MORPHOLOGY OF EUV AND FUV MARTIAN AIRGLOW EMISSIONS OBSERVED BY THE EMUS INSTRUMENT ON BOARD THE EMIRATES MARS
MISSION.
S. K. Jain, J. Deighan, M. S. Chaffin, G. H. Holsclaw, Laboratory for Atmospheric and Space Sciences,
University of Colorado, Boulder, CO, United States, (Sonal.Jain@lasp.colorado.edu), R. Lillis, M. Fillingim, Space
Sciences Laboratory, University of California Berkeley, Berkeley, CA, United States, J. S. Evans, J. Correira,
Computational Physics Inc., Springfield, Virginia, United States, H. AlMatroushi, F. Lootah, Mohammed Bin Rashid
Space Center, Al Khawaneej, United Arab Emirates, S. England, Virginia Polytechnic Institute and State University,
Aerospace and Ocean Engineering, Blacks- burg, VA, United States, H. AlMazmi, UAE Space Agency, Abu Dhabi,
United Arab Emirates, E. M. B. Thiemann, F. Eparvier, P. Chamberlin, Laboratory for Atmospheric and Space
Sciences, University of Colorado, Boulder, CO, United States.

Introduction
The spectroscopy of the Martian atmosphere in extreme
and far-ultraviolet wavelengths has been extensively used
to study planetary atmospheres. The FUV and EUV
emissions provide information about the atmospheric
composition (both neutral and ionized) and structure
and can be used to study energy deposition, dynamics,
and chemistry. The Emirates Mars Mission Ultraviolet
Spectrometer (EMM/EMUS) is the first instrument capable of simultaneously observing the EUV and FUV
emissions in the Martian upper atmosphere (Holsclaw
et al., 2021). Due to the large and unique orbit (55 hours
elliptical orbit) of the EMM spacecraft around Mars,
The EMUS disk observations cover the majority of temporal (dayside local hours) and spatial (latitudes and
longitude) conditions in a relatively small-time scale (in
few weeks of observations) (Holsclaw et al., 2021; Almatroushi et al., 2021). These disk observations of Mars
in the EUV and FUV wavelength regions are enabling
us to understand the global scale variations in the upper atmosphere. Figure 1 shows the average spectrum
from EMUS SYS15 observations. This paper present
a detailed analysis of global and local variations in the
state of the upper atmosphere and airglow emissions
(EUV and FUV) observed by the EMUS instrument.
The FUV spectrum is dominated by CO fourth positive
group band system along with the brightest atomic emissions of H Ly-α and O I 130.4 nm. The EUV wavelength
region of the spectrum is mostly dominated by atomic
emissions from atomic hydrogen, argon, nitrogen, and
oxygen along with Hopefield-Birge band system of CO.
The EMUS observations are consistent with previous
observations of Mars in the EUV and FUV wavelengths
(Feldman et al., 2000; Krasnopolsky and Feldman, 2002, cf.
Figure 1).

Data
In this analysis, we have used disk observations from
EMUS UOS-1 and UOS-2 (Holsclaw et al., 2021). Both

types of observations provide coverage across latitude,
longitude and local time. For the present analysis, we
have taken data limited to the SZA less 60 and emission
angles less than 70 degrees. We have used level2b which
uses the Poisson multiple linear regression approach to
reduce the spectral data into the radiance of various EUV
and FUV emissions. We used data from the start of the
nominal science of the EMM.
Observations and Results
In the present analysis, we have used the averaged disk
brightness to understand the spatial and temporal variations in the major EUV and FUV emissions. Figure 2
shows the average daily brightness for various emissions in FUV (C I 156.1 nm, O I 135.6 nm, OI 130.4
nm, and H I 121.6 nm) and EUV (Ar 106.6 nm, CO HB:
C-X; B-X bands). The figure also showed normalized
Lyman alpha irradiance measured by Extreme Ultraviolet (EUV) Monitor aboard the MAVEN (Eparvier et al.,
2015). From the start of nominal science observations
until 15 Sept 2021 (hereafter, the first time period) the
average disk brightness didn’t show significant variations that are in line with low solar activity during this
time period (please see Figure2-bottom panel). Between
Dec 2021 and Feb 2022 (hereafter, the second time period), all the major EUV and FUV emissions start to
show upward trends in the daily average disk brightness. During this time we also notice ramp up in the
Lyman alpha irradiance measured by the EUVM instrument. We found that both the EUV and FUV emissions
are correlated with the solar forcing, however, our analysis indicates that FUV emissions such as O I 135.6 nm
show a slightly lower correlation with solar forcing compared to the EUV emissions (such as CO B-X and Ar
106.6 nm). We also found that the correlation between
the solar EUV and OI 135.6 is lower during the first
time period when the solar forcing was not that strong.
This indicates that lower atmosphere coupling could be
affecting the brightness of OI 135.6 via waves.

Intensity [R/nm]

CO B–X (0,0)+OI

350
300

200
150
100

Ar I
Ly-γ
OI

CO C–X (0,0)

250

Ly-β + O I

CO 4PG A1Π → X1Σ+

Ly-α

CI

OI

OI
NI

N IC I

C II

50
0

100

110

120

130

140

150

160

170

180

Wavelength [nm]
Figure 1: The figure shows the average EMUS EUV and FUV spectrum from EMUS SYS15 observations. The blue curve shows
the disk observations taken from the Hopkins Ultraviolet Telescope (HUT) (Feldman et al., 2000). The Lyman alpha and OI 130.4
nm were out of scale in the data provided in Feldman et al. (2000).

Avg disk brightness. [R]
4000

HI 121.6 nm

2000
500
OI 130.4 nm

250
15
10

Ar 106.6

10
5

CO (C-X) HB

20
10
30
20
10

CO (B-X) HB
OI 135.6 nm

50
CI 156.1 nm

25
Norm Ly irr

1.00
0.75
2021-04

2021-05

2021-06

2021-07

2021-08

2021-09 2021-10
Date

2021-11

2021-12

2022-01

2022-02 2022-03

Figure 2: The daily average disk brightness for various emissions observed by EMUS instrument on board EMM. Solid star and
circle symbols show average brightness from EMUS USO-1 and USO-2 observing mode. The geophysical variations are 1-σ
standard deviation in the plots. Bottom panel shows normalized lyman alpha irradiance measured by EUVM monitor on board the
MAVEN spacecraft.

REFERENCES

References
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10.1007/s11214-015-0195-2.
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