This photo was taken September 1990 in Flagstaff, Arizona during a chance meeting between Doug Hollis and myself (David Weir), and with Clyde Tombaugh and his wife Patricia. They happened to be visiting the observatory, from which Clyde discovered the ninth planetThe term "planet" originally comes from the Greek word for "wanderer" since these objects were seen to move in the sky independently from the background of fixed stars that moved together through the seasons. The IAU last defined the term planet in 2006, however the new definition has remained controversial. Click on Term to Read More Pluto, to make their first stroll together down the newly constructed Pluto Walk. The photo was shared with Clyde and received his signature in May 1992.
Congratulations Clyde Tombaugh on your historic visit to Pluto!
NASA’s New Horizons spacecraft captured the above high-resolution enhanced color images of Pluto and Charon on July 14, 2015. The Pluto and Charon images resolve details as small as 0.8 miles and 1.8 miles, respectively. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
CR7 or Meta-CR (CR-like in MetBull 86; CR-an in MetBull DB)
Found March 2000, 20 ° 45.8′ N., 10 ° 26.5′ E.
A single mass of 3,636 g was found by a German team in the Ténéré region of the Sahara Desert in north-central Niger, specifically, at a location known as Grein. Provisionally named Te-1, it was classified by J. Otto and A. Ruh (Universitat Freiburg) as a metal-rich, coarse-grained, primitive achondriteAchondrite with an almost chondritic composition with age similar to the primordial chondrites. These should be better classified as "metachondrites".. OlivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion Click on Term to Read More grains are mostly 0.1–0.4 mm in size, but larger grains occur. They commonly exhibit triple-junctions, consistent with recrystallization. Large poikilitic pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification Click on Term to Read More grains are present, as well as small agglomerates of crystals, sometimes called ‘Sammelkristalle’, which usually form during melting and recrystallization processes. Unlike chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More, these structures are composed primarily of plagioclaseAlso referred to as the plagioclase feldspar series. Plagioclase is a common rock-forming series of feldspar minerals containing a continuous solid solution of calcium and sodium: (Na1-x,Cax)(Alx+1,Si1-x)Si2O8 where x = 0 to 1. The Ca-rich end-member is called anorthite (pure anorthite has formula: CaAl2Si2O8) and the Na-rich end-member is albite Click on Term to Read More poikilitically enclosing minor olivines and pyroxenes, and are often accompanied by FeNi-metal. Te-1 is a freshly fallen meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More with a weathering grade of W0, and it has a shock stageA petrographic assessment, using features observed in minerals grains, of the degree to which a meteorite has undergone shock metamorphism. The highest stage observed in 25% of the indicator grains is used to determine the stage. Also called "shock level". Click on Term to Read More of S1–2.This primitive achondriteAn achondrite is a type of stony meteorite whose precursor was of chondritic origin and experienced metamorphic and igneous processes. They have a planetary or differentiated asteroidal origin where the chondritic parent body reached a sufficient size that through heating due to radioactive decay of 26Al (aluminum isotope) and gravitational Click on Term to Read More has a chemical and mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous Click on Term to Read More composition unlike that of any other meteorite. It has an O-isotopic composition distinct from any other achondrite group, plotting within the CR-field, and interestingly, very near to that of the ungroupedModifying term used to describe meteorites that are mineralogically and/or chemically unique and defy classification into the group or sub-group they most closely resemble. Some examples include Ungrouped Achondrite (achondrite-ung), Ungrouped Chondrite (chondrite-ung), Ungrouped Iron (iron-ung), and Ungrouped Carbonaceous (C-ung). Click on Term to Read More basaltic meteorite NWA 011. OxygenElement that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only Click on Term to Read More isotopes are similar to those of the lodraniteRare type of primitive achondrite named after the Lodran meteorite that fell in Pakistan in 1868. Initially, lodranites were grouped with the stony-iron meteorites because they contain silicates (olivine, orthopyroxene, and minor plagioclase) and Fe-Ni metal in nearly equal proportions. However, since discovery of the closely related acapulcoite group, lodranites Click on Term to Read More/acapulcoite parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More but are not an exact match. The mineral composition and noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. Click on Term to Read More content of Te-1 are very similar to that of the brachinites and the brachinite-like meteorite, Divnoe; moreover, the olivine and pyroxene compositions are nearly identical to those of Brachina. Furthermore, the composition of chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups. Click on Term to Read More and metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn Click on Term to Read More in Te-1 is also indicative of a very close relationship with Divnoe. These varied characteristics are most consistent with the grouping of Te-1 as a brachinite-like primitive achondrite. See the Tafassasset page for further information.
Te-1 has a CRE age of 45 m.y. The specimen shown above is a 1.72 g partial slice with fresh fusion crustMelted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of 4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below. Click on Term to Read More on one end. The photo below shows the main massLargest fragment of a meteorite, typically at the time of recovery. Meteorites are commonly cut, sliced or sometimes broken thus reducing the size of the main mass and the resulting largest specimen is called the "largest known mass". Click on Term to Read More of Te-1 with an end slice removed.
As with other ureilites, Almahata Sitta falls on the carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than Click on Term to Read More anhydrous mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous Click on Term to Read More line. Although complex organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. Click on Term to Read More compounds commonly occur in many other carbonaceous chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More groups, Glavin et al. (2010) conducted the first such analysis on a ureilite—Almahata Sitta. Compared to over 80 amino acids identified in some CM chondrites, only 19 amino acids and their enantiomers were identified in Almahata Sitta, along with 4 amines (produced by thermal decomposition of amino acids), plus other unidentified amino acids belonging to the 5-carbon group.
Since these organic compounds rapidly decompose at temperatures of 500–600°C, and it is generally accepted that ureilites experienced temperatures twice that, conditions for the formation of organics are tightly constrained. The amino acids could have been introduced by collisions with carbon-rich asteroids, or peak temperatures might not have been high enough to destroy them all; however, it is thought most likely that the organics were formed by catalytic reactions after asteroid 2008 TC3 had cooled.
As in all groups, these organic compounds have a nonbiogenic origin. The following organic compounds have been isolated from Almahata Sitta (Glavin et al., 2010):
ORGANIC COMPOUNDS IDENTIFIED IN THE UREILITE ALMAHATA SITTA
D- and L-aspartic acid
D- and L-glutamic acid
D- and L-serine
D- and L-threonine
D- and L-alanine
D- and L-β-amino-n-butyric acid
α- or β-aminoisobutyric acid
D-2-amino-2-methylbutanoic acid (D-isovaline)
L-2-amino-2-methylbutanoic acid (L-isovaline)
L-2-amino-3-methylbutanoic acid (L-valine)
D-2-amino-3-methylbutanoic acid (D-valine)
D-2-aminopentanoic acid (D-norvaline)
L-2-aminopentanoic acid (L-norvaline)
MesosideriteOne of two main types of stony-iron meteorite, the other being pallasites. Mesosiderites are a mixture of approximately 50% basaltic, gabbroic and orthopyroxenitic silicates and 50% Ni-Fe metal and sulfides. The name derives from the Greek "mesos" meaning "middle" or "half" and "sideros" for "iron;" hence "half-iron". The silicates are Click on Term to Read More, subgroup 2C (subgroup 2B in Metbull 88)
Found 2002, no coordinates recorded
A very small fusion-crusted stone weighing only 13.52 g was purchased in Erfoud, Morocco by M. Farmer in March 2003. Analysis and classification was completed at Northern Arizona University. Although the MetBull #88 lists NWA 1912 as belonging to subgroup 2B, it exhibits only minor recrystallization and has a matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More composed predominantly of large orthopyroxeneOrthorhombic, low-Ca pyroxene common in chondrites. Its compositional range runs from all Mg-rich enstatite, MgSiO3 to Fe-rich ferrosilite, FeSiO3. These end-members form an almost complete solid solution where Mg2+ substitutes for Fe2+ up to about 90 mol. % and Ca substitutes no more than ~5 mol. % (higher Ca2+ contents occur Click on Term to Read More grains along with some plagioclaseAlso referred to as the plagioclase feldspar series. Plagioclase is a common rock-forming series of feldspar minerals containing a continuous solid solution of calcium and sodium: (Na1-x,Cax)(Alx+1,Si1-x)Si2O8 where x = 0 to 1. The Ca-rich end-member is called anorthite (pure anorthite has formula: CaAl2Si2O8) and the Na-rich end-member is albite Click on Term to Read More, features that are consistent with assignment to subgroup 2C. Furthermore, it is considered likely that NWA 1912 is a member of the NWA 1827 pairing group, assigned to subgroup 2C (Bunch et al., 2004).
Northwest Africa 1912 is an unshocked meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More (S1) that shows only minor signs of weathering. The specimen in the photo above is a 0.64 g partial slice, which exhibits green orthopyroxene fragments in a metallic matrix, along with lesser amounts of anorthitic plagioclase, chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups. Click on Term to Read More, troiliteBrass colored non-magnetic Fe sulfide, FeS, found in a variety of meteorites., and silicaSilicon dioxide, SiO2..
Separating Myth from Fact: Is the Nakhla Dog Real?
A Personal Analysis By David Weir
Although my skeptical nature leads me to scrutinize the impact dog event, I remain open-minded to new evidence supporting either side. Despite the absence of eyewitnesses and newspaper articles, I am of the mind that the probability of such a dog impact in Denshal can be further assessed through the scientific method, using the data and theoretical applications currently available.
While looking through the literature for any helpful data, I found a non-peer-reviewed paper published by Eugster et al. in LPSC 33 (2002), in which they describe research on ‘The Pre-Atmospheric Size Of Martian Meteorites’. The upper limit of the radii of martian ejectaFractured and/or molten rocky debris thrown out of a crater during a meteorite impact event, or, alternatively, material, including ash, lapilli, and bombs, erupted from a volcano. Click on Term to Read More translates to masses of 150–270 kg–too high to be a limiting factor when considering a Nakhla strewn fieldArea on the surface containing meteorites and fragments from a single fall. Also applied to the area covered by tektites, which are produced by large meteorite impacts. Strewnfields are often oval-shaped with the largest specimens found at one end. Given that the largest specimens go the greatest distance, a meteoroid's that might extend all the way to Denshal. However, in a diagram that compares the minimum pre-atmospheric weights of several Martian meteorites–including Nakhla, Zagami, Shergotty, QUE 94201, Chassigny, Los Angeles, and SaU 005–it is Nakhla that has the lowest, i.e., the smallest size. Therefore, one might reasonably expect Nakhla to also be at the low end of the range of weights of all martian meteoriteOver 30 of the meteorites found on Earth almost certainly came from Mars (see http://www.imca.cc/mars/martian-meteorites.htm and http://www2.jpl.nasa.gov/snc/). All but one belongs to the group known as SNC meteorites, which includes the shergottites, nakhlites, and chassignites. SNC meteorites contain minerals that crystallized within the past 1.35 to 0.15 Ga, making them Click on Term to Read More falls, especially if a pattern is evident. The falls include the following four meteorites, listed in order from the smallest to the largest minimum calculated pre-atmospheric size, with the actual fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If Click on Term to Read More weights given in parentheses: Nakhla (10 kg), Zagami (18 kg), Shergotty (5 kg), and Chassigny (4 kg).
For those Martian meteorites that are finds, the two with the largest minimum pre-atmospheric masses, again with the actual fall weights given in parentheses, are SaU 005 (1.3 kg, but 10.6 kg with paired masses included) and then Los Angeles (0.7 kg), either of which may or may not be representive of their cumulative fall weights. In addition, having a minimum pre-atmospheric size similar to that of Chassigny, the Antarctic QUE 94201 (0.012 kg) likely does not represent its total fall weight. Although not included in this study, two other martians with large recovered weights can be mentioned for comparison–EET 79001 (7.9 kg) and the DaG 476 grouping (6.3 kg).
While I don’t observe a pattern, I would not expect the Nakhla fall to be much bigger than these. To my speculation, a greatly extended strewn field for Nakhla, with the usual pattern of larger masses falling further down range (into Denshal and the dog), would significantly increase the fall weight of Nakhla–a weight that presently seems to fit among the others quite comfortably, especially considering it was ascribed the lowest minimum pre-atmospheric weight.
While this is admittedly only a rudimentary stab at resolving the issue, I think there are other data out there, which taken together, could establish a preponderance of evidence and tip the scale one way or the other. For instance, in The Shergotty Consortium, published in Geochimica vol. 50, 1986, there are peer-reviewed papers concerning the pre-atmospheric and final fall sizes of certain shergottitesIgneous stony meteorite with a Martian origin consisting mainly of plagioclase (or a shocked glass of plagioclase composition) and pyroxene. They are the most abundant type of SNC meteorites and the type member is the Shergotty meteorite, which fell in India in 1865. Shergottites are igneous rocks of volcanic or Click on Term to Read More. Following a determination of CRE ages from known profiles, cosmic ray track densitiesMass of an object divided by its volume. Density is a characteristic property of a substance (rock vs. ice, e.g.). Some substances (like gases) are easily compressible and have different densities depending on how much pressure is exerted upon them. The Sun is composed of compressible gases and is much Click on Term to Read More of specific samples were used to calculate the sample’s shielding depth and ablationGradual removal of the successive surface layers of a material through various processes. • The gradual removal and loss of meteoritic material by heating and vaporization as the meteoroid experiences frictional melting during its passage through the atmosphere. The resulting plasma ablates the meteor and, in cases where a meteor Click on Term to Read More characteristics on the pre-atmospheric meteoroidSmall rocky or metallic object in orbit around the Sun (or another star).. This information was then used to calculate the size of the pre-atmospheric mass. From this calculated meteoroid size, the production rate of cosmogenic nuclides at different depths was used to better constrain the CRE age. For Shergotty, a pre-atmospheric size of ~12 cm was calculated. This is equal to a mass of 26 kg, of which only 5 kg was recovered, inferring an ablation rate of 80%. Ablation rates of 50–80% were determined for other shergottites.
This type of study could be done for Nakhla. Each piece of Nakhla studied would have cosmic ray track densities that were consistent with a specific shielding geometry, which should be consistent with the pre-atmospheric size as calculated from production rates of cosmogenic and radiogenic nuclides. An examination of a representative sampling of Nakhla fragments should be able to constrain its size and ablation characteristics, and perhaps determine if any anomalies in its fall weight are present. If not, it would be evidence tipping the scale in favor of a limited strewn field, thus ruling out an impact on a dog 33 km downrange in Denshal.