Engineering topics

Engel, Steffi

Publications and source records attributed to Engel, Steffi.

3 records

NASA NTRS1994

Silicate interactions with ammonia-water fluids on early Titan

Plausible models of the early history of Titan suggest that ammonia and water were present in liquid form at the surface. We show here by thermodynamic modeling that such an ocean could have reacted with silicates to put substantial quantities of sodium and potassium into solution. Following the formation of an ice crust by cooling, mantle ammonia-water fluids enriched in potassium would have been brought to the surface through the cryogenic equivalent of volcanism. Later impacts would have released the Ar-40 produced by decay of the K-40 into the atmosphere. The abundance of atmospheric Ar-40, measurable by the Huygens probe gas chromatograph mass spectrometer, may be dominated by this source and hence gives a proxy indication of the volume of ammonia-water resurfacing on Titan over geologic time.

Engel, Steffi↗

NASA NTRS1991

Sublimation and reformation of icy grains in the primitive solar nebula

The quantity of water ice that sublimates during the free fall of grains into the solar nebula from a surrounding interstellar cloud varies from over 90 percent of the grain mass as 30 AU from the nebular center to less than 10 percent at more than 100 AU. Virtually all the water that is sublimated ultimately recondenses, since the cold nebular gas lying beyond 10 AU is unable to hold more than a small portion as vapor. The return of most of the gas to solid phase near the nebular ambient temperature, of about 50 K, may result in at least two grain populations consisting, in one case, of unaltered interstellar grains which did not undergo sublimation, and in the other of water ice which cocondensed with more volatile gases at nebular ambient temperatures to yield volatile-rich amorphous phases.

Lunine, Jonathan I.↗

NASA NTRS1990

Solar nebula origin for volatile gases in Halley's comet

The conditions for Comet Halley formation are presently considered in light of the application of physical and chemical processes in the solar nebula environments to the present data base on the composition of the comet's gases. Key molecular ratios are compared to solar nebula model predictions, and the nebular thermochemistry is quantified for a range of solar elemental compositions which correspond to varying water depletion states in the inner nebula. Assuming that inner nebula chemistry is catalyzed by reaction on grains, it is judged that the abundances of the volatile C species CH4, CO, and CO2 in Halley could have been supplied by the solar nebula.

Engel, Steffi↗