Dr. Michael A Disanti

Dr. Michael A Disanti

  • (AST, PLANETARY STUDIES)
  • 301.286.7036
  • NASA/GSFC
  • Mail Code: 693
  • Greenbelt , MD 20771
  • Employer: NASA
  • Curriculum Vitae



    Research

    RESEARCH EXPERIENCE:
    1. Compare modeled and observed H2CO line intensities, to accurately measure its abundance in comets, as well as to reveal potential discrepancies between model and data.
    2. Measure relative abundances of CO, H2CO, and CH3OH in observed comets, for comparison with the overall volatile chemistry.

    Details: Our group is recognized as the world-leader in studies of parent volatiles in comets through ground-based high-resolution spectroscopy at near-IR wavelengths (~ 1 - 5 µm). The work of late has been especially exciting. Using the high-resolution spectrometer (NIRSPEC) at the Keck2 10-m telescope, we observed the long-period (Oort cloud) comet C/2004 Q2 (Machholz) in Fall/Winter 2004/2005 and the short-period (Jupiter Family) comet 9P/Tempel-1 in June and July 2005, and measured the volatile (ice) composition of both objects.
    Comet Tempel-1 was the target of the NASA Deep Impact Mission, in which a projectile impacted the nucleus on July 4, 2005 at a speed of about 10 km/s. Our compositional measurements revealed a different chemical signature between the nucleus surface material (determined from pre-impact measurements) and the impact ejecta (from post-impact spectra; Mumma et al. 2005).
    M. DiSanti's research emphasizes the volatile carbon-oxygen chemistry, in particular the efficiency of converting carbon monoxide to formaldehyde and methyl alcohol on the surfaces of icy grain mantles prior to their incorporation into the nucleus. This process has been shown experimentally to be highly temperature-dependent between ~10 and 20-25 K. We have now measured CO, H2CO, and CH3OH in six long-period comets, plus comet Tempel-1. Our inferred conversion efficiencies among comets in our database range from as high as 80 percent (in C/2002 T7 (LINEAR), which displayed very strong signatures of both H2CO and CH3OH, yet relatively weak CO), to a relatively low efficiency (maximum of ~ 30 percent) in Tempel-1.
    Such measurements are important for establishing the role of comets in replenishing Earth's oceans and for delivery of the seed organic molecules from which life emerged. From an Astrobiological standpoint, along with HCN and NH3 (both of which we also study), H2CO is thought to play a particularly significant role in the latter process. DiSanti has applied a fluorescence model of H2CO to existing spectral observations of comets within our database. Comet 2002 T7 LINEAR provided an excellent test bed for the first detailed application of the model to high-resolution spectra, allowing a line-by-line comparison between predicted and observed line intensities. We have developed a methodology for accurately measuring molecular excitation (rotational temperature); this is essential for retrieval of robust production rates.
    From these measured abundances, determine the efficiency of CO conversion in an attempt to establish the conditions (e.g., H-atom density, temperature) to which the pre-cometary ices were exposed. This requires comparison with yields from irradiation experiments on cometary ice analogues as a function of temperature, and also with observational data on these ices in interstellar (and proto-stellar) sources.

    Positions and Appointments

    Staff Scientist, Planetary Systems Laboratory
    Appointments:
    2002 - Staff Scientist, NASA-GSFC, Planetary Systems Branch Code 693, Greenbelt, MD 20771
    1995-2002 Research Assoc. Professor, Dept. of Physics, Catholic University of America, Washington, DC. Research performed at NASA-GSFC, through a University Cooperative Agreement between Goddard and CUA.
    1993 - 95 Research Scientist, Universities Space Research Association, NASA- GSFC, Greenbelt, MD.
    1992 - 93 Research Management Associateship, National Research Council, NASA- Headquarters, Washington, DC.
    1989 - 92 National Research Council Postdoctoral Associate, NASA-GSFC.
    1986 - 89 NASA Graduate Student Researchers Program Fellow, Lunar and Planetary Laboratory, Univ. of Arizona.
    1983 - 86 Graduate Research Associate, Lunar and Planetary Lab, Univ. of Arizona.
    1981 - 83 Graduate Teaching Assistant, Dept. of Physics, Univ. of Arizona.
    1978 - 81 Graduate Teaching Assistant, Dept. of Physics and Astronomy, U. N. Mex.

    Teaching Experience

    E/PO activities:

    M. DiSanti mentored an undergraduate student, Constantinos Makrides, through the NAI Summer Undergraduate Internships in Astrobiology (SUIA) program. Mr. Makrides streamlined the calculation of line-by-line fluorescence efficiency factors for water, at one-degree intervals over a wide range of temperatures, for comparison with emissions seen in our comet spectra. This effort found immediate application in establishing the rotational temperature of H2O in, and amount of H2O released from comet Tempel-1. The methodology for measuring the excitation and production rate of H2O is completely analogous to that developed for H2CO.
    M. DiSanti is also the node contact for the research effort, within the Minority Institution Astrobiology Cooperative (MIAC), to systematically observe comets through emission-line filters at optical wavelengths. This effort is led by Dr. Donald Walter (South Carolina State University), and will utilize telescopes in Arizona. Imaging studies on the Kitt Peak 1.3-m telescope are in the science-testing phase. The molecules giving rise to the IR emissions are photo-dissociated in the coma, producing the .daughter. fragments (radicals) to be targeted by the MIAC filter imaging program.
    Lastly, M. DiSanti talked to three second grade classes (including his son.s) at Thunder Hill Elementary School about the solar system and how comets can tell us about its early stages, similar to how dinosaur fossils can tell us about Earth at earlier times.

    Education

    1989 Ph.D., Physics, University of Arizona, Tucson, AZ 85721.
    Thesis title: "The production and spatial distribution of neutral and ionized water vapor in comet P/ Halley."
    1980 M.S., Physics, University of New Mexico, Albuquerque, NM 87131.
    1978 B.S., Astrophysics, University of New Mexico;
    B.A., Chemistry, University of New Mexico.

    Publications

    In preparation DiSanti, M. A., et al… Formaldehyde emission in comet C/2002 T7 (LINEAR): Validation of a line-by-line fluorescence model at infrared wavelengths.
    2005 Mumma, M. J., M. A. DiSanti, B. P. Bonev , H. Kawakita, K. Magee-Sauer, N. Dello Russo, G. L. Villanueva, E. L. Gibb, S. Sugita, J. Lyke, R. Campbell, J. Aycock, A. Conrad, G. Hill, and F. H. Chaffee 2005. Direct Measurement of Parent Volatiles in comet 9P/Tempel 1: A comparison of volatile composition before and after Impact. Science 310, 270-274.
    2005 Dello Russo, N., B. P. Bonev, M. A. DiSanti, M. J. Mumma, E. L. Gibb, K. Magee-Sauer, R. J. Barber, and J. Tennyson 2005. Production rates, rotational temperatures and spin temperatures in comets C/1999 H1 (Lee), C/1999 S4, and C/2001 A2. Astrophys. J. 621, 537-544.
    2004 Bonev, B. P., M. J. Mumma, N. Dello Russo, E. L. Gibb, M. A. DiSanti, and K. Magee-Sauer 2004. Infrared OH prompt emission as a proxy of water production in comets: Quantitative analysis of the multiplet near 3046 cm-1 in Comets C/1999 H1 (Lee) and C/2001 A2 (LINEAR). Astrophys. J. 615, 1048-1053.
    2003 Gibb, E. L., M. J. Mumma, N. Dello Russo, M. A. DiSanti, and K. Magee-Sauer 2003. Methane in Oort cloud comets. Icarus, 165, 391-406.
    2003 DiSanti, M.A., M.J. Mumma, N. Dello Russo et al. 2003. Evidence for a dominant native source of CO emission in comet C/1996 B2 (Hyakutake). JGR Planets 108.
    2003 Brittain, S. D., T. W. Rettig, T. Simon, C. Kulesa, M. A. DiSanti, and N. Dello Russo 2003. CO emission from disks around AB Aurigae and HD 141569: Implications for disk structure and planet formation timescales. Astrophys. J. 588, 535-544.
    2002 DiSanti, M.A., N. Dello Russo, K. Magee-Sauer et al. 2002. CO, H2CO, and CH3OH in comet 2002 C1 (Ikeya-Zhang). In Proceedings Asteroids, Comets, Meteors 2002, Berlin, Germany. ESA-SP 500, pp. 571-574.
    2002 Dello Russo, N., M.J. Mumma, M.A. DiSanti et al. 2002. Production of ethane and water in comet C/1996 B2 (Hyakutake). JGR Planets 107.
    2002 Magee-Sauer, K., M.J. Mumma, M.A. DiSanti et al. 2002. Production of hydrogen cyanide in comet C/1996 B2 (Hyakutake). JGR Planets 107.
    2001 DiSanti, M. A., M. J. Mumma, N. Dello Russo, and K. Magee-Sauer 2001. Carbon monoxide production and excitation in Comet C/1995 O1 (Hale-Bopp): Isolation of native and distributed CO sources. .Icarus 153:361-390.
    2001 Dello Russo, N., M. J. Mumma, M. A. DiSanti, and K. Magee-Sauer 2001. Ethane production and release in Comet C/1995 O1 Hale-Bopp. Icarus 153:162-179.
    2001 Mumma, M. J., I. S. McLean, M. A. DiSanti, et al. 2001. A survey of organic volatile species in comet C/1999 H1 (Lee) using NIRSPEC at the Keck Observatory. Astrophys. J. 546:1183-1193.
    2001 Mumma, M. J., N. Dello Russo, M. A. DiSanti, et al. 2001. "Organic composition of C/1999 S4 (LINEAR): a comet formed near Jupiter?" Science 292:1334-1339.
    2001 Mumma, M. J., N. Dello Russo, M. A. DiSanti, et al. 2001. "Organic composition of C/1999 S4 (LINEAR): a comet formed near Jupiter?" Science 292:1334-1339.
    2001 Novak, R. E., M. J. Mumma, M. A. DiSanti, N. Dello Russo, and K. Magee-Sauer 2001. Photochemical mapping of ozone in the middle atmosphere of Mars near the 1997 aphelion. Icarus 158, 14-23.
    2000 Dello Russo, N., M.J. Mumma, M.A. DiSanti, K. Magee-Sauer, R. Novak, T.W. Rettig (2000). "Water production and release in comet C/1995 O1 Hale-Bopp Icarus 143, 324-337.

    Talks, Presentations and Posters

    Recent Conference Presentations

    2005 Abundances of CO, H2CO, and CH3OH in Comets: Measuring Conversion Efficiencies in Grain Mantles. M. A. DiSanti, M. J. Mumma, B. Bonev, N. Dello Russo, W. Anderson, K. Magee-Sauer, D. C. Reuter, E. L. Gibb, NAI Biennial Meeting, April 2005, Boulder, CO. (Poster presentation).
    2005 The Evolution of Gas and Dust Production in Comet Tempel-1 as a Result of the Deep Impact Event. M. A. DiSanti, M. J. Mumma, B. Bonev, K. Magee-Sauer, B. P. Bonev, G. Villanueva, H. Kawakita, N. Dello Russo, E. L. Gibb, S. Sugita, J. Lyke, R. Campbell, J. Aycock, A. Conrad, G. Hiill, F. Chaffee, BAAS 37 (3), 633 (2005). Contributed oral presentation at Division for Planetary Sciences meeting of the American Astronomical Society, September 2005, Cambridge, UK.
    2005 Astronomical and Spectroscopic Perspective of Comets: Direct Detection of Oxygen-bearing Parent Volatiles at Infrared Wavelengths. M. A. DiSanti, N. Dello Russo, Workshop on Oxygen in the Earliest Solar System, September 2005, Gatlinburg, TN. (INVITED)

                                                                                                                                                                                            
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