Department of Geology and Geophysics
1000 E. University Ave.
Laramie, WY 82071-2000
Planetary Geology, Remote Sensing, Infrared Instrumentation & Astronomy
Office Phone: 307-314-5149
Fax Phone: (307) 766-6679
Dept. of Geology & Geophysics
1000 University Ave.
Laramie, Wyoming 82071-3006 Office Room No: GE 222
Planetary Sciences, PhD, University of Arizona, 1980
Physics, BS, University of Michigan, 1974
The Nature of the Volcanic Activity at Loki: Insights from Galileo NIMS and PPR Data. R. R. Howell and R. M. C. Lopes, Icarus, 186: 448-461. 2007.
Active Volcanism: Effusive Eruptions. D. A. Williams and R. R. Howell, Chapter 7 in "Io after Galileo", Lopes & Spencer, ed. Springer-Praxis, Chichester, UK 2007.
The two Titan stellar occultations of 14 November 2003 B. Sicardy et al. J. Geophys. Res. 111: doi:10.1029/2005JE002624,2006
A High Spatial Resolution Infrared View of the T Tauri Multiple System. T. L. Beck, G. H. Schaefer, M. Simon, J. A. Stoesz, and R. R. Howell, Astrophys. J., 614: 235-251, Oct. 10, 2004
The Atmospheric Signature of Io's Prometheus Plume and Anti-jovian Hemisphere: Evidence for a Sublimation Atmosphere. K. L. Jessup, J. R. Spencer, G. E. Ballester, R. R. Howell, F. Roesler, M. Vigel, and R. Yelle, Icarus 169: 197-215, May 2004
See my personal web site at http://geofaculty.uwyo.edu/rhowell/index.htm for more details.
Volcanism on Jupiter's Moon Io
Io is the most volcanically active body in the solar system. It provides a unique laboratory for the study of volcanism under unusual conditions, for the study of the process of "tidal heating" in the outer solar system, and also for the study of planetary magnetospheres -- in this case derived from volcanically released sulfur dioxide. Observations from the earth can complement the observations being made by the Galileo spacecraft currently in Jupiter orbit. In the infrared a significant portion of the light from Io comes from the volcanic hotspots. Infrared monitoring can therefore be used to study the location, duration, and other characteristics of the volcanoes. As part of this general effort, infrared measurements of terrestrial lava flows are also being modelled.
X-Ray Observations of Planetary Objects
Recent observations by the Chandra X-Ray Observatory have detected emission from the Galilean Satellites Io, Europa, and Ganymede. The radiation, primarily in the oxygen K-alpha line, is most likely caused by high energy particles from the Jupiter magnetosphere impacting the satellite surfaces. The process is, on a very large scale, similar to that which takes place in the electron and ion microprobes commonly used to study the elemental composition of geologic materials. While measurements have not yet detected emission lines from other elements, the process has the potential for providing our first reliable estimates of the composition of these objects. Modeling efforts are underway to predict the expected fluxes for other common elements, and to more fully model the observed oxygen emission.
The observations described above rely for the most part upon infrared instruments built at Wyoming. The early speckle work and the lunar occultations were carried out with a specially optimized single-channel InSb detector. That instrument has recently been supplemented by a small format InSb camera built for high speed 3-5 micron work. I finished that camera (IoCam1) while on sabbatical at Lowell Observatory during the 1996/1997 academic year. It is now being used at the Wyoming 92" and the Lowell 72" telescopes.
High Angular Resolution Astronomy
The angular resolution obtained by ground-based telescopes is usually limited by the "seeing" caused by turbulence in the earth's atmosphere, but special techniques can be used to overcome this limitation. One technique, known as "speckle interferometry", makes use of multiple high-speed images of the object and a comparison star, coupled with Fourier analysis of the images. It is being used at Wyoming to study the volcanism on Io, as well as the processes taking place in regions surrounding recently formed stars and also stars undergoing mass loss. Another technique relies upon photometry obtained during occultations by the moon or by other bodies. Lunar occultations have been used at Wyoming to measure the binary frequency of T Tauri stars and to search for disks surrounding such stars. Occultations of Io by Jupiter allow us to measure the location of faint volcanic hotspots. Occultations of Io by the other Galilean satellites provide the highest possible spatial resolution. A series of such mutual events occurs every six years, with one currently underway in early 2003.