HED meteorites are differentiated meteorites, which were created by igneous processes in the crust of their parent asteroid. It is thought that the method of transport from Vesta to Earth is as follows: An impact on Vesta ejected debris, creating small (10 kilometres (6.2 mi) diameter or less) V-type asteroids.
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HED meteorites are differentiated meteorites, which were created by igneous processes in the crust of their parent asteroid. It is thought that the method of transport from Vesta to Earth is as follows: An impact on Vesta ejected debris, creating small (10 kilometres (6.2 mi) diameter or less) V-type asteroids.
Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites The howardite, eucrite and diogenite (HED) clan of meteorites are ultramafic and mafic igneous rocks and impact-engendered fragmental debris derived from a thoroughly differentiated asteroid.
Some researchers believe that an amazing 5% to 6% of all meteorites found on Earth originated from Vesta. [4] Vesta asteroid topography: Color topographic map of Vesta asteroid viewing the south polar area.
Eventually, perhaps billions of years later, the meteoroid was captured by Earth's gravitational field, and it fell through Earth's atmosphere to the ground. Although meteorites are extremely rare, thousands of them have been found on Earth's surface. Over 99% of all meteorites found on Earth are thought to be pieces of asteroids.
Where Do Meteorites Come From? All meteorites come from inside our solar system. Most of them are fragments of asteroids that broke apart long ago in the asteroid belt, located between Mars and Jupiter. Such fragments orbit the Sun for some time–often millions of years–before colliding with Earth.
As the Earth passes through a comet's tail, the rocky debris collides with our atmosphere, creating the colorful streaks of a meteor shower. Meteor storms are even more intense than showers, defined as having at least 1,000 meteors per hour. All the meteors in a meteor shower seem to come from one spot in the sky.
Composed almost entirely of pyroxene, a mineral found in lava flows, the meteorite bears the same spectral signals as Vesta. NASA's Dawn spacecraft, which visited the asteroid in 2012, discovered that the rocky body had a surprising amount of hydrogen on its surface.
The giant asteroid is almost spherical, and so is nearly classified a dwarf planet. Unlike most known asteroids, Vesta has separated into crust, mantle and core (a characteristic known as being differentiated), much like Earth.
The energy of the impact will vaporize the asteroid and a large amount of the Earth's crust, creating a crater more than one hundred kilometers across, throwing all that rock into the air. Some of this debris will be going so fast that it will fly right out of the Earth's atmosphere and go into orbit around the Earth.
When the meteor hits the atmosphere, the air in front of it compresses incredibly quickly. When a gas is compressed, its temperature rises. This causes the meteor to heat up so much that it glows. The air burns the meteor until there is nothing left.
NASA's Dawn spacecraft could settle the matter. Vesta was spotted 200 years ago and is officially a "minor planet" — a body that orbits the sun but is not a proper planet or comet.
Asteroid 4 Vesta is currently in the constellation of Aquarius. The current Right Ascension is 22h 06m 53s and the Declination is -21° 44' 11”.
Vesta is located approximately 100 million miles from Earth in the solar system's main asteroid belt—home to countless bodies that circle the sun between the orbits of Mars and Jupiter. Scientists believe the asteroid formed prior to the planets, making it one of the oldest objects in space that's within our reach.
ChicxulubA six-mile-wide asteroid called Chicxulub slammed into the waters off what is now Mexico, triggering a mass extinction that killed off more than 75 percent of Earth's species. Unfathomably powerful earthquakes rattled and rolled the planet's crust. Tsunamis more than 150 feet tall pummeled North America's shores.
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Overview. Vesta is a dwarf planet orbiting between Mars and Jupiter in the main portion of the asteroid belt. NASA JPL has not classified Vesta as potentially hazardous because its orbit does not bring it close to Earth.
17Every year, the Earth is hit by about 6100 meteors large enough to reach the ground, or about 17 every day, research has revealed. The vast majority fall unnoticed, in uninhabited areas. But several times a year, a few land in places that catch more attention.
When meteoroids enter Earth's atmosphere (or that of another planet, like Mars) at high speed and burn up, the fireballs or “shooting stars” are called meteors. When a meteoroid survives a trip through the atmosphere and hits the ground, it's called a meteorite.
Most meteorites found on Earth come from shattered asteroids, although some come from Mars or the Moon.
A meteor air burst is an air burst resulting from a meteor exploding mid-flight as it encounters the thicker part of the atmosphere. These types of meteors are also known as fireballs or bolides, with the brightest known as superbolides.
How do we know these meteorites came from Vesta? The composition of an asteroid's surface can be determined by the way it reflects sunlight. Vesta is the only large asteroid whose "light signature" matches the basaltic rock of the HED meteorites; each meteorite type matches a different part of Vesta's surface.
The three types of HED meteorites tell the story of the sometimes violent processes that shaped Vesta. The eucrites are hardened lava that flowed onto Vesta's surface; the diogenites come from rock buried deeper down; and the howardites are a mixture of the other two, created by impact mixing.
Just one group, the HED meteorites—composed of the howardites, eucrites and diogenites—has been traced back to a specific asteroid, Vesta.
Howardites were created by impacts that crushed and mixed different parts of Vesta and melted enough rock to cement them together. In both Kapoeta and Bholghati, the contrast between different colored materials is visible to the naked eye.
These bubbles formed when molten lava flowed onto Vesta's surface, where the sudden drop in pressure caused gases dissolved in the lava to form bubbles-just as bubbles form in soda when a bottle is opened.
Vesta is the second-largest asteroid in the solar system, with a diameter of 525 kilometers (325 miles). Covering most of one side is a giant crater with a central uplift. The huge impact that made this crater knocked off more than enough material to account for all the HED meteorites. P. Thomas, B. Zellner and NASA.
Eucrites resemble lava from Hawaiian volcanoes. They formed much the same way, when molten basaltic rock flowed onto Vesta's surface. This lava cooled and hardened so quickly that only very small crystals had time to form.
This information has confirmed that HED meteorites, a subgroup of stony achondrite meteorites, are pieces of Vesta that have fallen to Earth.
They are thought to have originated from Vesta. There are three subgroups: Howardites, Eucrites, and Diogenites.
At least three lunar-resident meteorites have been found by NASA moon landings. In addition, trace element evidence of extralunar materials has been found in lunar regolith samples. NASA's Mars Rovers have encountered and photographed several impressive meteorites on the surface of Mars. More Meteorites.
Researchers have learned a lot about the chemistry, mineralogy, and isotopic composition of rocks from the Moon by studying specimens brought back to Earth by NASA's lunar missions. The characteristics of rocks on Mars have been determined through analyses done by rovers and other equipment sent to that planet. By comparing the composition of meteorites to this data, researchers have been able to identify meteorites that are probably pieces of Moon and Mars.
Although meteorites are extremely rare, thousands of them have been found on Earth's surface. Over 99% of all meteorites found on Earth are thought to be pieces of asteroids. A few of the meteorites found on Earth have been attributed to specific solar system bodies.
A meteorite is a rock that was once part of another planet, a moon, or a large asteroid. It was dislodged from its home by a powerful impact event. That impact launched the rock with enough force to escape the gravity of its home body and propel it through space.
The Rheasilvia Crater is about 500 kilometers in diameter (300 miles). The floor of the crater is about 13 kilometers (8 miles) below the undisturbed surface of Vesta and its rim, a combination of upturned strata and ejecta, rises between 4 and 12 kilometers (2.5 and 7.5 miles) above the surface of the undisturbed surface of Vesta.
Compositional characteristics of the HED meteorites have been used for classification and also to better understand the origin of the different groups and subgroups. The Fe/Mn ratios of pyroxenes have been used to distinguish HED meteorites from other FeO-rich and pyroxene and plagioclase-bearing basalts such as lunar and martian basaltic meteorites (Figure 6; Karner et al., 2006; Goodrich and Delaney, 2000).
Figure 6: Mn and Fe2+ contents of pyroxenes from basalts from Earth, Moon, Mars and 4 Vesta (HED parent body) from the paper of Karner et al. (2006). The HED meteorite pyroxenes have the lowest Fe/Mn ratios of all samples. There is slight overlap with martian samples but these can be distinguished based on other data such as oxygen isotopes, and the presence of maskelynite and the lack of reduced FeNi metal in maritan basalts.
Howardites are brecciated mixtures of diogenite and eucrite material. As one might imagine, there is some difficulty in drawing the line between a howardite, a polymict eucrite, and a brecciated diogenite with some eucritic material. As such there are many cases in the literature of samples being characterized as "howardite or diogenite", or "howardite or polymict eucrites". Howardites are defined as having >10% diogenite or eucrite material (Figure 3), and they are also known to contain foreign material such as carbonaceous chondrite clasts (Mittlefehldt and Lindstrom, 1991; Buchanan and Reid, 1991; Buchanan et al, 1990, 1993, Metzler et al, 1995; Buchanan et al, 2000; Buchanan and Mittlefehldt, 2003). To get around the limitations of making a classification based on one thin slice through such a meteorite, some have attempted to classify based on bulk composition (Figure 4), somewhat analogous to the way lunar breccias are defined (e.g., Korotev, 2005).
Although olivine is typically < 10%, there is a growing group of olivine-rich diogenites that contain up to 50% olivine. These are of great interest to HED meteorite specialists because they may offer insight into the HED mantle, or to one end-member of magmatic evolution that had olivine and orthopyroxene crystallizing together.
Eucrites are basaltic rocks comprised of pigeonite (low Ca clinopyroxene) and plagioclase feldspar, with minor phosphate, metal, troilite, silica, and ilmenite, and come in several different types based on their textures (Figure 1). First are basaltic textures such as coarse-grained ophitic and sub-ophitic, fine grained aphyric, ...
In this group are basaltic rocks that have been recrystallized into fine grained granulitic textures, and represent metamorphosed basalts (Yamaguchi et al., 1996, 1997). Diogenites have also experienced thermal metamorphism (e.g., Mori and Takeda, 1981; Yamaguchi et al., 2010) and this must be kept in mind when considering igneous formation models.
This also works and has some advantages over petrography, but as always the divisions between fields must be defined well. Howardites also contain glassy spherules, perhaps from impact processes, and can contain dark fine grained clasts that may also be shock or impact related.
The HED meteorites have several distinctive compositional characteristics. Among these is a general paucity of moderately volatile and volatile lithophile elements. The Na/Al ratios of basaltic eucrites is roughly a factor of 10 lower than that of solar abundances and of ordinary chondrite abundances, and a factor of ∼3 lower than for CV and CK chondrites ( McSween et al., 2011 ). The latter are the most volatile-depleted chondrite groups (see Lodders and Fegley, 1998 ). The more volatile alkali elements (Rb, Cs) are at much lower abundances relative to refractory elements ( Mittlefehldt, 1987 ). Estimates of the bulk composition of the HED parent asteroid have abundances of moderately volatile and volatile elements similar to those of the Moon (e.g., Anders, 1977, Dreibus and Wänke, 1980 ). Other distinctive characteristics of eucrites and diogenites are their very low abundances of siderophile elements. For example, typical CI-normalized abundances for basaltic eucrites are Co ∼10 −2, Ni ∼10 −3 to 10 −6, and Ir ∼10 −4 to 10 −7 ( Warren et al., 2009 ). Cumulate eucrites and diogenites have on average higher siderophile element abundances than basaltic eucrites, but their abundances are low ( Warren et al., 2009 ). In spite of their very low siderophile element abundances, basaltic eucrites are rich in FeO, with the most primitive basalts having mg#s of ∼40–42.
The crystallization ages of HED igneous lithologies as determined by long-lived chronometer systems – Rb-Sr, Sm-Nd, Pb-Pb – demonstrate that magmatism on Vesta occurred very early in Solar System history (e.g., Allègre et al., 1975, Birck and Allègre, 1978, Nyquist et al., 1986, Papanastassiou and Wasserburg, 1969, Smoliar, 1993, Tera et al., 1997 ). However, almost all eucrites and diogenites have been brecciated and/or thermally metamorphosed, and the different geochronometers have responded differently to these post-crystallization perturbations depending on the relative diffusivities of the parent and daughter elements. The unbrecciated cumulate eucrites Moore County and Serra de Magé yield Pb-Pb model ages ( Tera et al., 1997) that are resolvably lower than the best estimate of the age of magmatism for the basaltic eucrites based on Rb-Sr data ( Smoliar, 1993 ). The cumulate eucrites have textures and pyroxene exsolution characteristics that indicate they were formed deep in the vestan crust and cooled slowly (e.g., Miyamoto and Takeda, 1977, Takeda, 1979 ). Similarly, a Rb-Sr isochron age for diogenites Johnstown and Tatahouine ( Takahashi and Masuda, 1990) is resolvably lower than the estimate age of basaltic eucrite magmatism. Johnstown is a breccia and Tatahouine suffered shock damage, potentially resetting the Rb-Sr chronometer. Thus, while long-lived chronometer systems provide evidence that magmatism occurred very early on Vesta, the derived ages are neither robust enough nor precise enough to detail the fine-scale history of vestan global igneous evolution.
Northwest Africa 011 was the first basaltic achondrite described that is petrologically very similar to eucrites but demonstrably from a different parent asteroid ( Yamaguchi et al., 2002 ). It and its pairs remain the most distinct from HEDs in O isotope composition ( Fig. 11 a). Subsequently, I argued that the unusual basaltic eucrite Ibitira was also unrelated to HEDs. This rock is one of a very few meteoritic basalts to have vesicles ( Wilkening and Anders, 1975) and has unusually low alkali element contents ( Stolper, 1977 ). It has an O isotope composition like angrites and very different from HEDs ( Greenwood et al., 2005, Wiechert et al., 2004 ), an Fe/Mn ratio in pyroxenes significantly higher than for basaltic eucrites, and ratios for some incompatible trace element that are different from those of basaltic eucrites ( Mittlefehldt, 2005 ). Subsequently, high precision O isotope analyses have shown that A-881394 and Bunburra Rockhole have similar O isotope compositions with Δ 17 O that lie ∼15 σ away from the HED mean composition ( Benedix et al., 2014, Bland et al., 2009, Scott et al., 2009 ). Preliminary data on unbrecciated cumulate gabbro EET 92023 and basaltic achondrite Emmaville, both classified as eucrites, show that they have O isotope compositions that are close to those of A-881394 and Bunburra Rockhole ( Greenwood et al., 2012, Greenwood et al., 2013 ). Dhofar 007 is a polymict breccia composed mostly of cumulate gabbro debris and is rich in metal and siderophile elements ( Dale et al., 2012, Yamaguchi et al., 2006 ). It contains materials with differing Δ 17 O within the range found for Bunburra Rockhole ( Greenwood et al., 2012 ). NWA 2824 has rare-earth-element contents like those of basaltic eucrites, but is more Mg-rich than eucrites ( Bunch et al., 2009 ). Its O-isotopic composition is very similar to Ibitira. Pasamonte and PCA 91007 lie ∼5 σ from the HED mean, and NWA 1240 lies ∼4 σ from the mean ( Scott et al., 2009) ( Fig. 11 b).
The earliest petrogenetic model for asteroidal differentiation was based on the petrology and mineralogy of HED meteorites, pallasites and iron meteorites and envisioned total melting and crystallization to produce a suite of igneous rocks. Mason (1962) observed that the lithologies of the HED clan could represent a fractional crystallization sequence from early magnesian orthopyroxenites, through a series of rocks with increasing plagioclase content and Fe-enrichment of pyroxene, ending with basaltic eucrites as residual melts. He inferred that an iron core and dunitic mantle would occur in the deep interior. (Note that at this time, Mason thought howardites were a brecciated igneous rock type, and not an impact-engendered mixture of distinct lithologies.)
Howardites with higher noble gas contents contain two components, planetary- and solar-type gases (e.g., Mazor and Anders, 1967 ). These authors thought that these gases were added to the regolith by a single carrier phase because the planetary- and solar-type gas contents were correlated. Characterization of carbonaceous chondrite fragments in howardites ( Wilkening, 1973) led to the identification of these clasts as the carriers of the planetary-type gases ( Wilkening, 1976 ). Experiments have shown that the solar-type gases are a surface correlated component in mineral and glass fragments of HED parentage, not just of the chondritic materials ( Black, 1972, Caffee et al., 1983, Padia and Rao, 1989, Rao et al., 1991 ). These solar-type gases represent solar wind and fractionated solar wind implanted in the outer few μm of grains in the breccias. (The fractionated solar wind component was formerly referred to as a solar energetic particle component and thought to be derived from solar flares, cf. Grimberg et al., 2006 .) The solar wind component shows that some howardites were part of the true regolith of their parent body (see discussion in Cartwright et al., 2013, Cartwright et al., 2014, Mittlefehldt et al., 2013b ).
Siderophile elements are at low to very low abundances in HED igneous lithologies, and are generally highest in the polymict breccias. Chondritic debris is found even in supposedly monomict breccias (e.g., Mittlefehldt, 1994 ), and for this reason, the siderophile element contents of HED igneous lithologies need to be evaluated cautiously. Cobalt is a moderately siderophile element and HED igneous lithologies show ranges in Co contents from ∼3 to 9 μg/g for basaltic eucrites and up to ∼11–30 μg/g for diogenites. Nickel contents show much wider ranges: 0.1–50 μg/g for basaltic eucrites, 1–150 μg/g for diogenites ( Fig. 16 ). Carbonaceous chondrites have about 20–200 times as much Co, but 80 to 123,000 times the Ni. Contamination by chondritic debris in monomict breccias is therefore much less a problem for Co. A mixing model between the most Ni-poor basaltic eucrite and CM chondrites shows that the entire Ni range can be explained by as little as 0.5% chondritic debris in the breccias ( Fig. 16 ), but this engenders only a modest increase in the Co content. For the most part, the ranges in Co contents of basaltic eucrites, cumulate eucrites and diogenites likely reflect those of pristine igneous lithologies.
Airless rocky bodies in the Solar System are covered with a layer composed of fragmental debris, lithified breccias and solidified melt particles formed by hypervelocity meteoroid impacts onto the surface ( McKay et al., 1991 ). Howardites are polymict breccias, the lithified remnants of that debris layer from Vesta, and are mostly composed of diogenitic and eucritic debris ( Duke and Silver, 1967 ). There are also polymict breccias consisting only of debris from different types of eucrites ( Miyamoto et al., 1978, Olsen et al., 1978, Takeda et al., 1978b ), and a few diogenites contain basaltic eucritic clasts (e.g., Lomena et al., 1976 ). Thus, the suite of polymict breccias includes rocks with eucrite:diogenite-mixing ratios outside the range of “traditional” howardites ( Mason et al., 1979 ). The HED classification system now recognizes a continuum of breccia types from monomict basaltic eucrite to monomict diogenite breccias ( Fig. 1 c). Polymict eucrites are eucrite-rich breccias containing <10% diogenitic material, and polymict diogenites contain <10% eucritic material ( Delaney et al., 1983 ). Very few polymict breccias are composed only of mixtures of cumulate and basaltic eucrite materials. Binda is one ( Yanai and Haramura, 1993 ), and is classified as a polymict cumulate eucrite ( Delaney et al., 1983 ). Similarly, polymict breccias composed only of diogenites and cumulate eucrites seem very rare; Y-791073 is an example ( Takeda, 1986 ). Howardites fall into two subtypes: regolithic howardites, the lithified remnants of the active regolith of Vesta; and fragmental howardites, simpler polymict breccias ( Mittlefehldt et al., 2013b, Warren et al., 2009 ). Most of the material in the polymict breccias is essentially the same as basaltic eucrites, cumulate eucrites or diogenites, and their descriptions need not be repeated. Here I will focus on material formed by regolith gardening and on unusual lithologic components.