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| Titel |
Photochemical escape of oxygen from the Martian atmosphere: first results from MAVEN |
| VerfasserIn |
Rob Lillis, Justin Deigan, Jane Fox, Steve Bougher, Yuni Lee, Thomas Cravens, Ali Rahmati, Bruce Jakosky |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105411
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| Publikation (Nr.) |
 EGU/EGU2015-8701.pdf |
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| Zusammenfassung |
| One of the primary goals of the MAVEN mission is to characterize rates of atmospheric
escape at the present epoch and relate those escape rates to solar drivers. One of
the major escape processes is known as photochemical escape, which is broadly
defined as a process by which a) an exothermic reaction in the atmosphere results
in an upward-traveling neutral particle whose velocity exceeds planetary escape
velocity and b) the particle is not prevented from escaping through any subsequent
collisions. At Mars, photochemical escape of oxygen is expected to be a significant
channel for atmospheric escape, particularly in the early solar system when extreme
ultraviolet (EUV) fluxes were much higher. Thus characterizing this escape process
is central to understanding the role escape to space has played in Mars’ climate
evolution.
Because escaping hot atoms cannot easily be directly measured, models of production and
transport (through the atmosphere) of such atoms must be used to constrain escape rates.
These models require altitude profiles of neutral densities and electron and ion densities and
temperatures, as well as compositional information.
All the relevant quantities upon which photochemical escape depends will be measured
by MAVEN at the relevant altitudes (150-250 km). LPW will measure electron density and
temperature, NGIMS will measure neutral and ion density and STATIC will measure ion
density and temperature. 4 separate calculations must be made for every altitude
profile:
Profiles of O2+dissociative recombination (DR) rates will be calculated
straightforwardly from electron temperature, electron density and O2+density.
Profiles of rotational and vibrational distributions of O2+ ions will be calculated
from profiles of CO2, O, O2, O+, CO2+ and CO+ via a lookup table from an
empirical model.
Profiles of energy distributions of hot O atoms will be calculated from the results
of step 2 and from profiles of electron and ion temperatures.
Profiles of all neutral densities will be input into models of hot O transport in
order to calculate photochemical escape fluxes from DR of O2+.
We will present photochemical escape fluxes as a function of all relevant factors, in particular
solar zenith angle and EUV flux. The latter will change with solar activity, solar rotation and
Mars heliocentric distance, while MAVEN will sample the former from 40 to 150
degrees as the periapsis location precesses over the first 5 months of the primary
mission.
This, combined with further simulations with progressively higher EUV fluxes, will
eventually enable a total integrated loss estimate over the course of Martian history and hence
a determination of the impact of this loss process on the evolution of the Martian climate. |
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