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Title - Wiki page of Comet 81P / Wild 2
Size - 3 km x 5 km (5 km comet)
Extracts - Stardust probe was launched in 1999, returned comet samples in Jan 2006 & went on a extended mission to other objects (asteroid 5535 Annefrank & comet Tempel 1) till 2011.
Comet Wild 2 is a fresh comet. Jupiter changed its orbit in 1974 & it now travels much closer to the sun, between Jupiter and the Earth. Because it has not been exposed to the Sun at close range, its composition has not been altered much from its original condition. By the time Stardust encounters it, Comet Wild 2 will have made only 5 trips around the sun. 72 close-up shots were taken of Wild 2 by Stardust.
Stardust mission brought back samples that consists of thousands of cometary dust particles measuring less than 100 µm each, and around 100 interstellar dust grains of mostly sub-micron size. The total mass of returned sample is estimated to be approximately 1 mg.
Returned samples reveal a wide range of organic compounds, including two that contain biologically usable nitrogen; indigenous aliphatic hydrocarbons with longer chain lengths than those observed in the diffuse interstellar medium; abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene, proving consistency with the mixing of Solar System and interstellar matter, previously deduced spectroscopically from ground observations; hydrous silicates and carbonate minerals were found to be absent, suggesting a lack of aqueous processing of the cometary dust; limited pure carbon (CHON) was also found in the samples returned; methylamine and ethylamine was found in the aerogel but was not associated with specific particles.
In April 2011, scientists from the University of Arizona discovered iron and copper sulfide minerals in the comet sample, that are assumed to have formed in the presence of water. This is considered as evidence for the presence of liquid water in comet Wild 2. The discovery shatters the existing paradigm that comets never get warm enough to melt their icy bulk. The comet samples show that the outer regions of the early Solar System were not isolated and were not a refuge where interstellar materials could commonly survive. The data suggest that high-temperature inner Solar System material formed and was subsequently transferred to the Kuiper belt.
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Title - Stardust: A Mission With Many Scientific Surprises
By - Don Brownlee (Stardust Principal Investigator), 2009
Extracts - What we found was remarkable! ... our comet's rocky material had formed under white-hot conditions. We now know that comets are really a mix of materials made by conditions of both "fire and ice". Comet ice formed in cold regions beyond the planet Neptune but the rocks, probably the bulk of any comet's mass, formed much closer to the Sun in regions hot enough to evaporate bricks. The materials that we collected from comet Wild 2 do contain pre-solar "stardust" grains, identified on the basis of their unusual isotopic composition, but these grains are very, very rare.
"It was very exciting to find that pieces of CAIs and chondrules in the comet and the scientific implications of this are profound. When we first presented the discovery of comet CAIs at the annual LPI conference, just 3 months after Stardust landed, you could see jaws drop in the room crowded with 600 scientists (2006). It was just phenomenal to discover something this profound, right in the beginning of the analysis program. The discovery of chondrules and CAIs proves that matter abundantly formed in the inner solar system was somehow transported to the edge of the young solar system where comets formed.
There are some theories that suggest that CAI's formed just a few radii from the surface of the Sun, 4.567 billion years ago. The finding that inner solar system materials, formed at very high temperature, were transported all the way to the edge of the Solar System to the region where Pluto is one of the major scientific findings of Stardust. In other words, instead of being dominated by particles formed around other stars, our comet's rocks were predominantly formed close to the Sun. Thus, these comet sample studies have provided a direct look at the nature and origin of the building blocks of planets, materials that were sprayed all over the young solar system and must have been incorporated into all planets and moons.
One of the most unexpected was the 2009 discovery of the amino acid glycine by a team of scientists from the Goddard Space Flight center.
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Title - Stardust Findings Suggest Comets More Complex Than Thought
By - NASA, 2006
Extracts - "We have found very high-temperature minerals, which supports a particular model where strong bipolar gas jets coming out of the early sun propelled material formed near to the sun outward to the outer reaches of the solar system," said Michael Zolensky, NASA cosmic mineralogist and Stardust co-investigator at the Johnson Space Center (JSC), Houston. "It seems that comets are not composed entirely of volatile rich materials but rather are a mixture of materials formed at all temperature ranges, at places very near the early sun and at places very remote from it."
Scientists have long thought of comets as cold, billowing clouds of ice, dust and gases formed on the edges of the solar system. But comets may not be so simple or similar. They may prove to be diverse bodies with complex histories. Comet Wild 2 certainly is made up of components with a more complex history than thought.
Scientists found a wide variety in particle composition and size in the Wild 2 samples. Most of the Wild 2 samples appear to be weakly constructed mixtures of very small grains with a few larger grains. Also, a wide range of high- and low-temperature minerals, from olivine to low- and high-calcium pyroxene compositions, is present in the Wild 2 samples.
Such a diversity of high- and low-temperature minerals requires a wide range of formation conditions, probably reflecting different formation locations. Many particles did not form in the cold environment and locations where cometary ices condensed.
The captured Wild 2 samples are predominantly fine-grained, loosely bound aggregates, most also containing much larger individual crystals of olivine, pyroxene and iron/nickel sulfides.
Scientists found a much wider diversity of particle densities, including dense minerals, than advocated earlier by some researchers.
"We see and demonstrate for the first time that there is a continuum between fine particles and more dense objects, the latter including pure minerals of, for example, olivine and iron sulfide," said Horz. "The range in density and cohesion that we saw and infer thus disagrees specifically with the popular model that comets are composed of only fine grains. A minority, however, did allow for particles of variable density. We have confirmed the latter viewpoint."
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By - Don Brownlee et al, 2006
Extracts - But unfortunately, it is not presently possible to prove that any particular meteoritic sample is positively from a comet.
Most of the analyzed Wild 2 materials that have been examined have been coarser grained and appear to be closely related to common meteoritic materials. Most Wild 2 materials formed at high temperature (greater than the 1000 K / 727 C temperature proposed for the annealing of interstellar amorphous silicates) and, like the major meteoritic components, they presumably formed in the inner solar system.
One of the very first Stardust tracks analyzed was made by a 20 μm CAI-like particle composed of spinel rimmed pyroxene nodules. This particle is rich in Oxygen 16 isotope, like common CAIs and the Sun, and it contains a host of refractory minerals including Al-rich, Ti-bearing and Ti-free clinopyroxene, Mg-Al spinel, anorthite, melilite, perovskite, refractory metal, and osbornite (TiN) grains. Other tracks also contain refractory materials, but the abundance of CAIs or even CAI-like particles has not been well determined. It is probably in the range of 1–10%, an abundance that is lower than CAI-rich chondrites such as Allende, but much higher than in unequilibrated ordinary chondrites.
Wild 2 is a potpourri of such remarkably diverse meteoritic materials that it seems unlikely that the comet can be matched to any given chondrite class. The diversity of mineral compositions even within individual particles suggests that the Wild 2 samples are at least as primitive as the most primitive type 3.0 chondrites. The high Chromium content of some Wild 2 olivine grains indicates a lack of parent body heating beyond what was experienced by type 3.0 chondrites. [ chondrites can also be categorized according to their petrologic type, which is the degree to which they were thermally metamorphosed or aqueously altered (they are assigned a number between 1 and 7). The chondrules in a chondrite that is assigned a "3" have not been altered. ]
The presence of abundant freely-released submicron particles in the Wild 2 dust coma, practically guarantees that this comet, or at least its portions released to space, did not suffer pervasive internal aqueous or other thermal alteration, that would have caused consolidation of fines into more strongly bonded composites. Although phyllosilicates have not been seen in Wild 2 samples, there are a number of reports of small amounts of secondary phases that are generally associated with aqueous alteration and these will be discussed later in this article.
The solar nebula contained multiple regions that could be considered to be “rock factories,” regions that made many of the coarse materials in primitive chondrites such as chondrules and CAIs. The millimeter products of these factories are typically a billion times more massive than typical interstellar dust grains that initially delivered rock-forming elements in the early solar system. The nebular rock factories did not produce meteoritic components by mild processes such as subsolidus annealing of presolar grains. They formed new generations of materials under much more extreme conditions that involved melting, vaporization, and condensation. The most common rock product in the solar nebula appears to have been chondrules, nebular components that commonly formed by episodes of brief heating in the 1400–1750° C range. The majority of the well-preserved Wild 2 materials appear to be products of the rock factories that made the bulk of the materials in chondrites. The initial nebular rock-forming episodes began with CAI formation and ended a few million years later when the last chondrules formed or were reworked. Rocks were also made inside strongly heated parent bodies. Impact debris from aqueous altered, strongly heated and differentiated parent bodies must have joined the ensemble of orbiting debris that could spread across the solar nebula and reach the regions where comets accreted.
The Wild 2 data imply that particles at least as large as 50 μm were transported radially across the full width of the solar nebula.
The asteroid region was a complex region of the solar nebula because it was near the snow line, Jupiter, the Sun, the regions where chondrules formed, and near the boundary between the terrestrial and Jovian planets. Dobrica et al. (2009) and Gounelle (2011) suggest that there is a continuum between comets and asteroids, and this seems likely for the rocky components, if comets and asteroids are composed of different mixes of basic nebular materials.
In spite of all of these observed differences, it is possible that JFCs all eject very similar solid contents.
Taken at face value, this spectral fitting model (of comet Tempel 1) is a very poor match to the laboratory analytical data on comet Wild 2 samples.
There is some overlap, but the Tempel 1 mineralogical interpretation is not consistent with Wild 2 or any type of extraterrestrial material that has been analyzed in the laboratory. The high abundances of ferrosilite, niningerite, and the high fayalite/forsterite ratio, put Tempel 1 in a unique category. Unfortunately, there is no sure way to test how meaningful a spectral match to so many phases is, without ground truth, an actual sample return from Tempel 1, or perhaps a landed experiment package that can determine the mineralogy of submicron materials.
A remarkable aspect of the post-impact infrared spectrum of Tempel 1 (short period comet from the Kuiper belt) is that it is nearly identical to that of the bright, long period, Oort cloud comet Hale Bopp. This implies that the dust liberated by the impact on the short period comet Tempel 1 from the Kuiper belt is similar to the dust released by Hale Bopp, an Oort cloud comet that is generally believed to have accreted interior to Neptune’s orbit before being ejected into the Oort cloud. The similarity of Tempel 1 and Hale Bopp IR spectra is notable because short period and long period comets are usually seen to have quite different spectra, indicating a possible difference between these types of comets. Before the impact, Tempel 1 had a typical short period comet spectrum with only a weak silicate feature above continuum. After the impact, the spectra changed dramatically to show a spectrum with very strong features, nearly identical to Hale Bopp. This astonishing transformation from the same comet suggests that the apparent differences between long and short period comets is not a fundamental property of the material inside the comet, but is related to the form of the material that is ejected to space.
The energetic liberation of fine materials from the impact produced a spectacular long period comet spectrum, rich in silicate spectral features, from a short period comet ! It is also conceivable that the difference between the preimpact and postimpact spectra is solely due to profound heterogeneity in the comet.
We have suggested that the rocky components of comets may be similar mixtures of materials, made in the inner regions of the solar system, but this might not be true for all comets. Comets like Wild 2 were made when there was a very efficient outward flow, a diffuse “Grand Radial Express,” that carried material to the region beyond Neptune. This radial express is no longer in operation and it probably did not occur either in the first or the final stages of nebular evolution.
There may have been times when the outward flow of inner solar nebula material did not dominate the flux of presolar grains falling onto the nebula. At such times, there might have been comets that formed largely from presolar interstellar grains as suggested by Greenberg and Li (1999) — with their ice and organic coatings intact. It will be an interesting challenge for future research and future missions to see if the solar system did produce two kinds of comets with drastically different rocky components.
Most meteorites are too strong to be related to typical cometary meteoroids whose low strength is determined by the high altitude fragmentation of material in cometary meteor showers. Rare cometary meteors, or small fragments of cometary meteors, perhaps hardened by parent body impacts or aqueous alteration, do have strength similar to chondrites, but these are uncommon and are not representative of typical material released by comets.
Gounelle et al. (2008) discussed the possibility that some fraction of existing meteorites, including Orgueil, could have formed in the outer solar system. Dobrica et al. (2009) provide arguments that micrometeorites are cometary and discuss similarities to Wild 2 samples.
It has long been understood that some of the cosmic dust particles collected in the stratosphere must be from comets, but solar system dust models implied that the majority of collected samples should have asteroidal origins. A far-reaching change in this view occurred with the model of Nesvorný et al. (2010) that predicts that 85% of IDPs are cometary !
The Nesvorný et al. model is a radical change from the past and implies that the majority of stratospheric IDPs may be cometary samples. If this is true, then it marks a major sea change in IDP and micrometeorite work and implies that we already have in hand thousands of meteoritic comet samples from perhaps a significant number of different comets.
The rocky materials in Wild 2 must have been totally devoid of all volatiles after their high temperature origin, and ice and organics must have become associated with them at a later time. The presence of ice and organics in comets implies that these components formed in quite different environments than the rocky components.
Conclusion :
Assuming that the sampled comet is a typical Jupiter family comet, the results paint a quite different picture of how planetesimals formed in the outer solar system than was imagined before the Stardust mission was flown. Their rocky components, often the majority of their mass, formed in high-temperature nebular environments that were quite distinct from the environments that produced their icy and organic materials.
The materials were apparently transported over long distances to environments where they could accumulate to form ice-rich bodies. The sample results lead to a testable hypothesis that comet Wild 2 solids are a population of rocky materials that were distributed across the full breadth of the solar nebula. The hallmark signature of cometary rocky materials may be that they are a diverse set of materials whose nebular-related properties cover the full range of solids made in the solar nebula. It is reasonable to imagine that the materials that formed comets were derived from all dust-bearing regions of the early solar system. The comet solids are dominated by this component and the same solids are also found in asteroids that have produced meteorites, but they are highly diluted by locally produced materials.
We also predict that the dust and rocks from other comets will be similar to those that formed Wild 2 with the caveat that there might be an additional class of comets that are dominated by presolar grains. Stardust was limited because of restraints on submicron components that complicated the study of organics, presolar grains, and other fine components. The lack of millimeter size components complicates the comparison with meteoritic components such as chondrules and CAIs. The data from well-preserved samples clearly show that Wild 2 is an unequilibrated object at least as unaltered as type 3.0 chondrites. Wild 2 contains abundant materials that formed at high temperature, but the comet is a very primitive body in the sense that it appears to have excellently preserved its originally accreted solids.
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Title - Comet from coldest spot in solar system has material from hottest places
Extracts - .
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Title - Oxygen isotopic composition of coarse- and fine-grained material from comet 81P/Wild 2
By - Ryan Ogliore et al, 2015
Extracts - Oxygen isotopic composition of 7 Stardust fragments (larger than 2 μm), show a relatively narrow range that is consistent with O16-poor phases commonly seen in meteorites. Many of the larger Stardust fragments studied so far have chondrule-like mineralogy, which is consistent with formation in the inner Solar System. The fine-grained material shows a very broad range of oxygen isotopic compositions, suggesting that Wild 2 fines are either primitive outer-nebula dust or a very diverse sampling of inner Solar System compositional reservoirs that accreted along with a large number of inner-Solar-System rocks to form comet Wild 2.
News - Comet Wild 2: A window into the birth of the solar system ?
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Title - Comets Throw Light On Solar System's Beginnings
By - British Association for the Advancement of Science, 2008
Extracts - A new picture of the composition of comets is emerging. The early solar system is commonly believed to have been formed from a cold outer region and a hot inner region, which did not exchange material. But the comet Wild-2 contains both iron oxides, which suggests that it was exposed to small trickles of water, and chromium oxide (a high temperature mineral). This means that material must have moved between the two regions.
Scientists from the Space Research Centre at the University of Leicester have discovered that the old model of comets as dusty iceballs is not the whole picture [ it is wrong, in fact]. This change in perspective was brought about after using microfocus spectroscopy on comet Wild 2 samples – with a bright & powerful X-ray beam, equivalent to one 25th of a human hair. "Comets are starting to look a lot more complicated than the old dusty iceball idea"- Dr. John Bridges, Space Research Centre, UK.
He says, "For one thing Wild-2 contains material, like chromium oxides, from the hot inner Solar System – so how did that material get mixed in with a comet which has spent most of its life beyond Neptune? It suggests that there has been major mixing of material from inner and outer parts of the Solar System in its earliest stages."
"We have also been finding X-ray signatures of iron oxides. These are important because they show that on the Wild-2 nucleus there could have been small trickles of water that deposited these minerals. Similar grains are found in carbonaceous chondrite meteorites. This might mean that there have been localised heating events, perhaps caused by impact on the Wild-2 nucleus that melted some of its ice." [ but the ice is totally speculative ]
Their samples, which were born in the Kuiper Belt near Neptune, were collected by the Stardust space mission, which involved a seven year long, five billion km, journey.
Dr Bridges adds, ‘It’s now becoming clear that not all comets are the same. For instance, comet Wild-2 may have more similarities to some asteroids and primitive meteorites than comets from the Oort Cloud, which extends to the outer limits of our Solar System and which are infrequent visitors to Earth.
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Title - Comet Wild 2's Complex Chemistry
By - cen.acs.org, 2007
Extracts - Among the particles are inorganics such as the silicate minerals olivine and pyroxene and a host of organics, some contained in the dust and others in the form of gas. Theories of the solar system's formation abound, but as a result of the new findings, a new theory postulates that the early solar system actually flung material far and wide via radial jets spewing out of the sun, rather than being a neat, concentric disk of dust and gas.
"It tells us the early solar nebula was a pretty wild place," says Scott A. Sandford, an astrochemist at NASA's Ames Research Center, in Moffett Field, Calif. Given the relative delicateness of organic compounds compared with minerals, scientists were pleased that so many organics survived the impact with the aerogel and the journey to Earth. Jason P. Dworkin and Daniel P. Glavin of the astrobiology analytical lab at Goddard Space Flight Center, in Greenbelt, Md., found much of the organics in seemingly blank portions of aerogel that don't contain particles, implying that the aerogel captured molecules in the gas phase.
In the Stardust grains, scientists have found polycyclic aromatic hydrocarbons (PAHs), which have been found in meteorites, and also a host of nitrogen- and oxygen-rich compounds. These molecules are more "primitive" than organics generally found in meteorites, meaning they haven't been processed thermally since the comet assembled. If the compounds had been "really cooked," Sandford says, nitrogen and oxygen would have been driven out, and the compounds would have become carbon-rich. "It really implies comets have been great little storage refrigerators since 4.5 billion years ago," he says.
In particular, mission scientists have been able to identify methylamine and ethylamine, which have not been detected in comets before. The group also has identified possible traces of glycine, the simplest amino acid, and 3-aminopropionic acid. "There are lots of amino acids in carbonaceous meteorites, so there's no reason to believe they wouldn't exist in comets," Glavin says. Sifting through the organics captured by Stardust presents a unique challenge, scientists say: Which molecules actually survived intact, and which are the result of processing after impact with the aerogel?
Contaminants are also ubiquitous. Anticipating this, the project's designers included an aerogel sample that flew on the craft but was not exposed to the comet. Because that sample contained far less ethylamine or methylamine than the exposed sample, it's a pretty safe bet the bulk of these compounds came from the comet. Mission scientists also frequently detect 6-aminohexanoic acid, the hydrolysis product of nylon 6. The sources of this molecule, Dworkin and Glavin determined, are the nylon bags and containers used to curate the samples. In fact, its discovery solves a long-standing mystery. For years, this spectral peak was seen in Antarctic meteorite samples that were also bagged in nylon. Even ALH84001, the famous Martian meteorite once posited to contain traces of life, may show this nylon contamination. "The good news is we've convinced the curation office to stop using nylon," Glavin says.
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Title - Stardust: The mission that forever changed our understanding of comets
By - Astronomy magazine, 2022
Extracts - Don Brownlee, Stardust Principal Investigator : The major finding is that the rocky components of the comet, most of its total mass, formed at red hot temperatures. Comet formation included fire and ice. Some of the ice formed at near absolute zero temperature(s), but the rocky materials formed at white hot conditions.
Many of the materials in the comet have also been found in meteorites. Comet Wild 2 is a broader mix of components suggesting that materials from a broad range of locations were transported out beyond Pluto where the comet formed. The rocky materials mostly formed at temperatures above 1,832 F / 1,000 C and could not have had any ices or organics on them at their time of formation. The comet's rocky silicate materials formed first, then assembled with ice and organics in a drastically colder place. This proved that the formation of comet dust and ice was clearly decoupled. The samples proved that the outer solar system was not isolated from the inner solar system, and that materials were clearly mixing over regions from near the Sun to regions beyond the orbit of Pluto.
Probably my greatest thrill of the mission was presenting the first results of the sample analysis at the annual Lunar and Planetary Science Conference just 3 months after landing. When I showed results to 600 people packed into the room, you could hear gasps and see jaws drop. We had gone to a type of body that is famed for its ices, a body whose dust was believed to be dominated by solids formed around other stars. We had found that it contained the highest temperature material that could ever have existed in the solar system. To find such material in a comet was revolutionary. Our modest mission had returned samples to Earth that told us things about comets that could never have been known by remote sensing methods.
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Video Title - Interstellar & early solar system organics in Stardust samples from Comet 81P / Wild 2
By - Scott Sandford, 2009 (Co-investigator, Stardust Mission)
Extracts - Click here to see full extract. Totally worth your time. This is GOLD info.
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Title - Look into the Seeds of Time
By - Science magazine, Dec 2006
Extracts - Isotopically, the comet specks (of Wild 2) resemble rocks from the inner solar system; virtually no grains that pre-date the Sun were seen. A single grain contains minerals produced at high temperatures, in a region close to the Sun, and with isotope ratios similar to those of some meteorites. Thus, material has been mixed across the solar system, from the innermost portion to the outer regions of the Kuiper belt where this comet originated. Although this mixing makes it difficult to explain comet histories, it also means that the Stardust samples might tell us much more about how planets formed.
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Title - Results of the preliminary investigation of comet Wild 2 samples
By - Meteorites & Planetary Science, Feb 2008
Extracts -
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Title - NASA Study Finds New Kind of Organics in Stardust Mission
By - NASA, Dec 14, 2006
Extracts -
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Title - Looks like a comet but feels like an asteroid? That’s wild !
By - The Conversation, 2013
Extracts - See extracts page
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Title - Non-gravitational force modeling of comet 81p/Wild 2. Part 1 - A nucleus bulk density estimate
By - Bjorn Davidsson & Pedro Gutierrez, 2006
Extracts - The active area fraction is difficult to constrain, but at most 60% of the nucleus is likely to have near-surface ice.
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Title - Non-gravitational force modeling of Comet 81P/Wild 2. Part 2 - Rotational evolution
By - Pedro Gutierrez & Bjorn Davidsson, 2006
Extracts - .
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By - Edward Drobyshevski, 2008
Summary - Findings of Deep Impact mission (comet 9P/Tempel 1) and Stardust mission (comet 81P/Wild2) are at odds with the traditional condensation-sublimation paradigm treating comets as a dead product of accretion of matter that had condensed in the outer cold fringes of the Solar system. More in extracts page
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By - Noriyuki Kawasaki et al, Dec 2022
Summary - .
News - lpi.usra.edu
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Title - Comet Wild 2: A window into the birth of the solar system ?
By - Hawaii.edu article, 2015
Summary - The larger-sized dust appears to be similar to rocks found in primitive meteorites called chondrites. The smaller-sized dust, on the other hand, displays the entire range of known oxygen isotopic compositions that have been measured for objects from the inner solar system (from the Sun to the asteroid belt). This unexpected combination of material has deepened the mystery of Wild 2’s past. More in extracts page
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Title - Photometric analysis of the nucleus of Comet 81P/Wild 2 from Stardust images
By - Jian-Yang Li et al, 2009
Summary -
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Title - Comet 81p/Wild 2 under a Microscope
By - Don Brownlee et al, 2006
Summary - The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.
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Title - The Abundance Of Presolar Grains In Comet 81P/Wild 2
By - Christine Floss et al, 2013
Summary - Cometary activity since Wild 2 entered the inner solar system has caused it to lose its original surface, through the sublimation of water ice, leading to loss of gas, rocks, and dust at rates of tons per second (Brownlee et al. 2006). Moreover, the particles sampled by the Stardust collectors originated from numerous collimated jets of solid particles ejected from the interior of the comet and, therefore, should be representative of the material that accreted (along with ices) to form the comet 4.5 billion years ago.
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Title - Physical studies of 81P/Wild 2 from the last two apparitions
By - Z.-Y. Lin et al, 2012
Summary - We observed the switch-off of jet C after January 2010. This phenomenon can be explained by the depletion of the sublimating material in the associated active region. We find that the dust brightness radial profile and dust production rate for Jan 14 are very distinct, with Afρ being higher in a factor of 1.5 compared to other days. Unfortunately, no observations are available before January 14, so we are unable to draw a conclusion about whether we witnessed an outburst or if there was some other earlier event.
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By - Eve Berger et al, 2011
Summary - The discovery of iron sulfides (bearing nickel, copper & zinc) from comet 81P/Wild 2 represents the strongest evidence, in the Stardust collection, of grains that formed in an aqueous environment. We investigated 3 microtomed TEM sections which contain crystalline sulfide assemblages from Wild 2 and 12 thin sections of the hydrothermally altered CI chondrite Orgueil. Detailed structural and compositional characterizations of the sulfide grains from both collections reveal striking similarities. The crystal structures, compositions, and petrographic relationships of these sulfides constrain formation and alteration conditions. Taken together, these constraints attest to low-temperature hydrothermal processing. Our analyses of these minerals provide constraints on large scale issues such as:
- heat sources in the comet-forming region
- aqueous activity on cometary bodies
- the extent and mechanisms of radial mixing of material in the early nebula
The sulfides in the Wild 2 collection are most likely the products of low-temperature aqueous alteration. They provide evidence of radial mixing of material from the inner solar system to the comet-forming region and possible secondary aqueous processing on the cometary body.
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Title - Frozen comet had a watery past, University of Arizona scientists find
By - University of Arizona, 2011
Extracts - The paper referenced by this article is linked above. For the first time, scientists have found convincing evidence for the presence of liquid water in a comet, shattering the current paradigm that comets never get warm enough to melt the ice that makes up the bulk of their material.
"Current thinking suggests that it is impossible to form liquid water inside of a comet," said Dante Lauretta, an associate professor of cosmochemistry and planet formation at the UA's Lunar and Planetary Laboratory. Lauretta is the principal investigator of the UA team involved in analysis of samples returned by NASA's Stardust mission.
"In our samples, we found minerals that formed in the presence of liquid water," said UA graduate student Eve Berger, who led the study said. "At some point in its history, the comet must have harbored pockets of water."
"When the ice melted on Wild-2, the resulting warm water dissolved minerals that were present at the time and precipitated the iron and copper sulfide minerals we observed in our study," Lauretta said. "The sulfide minerals formed between 50 - 200 C, much warmer than the sub-zero temperatures predicted for the interior of a comet".
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Title - Few slides showing microscope photos of comet Wild 2 particles
By - Brownlee et al, 2006
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Comet 81P/Wild2 is referenced in a 2021 paper on asteroid Itokawa (paper no.3)
Extracts - Cubanite is stable only at temperatures below around 250 °C and has thus far only been identified in CI carbonaceous chondrites and the comet 81P/Wild2 sample suite. Cubanite, a Cu-Fe-sulfide, is known only in terrestrial ore deposits, comet 81P/Wild2, and CI-chondrite materials. Additionally, the cubanite in the comet Wild2 sample suite may have formed during alteration of the comet, which in turn could mean that cometary material is also a possible source for the cubanite on Itokawa, although such alteration is not thought to be pervasive on comets.
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Title - NASA Researchers Make First Discovery of Life's Building Block in Comet
By - Bill Steigerwald, 2009
Summary - Glycine, a fundamental building block of life, has been found in samples of comet Wild 2. "Our discovery supports the theory that some of life's ingredients formed in space and were delivered to Earth long ago by meteorite and comet impacts", said Dr. Jamie Elsila.
"The discovery of glycine in a comet supports the idea that the fundamental building blocks of life are prevalent in space, and strengthens the argument that life in the universe may be common rather than rare," said Dr. Carl Pilcher, Director of the NASA Astrobiology Institute which co-funded the research.
A glycine molecule from space will tend to have more of the heavier Carbon 13 atoms in it than glycine that's from Earth. That is what the team found. "We discovered that the Stardust-returned glycine has an extraterrestrial carbon isotope signature, indicating that it originated on the comet," said Elsila.
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Title - Cometary glycine detected in samples returned by Stardust
By - Jamie Elsila et al, 2010
Summary -
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Title - Stardust's Big Surprise
By - Don Brownlee, 2007
Summary -
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Title - NASA's Stardust Findings May Alter View of Comet Formation (2006)
Extracts - "We have found very high-temperature minerals, which supports a particular model where strong bipolar jets coming out of the early sun propelled material formed near to the sun outward to the outer reaches of the solar system," said Michael Zolensky, Stardust curator and co-investigator at NASA's Johnson Space Center, Houston. "It seems that comets are not composed entirely of volatile rich materials but rather are a mixture of materials formed at all temperature ranges, at places very near the early sun and at places very remote from it."
One mineral found in the material brought back by Stardust is olivine, a primary component of the green sand found on some Hawaiian beaches. It is among the most common minerals in the universe, but scientists were surprised to find it in cometary dust. Olivine is a compound of iron, magnesium and other elements. The Stardust sample is primarily magnesium. Along with olivine, the dust from Wild 2 contains high-temperature minerals rich in calcium, aluminum and titanium. In addition to cometary particles, Stardust also gathered interstellar dust samples during its 7 year journey.
Stardust passed within 240 km of comet Wild 2 in Jan 2004, trapping particles from the comet in an exposed aerogel. Samples have been distributed to approximately 150 scientists for study.The grains are tiny, most smaller than a hair's width. Thousands of them appear to be embedded in the glass-like aerogel. A single grain of 10 microns, only one-hundredth of a millimeter (.0004 inches), can be sliced into hundreds of samples for scientists.
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Title - Why Comet Wild 2 ?
Extracts - It is a fresh comet. Jupiter changed its orbit in 1974 & it now travels much closer to the sun, between Jupiter and the Earth. Because it has not been exposed to the Sun at close range, its composition has not been altered much from its original condition. By the time Stardust encounters it, Comet Wild 2 will have made only 5 trips around the sun. By contrast, Comet Halley has passed the sun more than 100 times, coming close enough to have been greatly altered from its original condition.
When a comet comes close enough to the sun to get heated up, it loses some of its material through the process of sublimation. This happens when a solid becomes a vapor without first melting into a liquid. After about 1,000 trips past the Sun, a comet loses most of these volatile materials and no longer generates a coma, which is made up of the gases that sublime off its surface. Since it is the escaping gases that drive the dust particles from the nucleus - the solid part of the comet - the comet no longer creates the long beautiful dust tail that we can sometimes see in the night sky.
Since Wild 2 has passed the sun only a few times, it still has most of its dust and gases and it is relatively pristine condition. This is important because comets are made up of material left over from the solar nebula after the planets were formed. Unlike the planets, most comets have not changed very much since the formation of the solar system. Therefore, comets may hold the key to understanding the early development of the Solar System. Comet Wild 2 should contain much of this ancient material, making it an ideal choice for study.
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Title - Stardust : Science In Depth (1994, pre-mission)
Extracts - .
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https://solarsystem.nasa.gov/stardust/science/feature001.html
https://solarsystem.nasa.gov/stardust/news/stardust.html
https://solarsystem.nasa.gov/stardust/photo/cometwild2.html#row4
https://solarsystem.nasa.gov/stardust/links/comets.html
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Title - Cometary activity, active areas, and a mechanism for collimated outflows on 1P, 9P, 19P, and 81P
By - Michael Belton, 2010
Summary - The properties of 50 jet and jet-filament outflows from 27 active areas observed on the 4 comet nuclei that have been visited by spacecraft (1P/Halley, 19P/Borrelly, 81P/Wild 2, and 9P/Tempel 1) are investigated and we propose a taxonomic categorization in which there are 3 types of active areas :
- Type I that is dominated by the sublimation of H2O through the porous mantle
- Type II that is controlled by the localized and persistent effusion of super-volatiles from the interior
- Type III that is characterized by episodic releases of super-volatiles
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Title - Comet 81P/Wild 2 size, shape, and orientation
By - Thomas Duxbury & Ray Newburn, 2004
Summary - Spectacular images, taken during the flyby of 81P/Wild 2 by the NASA Stardust spacecraft, were used to determine that the shape of the comet 81P/Wild 2 nucleus can be reasonably modeled as a triaxial ellipse having a radii of 1.65 x 2 x 2.75 km (diameter of 3.3 x 4 x 5.5 km).
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Title - Physical and compositional studies of Comet 81P/Wild 2 at multiple apparitions
By - Tony Farnham & David Schleicher, 2005
Summary - The comet has a low dust-to-gas ratio. Analysis of the dust and gas production rates as a function of heliocentric distance, revealed a substantial seasonal effect where the production of OH, NH, and dust peaks 11–12 weeks before perihelion. The CN, C2, and C3 production show no such asymmetry, suggesting that there may be heterogeneities among different sources on the nucleus. The primary jet persists for several months and is roughly aligned with the spin axis, while the secondary jet is located on the opposite hemisphere. Images at different wavelengths show that the jets have the same colors as the dust in other regions in the coma and tail, indicating that the grain properties are similar throughout the coma.
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Title - Modeling the Nucleus and Jets of Comet 81P/Wild 2 Based on the Stardust Encounter Data
By - Zdenek Sekanina et al, 2004
Summary - Triangulation of 20 jets shows that 2 emanate from the nucleus dark side and 16 emanate from sources that are on slopes where the Sun's elevation is greater than predicted from the fitted triaxial ellipsoid. Seven sources, including five in the Mayo depression, coincide with relatively bright surface spots. Fitting the imaged jets, the spikelike temporal distribution of dust impacts indicates that the spacecraft crossed thin, densely populated sheets of particulate ejecta extending from small sources on the rotating nucleus, consistent with an emission cone model.
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