated igneous rock in our Solar System.

"Meteorites from space that arrive on Earth mainly come from asteroids that orbit between Mars and Jupiter. These asteroids formed around the young Sun at the very beginning of our Solar System some 4.56 billion years ago. These meteorites are our only direct record of the birth of our Sun and formation of planets around it and, ultimately, why we are here on Earth" - Dr Joel Baker.

The research shows that asteroids hundreds of kilometres across grew in a few hundred thousand years and then melted incredibly quickly.

"However, melting of these asteroids was not caused by the same processes which produce volcanism on Earth. The melting was driven by heating from the decay of short-lived radioactive isotopes that were injected into the young Solar System from the supernova, or explosion, of a nearby dying star. This process may have ultimately triggered Solar System formation, which our results now indicate is at least three million years older than previously thought"

Victoria’s Dean of Science, Professor David Bibby, says Dr Baker has made a remarkable discovery and demonstrated that he is a world leader in his research area.

"Dr Baker is pushing the boundaries in isotopic geochemistry – a field that has exciting applications in fields as diverse as geology, environmental chemistry, archaeology, palaeontology, mining, medicine and, of course, astronomy. The article in Nature recognises the importance of Dr Baker’s research and once again confirms Victoria’s reputation for having leading researchers teaching our students."




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RE: Early Sun

Researchers have found that the Sun was shining brightly, more than 4.5 billion years ago, as dust and gas were still forming the planets of the solar system.
The findings are the first conclusive evidence that the so-called protosun affected the developing the solar system by emitting enough ultraviolet energy to catalyse the formation of organic compounds, water and other elements necessary for the evolution of life on Earth.
It was thought that a strong solar wind from the protosun blew matter from the core into the flat accretion disk (the layer of gas and matter from which meteorites, asteroids and planets later formed).

"The basic question was, Was the sun on or was it off?.
There is nothing in the geological record before 4.55 billion years ago that could answer this
" - Mark Thiemens, University of California San Diego, who led the study.

Thiemens and colleagues studied isotopes, chemical variants, of sulphide compounds, chemical "fingerprints", preserved in primitive chondrite meteorites.
It is no good looking for anything on Earth, which has undergone extensive change since it was formed. But primitive meteorites have been less subject to chemical reactions since they were formed.

The researchers determined that a slight excess of one isotope of sulphur, called 33S, suggests that there were photochemical reactions going on when the little chunks of meteorite coalesced.
The researchers have developed an analytical capability to measure stable isotope variations at ultra-high precision (0.04 parts per thousand) in sulphur (34S/32S, 33S/32S), oxygen (18O/16O, 17O/16O), carbon (13C/12C), and nitrogen (15N/14N).

"This measurement tells us for the first time that the sun was on, that there was enough ultraviolet light to do photochemistry. Knowing that this was the case is a huge help in understanding the processes that formed compounds in the early solar system" - Mark Thiemens.

The researchers hope to use the same technique to look for other elements in meteorites and learn more about the very early solar system.

The study will be published in the near future.



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Scientists at the U.S. National Science Foundation and the European Commission of the European Union have announced a new initiative - called CRONUS, for cosmic-ray produced nuclide systematics--to measure cosmic rays from far-distant supernovas to time the history of the Earth's surface.

Galactic explosions known as supernovas unleash torrents of fantastically energetic atomic particles. Billions of these cosmic rays impact Earth every year.
The infinitesimal particles blast apart the atoms of Earth's atmosphere and rocks, changing them into new elements. Now, NSF has awarded $5.8 million over five years for geologists to measure the accumulated results of these atomic transmutations in rocks at Earth's surface.
Fred Phillips of the New Mexico Institute of Mining and Technology will coordinate the U.S. arm of the project, which includes 13 U.S. universities.

"The CRONUS initiative will benefit all disciplines in the Earth sciences. (Whether geomorphology, tectonics, volcanology, hydrology, geologic hazards, or paleoclimatology) Each needs an improved understanding of geochronology at the Earth's surface" - Herman Zimmerman, director of NSF's division of earth sciences.

Supernovae such as this one, named SN 1993J, give off blasts of cosmic rays that bombard the Earth and change the atomic make up of its surface rock. Researchers supported by the international CRONUS project will measure the effects of cosmic rays to determine the timing of ancient geologic events.

The European Union, through its Marie Curie Actions, has awarded 3.4 million Euro over four years for the project, a research-training network involving research teams in France, Germany, Netherlands, Slovakia, Switzerland the United Kingdom.
Training of early stage and experienced researchers in the novel technique is an integral part of the European CRONUS effort to contribute to the mobility, exchange and training of high-quality European scientists.
Tibor Dunai, now at the Vrije Universiteit, Amsterdam, will coordinate the European arm. He will relocate to the University of Edinburgh in the fall of 2005.

"The ability to date changes in landscapes with cosmogenic nuclides has already revolutionized our understanding of Earth processes. CRONUS will allow us to unlock the great potential this novel technique has, helping us to better understand the environment around us" - Tibor Dunai.

Powerful cosmic-ray particles penetrate only a few feet below the Earth's surface, so deeper rocks are shielded from the buildup of cosmic-ray transmutations. The number of new atoms produced by cosmic rays can thus show the amount of time passed since geological events such as earthquakes, landslides and glaciers.
They can also reveal how fast Earth's surface changes from such forces as erosion by rivers.

"As scientists who use geochronology techniques in the course of their research. We need to know exactly how cosmic rays are distributed on our planet's surface, taking into account variables like longitude, latitude, and elevation, as well as changes occurring over geologic time scales, such as periodic shifts in Earth's magnetic field" - Fred Phillips.

Scientists affiliated with CRONUS will work to understand the fundamentals of cosmic-ray reactions so that they can routinely use them as methods for reconstructing and analyzing environment changes.
When perfected, the new cosmic-ray methods will shed light on Earth's past climate cycles, changes in soil erosion, frequency of floods and landslides, and how weathering of rocks affects global warming and cooling.
Scientists from the United States and Europe will work together sampling rocks from key sites around the world, exposing elements to nuclear beams in high-energy accelerators, and counting cosmic-ray impacts with detectors aboard high-altitude aircraft. These results will all be synthesized in a broad-ranging effort to understand all aspects of the cosmic phenomenon.

"This is a way of bringing the projectiles of exploding stars down to very practical use on earth" - Fred Phillips.




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RE: Solar supernova

NASA and University of Arizona researchers have discovered pristine mineral grains that formed in an ancient supernova explosion.

The grains were among other extraterrestrial dust plucked by high-flying NASA research aircraft from Earth's upper atmosphere after they were delivered to Earth by a comet or primitive asteroid.

It is the first time anyone has ever discovered silicate grains, in this case olivine, from a supernova. They reveal important new information on how much material supernovae contributed to making our sun and planets, including radioactive material used in isotope age-dating techniques.
The discovery also gives astrophysicists important new physical evidence they need to verify complex numerical models of supernovae explosions.

Scott Messenger and Lindsay P. Keller of the NASA Johnson Space Centre in Houston and Dante S. Lauretta of UA's Lunar and Planetary Laboratory are publishing their findings in the current (June 30) issue of Science.

A supernova is a massive star that burns through its nuclear fuel -Layers of hydrogen, of helium, of carbon, oxygen, silicon, sulphur, etc. - all the way down to the element iron. Iron is the end point for stellar nucleosynthesis -- a star can't get energy by fusing iron. When the star runs out of fuel it collapses, forms an incredibly dense neutron ball and rebounds in a cosmically violent supernova explosion. The star's successive shell-like layers of burning hydrogen, helium, carbon, oxygen, etc. undergo catastrophic mixing and eject tremendous amounts of dust and gas into the Galaxy.

Researchers don't know whether a supernova led to the formation of our own solar system, but some have found evidence that a supernova produced radioactive atoms a few million years before our solar system formed.

Messenger used a new kind of ion microprobe call the NanoSIMS to measure oxygen isotopes in the unusual grains.

Results showed that the olivine doesn't come from anywhere in our solar system, plentiful as olivine is in our solar system.
"Olivine, which includes gem-quality peridot, is a very common mineral in meteorites and makes up the bulk of the mantle of the Earth. That's why it's been so hard to identify olivine that came in from another star system." - Dante Lauretta

"The supernova grains have oxygen isotopic ratios that have never been seen before in meteorites or comet dust, but are predicted in astrophysical models of supernova explosions" - Scott Messenger.

Keller identified the mineral composition using a transmission electron microscope. The NASA scientists then asked Lauretta if the grain could possibly be a supernova grain.

Lauretta used well-known supernova structure models to calculate whether the grain could have condensed directly from cooling supernova gas, as its mineral make-up suggested.

Lauretta said his computational chemical analysis matched the grain's actual isotopic and mineral composition "dead on." Messenger's isotopic ratios enabled the team to pinpoint where in the supernova explosion the grains formed.

Although there is no way to directly measure the age of the supernova olivine grain, the scientists said that mineral has remained so strikingly unaltered since it formed that it probably hasn't spent much time in the interstellar medium.

"We know from astronomical observations that crystalline silicates formed in stars are quickly destroyed by the harsh environment in the Interstellar medium. So the survival of these grains in pristine condition is remarkable." - Lindsay Keller.

The scientists have pieced together the olivine's intriguing history:

o The mineral comes from elements that mixed during the violent explosion of a collapsed, dying star about 15 times as massive as the sun.

o The olivine crystallized when the supernova gas cooled to form dust. Numerous tiny olivine grains in one parcel of gas condensed and stuck together to form a submicron-sized olivine rock.

o The olivine bided its time in the interstellar medium for millions of years, until it was swept up into a cold dust cloud and coated with a thin veneer of organic matter.

o At some stage, the cloud collapsed to form our solar system, and the grain became trapped within a comet or asteroid for 4.5 billion years, the age of our solar system. If it was an asteroid, the asteroid would have to be a primitive asteroid, the kind that hasn't been heated enough to destroy such presolar grains.

o The pristine olivine was recently delivered to Earth's upper atmosphere, where it was snatched up with other interplanetary dust by an oily collector on a high-altitude NASA research aircraft

"These are the closest analogues we have now to what we think Stardust samples will look like" - Dante Lauretta.

The NASA Stardust mission rendezvoused with comet Wild 2 in January 2004.

"We basically stuck out an ice cube tray full of aerogel as we flew through the coma, picked up a bunch of dust, and retracted the sample tray for the trip back home" Dante Lauretta.

Stardust returns to Earth in January 2006.

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