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Science@NASA: Rosetta Discovers Haunting Beauty in Deep Spac

Posted: Thu Jul 15, 2010 1:37 am
by bystander
Rosetta Discovers Haunting Beauty in Deep Space
NASA Science News | 14 July 2010
The European Space Agency's Rosetta spacecraft has beamed back close-up photographs of asteroid Lutetia, an ancient, cratered relic from the dawn of the solar system. Scientists are abuzz about the stunning images, which reveal a worldlet of haunting, alien beauty.

"I've never seen anything like it," says Claudia Alexander, project scientist for the U.S. Rosetta Project. "It looked as though it could have been fractured off of a mother asteroid – it was all angles and flat planes, ancient impacts overlaid by newer ones, covered by dust of some kind."
...
"Right now we have more questions than answers," Alexander continues. "We can only speculate at this point about what we're seeing in the pictures."
...
"Rosetta took measurements with 17 different instruments," says Rita Schulz, ESA Project Scientist for the Rosetta Mission. "When all the data are analyzed, Lutetia will be one of the best known asteroids out there."

"These spectacular images," she says, "are just the beginning."

Re: Science@NASA: Rosetta Discovers Haunting Beauty in Deep

Posted: Thu Jul 15, 2010 2:10 pm
by neufer
Image
bystander wrote:Rosetta Discovers Haunting Beauty in Deep Space
NASA Science News | 14 July 2010
The European Space Agency's Rosetta spacecraft has beamed back close-up photographs of asteroid Lutetia, an ancient, cratered relic from the dawn of the solar system. Scientists are abuzz about the stunning images, which reveal a worldlet of haunting, alien beauty.

"I've never seen anything like it," says Claudia Alexander, project scientist for the U.S. Rosetta Project. "It looked as though it could have been fractured off of a mother asteroid – it was all angles and flat planes, ancient impacts overlaid by newer ones, covered by dust of some kind."

Re: Science@NASA: Rosetta Discovers Haunting Beauty in Deep

Posted: Fri Jul 16, 2010 7:32 am
by jumpjack
"These spectacular images," she says, "are just the beginning."
so where is the remaining?!? :|

Re: Science@NASA: Rosetta Discovers Haunting Beauty in Deep

Posted: Fri Jul 16, 2010 10:56 am
by neufer
jumpjack wrote:
"These spectacular images," she says, "are just the beginning."
so where is the remaining?!? :|
Rosetta has a host of scientific instruments whose data on Lutetia require some analysis.
http://www.planetary.org/blog/article/00002585/ wrote:
How does Lutetia compare to the other asteroids and comets visited by spacecraft?
The Planetary Society Blog By Emily Lakdawalla Jul. 15, 2010

<<Almost a week after Rosetta flew past Lutetia, the asteroid is now a distant pinprick of light to the spacecraft, and the science team is getting down to the business of analyzing their data.
To help them place things in context, I've prepared a new version of my "asteroids and comets to scale" image, laid out to be easy to drop into your slide presentation software of choice:

The total of four comets and nine asteroid systems (including ten separate bodies) that have been examined up close by spacecraft are shown here to scale with each other (100 meters per pixel, in the fully enlarged version). Most of these were visited only briefly, in flyby missions, so we have only one point of view on each; only Eros and Itokawa were orbited and mapped completely.

Credits: Montage by Emily Lakdawalla. Ida, Dactyl, Braille, Annefrank, Gaspra, Borrelly: NASA / JPL / Ted Stryk. Steins: ESA / OSIRIS team. Eros: NASA / JHUAPL. Itokawa: ISAS / JAXA / Emily Lakdawalla. Mathilde: NASA / JHUAPL / Ted Stryk. Lutetia: ESA / OSIRIS team / Emily Lakdawalla. Halley:: Russian Academy of Sciences / Ted Stryk. Tempel 1: NASA / JPL / UMD. Wild 2: NASA / JPL.>>

UT: Rosetta Uncovers a Thick Dusty Blanket on Lutetia

Posted: Wed Oct 06, 2010 4:32 pm
by bystander
Rosetta Uncovers a Thick, Dusty Blanket on Lutetia
Universe Today | 04 Oct 2010
If you think that asteroids are boring, unchanging rocks floating in space waiting only to crop up in bad science fiction films, think again. Images and data that are being returned from various asteroid flybys – such as those by the Rosetta spacecraft and Hayabusa sample return mission – show that asteroids are dynamic, changing miniature worlds unto themselves.

During the recent flyby of the asteroid 21-Lutetia in July, the ESA’s Rosetta spacecraft took an amazing amount of data. After combing through all of this data over the past few months, astronomers have calculated that the asteroid is covered in a 2000-foot (600 meter)-thick blanket of rocks and dust called regolith. This dust is not unlike the outer layer of the Earth’s Moon, consisting of pulverized material that has accumulated over billions of years.

ESA Rosetta
ASA DPS: Asteroid Lutetia: Results from Rosetta.
Huge Asteroid Wrapped in Thick Dust Blanket
Space.com | Science | 05 Oct 2010

Re: UT: Rosetta Uncovers a Thick Dusty Blanket on Lutetia

Posted: Wed Oct 06, 2010 5:07 pm
by rstevenson
If you think that asteroids are boring, unchanging rocks floating in space waiting only to crop up in bad science fiction films, think again. ...
Why mention Bruce Willis in a science forum?

Rob

Re: UT: Rosetta Uncovers a Thick Dusty Blanket on Lutetia

Posted: Wed Oct 06, 2010 5:09 pm
by bystander
rstevenson wrote:Why mention Bruce Willis in a science forum?
Why, indeed? :wink:

More Meteoroids, please.

Posted: Fri Oct 07, 2011 9:41 pm
by neufer
http://www.planetary.org/blog/article/00003214/ wrote:
Notes from Day 5 of the EPSC/DPS meeting
The Planetary Society Blog, By Emily Lakdawalla | Oct. 7, 2011

<<A few talks on Lutetia: According to M. Pätzold, Despite some challenges with the geometry of the flyby, Rosetta determined Lutetia's mass much more precisely than ever before, and found that previous attempts to determine its mass (from astrometry, using its influence on other asteroids and Mars) systematically overestimated its mass by more than 50%. The actual mass is 1.70 ± 0.017 x 1018 kg, giving it a density of 3400 ± 300 kg/cubic meter, where the error is dominated by the error in the volume estimate. This is pretty dense, especially if Lutetia has any significant amount of porosity, so it's largely rock with some metal.

According to M. Küppers, the largest craters on both Lutetia (132 x 101 x 76 km) and Steins :b: (5.9 x 4.0 km) both formed geologically recently, in the last several hundred million years. Based on previous estimates of the size of the asteroid population. Impacts of this size are only expected to occur once every few billion years. It's statistics of small numbers, but there is a commonality of asteroids having large craters at a higher rate than statistics suggest is likely. This implies that there may be more small asteroids (1 to 100 meters in size) than previously thought; this part of the asteroid population is basically unobserved. Bill Bottke said this may be consistent with WISE observations.>>

Re: PS: 21 Lutetia, Rosetta's July target

Posted: Fri Oct 28, 2011 11:34 pm
by bystander
Primal rock in space
Max Planck Gesellschaft | 2011 Oct 27
The Lutetia asteroid could be a remnant from the early phase of the solar system.

Lutetia is a real fossil: several areas of the asteroid's surface are around 3.6 billion years old and thus some of the oldest in the planetary system. Its high density means Lutetia is also a planetesimal, the first stage of development on the way to becoming a planet. These findings have been obtained by scientists headed by the Max Planck Institute for Solar System Research. The team has evaluated images which the Rosetta space probe recorded during its fly-by of Lutetia in July 2010.

Some 4.5 billion years ago the solar system looked totally different to what it does today: instead of the eight large planets there was first a cloud, then later a disk of gas and dust orbiting the newly formed Sun. This matter gradually amalgamated to form irregular shaped lumps, so-called planetesimals. Some of them fused to even larger rocks, the proto-planets – although they were still smaller than today’s planets they were already spherical and had an inner layered structure. Space is a dynamic place, however: most planetesimals and proto-planets which did not develop further into real planets fragmented again as the consequence of massive collisions.

“Lutetia is a bit of luck for us,” says Holger Sierks, scientist at the Max Planck Institute for Solar System Research, head of the OSIRIS camera team and lead author of the study now published in Science. “Only a very small number of celestial bodies have remained from such an early phase of development. They enable us to cast a look back into the past.”

A further example is the asteroid Vesta, which NASA’s Dawn space probe has been orbiting since July of this year. Researchers assume that Vesta is also one of the few remaining proto-planets. Lutetia could now enable researchers to look even further back – to the very origins of the solar system. Its small size, irregular shape and, above all, its high density point to the fact that it is a planetesimal. “From the images we have now been able to determine the volume of Lutetia very accurately and then in a second step its density,” explains Sierks. At 3.4 grams per cubic centimetre it is considerably higher than that of granite.

“Most of the other planetoids which we know in more detail have a much lower density,” says Sierks. “We think these asteroids are a kind of cosmic fragment – i.e. relatively loose, porous conglomerations of bodies from previous collisions.” Lutetia, in contrast, appears to be significantly more compact – and thus older.

The distribution of the craters on Lutetia’s surface, which were formed by later impacts, also indicates a compact structure. This is because, compared to other asteroids, Lutetia has an astonishingly low number of smaller craters with a diameter of less than ten kilometres in particular. The situation resembles the experiment with a steel ball which is thrown with great force either onto concrete or into a sand pit. Since the loose sand can absorb a large portion of the impact energy, only a small hollow is formed in the sand. The same shot produces a large indentation in the significantly more compact concrete, however.

The very high total number of craters also told the scientists that parts of the surface of the asteroid are up to 3.6 billion years old, because the longer a surface is exposed to the continuous cosmic bombardment, the more craters it will have. “Whether Lutetia also has the beginnings of an inner layered structure cannot be said with any certainty at this point in time,” explains Holger Sierks. There are a number of indications, but only further investigations of the data obtained can bring certainty here.

“Lutetia has taken us completely by surprise,” admits the Max Planck researcher. “Instead of a uniform, comparatively inconspicuous asteroid we have found a small world of its own – with a complex geography.” The scientists not only discovered huge craters with diameters of more than 55 kilometres on the images, but also indications of landslides, deep furrows and mountain chains. Overall, the experts were able to identify seven regions, whose morphological characteristics mean there are significant differences between them.

Asteroid Lutetia: postcard from the past
ESA Space Science | 2011 Oct 27
ESA's Rosetta spacecraft has revealed asteroid Lutetia to be a primitive body, left over as the planets were forming in our Solar System. Results from Rosetta's fleeting flyby also suggest that this mini-world tried to grow a metal heart.

Rosetta flew past Lutetia on 10 July 2010 at a speed of 54 000 km/hr and a closest distance of 3170 km. At the time, the 130 km-long asteroid was the largest encountered by a spacecraft. Since then, scientists have been analysing the data taken during the brief encounter.

All previous flybys went past objects, which were fragments of once-larger bodies. However, during the encounter, scientists speculated that Lutetia might be an older, primitive 'mini-world'.

Now they are much more certain. Images from the OSIRIS camera reveal that parts of Lutetia's surface are around 3.6 billion years old. Other parts are young by astronomical standards, at 50–80 million years old.

Astronomers estimate the age of airless planets, moons, and asteroids by counting craters. Each bowl-shaped depression on the surface is made by an impact. The older the surface, the more impacts it will have accumulated. Some parts of Lutetia are heavily cratered, implying that it is very old.

On the other hand, the youngest areas of Lutetia are landslides, probably triggered by the vibrations from particularly jarring nearby impacts.

Debris resulting from these many impacts now lies across the surface as a 1 km-thick layer of pulverised rock.

There are also boulders strewn across the surface: some are 300–400 m across, or about half the size of Ayers Rock, in Australia.

Some impacts must have been so large that they broke off whole chunks of Lutetia, gradually sculpting it into the battered wreck we see today.

"We don't think Lutetia was born looking like this," says Holger Sierks, Max-Planck-Institut für Sonnensystemforschung, Lindau, Germany. "It was probably round when it formed."

Rosetta's VIRTIS spectrometer found that Lutetia's composition is remarkably uniform across all the observed regions.

"It is striking that an object of this size can bear scars of events so different in age across its surface while not showing any sign of surface compositional variation," says Fabrizio Capaccioni, INAF, Rome, Italy.

This is just the start of the mystery.

Read further

Battered asteroid may have warm core
Massachusetts Institute of Technology | 2011 Oct 28
New analysis of Lutetia finds evidence for molten interior.

On July 10, 2010, the European Space Agency’s Rosetta probe flew by the asteroid 21 Lutetia, which at the time was the largest asteroid ever to have been visited by a spacecraft. The fly-by occurred 282 million miles from Earth; close-up images taken by the probe revealed cracks and craters running across Lutetia’s surface, evidence of the asteroid’s long and battered history.

Now an international team of researchers from France, Germany, the Netherlands and the United States has analyzed Lutetia’s surface images, and found that underneath its cold and cracked exterior, the asteroid may in fact have once harbored a molten-hot, metallic core. The findings suggest that Lutetia, despite billions of years of impacts, may have retained its original structure — a preserved remnant of the very earliest days of the solar system.

The results are published in a series of three papers in the journals Science and Planetary Space Science (PSS).

Benjamin Weiss, an associate professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says a melted core within Lutetia may exemplify a “hidden diversity” within the greater asteroid belt.

“There might be many bodies that have cores and interesting interiors that we never noticed, because they’re covered by unmelted surfaces,” says Weiss, who is a co-author on both Science papers and lead author for the paper in PSS. “The asteroid belt may be more interesting than it seems on the surface.”

More than a rubble pile

Most asteroids careening through the asteroid belt, between the orbits of Mars and Jupiter, are scrambled versions of their former selves: essentially mashed-up masses of rock and metal that have collided and cooled over billions of years. These rocky conglomerations are relatively small and light, with voids and cracks in their interiors that make them very porous. It had been thought that the vast majority of these bodies never melted to form dense, metallic cores, but instead are just primordial piles of space rocks and dust.

In contrast, the Rosetta team — led by Holger Sierks of the Max-Planck Institute for Solar System Research and Martin Pätzold of the Rheinisches Institut für Umweltforschung, both in Germany — found that Lutetia is extremely dense. The team drew up a model of the asteroid’s shape, based on images taken by the Rosetta probe. The researchers then calculated Lutetia’s volume, mass and finally its density, which they found, in collaboration with the MIT team, to be greater than most meteorite samples measured on Earth.

The asteroid’s density would make sense if it were completely solid, free of voids or cracks. However, Rosetta researchers measured the asteroid’s surface craters and identified huge fractures throughout, suggesting the asteroid is relatively porous, a finding that didn’t quite square with the team’s density measurements — after all, the more porous an object, the less dense it should be.

Weiss and his colleagues, including MIT professor Richard Binzel and former MIT professor Linda T. Elkins-Tanton, now head of the Carnegie Institution for Science’s Department of Terrestrial Magnetism, offered a likely explanation for the discrepancy: Perhaps the space rock contains a dense metallic core, with a once melted interior underneath its fractured crust.

The direct observations from Lutetia may provide evidence for a theory developed last year by Weiss, Elkins-Tanton and MIT’s Maria Zuber. The team studied samples of chondrites, meteorites on Earth that have remained unchanged since their early formation. They found samples from the meteorite Allende that were strongly magnetized, and theorized that such magnetization most likely occurred in an asteroid with a melted, metallic core. The theory was seen as a big shift from the traditional picture of most asteroids as primordial, unmelted objects.

Planetary arrested development

If a metallic core does indeed exist, Lutetia would be the first asteroid known to be partially differentiated: having a melted interior overlain by progressively cooler layers. The asteroid would also represent a snapshot of early planetary development.

As the solar system began to take form 4.5 billion years ago, planets formed from collisions first of dust, then of larger chunks of rock. Numerous chunks remained relatively small, cooling quickly to form asteroids, while others grew with each collision, eventually reaching the size of planets. These large bodies generated an immense amount of heat — but as a new planet melted from the inside, it cooled from the outside, forming a crust around a molten core.

According to Weiss, Lutetia is a case of arrested development. The asteroid may have reached a size large enough to develop and retain a melting core, and then simply avoided the larger collisions that accelerated planet formation.

“The planets … don’t retain a record of these early differentiation processes,” Weiss says. “So this asteroid may be a relic of the first events of melting in a body.”

Erik Asphaug, a professor of planetary science at the University of California at Santa Cruz, studies “hit-and-run” collisions between early planetary bodies. He says the work by Weiss and his colleagues is a solid step toward resolving how certain asteroids like Lutetia may have evolved.

“We’ve had decades of cartoon speculation, and here’s speculation that’s anchored in physical understanding of how the interiors of these bodies would evolve,” says Asphaug, who was not involved in the research. “It’s like getting through the first 100 pages of a novel, and you don’t know where it’s leading, but it feels like the beginnings of a coherent picture.”

Weiss says while the images and measurements of Lutetia are intriguing evidence for a partially differentiated asteroid, a “smoking gun” could be provided by a sample taken directly from an asteroid. Binzel and Weiss are part of a NASA team that plans to launch a probe to an asteroid in 2016, which will take a sample and return it to Earth.

Weiss says there are a number of hurdles he and his colleagues will have to surmount before obtaining definitive evidence for a molten core.

“The challenge is, the body has to be big,” Weiss says. “If it’s not big, then it’s not going to retain a molten interior. The problem then is, all the big bodies are not going to be easily excavated. So it’s sort of a Catch-22.”

The Lutetia asteroid – a prehistoric relic
Academy of Finland | 2011 Oct 28
New information has been published about the Lutetia asteroid that was observed in 2010 and its properties. The analysis of the data collected during the spacecraft fly-by indicates that Lutetia is a dense, intact relic dating back to the birth of our solar system. The Rosetta spacecraft, owned and operated by the European Space Agency (ESA), passed the Lutetia asteroid at close range in summer 2010. The asteroid was measured to be more than 100 kilometres in diameter. The new research results on the asteroid, published this week in Science magazine, were acquired through international cooperation, and the analysis was based on a mathematical method developed by Professor Mikko Kaasalainen. The analysis conducted at Tampere University of Technology is part of the research of the Finnish Centre of Excellence in Inverse Problems Research, and is being funded by the Academy of Finland.

The density of the Lutetia asteroid was determined by calculating its mass from changes along the flight path of the spacecraft, and its volume from a model of the entire asteroid. The model was constructed mathematically, even though the spacecraft originally viewed only about half of the surface of the asteroid while flying past. Using Kaasalainen’s method, developed specifically for spacecraft fly-bys, it is possible to combine ground-based light-curve measurements and adaptive-optical imaging with images taken by the space probe. “This method enabled us to create a reliable model of the part of Lutetia that wasn’t visible to the spacecraft, and thereby, to calculate Lutetia’s density, which proved to be much larger than the values that we’ve been able to get for other asteroids,” Kaasalainen explains.

Mathematics in space research

“Lutetia’s history was constructed much like a puzzle; research groups from different fields all around the world contributed their input to create the final result,” says Kaasalainen. “The high density, large number of old impact traces, and other surface characteristics led geologists to conclude that Lutetia likely has a metallic core surrounded by a more porous outer layer. Despite its dents and knocks, Lutetia has remained nearly in its original shape, unlike the majority of asteroids, which mostly have come together from a number of impact fragments. Targets such as Lutetia are extremely valuable, because they provide us with information about the conditions that existed at the dawn of our solar system.”

The Lutetia fly-by also proved the accuracy of the generalised method for asteroid modelling, which is based only on ground-based analysis and was developed by Kaasalainen in collaboration with the international research network. “We were amazed to notice that the preliminary model made of Lutetia prior to the fly-by and used in the planning of the flight path of the spacecraft proved valid with the accuracy of a minor percentage for the entire area of which we got spacecraft images.”

In autumn 2008, Rosetta made a similar fly-by past the notably smaller Steins asteroid. The asteroid was analysed using the same method as Lutetia, and the results were published in Science magazine in 2010. In terms of its structure, Steins is quite different from Lutetia. It more closely resembles a gravel heap, and its development has been shaped by the effect of sunlight on its spin state. The observations concerning this phenomenon, as made by Kaasalainen’s team, were published in Nature magazine in 2007. The Rosetta spacecraft is currently heading toward its final destination, the comet Churyumov-Gerasimenko, which it is expected to reach in 2014.

Kaasalainen is involved in ESA’s Rosetta research consortium, which has 58 members representing 11 countries and 33 different research institutes. It is this consortium that is responsible for the Lutetia publication. Kaasalainen is also vice director of the Finnish Centre of Excellence in Inverse Problems Research, which develops and applies mathematical methods for the interpretation of different observational data for many different fields, ranging from biology to cosmology.

Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the Early Solar System - H. Sierks et al Asteroid 21 Lutetia: Low Mass, High Density - M. Pätzold et al The Surface Composition and Temperature of Asteroid 21 Lutetia As Observed by Rosetta/VIRTIS - A. Coradini et al
Asteroid Fails to Make It Big
Discovery News | Irene Klotz | 2011 Oct 27

Unveiling Asteroid Lutetia's Secrets: Photos
Discovery News | Jennifer Ouellette | 2011 Oct 27

Most pristine known asteroid is denser than granite
New Scientist | Lisa Grossman | 2011 Oct 278

A Surprise at Lutetia
Centauri Dreams | Paul Gilster | 2011 Oct 28

Simply Enstatite!

Posted: Sun Nov 13, 2011 6:58 pm
by neufer
http://www.universetoday.com/90920/asteroid-lutetia-a-piece-of-earth/#more-90920 wrote:
Asteroid Lutetia… A Piece Of Earth?
by Tammy Plotner on November 12, 2011

<<According to data received from ESA’s Rosetta spacecraft, ESO’s New Technology Telescope, and NASA telescopes, strange asteroid Lutetia could be a real piece of the rock… the original material that formed the Earth, Venus and Mercury! By examining precious meteors which may have formed at the time of the inner Solar System, scientists have found matching properties which indicate a relationship. Independent Lutetia must have just moved its way out to join in the main asteroid belt…

A team of astronomers from French and North American universities have been hard at work studying asteroid Lutetia spectroscopically. Data sets from the OSIRIS camera on ESA’s Rosetta spacecraft, ESO’s New Technology Telescope (NTT) at the La Silla Observatory in Chile, and NASA’s Infrared Telescope Facility in Hawaii and Spitzer Space Telescope have been combined to give us a multi-wavelength look at this very different space rock. What they found was a very specific type of meteorite called an enstatite chondrite displayed similar content which matched Lutetia… and what is theorized as the material which dates back to the early Solar System. Chances are very good that enstatite chondrites are the same “stuff” which formed the rocky planets – Earth, Mars and Venus. “But how did Lutetia escape from the inner Solar System and reach the main asteroid belt?” asks Pierre Vernazza (ESO), the lead author of the paper.

It’s a very good question considering that an estimated less than 2% of the material which formed in the same region of Earth migrated to the main asteroid belt. Within a few million years of formation, this type of “debris” had either been incorporated into the gelling planets or else larger pieces had escaped to a safer, more distant orbit from the Sun. At about 100 kilometers across, Lutetia may have been gravitationally influenced by a close pass to the rocky planets and then further affected by a young Jupiter. “We think that such an ejection must have happened to Lutetia. It ended up as an interloper in the main asteroid belt and it has been preserved there for four billion years,” continues Pierre Vernazza.

Asteroid Lutetia is a “real looker” and has long been a source of speculation due to its unusual color and surface properties. Only 1% of the asteroids located in the main belt share its rare characteristics. “Lutetia seems to be the largest, and one of the very few, remnants of such material in the main asteroid belt. For this reason, asteroids like Lutetia represent ideal targets for future sample return missions. We could then study in detail the origin of the rocky planets, including our Earth,” concludes Pierre Vernazza.>>
http://en.wikipedia.org/wiki/Enstatite_chondrite wrote: <<Enstatite chondrites (also known as E-type chondrites) are a rare form of meteorite thought to comprise only about 2% of the chondrites that fall on Earth. Only about 200 E-Type chondrites are currently known.

E-type chondrites are among the most chemically reduced rocks known, with most of their iron taking the form of metal or sulfide rather than an oxide. They tend to be high in the mineral enstatite (MgSiO3), from which they derive their name. Based on spectral analysis, it has been suggested that the asteroid 16 Psyche may be the common parent for this type of meteorite. Some examples may have originated from the planet Mercury.

Unlike most other chondrites, the minerals in enstatite chondrites contain almost no iron oxide; they are the most oxygen-poor objects known. Metallic Fe-Ni (iron-nickel) and Fe-bearing sulfide minerals contain nearly all of the iron in this type of meteorite. Enstatite chondrites contain a variety of unusual minerals that can only form in extremely reducing conditions, including oldhamite (CaS), niningerite (MgS), perryite (Fe-Ni silicide), and alkali sulfides (e.g., djerfisherite and caswellsilverite). All enstatite chondrites are dominantly composed of enstatite-rich chondrules plus abundant grains of metal and sulfide minerals. Dusty matrix material is uncommon and refractory inclusions are very rare. Chemically, enstatite chondrites are very low in refractory lithophile elements. Their oxygen isotopic compositions are intermediate between ordinary and carbonaceous chondrites, and are similar to rocks found on the Earth and Moon. Their lack of oxygen content may mean that they were originally formed near the center of the solar nebula that created the solar system, possibly within the orbit of Mercury. Most enstatite chondrites have experienced thermal metamorphism on the parent asteroids.

The largest known recorded E-type chondrite fall happened in the town of Abee, in Alberta in 1952. The 107 kg stone fell in a farmer's wheat field, creating an impact pit 0.7 m in diamter and 1.5 m deep. Based on estimates of its velocity and inclination, it is thought to have arrived on a relatively low-speed, low-inclination orbit that had a perihelion near 0.95 AU and an aphelion probably close to 2.74 AU. It in classified as being a shock-melted breccia, its minerals having recrystalized after the impact that knocked it off of its parent body.>>
http://en.wikipedia.org/wiki/16_Psyche wrote:
<<16 Psyche (Greek: Ψυχή) is one of the ten most massive main-belt asteroids. It is over 200 kilometers in diameter and contains a little less than 1% of the mass of the entire asteroid belt. It is the most massive of the metallic M-type asteroids. Psyche was discovered by Annibale de Gasparis on March 17, 1852 from Naples and named after the Greek mythological figure Psyche. The first fifteen asteroids to be discovered were given symbols by astronomers as a type of short-hand notation. In 1851, however, J. F. Encke suggested using a circled number. 16 Psyche was the first new asteroid to be discovered that was designated with this scheme (in 1852 by J. Ferguson).

Radar observations indicate a fairly pure iron-nickel composition. Psyche appears to be a genuine case of an exposed metallic core from a larger differentiated parent body. Unlike some other M-type asteroids, Psyche shows no sign of the presence of water or water-bearing minerals on its surface, consistent with its interpretation as a metallic body. Small amounts of pyroxene appear to be present.

If Psyche is the core remnant of a larger parent body, we might expect other asteroids on similar orbits. Psyche does not belong to any asteroid family. One hypothesis is that the collision occurred very early in the solar system's history, and all the other remnants have since been ground into fragments by subsequent collisions or had their orbits perturbed beyond recognition.

Psyche is massive enough that its perturbations on other asteroids can be measured, which enables a mass measurement. IRAS data shows Psyche to have a diameter of 253 km. Observations of an occultation using five chords suggest an outline of 214×181 km. Recent estimates of Psyche's smaller size has resulted in an increase in the estimated density which is more appropriate for a metallic asteroid. Psyche appears to have a fairly regular surface and is approximately ellipsoidal in shape. Recent lightcurve analysis indicates that its pole points towards either ecliptic coordinates (β, λ) = (-9°, 35°) or (β, λ) = (-2°, 215°) with a 10° uncertainty. This gives an axial tilt of 95°.

Two stellar occultations by Psyche have been observed (from Mexico on March 22, 2002, and another on May 16, 2002). Lightcurve variations indicate a non-spherical body, consistent with the lightcurve and radar results. It is possible that at least some examples of enstatite chondrite meteorites originated from this asteroid, based on similar spectral analysis results.>>

Re: PS: 21 Lutetia, Rosetta's July target

Posted: Sun Nov 13, 2011 7:25 pm
by bystander
neufer wrote:Asteroid Lutetia… A Piece Of Earth?
Universe Today | Tammy Plotner | 2011 Nov 12
Lutetia: a Rare Survivor from the Birth of the Earth
European Southern Observatory | 2011 Nov 11

Asteroid (21) Lutetia as a remnant of Earth’s precursor planetesimals - P. Vernazza et al