2011 Annual Science Report
NASA Goddard Space Flight Center Reporting | SEP 2010 – AUG 2011
Organic Chemistry in a Dynamic Solar Nebula: Lab Studies and Flight Mission Implementation
Over the past year we have concentrated on four major activities. The first is laboratory research on the generation of organics and the trapping of noble gases via Fischer-Tropsch type (FTT) reactions. The second is an attempt to understand and model the interrelated carbon and oxygen chemical cycles in a dynamic, turbulent nebula. The third is preparation for the design phase of the OSIRIS-REx mission, especially the characterization of regolith properties of the Type B asteroid that we are targeting. The final is proposal activity leading to the (possible) selection of a Discovery-class comet exploration mission (Comet Hopper or CHopper). In both of the mission activities, my goal has been to ensure that the missions can extract the maximum knowledge of the chemical and physical processes that occurred in the early solar system from the bodies that will be visited.
FTT Reactions and Noble Gas Trapping: No new experiments have been conducted over the past year since we won an Exobiology award to support this work. However, we have made excellent progress on construction of the 10 new experimental systems that we proposed. All of the glassware has been ordered, and most of this has been delivered. We have taken delivery on the 10 new FTIR spectrometers and have set them into the rack mount required for the new systems. We have taken delivery of the temperature controllers, heaters, bellows pumps, pressure gauges and other equipment required and have installed everything on the laser table used to mount the new system. We are in the process of installing the vacuum plumbing and individual gas circulation systems for the experimental units. We expect that the first set of these units will be operational by the early spring and we will begin the long term (~7 year), low temperature (475K) experiments that were proposed.
Dynamic Nebular Chemistry: Nebular CO has been invoked as the carbon source material for FTT reactions and also as the source for non-mass-dependently fractionated oxygen via the mechanism of CO self shielding. In this latter mechanism it is essential to preserve the undissociated, 16O-rich CO from ever reacting with nebular dust in order to preserve the oxygen fractionation. Advocates of this model have always assumed that CO is highly stable and non-reactive. Our work on FTT reactions and on nebular circulation casts doubt on that primary assumption and we are working to qualitatively construct a preliminary version of the nebular CO cycle, including destruction via photo-dissociation and FTT reactions and regeneration from the reaction of carbon-coated oxides in both hot regions of the nebula as well as in growing planetesimals.
At the same time we are advocating a new model for the generation of the non-mass-dependent oxygen isotopic fractionation in nebular dust based on our earlier experiments. These demonstrated that dust condensed from a plasma source becomes non-mass-dependently fractionated. Such chemistry should be an integral component of nebular lightning. We are now modeling dust evaporation, condensation, growth and fractionation in nebular lightning over the last few million years of nebular accretion. These studies show that this newly proposed mechanism for the generation of non-mass-dependently fractionated oxygen via nebular lightning appears to be promising. Of course, lightning induced nebular chemistry may also be a significant source of nebular organics if the Miller-Urey synthesis operates at pressures as low as those expected throughout the solar nebula. The most important uncertainty in such calculations is the frequency and timing of nebular lightning, as this will determine the relative importance of all of the processes driven by this mechanism.
Flight Projects – OSIRIS-REx: The OSIRIS-REx Mission will survey and return samples from the B-type asteroid 1999 RQ36. Launch will occur in September 2016 with samples returning to Earth in September 2023. No mission has ever visited a B-type asteroid before and therefore speculation over the properties of the regolith, especially with regard to the possibility of sampling this material using the proposed “inverted vacuum” and metallic Velcro techniques, has been an ongoing debate. Nuth has been working to understand likely regolith size distributions and particle “stickiness” (due to the possible presence of long chain hydrocarbons) as a member of the Regolith Development Working Group. This group has made several recommendations to the OSIRIS-REx project regarding test materials for the TAGSAM (Touch-And-Go-Sample-Acquisition-Mechanism), possible modifications to the current design and configurations and materials to be used for the surface sampling mechanism. Our goal is to minimize contamination of the surface sample during the collection of the bulk sample. While the bulk sample has the most important information concerning the generation of nebular organic materials, the surface sample may be the key to interpretation of the remote sensing data from primitive asteroids and/or dead comets. The organics coating or contained within the surface sample will also yield data on the space weathering of organics exposed on the surfaces of small bodies. This data may be quite useful in extending what we learn directly from the study of RQ36 to interpretation of remote sensing data of other primitive objects.
Flight Projects – Comet Hopper: The Comet Hopper (CHopper) is a Discovery-class Mission that is currently in Phase A and that will study the dynamics and evolution of a single comet (47P/Wirtanen) from aphelion to perihelion in a series of surface excursions. While the mission goal is to understand the forces that drive comet evolution by mapping the surface and coma from orbit as well as landing on the surface to measure the surface strength and local outgassing conditions, the mission also serves as a precursor to a possible New Frontiers-class comet surface sample return mission and to a Flagship-class comet cryogen sample return mission. Experiments carried on CHopper aim to test the strength of the regolith in as many different surface lithologies as possible, measure the composition and density of outgassing volatiles and heat both the surface and interior (down to 30-cm) to release volatiles for characterization via mass spectrometer. Our job is to ensure that the maximum information can be extracted from the mission concerning the origin and evolution of comets, the volatiles and dust that they contain as well as their evolution over at least 1 passage from aphelion to perihelion. A possible extended mission would follow the changes in volatile emissions and the development of the surface as the comet returned to aphelion, thus completing the cycle that drives its short-term evolution.
Abstracts and Publications
“METEORITES, ORGANICS AND FISCHER-TROPSCH TYPE REACTIONS: PRODUCTION & DESTRUCTION.” N. M. Johnson, A. S. Burton1, and J. A. Nuth III., 74th Annual Meteoritical Society Meeting, London, U.K., August 2011 Abstr.5404.
“PRODUCTION OF ORGANIC GRAIN COATINGS BY SURFACE-MEDIATED REACTIONS AND THE CONSEQUENCES OF THIS PROCESS FOR METEORITIC CONSTITUENTS “ Joseph A. Nuth III and Natasha M. Johnson, Workshop on the Formation of the First Solids in the Solar System, Kauai, HI, November 2011, Abstr.9021
“A QUANTITATIVE, TIME-DEPENDENT MODEL OF OXYGEN ISOTOPES IN THE SOLAR NEBULA: STEP 1” J. A. Nuth, J. A. Paquette, A. Farquhar and N. M. Johnson, 74th Annual Meteoritical Society Meeting, London, U.K., August 2011 Abstr.5385.
“LIGHTNING PROCESSING OF DUST IN THE SOLAR NEBULA” J. A. Nuth, J. A. Paquette, A. Farquhar and N. M. Johnson, Workshop on the Formation of the First Solids in the Solar System, Kauai, HI, November 2011, Abstr.9019.
“A QUANTITATIVE, TIME-DEPENDENT MODEL OF OXYGEN ISOTOPES IN THE SOLAR NEBULA” Joseph A. Nuth, Gordon Research Conference On the Origins of Solar Systems, July 2011.
PROJECT INVESTIGATORS:Joseph Nuth
PROJECT MEMBERS:Natasha Johnson
RELATED OBJECTIVES:Objective 3.1
Sources of prebiotic materials and catalysts
Origins and evolution of functional biomolecules
Biosignatures to be sought in Solar System materials