PDS: The Planetary Atmospheres NodePlanetary Atmospheres
Cover Page/Proposal Summary
ROSS-00 NRA 00-OSS-01
Date Due: 4/28/2000
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This proposal shall be used and disclosed for evaluation purposes only, and a copy of this Government notice shall be applied to any reproduction or abstract thereof. Any authorized restrictive notices that the submitter places on this proposal shall also be strictly complied with. Disclosure of this proposal for any reason outside the Government evaluation purposes shall be made only to the extent authorized by the Government. |
| Proposal Type: New Proposal |
| Proposal Category: Comets |
| Major Equipment Proposal? No |
| Do you intend to submit an Education/Public Outreach (E/PO) proposal? No |
| Proposal Title: |
| Investigation of the Comet Nucleus-Coma Boundary Layer |
| Abbreviated Proposal Title: |
| Comet Nucleus-Coma Boundary Layer |
| Principal Investigator: |
| Dr. Walter Huebner Instrumentation and Space Research Southwest Research Institute 6220 Culebra Rd. San Antonio, TX 78238-5166 Phone: 210-522-2730 Fax: 210-543-0052 E-mail: whuebner@swri.edu |
| Signature | Date |
| _____________________________________ | ____________ |
| Co-Investigators and Collaborators: | |||
| Type | Name | Affiliation | |
| Sci Co-I | Dr. Richard Link | SwRI | rlink@swri.edu |
| Sci Collab | Dr. Samuel Gulkis | JPL | samuel.gulkis@jpl.nasa.gov |
Proposal Summary:
Gas emitted from a comet nucleus into near vacuum is not in thermodynamic equilibrium. The initial velocity distribution just above the surface is a truncated Maxwell distribution weigthed with velocity components only in the direction away from the emitting surface. Fast molecules overtake slow molecules and collide with them. After a sufficiently large number of collisions a new (drifting) Maxwell velocity distribution is established. Ignoring a small return flux, we have solved this problem analytically based on conservation of momentum and energy. We now propose to investigate the details in this boundary layer (Knudsen layer) by solving the Boltzmann equation using the discrete ordinates method (DOM). The following cases will be investigated: (1) A one-component gas (e.g., H2O), (2) a multi-component gas (e.g., H2O, CO, CH3OH, and NH3), and (3) a gas with dust entrainment. Dust will be simulated by various values of cross sectional area per unit mass. The derived velocity distribution for each molecular species will produce a spectral line profile different from the Doppler line profile commonly used to analyze very low-pressure line shapes in the radio region of the spectrum. The derived non-equilibrium line shapes will be useful in future spacecraft investigations such as the MIRO experiment on Rosetta which will investigate microwave molecular spectral lines in the inner coma with very high spectral resolution. We plan to explore the possibility that measured non-equilibrium line shapes might be used as a probe to determine physical conditions on and near the surface of a comet nucleus. We will also investigate the increase in the thickness of the Knudsen layer with decreasing gas production rates which occur, for exmple, in the transition from dayside to nightside close to the nucleus or with increasing heliocentric distance of the comet.
Certification of Compliance with Applicable Executive Orders and U.S. Code
By submitting the proposal identified in this Cover Sheet/Proposal Summary in response to this NRA or AO, the Authorizing Official of the proposing institution (or the individual proposer if there is no proposing institution) as identified below:
Willful provision of false information in this proposal and/or its supporting documents, or in reports required under an ensuing award, is a criminal offense (U.S. Code, Title 18, Section 1001).
