Experiments

GETTING MY HANDS DIRTY

Most of my experiments involve ice, or icy materials, so I spend a lot of time in cold rooms. There I can prepare samples to my heart’s content, without worrying about accidental melting, although this does invariably mean wearing a big green balaclava most of the day.

I’m interested in planetary ices, so this involves ice at low temperatures (and high pressures for icy moon interiors), and hydrated and hydrous minerals. I’m particularly interested in hydrated sulfate minerals, both on Mars and in the icy moons. My experiments can be split onto two main categories: mechanical properties and diffusion.

The results of these experiments feed directly back into the modelling, and are constrained by observations.

MECHANICAL PROPERTIES

The goal of these experiments is to better understand the mechanical properties of materials that occur on mars and the icy moons. I use three main ways of conducting these experiments, by using equipment at UCL, and also at the Rutherford Appleton laboratory. Most of my time in these experiments is spent preparing samples and setting up the uniaxial and triaxial rigs for running low-temperature experiments.

ISIS PULSED NEUTRON SOURCE

The main aim of using the triaxial deformation cells is to better understand the roles that different parameters such as temperature, pressure, grain size and growth and strain rate have on the rheology of ice and other condensed volatile materials. Have a look at the paper by Durham and Stern (2001) for a nice introduction to the complexities of ice rheology.

The uniaxial cell is the workhorse, and with the environmental chamber fitted, is capable of very low temperatures. The main advantage of this equipment is the ability to perform cyclic loading tests in order to quantify the evolution of the elastic moduli, while also monitoring the acoustic emission.

DIFFUSION

The goal of these experiments is to determine the rate of diffusive exchange between the surface and atmosphere of mars. I’m particularly interested in understanding the exchange of water vapour, and how the rate of diffusion has changed over time. It is the rate of diffusion that controls whether the martian surface and atmosphere are in equilibrium at timescales ranging from tens of thousands, to hundreds of millions of years.

During my fellowship I designed and built the vacuum system and the monitoring set-up, so that I can measure the mass, temperature, and humidity of four different samples at the same time. This method means that I can carry out four simultaneous experiments for a single pump-down, which comes in handy. The kit is working well and has been calibrated at room temperature, and I’m currently running tests looking at the low-pressure-driven precipitation of sulfates, and whether it (1) causes significant rock damage, and (2) causes a significant changes in the diffusion coefficient.

Have a look at my publications page for details of experiments, there should be more there in the future.

Modelling

OF THE THEORETICAL KIND

In addition to experiments and in situ and remote sensing observations, I also develop and use models for understanding planetary evolution.

These models vary greatly depending on the problem being addressed. ranging from modelling the possible magma overpressure beneath radially-fractured centres on Venus, to looking at the internal structure and thermal evolution of Titan over 4 billion years, to modelling the combined topographic pumping of groundwater and the resulting evaporation-driven crystallization in canyons on Mars.

For my postdoc, I spent a fair amount of time modelling the behaviour of icy moons. I worked on the possibility of mud volcanoes on Titan, predicted explosive volcanism to be widespread on Titan, and determined whether an ammonium sulfate ocean can survive inside titan to the present day. All these papers can be found on my publications page.

For my fellowship I incorporated experimental results into models of the martian surface and near sub-surface. I’ve looked at the strength of hydrated sulfate minerals as a function of depth, and predicted the topographic pumping and associated groundwater upwelling in canyons on Mars both with and without a large central mound. At the moment I’m interested in looking at the diffusive exhchange between the surface and atmosphere, and particularly the role that hydrated minerals might have in changing this process. Again, more details on my publications page.

Remote Sensing

Planetary GIS

Synthesis of the experimental and theoretical studies can only be achieved by application to features visible today on the surfaces. To this end, I use data sets from different missions and instruments that employ visible and near-infrared wavelengths to determine how different processes have affected the surface of Mars and over what time scales.

Specific techniques include combining high-resolution stereo digital terrain models (HiRISE, CTX, MOC) with near-IR spectroscopy, and the analysis of in situ rover data, to understand the evolution of features on Mars that demonstrate the behaviour predicted by the experiments and modelling, and vice versa. Fundamental to this method is understanding the relative and absolute timing of changes in the geological record, garnered from crater count studies.

At the heart of this approach is the use of GIS environment, and adapting terrestrial techniques, software and experience for use with planetary data. This means taking the data from the PDS, processing them (usually) using ISIS and also SocetSet, and then importing into ArcGISr or ENVI to begin work.

I’ve also recently been making DTMs from HiRISE and CTX stereo images. Some of these DTMs have been animated by Doug Ellison, and you can see some of those results at his youtube channel. I particularly urge you to have a look at the pathfinder animation below – we were pretty chuffed with the results!

Have a look on my publications page for recent work using these methods. Or get in touch if you’re interested in using planetary data or collaboration.