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Pluto Walk, Lowell Observatory

pluto walk
Discoverer of the (Dwarf) Planet: Clyde Tombaugh

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 planet 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!

Pluto: Dwarf Planet
Pluto’s Moon: Charon

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.

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TENERE-1 (Provisional)

standby for te-1 photoCR7 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 achondrite. Olivine grains are mostly 0.1–0.4 mm in size, but larger grains occur. They commonly exhibit triple-junctions, consistent with recrystallization. Large poikilitic pyroxene grains are present, as well as small agglomerates of crystals, sometimes called ‘Sammelkristalle’, which usually form during melting and recrystallization processes. Unlike chondrules, these structures are composed primarily of plagioclase poikilitically enclosing minor olivines and pyroxenes, and are often accompanied by FeNi-metal. Te-1 is a freshly fallen meteorite with a weathering grade of W0, and it has a shock stage of S1–2.This primitive achondrite has a chemical and mineral 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 ungrouped basaltic meteorite NWA 011. Oxygen isotopes are similar to those of the lodranite/acapulcoite parent body but are not an exact match. The mineral composition and noble gas 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 chromite and metal 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 crust on one end. The photo below shows the main mass of Te-1 with an end slice removed.

standby for te-1 photo

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As with other ureilites, Almahata Sitta falls on the carbonaceous chondrite anhydrous mineral line. Although complex organic compounds commonly occur in many other carbonaceous chondrites 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):





D- and L-aspartic acid
D- and L-glutamic acid
D- and L-serine
D- and L-threonine
D- and L-alanine
γ-amino-n-butyric acid
D- and L-β-amino-n-butyric acid
α- or β-aminoisobutyric acid
D,L-α-amino-n-butyric acid
3-amino-2,2-dimethylpropanoic acid
D,L-4-aminopentanoic acid
D,L-4-amino-3-methylbutanoic acid
D,L-3-amino-2-methylbutanoic acid
D,L-3-amino-2-ethylpropanoic acid
5-aminopentanoic acid
D,L-4-amino-2-methylbutanoic acid
3-amino-3-methylbutanoic acid
D,L-3-aminopentanoic 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)
ε-amino-n-caproic acid







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NWA 1912

standby for northwest africa 1912 photoMesosiderite, 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 matrix composed predominantly of large orthopyroxene grains along with some plagioclase, 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 meteorite (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, chromite, troilite, and silica.

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Denshal Dog Data: Is the Nakhla Dog Real?

Separating Myth from Fact: Is the Nakhla Dog Real?

A Personal Analysis By David Weir

standby for nakhla photo 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 ejecta translates to masses of 150–270 kg–too high to be a limiting factor when considering a Nakhla strewn field 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 meteorite 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 fall 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 shergottites. Following a determination of CRE ages from known profiles, cosmic ray track densities of specific samples were used to calculate the sample’s shielding depth and ablation characteristics on the pre-atmospheric meteoroid. 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.