Y.R.F.: Science

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. Here're some projects I'm working on either as PI or as coI, in no particular order:

• 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.
  
  

• Behavior of comet 29P/Schwassmann-Wachmann 1.

  • Comet S-W 1 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. Most of the data we have are images at visible wavelengths.
  
  

• Size and albedo distributions of cometary nuclei.

  • We have obtained a great deal of infrared and visible imaging of cometary nuclei so that we can determine the ensemble of nuclear properties. So far our survey is focussed on the Jupiter-family comets. Knowing the size distribution is important for understanding how the JFCs evolve over time; the shape of the distribution will tell us something about what physical processes dominate. The albedo distribution is important to know since no-one has yet done a strong test of the very widespread assumption that nuclei have geometric albedos near 4%. This seems to be a reasonable assumption but it is based on very few data points.
  
  

• Thermal properties of cometary nuclei.

  • With infrared photometry, we can use thermal models to infer the thermal properties of the nuclei. For the most part, nuclei are expected to be porous, poorly-conducting bodies, so that when sunlight heats a patch of surface, it is very hard for that energy to be conducted to nearby areas. Our results so far indicate that most nuclei have low thermal inertia, and that there is not much infrared beaming (which might be expected from a surface that had say many craters or similar-shaped topography). There are a few nuclei that intriguingly seem to have different thermal properties however. This science question is important for understanding how the evolutionary processes that comets suffer actually affect their bulk properties.
  
  

• Long-term studies of comet C/1995 O1 Hale-Bopp.

  • Comet Hale-Bopp excited the world in 1997, and it is now receding from the Sun. It is nearly 30 AU away yet it still seems to have some coma. We are working on understanding how and why this comet still shows dust, and what the properties of the dust are. We also want to compare this dust to what was emitted back in the 1990s -- is the dust different? Does the driver of activity in a comet change the properties of the dust that comes out? How is energy transported through the nucleus? Do outbursts still occur even at such large heliocentric distances?
  
  

• Behavior of comet 9P/Tempel 1 after Deep Impact.

  • We participated in observing this comet before, during, and after the very successful Deep Impact event. One of many interesting things that came out of that was the realization that the impact did not create a new active area. We are using large-scale imaging of the coma to analyze the dynamical behavior of the ejecta and thereby understand the physical properties of the liberated dust grains. We are also interested in comparing that dust to the pre-impact dust. Furthermore, we are interested in the photometric properties of the ejecta; we have infrared data that indicate the ejecta became bluer over time (in terms of its near-IR color). We are investigating what the physical reason for this phenomenon is.
  
  

• Activity of distant comets and Centaurs.

  • Comet S-W 1 counts as an active Centaur, in addition to being a short-period comet. Other Centaurs are also active, 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.
  
  

• Physical, thermal, and reflectance propreties of Jovian Trojans.

  • We've been using infrared and visible photometry to understand the properties of Jovian Trojans. In particular we're interested in understanding why the albedos of the small Trojans vary so widely, when the large Trojans are so uniformly reflective. Trojans probably formed with a lot of ice, so we would like to now how much ice is left in the big ones and in the little ones, and whether or not the Trojans could be another source of the current comet population. Since Trojans may have formed much farther out in the Solar System, according to the Nice model, there may be some similarities/differences between Trojans and TNOs that could shed light on the question of the Trojans origin.
  
  

• Thermal, compositional, and reflectance properties of outer Solar System objects.

  • As many other people are, we are interested in the properties of TNOs. This involves imaging and spectroscopy at various wavelengths. Space-based studies are very useful for addressing this topic, since there are not that many TNOs that one can really study in the first place. Many are too faint.
  
  

• Surface properties of asteroids in short-period and long-period cometary orbits (a.k.a. extinct-comet candidates).

  • What happens to comets when they die? Some die catastrophically when they break up into many fragments that eventually dissipate. However some probably stick around long enough to lose all their volatiles and cease activity. At that point, a comet will look a lot like an asteroid. Is there a way to tell if a given "asteroid" in near-Earth space is actually a dead comet? We are investigating ways in which the surfaces of dead comets and asteroids might differ (thermal behavior, reflectance, etc.). We are also very interested in the proto-typical dead comet -- or really, dormant comet -- 107P/Wilson-Harrington. This comet was active in 1949 but has not been active since. Why is this? Are there any unusual surface properties that could tell us about the recent history of the comet? Alternately, perhaps there has been some very low-level activity going on that is just not easy to see without good spatial resolution and good sensitivity.
  
  

• Surface properties of near-Earth asteroids.

  • We're studying not only NEAs that might be dead comets but NEAs in general. For example, what happens to NEAs that are in orbits that take them very close to the Sun? If they are heated to high temperatures (~600K to 1400 K) many times, what chemistry happens on their surfaces? Do they evolve differently than NEAs that stay cooler?

• Postdoc Dr. Charles Schambeau
• Grad student Mary Hinkle
• Grad student Brynn Presler-Marshall
• Grad student Jennifer Larson

updated august 2018