Science Seminars

5/5/2016 – Karly Pitman; Advances in Optical Constants For Space and Planetary Applications

Speaker: Karly Pitman (SSI)
Date: Tuesday, May 05, 2020
Time: 4:00 PM
Location: SPSC W120

Seminar Abstract:

This talk will discuss the light scattering properties of different species of micron-scale dust particles and how to quantify their chemical composition and physical properties (e.g., size, shape, packing density or porosity of collections of grains) through a combination of radiative transfer modeling and laboratory analog spectroscopy at UV to IR wavelengths. The value of this type of work is to be able to unambiguously identify the type of dust suspended in space or occurring on the surfaces and atmospheres of planets and their satellites, which give clues to those bodies’ evolution, age, climate, etc. We will cover different experiments related to interstellar/circumstellar and Solar System environments, e.g.,

– For example, optical constants (real and imaginary indices of refraction) in the astronomy literature are often derived from compositionally and structurally different samples or kluges of observational, laboratory, and extrapolated or interpolated values to get full wavelength coverage. Depending on how a scientist combines these values, interpretations of observations and models can be affected.

– To better identify the specific chemical compositions and quantify the abundances of minerals on the martian surface, for example, there is a need to increase for laboratory comparison spectra and optical constants for different polymorphs and hydration states of carbonates and sulfates. Knowing the specific chemical type and hydration state of these minerals is important because these values are tracers of environmental conditions (e.g., temperature) and aqueous chemistries; from this information, one can infer transport and alteration mechanisms present at the time of their formation.

– Taking the properties of aggregates into account when deriving optical constants is also important. Whereas spectral properties are dominated by the aggregates, analytic radiative transfer solutions used to interpret planetary surfaces assume that individual, well-separated particles dominate the spectral signature. This has implications for single scattering albedo, phase function, and optical constants derivation, which further impacts determinations of composition, grain sizes and abundances.

We will explore these topics from the perspective of how physics informs geology, how geology informs astronomy, and how techniques from atmospheric science can be employed to study surfaces.