nai

Project Progress

Project 2. Origin and Evolution of Organic Matter in the Solar System

2.1 Origin of Ultra Red Kuiper belt objects.

CoI Shepperd has been focusing on understanding the origin of the Kuiper Belt. Bodies captured into the outer Neptune resonances such as the 2:1 and 5:2 at about 48 and 55 AU respectively, should contain a significant fraction of objects pushed out of the main Kuiper Belt (between about 42-45 AU) if Neptune had a slow and smooth migration history into the outer solar system. This is because a slow and smooth migration outwards would cause the 2:1 and 5:2 Neptune resonances to gently sweep through the main Kuiper Belt and thus allow the trapping of objects into these outer resonances along the way.

The main Kuiper Belt is dominated by ultra-red surface type objects not seen very often elsewhere in the solar system. Ultra-red colors are likely created from material rich in very volatile ices and organics. We observed the surfaces of objects in these outer resonances to determine if they matched the ultra-red colors seen in the main Kuiper Belt. With the limited color data to date, the outer 2:1 and 5:2 Kuiper Belt resonances do not show a high fraction of ultra-red objects at low inclinations. This suggests the surfaces of the objects in the outer resonances are different than the classical Kuiper Belt objects in the main Kuiper Belt. If true, this makes it unlikely Neptune had a significant slow smooth migration phase in its past since these outer resonances would be expected to have a significant ultra-red low inclination component similar to the ultra-red objects in the low inclination classical Kuiper belt that the resonances would have swept through. Instead, Neptune likely had a much more chaotic migration history in which the trapping and transporting of small objects during migration would have been much more difficult.

2.2 Targeted analysis of the Tagish Lake Meteorite Clasts

Co-Is Alexander, Nittler and Cody continued their detailed, multi-technique study of the organic material in the Tagish Lake meteorite and a detailed paper is now in press. The Tagish Lake meteorite fall is comprised of multiple stones that experienced different degrees of hydrothermal alteration. Thus, it is an ideal meteorite for exploring the effects of hydrothermal processes on organic material in asteroid parent bodies, particularly the macromolecular insoluble organic material (IOM) that is the major organic component of chondrites. There is some controversy over how much of the range of IOM elemental, isotopic, and functional group chemistry in meteorites is due to parent body processes and how much is due to heterogeneity of the accreted organics. We have shown that the IOM from various Tagish Lake lithologies covers almost the entire range of IOM compositions, implying that most or all of the IOM variation is due to parent body processes. If the kinetics of the transformation of IOM can be measured, IOM compositions may provide important constraints on the poorly constrained thermal histories of aqueously altered meteorites/asteroids.

2.3 Water in Primitive Bodies and Martian Meteorites

Co-I Alexander and collaborators also continued efforts to use H isotopes (1) in Martian meteorites to constrain the evolution of water on Mars, and (2) in chondritic meteorites to constrain the origin of water in the inner Solar System, including asteroids and the terrestrial planets. We have found evidence for a large new Martian water reservoir, possibly subsurface ice, that is intermediate in D/H between the Martian mantle and atmosphere. For chondrites, we recently published a paper proposing a new petrologic classification scheme for aqueously altered meteorites based on bulk H abundances and isotopes. This classification scheme should help in understanding the interaction of water and organic in chondrites, particularly across chondrite groups. We also have been using bulk and high spatial resolution in situ techniques to understand how the H isotopes of water evolved during the process of aqueous alteration of meteorites.

2.4 Coordinated Multi-technique studies of Meteoritic organic solids

Co-Is Nittler, Alexander, Stroud, and Cody have continued their coordinated multi-technique (transmission electron microscopy, secondary ion mass spectrometry, scanning transmission x-ray microscopy) microanalytical studies of meteoritic organic matter, both in situ and as isolated insoluble organic matter (IOM) residues. We published a comprehensive study on the isotopic, morphologic and chemical properties of nanoglobules – sub-micrometer hollow carbonaceous spheres – in IOM extracted from different meteorites. In this work, we identified two classes of nanoglobules: one with chemical properties similar to the bulk non-globular IOM and one with significantly higher aromaticity. The latter group generally exhibits more extreme isotopic compositions and probably represents a pre-accretionary, possibly interstellar, material. We enlarged the number of focused ion beam sections of primitive meteorites studied by our multi-technique pipeline and found in situ evidence for parent body modification of nanoglobules and other IOM. We also performed a large isotopic survey of a very primitive Antarctic CR chondrite, Dominion Range 08006, and found it to be rich in sub-micron grains of ¹⁵N-rich organic matter.

2.6 Investigation into a post Accretionary Origin for Chondritic organic solids

Post Doctoral researcher, Yoko Kebukawa and PI George Cody continued their laboratory investigations into the potential of post accretionary synthesis of extraterrestrial organic solids in planetesimal interiors through reactions of sugars formed through the condensation of formaldehyde. Previously, they had shown that at the organic functional group level, organic solids derived from formaldehyde are nearly identical to organic solids from primitive chondrites, Interplanetary Dust Particles (IDPs) and organic solids in Comet 81P/Wild 2 samples (obtained from the NASA Stardust mission). During the past year they focused on three core areas. 1) The role that ammonia may have in enhancing the yield of organic solids formation, 2) a detailed analysis of the formation kinetics, and 3) D-H exchange kinetics. Using this formaldehyde based organic polymer as a analogue material for chondritic and cometary orgranic solids allows us place on considerable constraints on the internal thermal history of primitive planetesimals. During the past year one paper was published on this topic in the Astrophysical Journal and two other manuscripts are in preparation.

2.7 Direct Measurement of Deuterium molecular environments in Chondritic organic Solids

Post Doctoral researchers Ying Wang and PI George Cody have completed the first ever measurements of natural abundance D (2H) solid state Nuclear Magnetic Resonance (NMR) spectroscopy of isolated organic solids from two isotopically exotic carbonaceous chondrites, remnants of some of the most primitive materials in the Solar System. These analyses required an enormous amount of set up time and optimization as based on natural abundance and low magnetic moment, deuterons are the most difficult nuclei to detect with solid state. We have been successful and are currently working on a manuscript for submission. The results of this study will enable us to establish more precisely why certain primitive bodies have higher D contents than solar D/H and terrestrial ocean D/H.