Exploring Organic Environments in the Solar System (2007) / Chapter Skim
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4 Primitive Bodies
4 Primitive Bodies
Pages 52-71
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From page 52... ...
These objects include main belt asteroids, Trojan asteroids, small satellites, comets, Centaurs,1 and Kuiper belt objects (KBOs) .2 Because of their small size, and their often low albedos and large distances from the Sun and Earth that contribute to their faintness, the observation and understanding of their organic components are challenging.
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From page 53... ...
, which must be measured in the laboratory, are known for only a relatively small number of the compounds that are likely to be present. SYNTHESIS AND DESTRUCTION OF ORGANIC MATERIALS Organic molecules can be both synthesized and destroyed on outer solar system solids by irradiation.
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From page 54... ...
Further, with the developing plans to explore organic environments in the outer solar system, there is a need to understand the effect of radiation on any indigenous or delivered organics. As in the gas phase, the chemical reactions of interest in solids are driven primarily by bond breaking and ionization due to ultraviolet photons and energetic charged particles.
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From page 55... ...
However, for larger comet nuclei, such as Kuiper belt objects, models have shown that it is possible under certain interior conditions (which include specific porosities, the fraction of other volatiles present, and so on) to have melting in the interior creating reservoirs of liquid water.9 This possibility has interesting implications in view of recent experiments on organic compounds that show self-organizing behavior in the presence of liquid water.
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From page 56... ...
ORGANIC INVENTORY Surfaces of small primitive bodies are composed of varying fractions of refractory material and frozen volatiles. Many of these surfaces, in particular in the outer solar system, exhibit abundant evidence for dark materials that are generally spectrally neutral (i.e., they are equally bright at visual, red, and infrared wavelengths)
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From page 57... ...
The neutral gas mass spectrometer aboard the European Space Agency's Giotto provided measurements of several native species, including the retrospective identification of ethane.21 The so-called IKS infrared spectrometer on the former Soviet Union's Vega 1 spacecraft achieved detections of H2O, CO2, H2CO, and possibly CO.22 This instrument also detected a spectral signature in the 3.2- to 3.6-µm region attributed primarily to C-H stretching vibrations in one or more organics. The Particle Impact Analyser dust composition experiment on the Giotto spacecraft discovered a population of dust particles composed of an organic material containing CHON grains.
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From page 58... ...
Balsiger, and J Geiss, "Composition of the Volatile Material in Halley's Coma from In Situ Measurements," Space Science Reviews 90: 3-18, 1999; D
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From page 59... ...
This illustrates the difficulty of detecting and isolating organic species with low or moderate spectral resolution, and the need for high-resolution spectroscopic studies to provide a more complete picture of cometary chemistry. SOURCE: Image courtesy Michael J
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From page 60... ...
Measurements of the thermal emission from some of the Centaurs show that they have generally low albedos. Centaurs and Kuiper belt objects display a range of surface colors from neutral (solar)
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From page 61... ...
1996 TO66.33 Trojan Asteroids, Small Outer Solar System Satellites, and Rings Small Jovian Satellites and Trojans There is only sparse multispectral data for the jovian ring and inner satellites, with observations from the Hubble Space Telescope's Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) showing similar positive spectral slopes through the near-infrared, suggesting similar dusty compositions possibly due to contamination by Io.
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From page 62... ...
Trace quantities (<1 percent) of acetylene and propane also appear to be present.36 The plume, or rather plumes, of material appears to be venting from a series of anomalously TABLE 4.3 Carbon Compounds Inferred on Surfaces of Small Outer Solar System Bodies Planet System Object Carbon Inferred References Jupiter Prograde outer satellites C-type asteroidal material a Retrograde outer satellites D-type asteroidal material a Trojan asteroids P- and D-type asteroidal material b Saturn Hyperion D- or T-type asteroidal material c,d Iapetus Organic-rich, hydrated silicates e,f Phoebe C-type asteroidal material c Uranus Minor inner satellites Dark material g Rings Dark spectrally neutral material h Neptune Minor satellites and rings Dark spectrally neutral material i aM.V.
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From page 63... ...
Resolved spectra showed mineral absorption features at 1 and 2 µm that were charac teristic of orthopyroxene and olivine, and spectral models suggested that the red color of the surface was due to space weathering of nanophase iron.39 The infrared spectral data and results of the x-ray spectrom eter suggested a composition similar to that of a relatively primitive ordinary chondrite.40,41
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From page 64... ...
, a multi band imager (to enable topographic mapping and multiband polarimetry in eight spectral bands between 0.30 and 1.10 µm) , and a near-infrared spectrometer (to obtain high-resolution mineralogical maps at wavelengths from 0.85 to 2.10 µm)
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From page 65... ...
(Bottom) : The closest short exposure of the comet Wild 2, which NASA's Stardust spacecraft flew by on January 2, 2004, taken at an 11.4-degree angle, the angle between the camera, comet, and the Sun.
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From page 66... ...
The main goal of the Deep Impact mission was to examine the pristine interior of a comet by creating a controlled experiment to excavate beneath the evolved surface layers. The Deep Impact space craft was launched on January 12, 2005, and released a 360-kg impactor on July 2, 2005.
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From page 67... ...
However, by adding information about the albedo of the object, many of the ambiguities can be reduced.50 The Spitzer Space Telescope will undertake to measure the albedos of a large number of these outer solar system bodies, and thus researchers will soon be extremely well situated to investigate the organic compositions of these bodies with a combination of infrared spectroscopy and spectral modeling. Additional laboratory spectral measurements of model compounds and materials are needed to provide further information concerning organic materials possibly found on Triton, Pluto, Charon, Centaurs, and Kuiper
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From page 68... ...
Recommendation: Every opportunity should be taken to direct space missions to small bodies to do infrared spectral studies of these targets, especially a D- or P-type asteroid, to determine if these dark bodies contain an appreciable amount of carbon compounds and, if so, whether they are the sources of the carbonaceous meteorites and dust reaching Earth. In this regard, a possible opportunity to conduct such studies is as an adjunct to the Trojan Asteroid/Centaur Reconnaissance flyby mission described in the solar system exploration decadal survey.
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From page 69... ...
The task group points to the solar system exploration decadal survey report's recommendation for a New Frontiers-class Comet Surface Sample Return mission as an example of an activity that would greatly enhance understanding of the organic constituents of the solar system's primitive bodies.52 Not all existing and planned missions to primitive bodies have been optimized for the study of organic materials. The population of primitive small bodies, however, may preserve organic materials from a wide range of nebular heliocentric distances.
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From page 70... ...
Dalle Ore, "Spectral Models of Kuiper Belt Objects and Centaurs," Earth, Moon, and Planets 92: 313-330, 2003.
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From page 71... ...
Dalle Ore, "Spectral Models of Kuiper Belt Objects and Centaurs," Earth, Moon, and Planets 92: 313-330, 2003.
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