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2008 Annual Science Report

NASA Goddard Space Flight Center Reporting  |  JUL 2007 – JUN 2008

Accomplishments of Graduate Student Yana Radeva

Project Summary

Yana L. Radeva is a fourth year Ph.D. student at the University of Maryland – College Park, under the joint mentorship of GCA co-I Prof. Michael A’Hearn (Astronomy Dept.) and Michael Mumma (GCA P. I.). She is investigating the organic composition of comets, a key basis for understanding the formation and evolution of the Solar System, and for assessing delivery of water and organics to terrestrial planets.

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3 Teams
0 Publications
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Field Sites

Project Progress

Yana L. Radeva is a fourth year Ph.D. student at the University of Maryland – College Park, under the joint mentorship of GCA co-I Prof. Michael A’Hearn (Astronomy Dept.) and Michael Mumma (GCA P. I.). She is investigating the organic composition of comets, a key basis for understanding the formation and evolution of the Solar System, and for assessing delivery of water and organics to terrestrial planets.

During this period, she completed analysis of the organic chemistry of comet C/2000 WM1 (LINEAR) through high-resolution infrared spectroscopy (based on data acquired with the Near Infrared Echelle Spectrograph on the Keck II telescope). She derived production rates, rotational temperatures and abundances relative to water for the detected parent volatiles: CH4, C2H2, C2H6, H2CO, CH3OH, HCN, CO, along with H2O (the dominant species). Her results show that WM1 is depleted in organic parent volatiles, compared with a sample of “organics-normal” comets analyzed in a similar way (Mumma et al. 2003, 2008). WM1 is only the third comet characterized as “organics-depleted”, and thus Radeva’s research is providing an important addition to the emerging taxonomy for comets based on chemical composition.

Spectra of WM1 were acquired on three adjacent dates (23, 24 and 25 Nov. 2001) to test temporal changes in the relative abundances of the organic volatiles, and thus the degree of heterogeneity within the nucleus. For each species, the mixing ratios she derived for the three dates agree within error (Figure 1), consistent with homogeneous composition in the active regions of this cometary nucleus. Radeva presented her results at the AAS Division for Planetary Sciences Conference in October 2007; the Astrobiology Science Conference in April 2008; and the Asteroids, Comets, Meteors Conference in July 2008. She has prepared a draft manuscript for submission to the Astrophysical Journal.

Radeva also participated in the observations of comet 8P/Tuttle with NIRSPEC on the Keck II telescope (Mauna Kea, Hawaii) in December 2007, and in the subsequent analysis of the acquired data. These revealed highly unusual and unique organic composition, possibly related to the binary nature of the nucleus. She is a co-author of the paper “The Peculiar Volatile Composition of Comet 8P/Tuttle: A Contact Binary of Chemically Distinct Cometesimals?”, published in the Astrophysical Journal Letters.

Radeva is also pursuing ab initio fluorescence models for a new infrared band of ethane (C2H6) in comets, that promises to provide improved rotational temperatures for that species. This band is present whenever we search the appropriate spectral interval, and four comets in our database display line intensities with high S/N ratios, by which the theoretical model may be tested and refined. Once mature, the derived rotational temperature for C2H6 may be compared with those of other species observed simultaneously (H2O, HCN, CO) to test thermalization in the inner coma.

Yana Radeva received the Master’s degree in Astronomy during this period (University of Maryland, December 2007). In June 2008 she proposed a dissertation topic, with advisors Dr. Michael Mumma (NASA GSFC) and Dr. Michael A’Hearn (University of Maryland), and was admitted to candidacy for the Ph.D. degree in Astronomy.
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  • PROJECT INVESTIGATORS:
    Michael Mumma Michael Mumma
    Project Investigator
  • PROJECT MEMBERS:
    Yana Radeva
    Doctoral Student

  • RELATED OBJECTIVES: