the chemistry of comet hale-bopp wendy hawley journal club april 6, 2006
TRANSCRIPT
![Page 1: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/1.jpg)
The Chemistry of Comet Hale-Bopp
Wendy HawleyJournal ClubApril 6, 2006
![Page 2: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/2.jpg)
Paper
New molecules found in comet C/1995 O1 (Hale-Bopp).Investigating the link between cometary and interstellar materialBockelée-Morvan, D., Lis, D., Wink, J.E., et al. 2000A&A 353, 1101
![Page 3: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/3.jpg)
What is a Comet?
• A small (<50km nucleus) icy body orbiting the Sun in a highly elliptical orbit
• Anatomy of a comet:
![Page 4: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/4.jpg)
Historical Significance
Bayeux Tapestry (11th century) image of comet Halley
1857 drawing of a comet hitting Earth
![Page 5: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/5.jpg)
Scientific Significance
• Comets thought to contain pristine material
• Debate over origin of comets:– Interstellar material?– Solar nebula?
• Chemical composition of a comet gives clues about solar system formation
![Page 6: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/6.jpg)
Previous Work
• Biver et al. 1999 - production rates• Schleicher et al. 1998 - comet properties
• Greenberg 1982 - interstellar origin theory
• Lewis & Prinn 1980 - solar nebula affected composition
• Several papers about production rates in other comets, most notably Hyakutake and Halley
![Page 7: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/7.jpg)
Comet Hale Bopp
• Discovered in 1995 by Alan Hale and Thomas Bopp
• Named “the Great Comet of 1997”
• Perihelion: April 1, 1997, 0.91AU
![Page 8: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/8.jpg)
Scope of Paper
• Use spectroscopy to determine chemical composition of Hale-Bopp
• Compare to composition of interstellar clouds
• Answer questions about the origin of comets, and the origin of our solar system
![Page 9: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/9.jpg)
Observations• Taken during February to April 1997
• Identified six new species from spectra: HC3N, SO, HCOOH, SO2, NH2CHO, HCOOCH3
• HNCO and OCS also confirmed
Fig. 1
![Page 10: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/10.jpg)
Molecular Production Rates and Abundances
• Molecular column density: • Assumes optical thinness• nu calculated using local thermal equilibrium (LTE) approximation
• Local densities of parent and daughter species found with Haser’s model
• For some species, more in-depth modeling was done, yielding similar results to LTE
![Page 11: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/11.jpg)
![Page 12: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/12.jpg)
![Page 13: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/13.jpg)
Sulfur Species
• [SO]: 0.3% and [SO2]: 0.2% relative to water
• SO abundance could vary from comet to comet
• [SO]/[SO2]~1.6 - is SO2 only parent?
![Page 14: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/14.jpg)
Sulfur Species (cont.)
• [OCS]: 0.4% relative to water• In agreement with value found for Hyakutake (Gérard et al. 1998)
• [S]/[O]: 0.02 (solar system value)
![Page 15: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/15.jpg)
N- and CHO-bearing Species
• In agreement with upper limits for other comets (Crovisier et al. 1993)
• HC3N, NH2CHO and other species have low abundances with respect to NH3
• New CHO species have low abundances, do not contribute much to C or O abundance
![Page 16: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/16.jpg)
Volatile Composition
• Abundances are assumed to be abundance of cometary ices
• Does not account for extended sources– Both CO and OCS have additional 50% contribution from distributed source
– H2CO abundance uses extended source calculation
![Page 17: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/17.jpg)
Volatile Composition (cont.)
• Could coma chemical reactions cause minor species?– A model of HCN formation cannot reproduce the abundance
– Ion-molecule interactions could produce new species, but it’s unlikely•Ionic content too small (photoionization takes too long), formation requires two subsequent reactions and more complex ions
![Page 18: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/18.jpg)
Is Hale-Bopp Typical?
• C2 and CN abundances are typical (Schleicher et al. 1998)
• Parent molecules similar to those in other comets (Crovisier 1993)
• Hale-Bopp is assumed to be a representative for all comet-kind
![Page 19: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/19.jpg)
Comparison to Interstellar Medium
• Theories on comet formation range from pure interstellar origin to pure solar condensate origin
• Major constituents were studied, minor species left out
• Compare to hot cores and bipolar flows
![Page 20: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/20.jpg)
Hot Cores
• dense clumps of gas heated to above 100K by UV radiation and shocks from recently formed stars
• Gases may form from sublimation of icy particles
• Typically have large hydrogenated molecule abundance and organic material
![Page 21: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/21.jpg)
Bipolar Flows
Produced by young protostars, also help investigate icy particles sublimated in the presence of low-mass stars
![Page 22: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/22.jpg)
![Page 23: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/23.jpg)
N- and CHO- bearing speciesin good agreement, but S-bearing species there is scatter
![Page 24: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/24.jpg)
Future Work
• Further data on interstellar clouds needed
• Space missions to comets will provide more information about nucleus and composition
![Page 25: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/25.jpg)
For more Information• Deep Impact: http://deepimpact.jpl.nasa.gov/home/index.html
• Rosetta: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=13
• Stardust: http://stardust.jpl.nasa.gov/home/index.html
• Info on Hale-Bopp: http://www2.jpl.nasa.gov/comet/
![Page 26: The Chemistry of Comet Hale-Bopp Wendy Hawley Journal Club April 6, 2006](https://reader035.vdocuments.us/reader035/viewer/2022062719/56649ec15503460f94bcd505/html5/thumbnails/26.jpg)
Conclusion
• New species were detected using spectra
• Comparison of abundances to interstellar sources showed similarities
• There is a strong link between comets and interstellar ices
• Comets give clues about the origins of life, despite their historical role as omens of death and destruction