Atmospheric Variation and Distribution of Martian Meteoric Mg+ from
MAVEN/IUVS
M. M. J. Crismani1, R. M. Tyo1, N. M. Schneider2, J. M. C. Plane3, W. Feng3,4, J.D. Carrillo-Sanchez5,6, G.
L. Villanueva5, S. Jain2, J. Deighan2
1
California State University, San Bernardino, Department of Physics, CA USA (matteo.crismani@csusb.edu)
2
Laboratory for Atmospheric and Space Physics, Boulder, CO USA 3School of Chemistry, University of Leeds,
Leeds, UK 4National Centre for Atmospheric Science, University of Leeds, Leeds, UK 5NASA Goddard Space
Flight Center, Greenbelt, MD, USA 6Catholic University of America, Department of Physics, Washington DC,
USA

Introduction:
Since the discovery of atmospheric Mg+ at Mars
in 2015 by the Mars Atmosphere and Volatile Evolution (MAVEN) mission, there have been almost continuous observations of this meteoric ion layer in a
variety of seasons, local times, and latitudes. Here we
present the most comprehensive set of observations
of the persistent metal ion layer at Mars, constructing
the first grand composite maps of a metallic ion species. These maps demonstrate that Mg+ appears in
almost all conditions when illuminated, with peak
values varying between 100 and 500 cm-3, dependent
on season and local time. There exists significant
latitudinal variation within a given season, indicating
that Mg+ is not simply an inert tracer, but instead
may be influenced by the meteoric input distribution
and/or atmospheric dynamics and chemistry. Geographic maps of latitude and longitude indicate that
Mg+ may be influenced by atmospheric tides, and
there is no apparent correlation with remnant crustal
magnetic fields. This work also presents counterintuitive results, such as a reduction of Mg+ ions in
the northern hemisphere during Northern Winter in
an apparent correlation with dust aerosols.
Observations and Data Analysis:
The MAVEN spacecraft has a uniquely elliptical
orbit that benefits from atmospheric drag and subsequent fuel burns to change the location of periapse in
latitude and local time. Over the course of more than
seven Earth years, MAVEN has been able to observe
a variety of Martian seasons, geographic latitude and
longitudes, as well as local times. During the orbital
periapse segment the spacecraft descends through the
upper atmosphere (down to 140-160 km) so that insitu measurements of atmospheric atoms and ions, as
well as ambient E and B-fields can be measured
throughout. This spacecraft orbital geometry provides coverage of local times, solar zenith angles and
full longitude coverage over about 4-5 orbits (each
orbit is ~5 hours). IUVS is able to create vertical
profiles during its periapse orbital segment, when the
instrument is oriented orthogonally to the motion of
the spacecraft. Using the Mid-UltraViolet (MUV)
resonant fluorescent scattering of MgII at 285 nm,
IUVS investigates the abundance and structure of

this meteoric ion above 60 km, where scattered solar
light serves to limit the lowest altitudes from observation. In this work we present the first global results
of near continuous monitoring of Mg+ at Mars with
implications for the formation of mesospheric cloud
nuclei 1,2 and to provide the first constraints on a
seasonally varying meteor input function (MIF) 3,4.
As has been successfully accomplished at Earth 5,6,
this global view on meteoric ions also permits a direct investigation of the upper atmosphere, where the
dynamics and chemistry can be constrained with a
novel set of observations.
Results:
Prior to the Martian insertion of the MAVEN
spacecraft in 2014, ionospheric observations of a
transient M3 or Mm layer of electrons near 90 km,
coincident with modeled ablation heights 7,8, were
presented as evidence of intermittent meteoric ablation. However, after the meteor shower of comet
Siding Spring 9,10 and discovery of a persistent layer
of meteoric ions 11 provided the first observations of
atomic and ionic metal species it was possible to
determine that the origin of these radio occultation
observations was not meteoric 12. Initial monitoring
of the Mg+ layer due to sporadic meteors indicated
that it was a persistent layer with a fixed altitude and
abundance 11. However, such an early and simplified
view has been supplanted by the wealth of data accumulated since 2015.
The Mg+ layer seems to be dynamic, with peak
ablation altitudes shifting, abundances fluctuating,
and variations in the top and bottom-sides of the Mg+
layer, all likely directly related to the underlying atmospheric structure and meteoric chemistry. At the
equator, a multi-year analysis shows an enhancement
of Mg+ at morning local times whose layer topside
increases throughout the day. Separating these observations by season, the peak altitude Mg+ appears
to respond to the background atmosphere, as the
former shifts up and down in altitude. Using zonal
medians to compare across latitude, the Mg+ layer
peak altitude can dip as low as 80 km near the south
pole and as high as 105 km at equatorial/midlatitudes. Overall abundances also vary dramatically,
in excess of the average 250 ions cm-3 reported in 11
to averages of 300-500 ions cm-3 in some cases, but

also the reduction of Mg+ in specific seasons warrants further investigation. Finally, in two seasons the
geographic distribution may be linked to tidal variations in the background atmosphere.
This dataset represents nearly continuous monitoring of the Mg+ layer in a variety of geophysical
conditions, and the results found herein will provide
important constraints for the next generation of meteoric ion chemistry and atmospheric circulation
modeling at Mars. Model-observation comparisons
should provide insights into mesospheric transport,
chemistry and interplanetary dust particle sources.
Previous discrepancies between model predictions
and metal ion observations led to the development of
a novel nucleation scheme for mesospheric clouds2,
and we expect this dataset to provide the impetus to
future advances in atmospheric chemistry. Overall,
this represents the broadest investigation of meteoric
metal ions, summarizes their first-order behavior,
and outlines new model challenges for the future.
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