Download SBAG Outline - Laboratory Studies

SBAG ROADMAP: LABORATORY STUDIES
Questions and Issues for SBAG Laboratory Studies Report
Marla Moore and Reggie Hudson*
Astrochemistry Laboratory
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
The topics and questions in this outline are a first draft for an SBAG document
related to laboratory studies to support small-bodies exploration and research.
The emphasis so far has been on laboratory measurements, as opposed to field
work. There is, perhaps unavoidably, overlap among the various sections.
Comments and suggestions are welcome.
I. Gas-Phase Experiments
A review is needed of gas-phase photolytic rate constants, cross sections, and
lifetimes for molecules, to include products and branching ratios. This would
involve a survey of work done since Huebner’s 1992 review paper (AtmSS, 1992,
195, 1- 294).
New millimeter-wave rotational transitions for cometary comae candidates need
tabulating, particularly for some of the more-exotic molecular species.
Issues connected to ortho-para ratios for H2O, C2H2, etc. need exploration. For
example, to what degree are ortho-para states sensitive to alteration by icy and
mineral surfaces, light, radiation, and so on? To what degree do these limit the
ortho-para ratio’s application as a thermometer?
How much is known of gas-phase spectra of ions such as of OCN? Some IR
data is available, but what about radio wave? Is the IR data of sufficient
resolution?
II. Experiments with Solids: Ices and Ice-Mineral Mixtures
Measurements are needed of thermodynamic properties such as sublimation
rates, thermal conductivities, heat capacities, and energies of phase changes for
ices and ice mixtures at appropriate temperatures, pressures, and radiation
doses.
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* 7/31/2010, Reggie Hudson ([email protected]), Marla Moore
([email protected])
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There is a need to explore basic physical properties of ices (e.g., density,
porosity, tensile strength, hardness) under appropriate conditions of temperature,
pressure, and radiation dose. Such information will better characterize laboratory
samples that, in turn, are needed to understand extraterrestrial ones.
Basic optical properties (e.g., refractive index, optical constants) need to be
determined for different ices and ice phases at a variety of temperatures and
near-to-far-IR wavelengths. IR spectra can provide both compositional and
phase details.
Basic optical properties (e.g., refractive index, optical constants) also need to be
determined for different ices and ice phases at a variety of temperatures over farUV to visible wavelengths. To what degree can such data provide molecular
compositional detail for unknown mixtures?
A comprehensive set of reflection and absorption spectra of relevant surface
analogs (containing ices, organics, and minerals) over a range of temperatures,
grain sizes, geometries, and wavelengths is needed for use in interpretation of
data from missions.
In some cases, H2O-rich ices have dominated the interests of laboratory
astrochemists to the exclusion of the N2-rich, NH3-rich, and CH4-rich icy mixtures
that might be encountered on outer solar system objects. There remains a lack
of data (e.g., phases, optical constants) for such ices at appropriate outer solar
system temperatures.
What recent experiments have been done with clathrate and non-clathrate
hydrates? What recent work has been published on their formation, spectra,
resistance to radiolytic and photolytic destruction, and thermal properties?
To what degree will spacecraft exhaust components be adsorbed by (i.e.,
contaminate) asteroid candidate materials such as minerals, ices, and icemineral mixtures?
III. Experiments with Solids: Processed Materials
What roles do photolysis, radiolysis, and thermal cycling play in altering the
optical properties of icy materials?
How does the influence of space weathering depend on mineral composition?
There is a need to continue laboratory searches for products from solid-phase
thermal, radiation, and photochemical reaction chemistries. Such studies are
important for predicting the presence of new, and as yet identified, species. A
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knowledge of reaction mechanisms can narrow the conditions under which
certain molecules are or are not to be found.
Optical constants are needed at relevant temperatures for organic residues
resulting from thermal, radiolytic, and photolytic processing, and combinations
thereof.
IV. Experiments with Solids: Mostly Organics and Minerals
What influence does temperature have on the color or the spectral features of
relevant minerals in the 0.4 - 5 micron region? What influence do trace surface
contamination and surface chemistry have on colors and spectra?
Can mineralogical identifications be constrained by determining variations in
color or spectral features in the 0.4 - 5 micron region?
In the far-IR, to what degree are useful spectral measurements available for
minerals and PAHs? To what degree are such spectra available for irradiated
materials?
Dust properties: What is available concerning densities, spectra, surface areas,
porosity, and fluffiness of candidate dusts? To what extent are such properties
altered by adsorption of gas molecules on surfaces? What temperature
dependences have been studied?
How about ions on dust grains (non-icy surfaces)? How do they change the
chemistry and physics of materials?
Continued laboratory analyses are needed for collected IDP particles, which will
provide mineralogy, chemistry, and isotopic compositions to help constrain
origins and histories of parent bodies.
Can laboratory collision and laser ablation studies include a range of relevant
material types such as high- and low-density materials, a range of porosities, and
solid and ice-rich mixtures? Impact studies can examine thermal, chemical, and
magnetic changes in relevant surface analogs.
V. Liquid-Phase Studies
What are the key thermal, physical, and mechanical properties of liquid
inorganics and organics under temperature and pressure conditions relevant to
satellites and TNOs? What is the capability of mid-IR spectroscopy for
determining such properties by remote observations?
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Can laboratory studies of liquids, ices, and clathrates, under varying temperature
and pressure conditions, elucidate possible sources of endogenic surface
features or plume material?
What are the relevant properties (e.g., melting point, viscosity, electrical
conductivity) of salt solutions under temperature and pressure conditions relevant
to satellites?
VI. Studies of Ice Materials in Bulk
Bulk solids vs. thin films – similarities and differences? When are extrapolations
over nine orders of magnitude in sample size justified from laboratory results,
and when are they not?
Do adequate ice-storage facilities, as once discussed for comet sample-return
missions, exist? Could a focused cryogenic facility be used to support ongoing
bulk ice research and then evolve into a laboratory to analyze and store
cryogenic materials from sample-return missions?
VII. Different Techniques - Their Feasibility and Science Return
To what degree have miniature fiber-optic instruments (Raman, etc.) been
applied to laboratory samples at appropriate temperatures and surface conditions
(as opposed to incorporation into spacecraft instruments)?
Raman and fluorescence techniques, as applied to icy and ice-grain materials
likely to be encountered, need exploring.
Are there electron spin (paramagnetic) resonance (esr/epr) measurements that
can give information on free-radical chemistry in solids of astrochemical interest?
To what degree can x-ray emission methods that give atomic information be
relied on for molecular identifications in an unknown solid-phase mixture?
Similarly, to what extent can sputtering and back-scattering techniques be relied
on to give molecular identifications in an unknown solid-phase mixture?
How important is information about spatially resolved surface magnetism? Can it
be used to constrain the identification of certain magnetic minerals?
The ability of mid-IR spectra to provide molecular information is somewhat
compromised by the difficulty of recording such spectra for cold outer solar
system bodies. What can be done to improve this situation?
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