Geoscience Reference
In-Depth Information
OXYGEN CHEMISTRY IN THE VENUS
MIDDLE ATMOSPHERE
F. P. MILLS
∗,†,∗∗
, M. SUNDARAM
∗,‡
,T.G.SLANGER
§
,
M. ALLEN
¶,
and Y. L. YUNG
∗
Research School of Physical Sciences and Engineering
The Australian National University, Canberra, ACT 0200, Australia
†
Centre for Resource and Environmental Studies
The Australian National University, Canberra, ACT 0200, Australia
‡
Department of Physics, Faculty of Science
The Australian National University, Canberra, ACT 0200, Australia
§
Molecular Physics Laboratory, SRI International
Menlo Park, CA 94025, USA
¶
Jet Propulsion Laboratory, California Institute of Technology
Pasadena, CA 91109, USA
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 91109, USA
∗∗
Frank.Mills@anu.edu.au
Decades of research have sought to understand the similarities and differences
between Venus and Earth. Yet, it is still not clear what chemical processes
maintain the long-term stability of Venus' primarily CO
2
atmosphere because,
until recently, the observed limit on O
2
was an order of magnitude smaller
than predicted by photochemical model calculations. CO
2
dissociates into CO
and O after absorbing photons at wavelengths
<
205 nm. These O atoms should
combine to form O
2
, and observations of intense airglow, produced as oxygen
molecules in the O
2
(a
1
∆) and O
2
(c
1
Σ) states decay radiatively to the ground
state, confirm rapid production of O
2
on both day and night sides. Achieving an
appropriate balance in numerical models between this rapid production of O
2
and the rapid destruction implied by the observational upper limits on O
2
has
been a challenge for the past 25 years. Numerical modeling shows that recent
proposals may resolve this gap between theory and observations, depending
on the rates of poorly constrained reactions. The laboratory and observational
studies needed to help resolve remaining questions regarding oxygen chemistry
in the Venus middle atmosphere are outlined.
1. Introduction
Venus is the planet in our solar system that is most similar to Earth but
there are significant differences. One of the most striking is the compo-
sition of their atmospheres. Understanding how and why they differ can
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