GLOBAL MAPS OF ATOMIC OXYGEN IN THE THERMOSPHERE OF
MARS DERIVED FROM OI 135.6 NM EMISSION OBSERVED BY THE
EMIRATES
MARS
ULTRAVIOLET
SPECTROMETER
(EMUS)
INSTRUMENT
M. O. Fillingim, Space Sciences Laboratory, University of California, Berkeley, CA, USA
(matt@ssl.berkeley.edu), R. L. Lillis, Space Sciences Laboratory, University of California, Berkeley, CA USA,
J. Deighan, Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, CO USA, S. K.
Jain, Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, CO, USA, H. R. Al
Matroushi, Mohammed Bin Rashid Space Centre, Dubai, UAE, H. A. Al Mazmi, United Arab Emirates Space
Agency, Abu Dhabi, UAE, M. S. Chaffin, Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, CO, USA, J. Correira, Computational Physics, Inc., Springfield, VA, USA, S. L. England, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA, J. S. Evans, Computational Physics,
Inc., Springfield, VA, USA, G. M. Holsclaw, Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, CO, USA, F. H. Lootah, Mohammed Bin Rashid Space Centre, Dubai, UAE, F. G. Eparvier,
Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, CO, USA, E. M. B.
Thiemann, Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, CO, USA.

Introduction:
One of the key investigations of the Emirates
Mars Mission is to “determine the abundance and
spatial variability of key neutral species in the thermosphere on sub-seasonal timescales” [1]. The
Emirates Mars Ultraviolet Spectrometer (EMUS)
instrument observes ultraviolet emissions between
approximately 100 and 170 nm [2]. The
thermospheric column abundance of atomic oxygen
determined from measurements of the O I 135.6 nm
emission. On the Martian dayside, this emission feature is produced by oxygen atoms excited into the 5S
state by photoelectron impact transitioning to their
ground state.

Forward Modeling:
Our primary tool used to determine the
thermospheric oxygen abundance is a forward model
consisting of a one-dimensional photochemical equilibrium atmospheric model coupled to a photoelectron transport and emission model [3]. The coupled
model calculates the 135.6 nm emission rate accounting for a variety of external (solar EUV spectrum)
and internal (atmospheric structure) parameters. We
run the coupled model varying parameters such as
the solar EUV spectrum, mesosphere and exosphere
temperatures, N2 and Ar mixing ratios, and eddy
diffusion coefficient over reasonable expected parameter ranges. This results in a multidimensional
look up table constructed from several thousand individual runs.

Retrieving Atomic Oxygen:
We find that there is a nearly one-to-one relationship between the oxygen column abundance and the

predicted 135.6 nm emission over a broad range of
input values. Thus, for each pixel, the retrieved oxygen column abundances are those that are associated
with the best match from the lookup table to the
EMUS-observed brightness. Here we show initial
results of the spatial and temporal variability of
thermospheric oxygen abundance from the first few
months of EMUS observations.

Figure 1: Measured 135.6 nm brightness (left) and
retrieved O/CO2 column ratio (right).

References:
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