2004 EW95: A C Type Asteroid Found in Kuiper Belt

2004 EW95: A phyllosilicate bearing carbonaceous asteroid in the Kuiper Belt

Authors:

Seccull et al

Abstract:

Models of the Solar System's dynamical evolution predict the dispersal of primitive planetesimals from their formative regions amongst the gas-giant planets due to the early phases of planetary migration. Consequently, carbonaceous objects were scattered both into the outer asteroid belt and out to the Kuiper Belt. These models predict that the Kuiper Belt should contain a small fraction of objects with carbonaceous surfaces, though to date, all reported visible reflectance spectra of small Kuiper Belt Objects (KBOs) are linear and featureless. We report the unusual reflectance spectrum of a small KBO, (120216) 2004 EW95, which exhibits a large drop in its near-UV reflectance and a broad shallow optical absorption feature centered at ~700 nm. These features, confirmed through multiple epochs of spectral photometry and spectroscopy, have respectively been associated with ferric oxides and phyllosilicates. The spectrum bears striking resemblance to those of some C-type asteroids, suggesting that those objects may share a common origin with 2004 EW95. 2004 EW95 orbits the Sun in a stable mean motion resonance with Neptune, at relatively high eccentricity and inclination, suggesting it may have been emplaced there by some past dynamical instability. These results appear consistent with the aforementioned model predictions and are the first to show a reliably confirmed detection of silicate material on a small KBO.

Earth did NOT get its Water From Comets and Carbonaceous Chondrite Asteroids

In the new study, the researchers report the hydrogen isotope ratios of water trapped in glassy inclusions inside the basalts. The results, published online today in Science, reveal that the inclusions have a much lighter isotopic signature than does the ocean, suggesting that the composition of seawater has indeed evolved over time. Although scientists were aware of processes that could cause an isotopic shift in surface waters, Hallis says, “until we made our measurements, we didn’t know whether that would be a measureable difference or not.”

The new data suggest that the difference is vast. And Hallis suspects that the deepest, most primitive material in the mantle should have an even lighter isotopic composition than the inclusions her team measured. That’s because the rising magma that produced the lavas probably mixed with upper mantle rocks, which have been contaminated with isotopically heavy surface water that got dragged down by subducting slabs of tectonic plates.

So what does all this mean for the origin of Earth’s water? For one, the new data throw a wrench in the conventional story that carbonaceous chondrites—a water-rich variety of asteroid—delivered water to an initially dry Earth after its formation. That scenario has been bolstered by similarities in the isotopic signatures of the asteroids and seawater. But the chondrite signatures are too heavy to explain the deep Earth samples, Hallis says. “The carbonaceous chondrites don’t really work.”

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Evidence of Organic Molecules From Another Star System From Carbonaceous Chondrite Asteroid

Multiple Cosmic Sources for Meteorite Macromolecules?

Authors:

Sephton et al

Abstract:

The major organic component in carbonaceous meteorites is an organic macromolecular material. The Murchison macromolecular material comprises aromatic units connected by aliphatic and heteroatom-containing linkages or occluded within the wider structure. The macromolecular material source environment remains elusive. Traditionally, attempts to determine source have strived to identify a single environment. Here, we apply a highly efficient hydrogenolysis method to liberate units from the macromolecular material and use mass spectrometric techniques to determine their chemical structures and individual stable carbon isotope ratios. We confirm that the macromolecular material comprises a labile fraction with small aromatic units enriched in 13C and a refractory fraction made up of large aromatic units depleted in 13C. Our findings suggest that the macromolecular material may be derived from at least two separate environments. Compound-specific carbon isotope trends for aromatic compounds with carbon number may reflect mixing of the two sources. The story of the quantitatively dominant macromolecular material in meteorites appears to be made up of more than one chapter.

Abundances and Relative Frequencies of Amino Acids in Meteorites

Nature's Starships. I. Observed Abundances and Relative Frequencies of Amino Acids in Meteorites

Authors:

Cobb et al

Abstract:

The class of meteorites called carbonaceous chondrites are examples of material from the solar system which have been relatively unchanged from the time of their initial formation. These meteorites have been classified according to the temperatures and physical conditions of their parent planetesimals. We collate available data on amino acid abundance in these meteorites and plot the concentrations of different amino acids for each meteorite within various meteorite subclasses. We plot average concentrations for various amino acids across meteorites separated by subclass and petrologic type. We see a predominance in the abundance and variety of amino acids in CM2 and CR2 meteorites. The range in temperature corresponding to these subclasses indicates high degrees of aqueous alteration, suggesting aqueous synthesis of amino acids. Within the CM2 and CR2 subclasses, we identify trends in relative frequencies of amino acids to investigate how common amino acids are as a function of their chemical complexity. These two trends (total abundance and relative frequencies) can be used to constrain formation parameters of amino acids within planetesimals. Our organization of the data supports an onion shell model for the temperature structure of planetesimals. The least altered meteorites (type 3) and their amino acids originated near cooler surface regions. The most active amino acid synthesis likely took place at intermediate depths (type 2). The most altered materials (type 1) originated furthest toward parent body cores. This region is likely too hot to either favor amino acid synthesis or for amino acids to be retained after synthesis.