Matt Balme

Research Scientist
Planetary Science Institute

mbalme @psi.edu

Research Interests

My main research interests are Martian geomorphology and surface processes. Currently, I am studying aeolian processes (including small and large dunes, dust devils and sand transport), and fluvial processes - specifically the formation mechanisms of 'recent' Martian gullies.

1) TARs.

The project that forms the basis of my recently funded MDAP grant is a survey of MOC images in a large pole-to-pole study area to study small, ripple-like dunes on Mars called Transverse Aeolian Ridges (TARs). TARs have been described as ubiquitous, relatively old and probably formed from sand grade material but there is no real understanding of how they are distributed, what age they are, or of the particle sizes or compositions of the materials that form them. As aeolian action is the primary ongoing surface modification mechanism on Mars and that Mars contains few sinks for saltating material (unlike Earth where oceans, rivers and vegetation can all trap sand) understanding why dunes form where they do and how the dune material has got there is very important.

The major themes of the project are to investigate 1) the geographic distribution of TARs compared with local geomorphic units, surface roughness, topography and latitude, 2) the orientation of TARs compared with models of Mars' current wind regime - which ties into 3) the crater retention age of TARs, to understand if they are very recent and active today or if they formed many thousands of years ago perhaps during a period with a different climate, 4) the relationship of TARs with large dark dunes in regions where the two occur together to understand why they are so different in size, morphology and albedo, and 5) to estimate the total volume of sediment contained within TARs.

The overall aim of the project is to increase our understanding of sediment transport on Mars and to explore whether aeolian duneforms on Mars are sourced from the extensive sedimentary environments such as layered terrain, mantled terrain and polar layered terrain or are formed from ubiquitous local aeolian materials.

2) Dust devils.

As shown by recent Mars Orbiter Camera (MOC) and Mars Exploration Rover (MER) images, dust devils - small convective vortices that pick up sand and dust - are common on Mars and clearly are an agent for removal of material from the surface. However, it is unknown whether they are a relatively insignificant part of the dust budget (as is likely on Earth) or are in fact the dominant mechanism for maintaining the 2mm 'dust-haze' in the Martian atmosphere. The overall aim of this work is to understand how dust devils affect the surface and climate of Mars. My work covers several main areas:

i) The mechanisms of entrainment of surface material by vortices. Through laboratory and fieldwork studies I am attempting to determine if dust devils can be modelled as ordinary boundary layer winds 'rolled up' into a circle or if their turbulent flow and low pressure cores somehow enhance their ability to raise dust. These data are vital for modelling the effects of dust devils on the Martian surface

ii) Dust devil formation on Earth. Using data from recent and proposed fieldwork, I am attempting to determine whether thermodynamic expressions for dust devil intensity are valid. These data will help improve parameterisations of dust devil formation in Global Climate Models of Mars that are too low resolution to resolve individual vortices.

iii) Morphology of dust devil tracks on Earth and Mars. Dust devils frequently leave 'tracks' on Mars and recent observations in the Tenere desert, Niger, have shown this can also be the case on Earth. Whether these albedo features represent deposition, removal or simply disturbance of surface material is currently unknown. I hope to visit Niger in the near future to make the first in-situ observations of dust devils tracks on either Earth or Mars to answer this question. I am also working on a general classification and description of dust devil tracks on Mars.

3) Recent Gullies.

Geologically recent, 'fluvial-like' gullies on Mars werefirst noted in MOC Narrow Angle images in 2000. They are typically a few 100s of meters to a few kilometers in length, contain sinuous down-cut channels with an erosional alcove and deposition fan, and display morphologies consistent with formation by the action of a liquid flowing down a slope. In addition many appear to be almost pristine in their geomorphology and display few, if any, impact craters, indicating that they have formed very recently or might still be active today. Gully forming agents that have been suggested include brines, liquid carbon dioxide, dry avalanches of aeolian material, ice/water rich slurries and even liquid water. The simple suggestion that gullies might represent the ongoing action of liquid water has, of course, enormous implications for astrobiology research and has made studying gullies a priority for researchers throughout the world. Nevertheless, there is still no real agreement as to their formation mechanism, although the main contenders after five years of study almost all involve the action of liquid water whether by seepage/disgorgement of liquid from an aquifer or by melting of near surface ice by insolation/geothermal activity. Each model predicts different latitudinal distributions and different orientations of the gullies and has different implications for the likelihood of the existence of extant Martian life.

My ongoing work on gullies has two parts: Firstly, I am using High Resolution Stereo Camera images from Mars Express and MOC narrow angle images to measure the distribution, length and orientation of gullies over the entire southern hemisphere of Mars. The comparison of two data sets, one with huge individual image coverage but medium resolution and the other with poor individual image coverage but high resolution allows artefacts of sampling and resolution to be removed from the final results. I hope to answer finally the question of whether there is a preference for orientation of gullies and how this changes with latitude. Secondly, there is no clear definition of what is or is not a gully. There are many features on Mars that closely resemble these recent gullies but are clearly not formed by a liquid. I am therefore working on a detailed geomorphological description of gullies and their context that will aid recognition of what is, and is not, a 'gully'.

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