HYDROGEN CORONA OBSERVATIONS AND ANALYSIS USING
EMM/EMUS
Mike Chaffin (michael.chaffin@colorado.edu), Justin Deighan, Sonal Jain, Greg Holsclaw, LASP, University of Colorado, Boulder, Colorado, U.S.A., Hoor AlMazmi, UAE Space Agency, Abu Dhabi, United Arab
Emirates, Scott England, Virginia Polytechnic Institute and State University, Aerospace and Ocean Engineering, Blacksburg, VA, United States, Frank Eparvier, Ed Thiemann, LASP, University of Colorado, Boulder,
Colorado, U.S.A., John Correira, J. Scott Evans, Computational Physics Inc. Springfield, Springfield, VA,
United States, Matt Fillingim, Rob Lillis, Space Sciences Laboratory, University of California Berkeley,
Berkeley, CA, United States, Krishnaprasad Chirakkil, Susarla Raghuram, LASP and Khalifa University of
Science Technology and Research, Space and Planetary Science Center, Abu Dhabi, United Arab Emirates,
Fatma Lootah, Hessa AlMatroushi, Mohammed Bin Rashid Space Center, Al Khawaneej, United Arab Emirates
The Emirates Mars Mission [Amiri+2021]
Emirates Ultraviolet Spectrometer [Holsclaw+2021]
(EMM/EMUS) experiment makes observations of
the Martian disk and inner corona from all phase
angles as part of its routine science observations. A
key objective of the mission is to use these observations to constrain the 3D distribution of atomic hydrogen around the planet and the present-day escape
rate of H to space. For this purpose, we isolate H
emissions at 121.6 nm (Lyman alpha) and 102.6 nm
(Lyman beta) so that we can fit the EMUS observations with a 3D H corona model and retrieve H density, temperature, and escape rates. We will present
limb scan observations from the EMM insertion orbit
which demonstrate that the contribution of spectrally
indistinguishable O 102.6 nm emissions is limited to
altitudes below 500 km, so that fitting emission
above this altitude with an H-only model is appropriate. We will also present examples of simultaneous model fits to H Lyman alpha and beta, using
both spherically symmetric and fully 3D models of
the H density distribution around the planet. An example of such a fit for two orbits of EMUS observations is shown in Figure 1. There remain substantial
discrepancies between the modeled emissions and
the data, indicating that there is still a great deal to
learn about the H distribution around the planet, the
interplanetary hydrogen distribution, and the long
term water-loss history of Mars from this dataset.
References:
Amiri+2021:
https://doi.org/10.1007/s11214-021-00868-x
Holsclaw+2021:
https://doi.org/10.1007/s11214-021-00854-3

Figure 1. Examples of EMM/EMUS data, spherically symmetric model best fits, and deviance of the model and
data. Top/bottom show different collections of EMUS OS2 data and fits for the times indicated. Each set of six panels shows a collection of EMUS Lyman alpha and Lyman beta brightness and model fits using two or three slews of
the spectrograph slit across the planet. Spherically symmetric density + radiative transfer model best fits to the data
are shown in the middle column of each set. All of the data from each orbit is used to perform a model best fit for all
tangent altitudes above 500 km, below which O 102.6 nm contributions become important. Best fit parameters, including a model scale factor for each emission, are given adjacent to each plot. Model/data deviations usually indicate the presence of more or less H in reality than is present in the spherically symmetric model, but occasionally
indicate flat field issues or discrepancies between the data and the adopted interplanetary hydrogen model.