P14C-01 

Ion Composition measured in the environment of Comet 19P/Borrelly by Deep Space One

* Reisenfeld, D B (dan.reisenfeld@umontana.edu), Department of Physics & Astronomy, University of Montana 32 Campus Dr, Missoula, MT 59812, Williams, J D (john2.williams@umontana.edu), Department of Physics & Astronomy, University of Montana 32 Campus Dr, Missoula, MT 59812, Jessop, A (amberjessop@hotmail.com), Department of Physics & Astronomy, University of Montana 32 Campus Dr, Missoula, MT 59812, Janzen, P H (pjanzen@lanl.gov), ISR-1, Los Alamos National Laboratory P.O. Box 1663, MS-D446, Los Alamos, NM 87545, Harper, R (rharper@lanl.gov), ISR-1, Los Alamos National Laboratory P.O. Box 1663, MS-D446, Los Alamos, NM 87545,

We report in situ ion mass spectrometer (PEPE) measurements from the coma of Comet 19P/Borrelly, obtained during the flyby of the Deep Space One (DS1) spacecraft on 22 September 2001. The DS1 encounter with Borrelly is only the 4th encounter where the plasma environment of a comet has been sampled in situ, and this is the first encounter with a Jupiter family comet where a mass spectrometer was able to measure ions heavier than hydrogen. Cometary ions were detected at distances from ~ 5.5 × 10⁵ km to 2200 km from the nucleus of the comet. Previously, ion composition measurements by the PEPE instruments were reported at closest approach by Nordholt et al. (2003), where it was shown that the water group ion distribution was quite different from Comet Halley observations and cometary models. Of particular note is the small amount of H₃O⁺ (< 9%), as this was the most abundant molecular ion observed at closest approach to Halley. Here, we refine and extend that work and report on the cometary ion composition as a function of distance from the comet. The key advance in our analysis capability arises from a thorough calibration of the PEPE flight spare over a range of atomic and molecular species relevant to cometary composition.

P14C-02 

New Views of 2 Pallas From the Hubble Space Telescope

* Schmidt, B E (britneys@ucla.edu), UCLA-IGPP, 405 Hilgard Ave, Los Angeles, CA 90095, Russell, C T (ctrussel@igpp.ucla.edu), UCLA-IGPP, 405 Hilgard Ave, Los Angeles, CA 90095, Bauer, J M (bauer@scn.jpl.nasa.gov), JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, Li, J Y (jyli@astro.umd.edu), University of Maryland, Department of Astronomy University of Maryland, College Park, MD 20742, McFadden, L A (mcfadden@astro.umd.edu), University of Maryland, Department of Astronomy University of Maryland, College Park, MD 20742, Mutchler, M M (mutchler@stsci.edu), Space Telescope Science Institute, 3700 San Martin Dr, Baltimore, MD 21218, Parker, J M (joel@boulder.swri.edu), SWRI, 1050 Walnut St, Suite 300, Boulder, CO 80302, Rivkin, A S (andy.rivkin@jhuapl.edu), JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723, Stern, S A (alan.stern@nasa.gov), NASA-HQ, NASA Headquarters, Washington, DC 20546, Thomas, P C (pthomas@astro.cornell.edu), Cornell University, Department of Astronomy 610 Space Sciences Building Cornell University, Ithaca, NY 14853,

Asteroids are remnants of the earliest epoch of our solar system, and as such can provide constraints on the conditions that gave rise to the formation of planets. The largest asteroids represent objects that grew massive enough to undergo varying degrees of differentiation, but their growth was likely cut short by the gravity of Jupiter. However, Ceres, Vesta and Pallas are evolved, dynamic bodies. Ceres and Vesta are the targets of the Dawn Mission and have been extensively studied by ground based telescopes and HST. But there are many open questions regarding Pallas that warrant investigation. As Pallas is presently out of reach of the Dawn Spacecraft, we turn to the Hubble Space Telescope to study the asteroid. Pallas is a B-type asteroid with inclination of 31 degrees and a triaxial shape of 570 x 525 x 482 km. There is spectral evidence that Pallas, like Ceres, has been substantially altered by water. Pallas is at a similar distance from the Sun as Ceres, but is similar in mass to Vesta. Studying Pallas individually and in comparison with Ceres and Vesta may provide information about how a forming planet's size and location affect its composition and thermal history. Planned September observations of Pallas with Hubble's WFPC2 in five filters from 336 to 814 nm are discussed. These occur during Pallas' opposition with full rotational coverage and include a satellite search. This is the first major HST observing campaign ever planned for Pallas. In addition, during August and September, a ground-based campaign took place at three locations to support the HST observations. We present first results from our comprehensive survey of Pallas, and predictions for future analysis.

P14C-03 

The 2007 September 1 Aurigid meteor shower: predictions and first results from airborne and ground based observations

* Jenniskens, P (pjenniskens@mail.arc.nasa.gov), SETI Institute, 515 N. Whisman Road, Mountain View, CA 94043, United States Vaubaillon, J (vaubaill@ipac.caltech.edu), Caltech/IPAC, 1200 East California Boulevard, Pasadena, CA 91125, United States

We predicted the encounter of Earth with the dust trail of comet C/1911 N1 (Kiess) on 2007 September 1, when an outburst of meteors was expected from a radiant in the constellation of Auriga (EOS, Aug 7 issue). We anticipated that the shower would be best seen from the western states of the USA, Canada, and Mexico, including Hawaii and Alaska. It would be the only such Aurigid shower outburst in our lifetime. The meteoroids dated back to ejection around 4 A.D., give or take 40 years. These Aurigids were our best chance yet to study the 1-revolution dust trail of a known long-period comet, for measurements of the dust ejection conditions, and for clues about the possible presence of a cosmic ray induced crust in a comet which only recently returned from the Oort cloud. An airborne observing campaign was organized, called the Aurigid Multi-Instrument Aircraft Campaign, involving two Gulfstream GV aircraft, which were deployed from NASA Ames Research Center in Moffett Field, California. This enabled a team of 24 researchers, with an array of different cameras, to observe the shower from an altitude of 47,000 ft. The shower manifested much as expected, with a peak rate of about ZHR = 100 /hr, a peak time of 11:15 +/- 5 min. UTC, a duration of about 2 hours, and an abundance of bright +3 to -2 magnitude meteors. The shower was also well observed from the ground by both professional and amateur astronomers. Here, we will present some of those first results, discuss the shower's impact on the public, summarize the predictions, compare those to the observed shower activity, and report on the ongoing investigation of comet Kiess and its meteoroid stream. http://aurigid.seti.org

P14C-04 

The Oxygen and Hydrogen Isotope Composition of the Tagish Lake Meteorite

* Russell, S D (sdrussel@uwo.ca), Department of Earth Science The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada Longstaffe, F J (flongsta@uwo.ca), Department of Earth Science The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada King, P L (penny.king@uwo.ca), Department of Earth Science The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada

Carbonaceous chondrites provide a record of the earliest materials formed in the Solar System. We have demonstrated previously that the oxygen isotope compositions of chondrules and isolated olivine grains from the Tagish Lake meteorite describe a line (δ¹⁷O = 0.95 * δ¹⁸O – 3.24) similar to the carbonaceous chondrite anhydrous mineral line (Russell et al., 2004; Clayton et al., 1977). Clay minerals in the Tagish Lake meteorite provide a record of the aqueous alteration of its parent body. Here we report oxygen and hydrogen isotope compositions of clay-separates (saponite) and clay-rich whole-rock samples from the Tagish Lake meteorite. The clay-separates have oxygen isotope compositions (δ¹⁸O = 15.5 to 18.0 ‰; δ¹⁷O = 9.2 to 10.2 ‰; Δ¹⁷O = 0.5 to 0.8 ‰) within the range known for CI-type meteorites. The hydrogen isotope compositions (δD= 271 to 454 ‰) of the whole-rock and clay-separate samples are enriched in D relative to CI meteorites. The temperature of formation of Tagish Lake clay minerals and carbonates has been calculated using the oxygen isotope compositions of these phases, appropriate mineral oxygen-isotope thermometry equations and two possible models for the evolution of the water isotopic composition (cooling from 325 to 125 °C versus 100 to 10 °C). The Tagish Lake meteorite contains remnants of primitive phases (chondrules, isolated olivine grains and CAIs), unlike CI meteorites. We also note that the Tagish Lake meteorite has the highest δD values presently known for CI meteorites. There may be a trend of decreasing D-enrichment in CI meteorites, with the Tagish Lake example being among the most primitive of this class, or perhaps even its precursor.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.