I'm a fifth year graduate student at Brown University, working with Prof. John Mustard on the spectroscopy of iron oxides and sulfates on Mars and terrestrial Mars analogs.  I use visible/near-infrared spectroscopy to study iron oxide and sulfate mineral assemblages in order to better understand the climate and geological processes under which they form.  I currently devote most of my time to analysis of sulfates, iron oxides, and associated minerals in CRISM data. In past work, I have studied the mineral diversity of Rio Tinto, Spain, a mineralogic and astrobiological analog of Mars. 

On the Mars side, I am part of the team analyzing spectral data from the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) instrument on the Mars Reconnaisance Orbiter (MRO). CRISM began returning spectra of the martian surface in Fall 2006. Building on my work in Rio Tinto, I am specifically focused on identifying sulfates and coexisting iron oxide mineralogy. Deposits within Valles Marineris, a large canyon system east of the Tharsis volcanic province, show a variety of sulfate and ferric oxide signatures.  Understanding the geologic context of those mineral assemblages and their stratigraphic relationships will allow us to better constrain the environments of formation or alteration. I have also analyzed spectra from the OMEGA instrument in Mars Express, another hyperspectral visible/near-infrared mapping spectrometer, to look for hydrated iron-bearing locales within Valles Marineris.

            Rio Tinto                Sulfates on Mars

Rio Tinto. Identify iron oxide and hydrous sulfate minerals from field and remotely acquired spectra; use spatially coarse VNIR spectra to recognize areas in Rio Tinto that would be ideal targets for future field exploration; verify and validate those predicted targets from remotely sensed spectra with field work.

See Publications for abstracts, posters and talks about this research.

During fieldwork in January 2004 and August 2006, we collected spectra and hand-samples of sulfate and iron oxide mineralogy from Rio Tinto source springs and abandoned river terraces.  Sediments of different ages (recent to 2.1 Mya) reveals a trend of decreasing sulfate and increasing goethite mineralogy through analysis with an Elemental Analyzer and Inductively Coupled Plasma spectrometer.  Mineralogy evolved from iron sulfate- and oxide-rich (jarosite, rozenite, gypsum, schwertmannite, copiapite, goethite) in young sediments to hydrated iron oxides in preserved river terraces.

One of the key challenges in extraterrestrial exploration is how to identify promising targets from spatially coarse data for in situ investigation.  Our field work provided a unique opportunity to combine field spectra with RELAB library spectra and HYMAP 8-m spatial resolution aerial hyperspectral data. We have developed spatial scaling techniques with applications to CRISM and sulfate identification on Mars.

The method, called Spectral Variance Index, aggregate the Hymap spectra into 25 x 25 pixel cells and computes the average mean (albedo) and spectral variance over all wavelengths for each cell.  We next calculate the expected variance for each cell with a linear regression between the mean and spectral variance.  The number of standard deviations each cell's spectral variance is from the expected variance is the Spectral Variance Index (SVI) value.  We located ~20 areas with high SVI values within the tailing piles and along wide riverbanks downstream of the active mine from the Hymap data.

During the August 2006 trip to Spain, we validated the SVI method by testing if these areas with SVI values did indeed have high mineralogic diversity.  The outcome was promising, and this method has potential for use in other terrestrial or extraterrestrial settings.  The image below shows one mineralogically diverse area in the Rio Tinto discovered by the SVI method.

Thanks to my collaborators for support and assistance: John Mustard and Aline Gendrin (Brown University), Ricardo Amils and David Fernandez-Remolar (Centro de Astrobiologia, Madrid, Spain), Linda Amaral-Zettler (Marine Biological Laboratory), and Erik Zettler (Sea Education Association)

 

 

Sulfates on Mars. I am broadly interested in sulfate formation on Mars and the evolution of acid sulfate environments.  There are two main sulfate deposits on Mars -- in the Olympia Undae dune field that encircled the North Pole, and in light-toned mounds within Valles Marineris, a canyon system along the equator.  Current research involves mapping sulfate and associated iron oxide locations and creating regional stratigraphies to test ideas of sulfate formation mechanisms.

See Publications for abstracts, posters, and talks about this research.

Above is a mosaic of THEMIS nighttime IR images with OMEGA sulfate and iron oxide detections overlaid. The region is Capri Chasma, one of the canyons within Valles Marineris.  Red indicates kieserite, a monohydrated Mg sulfate, and blue and green indicate a polyhydrated sulfate.  Iron oxide deposits overlay or are mixed with many of these sulfates.  The formation mechanism for the iron oxide may be similar to that in Rio Tinto -- leaching and maturation of sulfate deposits. At 300m - 4km spatial resolution, OMEGA can distinguish outcrops and landscapes with sulfates.

 Studying the location and distribution of sulfates in Valles Marineris as identified by OMEGA and CRISM has raised provocative questions about the formation and preservation mechanisms of these sulfate deposits.  With new data from the CRISM spectrometer and HiRISE camera on the MRO mission, I investigate sulfate deposits throughout Valles Marineris on the scale of 20m -- now we can look at layering within the ILD and track compositional changes with stratigraphy. 

I combine spectral data with topographic and imaging data to investigate past Martian climate by understanding how the sulfate-rich ILDs in the Valles Marineris canyon system formed.  A better understanding of the mineralogy and formation mechanism of the ILDs should provide new insight into the prevalence and role of liquid water in past Martian climate.

To see a mosaic of mapping strips from CRISM, click here.

The other major sulfate deposit are the gypsum-bearing dunes near the North Pole. This deposit is thought to be much younger than the Valles Marineris sulfates, and to be the only confidently detected gypsum (CaSO4 .2H2O) on Mars. I am working with others on the CRISM team to understand how that sulfate formed and how old it is. To see CRISM data of the gypsum dunes around the North Pole, click here.