YRF Science

My area of research is comets and asteroids, which I have been studying since 1994. I am interested in the composition and physical properties of these objects, and how they compare to each other and other objects in the Solar System. Why? Because Small Bodies can tell us about the origin of the Solar System — what were the compositional and thermophysical conditions in the solar nebula and in the protoplanetary disk? Understanding the origin of the Solar System is the overall “big picture” question that I (and many planetary scientists) work toward. However to understand what the small bodies tell us about our origins, we need to know what has happened to these objects in the intervening 4.6 billion years sinice they formed. In other words, I study cometary and asteroidal evolution. This is not an easy task, but it is an interesting question in its own right, and it is critical if we are to make sense of what the Solar System is like today.

The experimental methods that I use almost always involve telescopes, both on the ground and in space. I primarily work at visible and infrared wavelengths, but have also done radio experiments as well.

You can get a sense for some of the projects I’m working on by checking out various paper databases: my CV, my ORCID entry, my ADS entry, and my Google Scholar entry. But below I have some descriptions of some of my projects.

Fun with specific objects:

  • Behavior and nucleus properties of comet 2P/Encke.
    • Comet Encke is an unusual comet with a very short orbital period. We have been working to understand the nucleus’s size (with infrared observations) and spin state (with visible observations). We would also like to figure out its shape since its diurnal light curve is very odd, having only one bright peak (instead of two). Furthermore, we are studying the comet’s activity behavior when it is near aphelion. The comet seems to be intrinsically brighter at 4 AU than it is at say 2 or 3 AU, even though one would expect a comet to become less active the farther it is from the Sun. Check out some of the P/Encke projects I’ve worked on.
  • Behavior of comet 29P/Schwassmann-Wachmann 1.
    • Comet 29P is in a near-circular orbit just outside Jupiter’s orbit. It has a long history of having outburst behavior, where its normal constant level of activity will be punctuated with brightenings of a few magnitudes. We are studying the evolution and devlopment of the comet’s coma before, during, and after these outbursts. By watching how the morphology of the coma changes over time, we hope to determine the comet’s spin state and active areas. We also are interested in understanding the nucleus’s size and shape. Check out some of the 29P projects I’ve worked on.

Fun with surveys:

  • Ensemble properties of cometary nuclei.
    • This is a catchall project for lots of work I’m doing on understanding the size distribution, albedo distribution, and variety of thermal properties among cometary nuclei. These are all important properties for understanding how the evolutionary processes that comets suffer actually affect their bulk properties. The size and shape distributions give clues about the collisional and fragmentation history of the bodies. The albedo distribution tests just how robust the classic “4%” assumption really is, plus will help us understand how cometary activity changes a surface as a comet migrates from more distant orbits to the inner Solar System. The thermal properties tell us about the structure of the nucleus, at least near the surface, which is again part of the evolutionary story. So there are lots of issues of evolution to be teased out here. I’m a Co-I on the NEO Surveyor mission, which hopefully launches in late 2027/early 2028, and will provide IR measurements of thousands of comets. In the meantime, I’m on other surveys using other telescope facilities; an example of some of the work is here and here. Furthermore, I’m involved as a hanger-on with the just-concluded NEOWISE mission, which detected the gas, dust, and nuclei of many comets year after year.
  • Activity of distant comets and Centaurs.
    • Comet 29P counts as an active Centaur, in addition to being a short-period comet. Centaurs are usually defined as objects that orbit among the giant planets, or more specifically have perihelia outside Jupiter’s orbit, but semimajor axes smaller than Neptune’s. Other Centaurs are also active, in fact there are over 30 active Centaurs known, and we’re interested in understanding the general phenomenon. Why are some Centaurs active and others not? What does activity do to their surfaces? Is the nature of the activity different compared to normal inner-Solar System cometary activity? These questions are important for understanding the evolution of icy bodies as they dynamically migrate from the Scattered Disk, through the giant planet region, and into the inner Solar System. One very exciting part of this project is that we have JWST data on several active Centaurs. In fact the team I’m part of has some papers out already. But we also have lots of ground-based visible data on many Centaurs and on several short-period comets that are just slightly outside the Centaur definition (and so tend to get overlooked).
  • Surface properties of near-Earth asteroids.
    • We’re studying not only NEAs that might be dead comets but NEAs in general. This includes obtaining thermal-infrared and reflected-sunlight measurements from asteroids at a range of viewing geometries, aspect angles, and sub-Earth latitudes in order to disentangle asteroid shape and surface properties. In particular, we are interested in figuring out how the details of shape can alter our interpretation of an asteroid’s thermophysical properties. I’m on a team that has done (and continues to do!) a lot of IRTF observing, and we have several papers and abstracts about this work.

Currently my group here is relatively small:

But I also work closely with the other comet group here at UCF: