My current research interests are focused on both laboratory spectroscopy
of geologic and meteoritic materials and analysis of spectroscopic data
returned from Mars by the
Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor
spacecraft, by the Thermal
Emission Imaging System (THEMIS) aboard the Mars Odyssey spacecraft,
and by the Mini-TES instruments on the
Mars Exploration Rovers. I am affiliated with the TES science team, and
I am a Participating Scientist on the THEMIS team.
In addition to the planetary geology research described above, I am striking
out in some new directions as well. For example, along with my colleague
Bayman in the Department of Anthropology at the University of Hawaii,
I have begun a pilot study investigating
the utility of visible to thermal IR spectroscopy as an archaeometric tool for
characterizing and sourcing archaeological artifacts made of geomaterials.
Another study that I'll be working on with colleague
Patty Fryer, also at the
University of Hawaii, will examine how we can use infrared spectroscopy
to rapidly characterize the composition
and orientation of minerals in seafloor rock samples from convergent plate margins
(subduction zones). We want to understand the relationship between these
characteristics and observed seismic anisotropy.
My curriculum vitae in PDF format.
Martian TES and THEMIS data analysis projects
- Mineralogy of rocks at the Gusev crater landing site: Five years after landing
on the surface of Mars, the Mars Exploration Rover Spirit has collected thousands
of thermal infrared spectra of rocks and soils. These spectra reveal a diversity of
mineralogies, and detailed analysis of these materials can give us insight into the primary
and secondary geologic processes that have occurred on Mars. This research is a collaborative
effort with Dr. Steve Ruff at Arizona State University.
- Visible, near infrared, and thermal infrared spectroscopy of cherts and amorphous
silica: Cherts and amorphous silica can be formed by both biogenic and abiogenic
processes, and they exhibit a wide variety of structural characteristics and hydration
states that can be indicative of their geologic history. Silica has been identified on Mars
in remote and in situ spectroscopic data across the VNIR and TIR wavelength regions, and it
is therefore important to understand the full range of spectral characteristics exhibited
by these materials as a function of chemical, structural, and physical properties, as well
as their environments of formation. In particular, little work has been done to acquire
emission spectra, which are essential for interpreting remote sensing (including in situ)
data. This research is led by my former graduate student, Dr. Meryl McDowell.
- Thermophysical and topographic characteristics of putative chloride deposits:
The recent THEMIS/TES discovery of putative chloride deposits on the Martian surface
raises many questions about the origin and history of these spectrally unusual materials.
Global characterization of their thermophysical and topographic properties may shed
more light on these intriguing deposits and what they may be able to tell us about the
past presence of water on Mars.
- Characterizing the diversity of olivine compositions across Mars:
Linear least squares modeling and spectral index mapping show that much of
the Martian surface is composed of olivine-bearing materials. The compositions
of the olivines vary from magnesium-rich (forsteritic) to relatively iron-rich
(fayalitic), indicating differences in the source magmas from which they were crystallized.
The results of this study were published by Koppen and Hamilton in the May 2008
issue of the Journal of Geophysical Research.
- Searching for the source regions of Martian meteorites (SNCs):
Systematic analysis of thermal infrared spectra of the Martian surface, using
laboratory spectra of the meteorites, has identified Martian meteorite-
like materials (olivine- and orthopyroxene-bearing) on the surface of Mars.
Understanding the geologic environments of these materials may help us
determine if they are potential source regions for the meteorites.
Identifying the physical origin of these Martian samples would allow
scientists to place these rocks into a geologic context that we currently
lack. And could ultimately allow us to assign better absolute ages to
portions of the Martian surface. See
the results of our global search.
- Spectroscopic analysis of compositional variations within Syrtis
Major and environs, Mars: Syrtis Major is a large, dark region on
Mars with some of the best exposed, relatively unweathered material on
the planet. Recent studies [Bandfield et al., 2000; Hamilton
et al., 2003] suggest that this region displays compositional variation
in TES data that merit more detailed investigation.
- Examinations of Martian fine materials: Based on the laboratory
studies of crushed and powdered rocks mentioned above, I have been able to
begin to place additional constraints on the compositions and mean apparent
particle size of the dusty surfaces that cover much of Mars. The nature of
these materials is still only poorly understood, so it is my hope that these
studies will help fill in the gaps in our knowledge.
Laboratory research projects
- Microspectroscopy of meteoritic materials: Meteorites contain a vast array
of minerals and other phases that represent a wide variety of geological processes,
relevant to the formation and evolution of asteroids and rocky planets. Many of
these phases are physically small or are difficult to obtain in significant quantities
on Earth, and are best analyzed using microscopic techniques. Acquiring their infrared
spectra helps us augment the spectral libraries used to interpret data collected
by remote sensing instruments throughout the solar system. This work is joint effort
with Dr. Gretchen Benedix of the Natural History Museum in London.
- Spectral characteristics of altered tephras: Palagonite, a
weathering product of mafic rocks, has long been proposed as a visible/near
infrared spectral analogue of Martian bright regions. The midinfrared
properties of this variable material are not well known. Obtaining a
spectral library of altered tephras, including palagonite, will help us
to determine if this material is also a viable analogue for midinfrared
spectra of Martian bright regions as well. This is a joint research effort
with Dr. Richard Morris of NASA Johnson Space Center. This work has been
published in a 2008 special issue of the Journal of Geophysical Research.
- Visible, near-, and middle infrared spectral investigation of the pyroxene
mineral series: Pyroxenes are important minerals in many
igneous rocks on Earth and on the Martian surface -- an understanding of their
variable spectral characteristics as a function of crystal structure and composition
will help us to better determine the chemistries of pyroxenes observed in Martian
spectra. Knowledge of these compositions will provide more specific information
about the conditions during eruption of pyroxene-bearing rocks on Mars. See an
example diopside spectrum.
- Middle infrared spectral characteristics of Martian meteorites (SNCs):
Martian meteorites, pieces of Mars on Earth,
are an important piece of our understanding of the geology of Mars. Unfortunately,
we do not know where on Mars these samples came from. By analyzing their
spectral signatures in the laboratory, we can look for similar spectra in
the Martian data returned by TES and THEMIS.
- Visible, near-, and middle infrared spectral properties of igneous rocks:
Only by studying the spectral characteristics of a wide variety of well-
understood terrestrial samples can we truly understand what spectral data
from Mars may be telling us.
- Middle infrared spectral studies of particulate rocks: In the
world of spectroscopy, the size of the particles being observed can influence
the appearance of the spectrum, making it difficult to recognize the mineralogy
of the material observed. In some cases, the physics of this process are
very difficult to understand, even for pure, single-mineral specimens. However,
it is important to know how particle sizes affect the spectral signatures of
crushed rocks so that we can recognize these effects in spectra of planetary
surfaces (e.g., Mars, asteroids) and use them to our advantage in interpreting
the compositions and physical properties of these bodies.
- Spectral characteristics of glasses and phyllosilicates: Some
phyllosilicates have spectral characteristics that are broadly similar to
those of glasses. The distinction between these phases in remote sensing
data has important implications for how remotely acquired spectral data
are interpreted. A thorough understanding of how well they can be
distinguished is proving critical to the interpretation of data from Mars.
- Quantitative modeling of visible, near-, and middle infrared spectra:
Ultimate application of the results of our laboratory studies to the
interpretation of remote sensing data requires a quantitative understanding of
how well spectral properties can be used to successfully predict mineralogy,
chemistry, and other properties of interest. Blind and semi-blind testing of
spectral/chemical correlations via numerical models (e.g., linear deconvolution,
gaussian modeling) is critical to this effort.
My interest in Venusian geology started with a NASA internship at the
Jet Propulsion Laboratory working with the Magellan science team.
Magellan was a synthetic aperture radar (SAR) orbiter that used radar
to map the surface of Venus through the thick cloud layer that
encircles the planet and prevents visual observations. The images
produced by Magellan look a lot like black and white photographs, but
they really are images of surface roughness and surface slopes. My
main interest is in a class of features called coronae, particularly
their occurrence in "chains" along semi-linear tectonically deformed
belts. The area I'm primarily interested in is central
There are several sites which provide access to information about the
Magellan Mission to Venus and Magellan data, including: the
Magellan Data Archives, JPL's Magellan Mission to Venus
homepage, and the
USGS Astrogeology Branch.
Venus SAR and Topography 442 k