Dr. Robert R. Howell

Research Projects

• Volcanism on Jupiter's moon Io
• High Angular Resolution Astronomy
• Infrared Instrumentation

Research Statement

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.

Infrared Instrumentation
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.

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Publications

Occultation Mapping of Io's surface in the Near-Infrared I: Inferring Static Maps. F. Bartolić, R. Luger, D. Foreman-Mackey, R. R. Howell, and J. A. Rathbun. The Planetary Science Journal 3: 67, March 2022 (abstract) (PSJ On-line)

Size and Shape of (11351) Leucus from Five Occultations. M. W. Buie, B. A. Keeney, R. H. Strauss, T. E. Blank, J. G. Moore, S. B. Porter, L. H. Wasserman, R. J. Weryk, H. F. Levison, C. B. Olkin, R. Leiva, J. E. Bardecker, M. E Brown, L. B. Brown, M. P. Collins, H. M. Davidson, D. W. Dunham, J. B. Dunham, J. A. Eaccarino, T. J. Finley, L. Fuller, M. L. Garcia, T. George, K. Getrost, M. T. Gialluca, R. M. Givot, D. Gupton, W. H. Hanna, C. W. Hergenrother, Y. Hernandez, B. Hill, P. C. Hinton, T. R. Holt, R. R. Howell, J. L. Jewell, R. L. Kamin, J. A. Kammer, T. Kareta, G. J. Kayl, J. M. Keller, D. A. Kenyon, S. R. Kester, II, J. N. Kidd, Jr., T. R. Lauer, C. W. S. Leung, Z. R. Lorusso, C. B. Lundgren, L. O. Magana, P. D. Maley, F. Marchis, R. L. Marcialis, A. E. McCandless, D. J. McCrystal, A. M. McGraw, K. E. Miller, B. E. A. Mueller, J. W. Noonan, A. M. Olsen, A. R. Patton, D. O'Conner Peluso, M. J. Person, J. G. Rigby, A. D. Rolfsmeier, J. J. Salmon, J. Samaniego, R. P. Sawyer, D. M. Schulz, M. F. Skrutskie, R. J. C. Smith, J. R. Spencer, A. Springmann, D. R. Stanbridge, T. J. Stoffel, P. Tamblyn, B. Tobias, A. J. Verbiscer, M. P. von Schalscha, H. Werts, and Q. Zhang, The Planetary Science Journal 2: 202, Oct. 2021 (abstract) (PSJ On-line)

Lower Atmosphere and Pressure Evolution on Pluto from Ground-based Stellar Occultations, 1988-2016. E. Meza, B. Sicardy, M. Assafin, and 156 more. Astronomy & Astrophysics 625: A42, May 2019 (abstract) (A&A On-line)

Eruptive behavior of the Marum/Mbwelesu lava lake, Vanuatu and comparisons with lava lakes on Earth and Io. J. Radebaugh, R. M. Lopes, R. R. Howell, R. D. Lorenz, and E. P. Turtle, Journal of Volcanology and Geotherm. Res. 322:105-118, 15 August 2016 (abstract) (JVGR On-line)

Temporal behavior and temperatures of Yasur volcano, Vanuatu from field remote sensing observations, May 2014. E. P. Turtle, R. M. C. Lopes, R. D. Lorenz, J. Radebaugh, and R. R. Howell, Joural of Volcanology and Geotherm. Res. 322: 158-167, 15 August 2016 (abstract) (JVGR On-line)

The roar of Yasur: Handheld audio recorder monitoring of Vanuatu volcanic vent activity. R. D. Lorenz, E. P. Turtle, R. Howell, J. Radebaugh, R. M. C. Lopes, Journal of Volcanology and Geotherm. Res. 322: 168-174, 15 August 2016 (abstract) (JVGR On-line)

Io: Eruptions at Pillan, and the time evolution of Pele and Pillan from 1996 to 2015. I. de Pater, C. Laver, A. G. Davies, K. de Kleer, D. A. Williams, R. R. Howell, J. A. Rathbun, and J. R. Spencer, Icarus 264: 198-212, Jan. 2016 (abstract) (Icarus on-line)

Pluto's atmospheric structure from the July 2007 stellar occultation. C. B. Olkin, L. A. Young, R. G. French, E. F. Young, M. W. Buie, R. R. Howell, J. Regester, C. R. Ruhland, T. Natusche, D J. Ramm, A. B. Giles, and J. G. Greenhill, Icarus 239: 15-22, Sept. 2014 (abstract) (Icarus on-line)

Io's active volcanoes during the New Horizons era: Insights from New Horizons imaging. J. A. Rathbun, J. R. Spencer, R. M. Lopes, and R. R. Howell, Icarus, 231: 261-272, Mar. 2014 (abstract) (Icarus on-line)

Composition and location of volatiles at Loki Patera, Io. R. R. Howell, C. E. Landis, and R. M. C. Lopes, Icarus, 229: 328-339, Feb. 2014 (abstract) (Icarus on-line)

The temperature and width of an active fissure on Enceladus measured with Cassini VIMS during the 14 April 2012 South Pole flyover. J. D. Goguen, B. J. Buratti, R. H. Brown, R. N. Clark, P. D. Nicholson, M. M. Hedman, R. R. Howell, C. Sotin, D. P. Cruickshank, K. H. Baines, K. J. Lawrence, J. R. Spencer, and D. G. Blackburn, Icarus, 226: 1128-1137, Sept.-Oct. 2013 (abstract) (Icarus on-line)

Morphology, temperature, and eruption dynamics at Pele.   R. R. Howell and R. M. C. Lopes,   Icarus, 213: 593-607,  June, 2011 (abstract) (Icarus on-line)

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,  February, 2007 (abstract) (Icarus on-line)

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  (abstract) (JGR on-line)

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  (abstract)  (Icarus on-line)

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  (abstract)  (Ap.J. on-line)

Loki, Io: A Periodic Volcano,  J. A. Rathbun, J. R. Spencer, A. G. Davies, R. R. Howell, and L. Wilson,  Geophys. Res. Lett., 29: 10, 1443, doi:10.1029/2002GL014747,  May 15, 2002 (abstract)  (GRL on-line)

Discovery of Soft X-Ray Emission From Io, Europa and the Io Plasma Torus,  R. F. Elsner, G. R. Gladstone, J. H. Waite, F. J. Crary, R. R. Howell, R. E. Johnson, P. G. Ford, A. E. Metzger, K. C. Hurley, E. D. Feigelson, G. P. Garmire, A. Bhardwaj, D. C. Grodent, T. Majeed,  A. F. Tennant, and M. C Weisskopf,  Astrophys. J.,  572:  1077-1082,  June 20, 2002   (abstract)  (Ap.J. on-line)

Ground-based Observations of Volcanism on Io in 1999 and early 2000.  R. R. Howell, J  R. Spencer, J. D. Goguen, F. Marchis, R. Prangé, T. Fusco, D. L. Blaney, G. J. Veeder, J. A. Rathbun, G. S. Orton, A. J. Grocholski, J. A. Stansberry, G. S. Kanner, and E. K. Hege,  J. Geophys. Res. (Planets) 106:  33129 - 33139,  Dec. 21, 2001.  (abstract)   (JGR on-line )

The Near-Infrared and Ice-Band Variability of Haro 6-10.  Ch. Leinert, T. L. Beck, S. Ligori, M. Simon, J. Woitas, and R. R. Howell,  Astronomy and Astrophysics  369:  215-221, April 2001.  (abstract), (A&A on-line)

The Inner Coma and Nucleus of Comet Hale-Bopp: Results from a Stellar Occultation.  Y. R. Fernández, D. D. Wellnitz, M. W. Buie, E. W. Dunham, R. L. Millis, R. A. Nye,J. A. Stansberry, L. H. Wasserman, M. F. A'Hearn, C. M. Lisse, M. E. Golden, M. J. Person, R. R. Howell, R. L. Marcialis, and J. N. Spitale, Icarus,  140:  205-220,  July 1999.  (abstract), (Icarus on-line)

Lunar Occultations of Young Stars in Southern Taurus.  M. Simon, Tracy L. Beck, T. P. Greene, R. R. Howell, S. Lumsden, and L. Prato,  Astronomical J.  117:  1594,  March 1999.  (abstract) , (A.J on-line)

Infrared Spectral Imaging of Martian Clouds and Ices.  D. R. Klassen, J. F. Bell III, R. R. Howell, P. E. Johnson, W. Golisch, C. D. Kaminski, and D. Griep,  Icarus  138:  36.  1999.  (Icarus on-line)

Thermal Emission from Lava Flows on Io.  R. R. Howell,  Icarus 127: 394-407, June 1997. (abstract)   (Icarus on-line)

Violent Silicate Volcanism on Io in 1996.  J. A. Stansberry, J. R. Spencer, R. R. Howell, C. Dumas, and D. Valik,   Geophys. Res. Lett. 24:  2455.   1997.  (GRL on-line)

The Thermal Structure of Triton's Atmosphere: Results from the 1993 and 1995 Occultations.  C. B. Olkin, J. L. Elliot, H. B. Hammel, A. R. Cooray, S. W. McDonald, J. A. Foust, A. S. Bosh, M. W. Buie, R. L. Millis, L. H. Wasserman, E. W. Dunham, L. A. Young, R. R. Howell, W. B. Hubbard, R. Hill, R. L. Marcialis, J. S. McDonald, D. M. Rank, J. C. Holbrook, and H. J. Reitsema,  Icarus,   129:  178-201, Sept. 1997. (abstract)   (Icarus on-line)