Research Topics

See below for simple introductions to past and present projects.

Click here for a list of publications with links.

This has not been updated with Pluto/Charon/New Horizons topics - pleases see the publications page for this info :).  

1)  Secondary craters and ejecta physics

As a complement to laboratory and theoretical studies of ejecta from impact craters, this project takes an empirical approach.  We use secondary craters around large impacts on icy satellites and the Moon as a record of fragments ejected during a large cratering event.  


(Left) Achelous Crater on Ganymede  (Right) Secondary Craters around Copernicus Crater on the Moon

What I do:

I map secondary craters.  I relate the secondary crater size and position to the size and ejection velocity of the fragment that formed them.  I can then characterize the size-velocity distribution of the ejecta fragments.  The size-velocity distribution is compared to that predicted from cratering physics (spallation and Grady-Kipp theories) and can be used to predict a variety of things: e.g., the size of secondary craters a given distance from a crater, or what is the maximum fragment size ejected at escape velocity.

2)  Jupiter's Moon Europa

Europa is of astrobiological interest because a subsurface ocean likely lies under an outer icy shell.  Europa has been greatly resurfaced and is not dominated by impact craters.  There are many geologic features of interest here.


What I do:

On Europa I map small circular features including pits, spots, uplifts and small regions of broken up and re-frozen ice called "chaos regions".  I look at the distribution of these features to try to say something about how they formed and also the moon as a whole.  They may also give us an indication of the thickness of the ice shell overlying Europa's subsurface ocean.

Find More Images Here

3)  Jupiter's Moon Ganymede

Ganymede is another unique moon - it is the only moon with its own magnetic field!  It has also been resurfaced, as shown below by the "grooved" terrain criss-crossing the surface. The same internal heat that allowed this tectonic resurfacing also allowed craters on the surface to "relax" which means that their topography is softened.   

What I do:

On Ganymede I map craters and characterize how relaxed they are.  I use this along with models to try to constrain how much heat flow was necessary to produce this relaxation.  You can see both fresher, bowl-shaped craters and also relaxed, flattened craters below.

Find More Images Here

4)  Saturn's Moon Iapetus

Iapetus is a very unique moon in many respects:

  • Iapetus the black and white tennis ball: 

(also known as the oddest albedo pattern/contrast in the solar system)

  • Iapetus the walnut: 

(also known as the oddest/only equatorial ridge in the solar system)


What I do:

I look for linear features which may indicate tectonic activity. If the features have a preferred orientation, this implies stress acted on this area in a specific way. I then model some of the possible causes of this stress and see if the predicted fault orientations match the observed features.  This work is published in Icarus.


 High Resolution Image of Iapetus' Dark Side

 Bright Side of Iapetus

Find More Images Here

I also examined extraordinarily long landslides on Iapetus - called long-runout landslides.  These landslides on Iapetus are a planet-scale experiment (compared to landslides on Earth - we changed the gravity, and the material from rock to ice, plus there is no air on Iapetus) that help us understand long-runout landslides in general.  These landslides also occur on Earth, Mars, and a few other solar system bodies.   This work recently came out in Nature Geoscience.

5)  Saturn's Moon Enceladus
Enceladus is one of the few moons in the solar system know to be currently active (along with Jupiter's moon Io and Neptune's moon Triton).  The south pole is crossed by long faults, known as the tiger-stripe region, and plumes also eminate from this region.  Enceladus is one active moon!

What I do:
Again, the same internal heat that allows for the amazing activity at the south pole of Enceladus also affected the other terrains on Enceladus - relaxing craters there.  I measure the relaxation state of the craters and relate the measurements to theories of how much heat flow is required to relax them.

Note:  All images on this page courtesy of NASA/JPL.