THE CASE AND APPROACH FOR CONTINUOUS, SIMULTANEOUS,
GLOBAL MARS WEATHER MONITORING FROM ORBIT
L. Montabone, Laboratoire de Météorologie Dynamique, IPSL, Sorbonne Université, Paris, France, and
Space Science Institute, Boulder, CO, USA (lmontabone@spacescience.org), N. G. Heavens, A. Pankine, M.
Wolff, Space Science Institute, Boulder, CO, USA, A. Cardesin-Moinelo, B. Geiger, European Space Astronomy Center, Madrid, Spain, F. Forget, S. Guerlet, E. Millour, A. Spiga, Laboratoire de Météorologie Dynamique, IPSL, Sorbonne Université, Paris, France, S. D. Guzewich, M. D. Smith, Goddard Space Flight
Center, Greenbelt, MD, USA, O. Karatekin, B. Ritter, L. Ruiz Lozano, C. B. Senel, O. Temel, Royal Observatory of Belgium, Brussels, Belgium, R. J. Lillis, University of California, Berkeley, CA, USA, K. S. Olsen, P.
L. Read, University of Oxford, Oxford, UK, A. C. Vandaele, F. Daerden, L. Neary, S. Robert, Belgian Institute for Space Aeronomy, Brussels, Belgium, S. Aoki, Graduate School of Frontier Sciences, The University of
Tokyo, Kashiwa, Japan, J. M. Battalio, Department of Earth and Planetary Sciences, Yale University, New
Haven, CT, USA, T. Bertrand, LESIA, Observatoire de Paris, Paris, France, C. Gebhardt, B. Guha, National
Space Science and Technology Center, United Arab Emirates University, Al Ain, UAE, R. M. B. Young, Department of Physics and National Space Science and Technology Center, United Arab Emirates University, Al
Ain, UAE, M. Giuranna, F. Oliva, P. Wolkenberg, Istituto di Astrofisica e Planetologia Spaziali
(IAPS/INAF), Rome, Italy, S. J. Greybush, Penn State University, University Park, PA, USA, J. HernándezBernal, A. Sánchez-Lavega, Universidad País Vasco UPV/EHU, Bilbao, Spain, A. Kleinboehl, M. A.
Mischna, L. K. Tamppari, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA,
USA, S. R. Lewis, M. Patel, P. Streeter, The Open University, Milton Keynes, UK, P. Machado, Instituto de
Astrofísica e Ciências do Espaço, OAL, Lisboa, Portugal, F. Montmessin, Laboratoire ATmosphères, Milieux,Observations Spatiales, Paris, Guyancourt, France, H. Nakagawa, Tohoku University, Sendai, Japan, K.
Ogohara, Faculty of Science, Kyoto Sangyo University, Kyoto, Japan, D. Titov, European Space Research and
Technology Centre, Noordwijk, The Netherlands, M. Vincendon, Institut d’Astrophysique Spatiale, Orsay,
France, H. Wang, Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics,
Cambridge, MA, USA.

Introduction:
Past and present orbiters (such as Mars Global
Surveyor, Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, and the ExoMars Trace Gas
Orbiter) have been able to provide a great picture of
Mars’ climate, and good insights into its meteorology. Other missions such as the Mars Atmosphere and
Volatile Evolution (MAVEN) mission, Mars Orbiter
Mission “Mangalyaan”, and Tianwen-1have also
provided sporadic observations of meteorological
phenomena. The Emirates Mars Mission “Hope” has
a specific low-inclination, high-altitude, elliptical
orbit that allows it to observe large portions of the
Martian disk at several local times, hence improving
the monitoring of the evolution of meteorological
phenomena.
However, weather observations by any single
spacecraft are more or less discontinuous and asynchronous. Furthermore, a replacement of the ageing
fleet of current spacecraft must be envisioned within
the current decade, if one wants to continue the multi-annual record of meteorological events without
interruptions.
Now is the right time to shift paradigm in atmospheric science at Mars and focus on weather monitoring, as a precursor to forecasting.

The Case for Weather Monitoring:
The dynamics of meteorological phenomena
such as dust storms and water/CO2 ice clouds are
characterized by rapid temporal variability (subhourly), and multi-scale spatial extension (local,
regional, planetary). As a result, only continuous,
simultaneous, global observations would ideally
allow comprehensive monitoring and understanding
of Martian weather phenomena. In practical terms,
this means carrying out observations at a sub-hourly
cadence for the largest possible portion of the planet
at once. Atmospheric and surface temperatures,
three-dimensional aerosol and water vapour distributions, atmospheric wind, and surface pressure can be
included in a list of recommended variables to be
retrieved from orbit.
Weather monitoring from orbit can provide answers to key, long-standing, scientific questions such
as “How do dust storms evolve into extreme, planetencircling events?” and “How do dust dynamics and
cloud formation vary throughout the diurnal cycle?”
Deep scientific understanding of the onset and evolution of dust storms as well as of the multiscale
weather dynamics is then likely to enable forecasting, which is a strategic requirement for future human exploration missions (see e.g. Goal IV, SubObjective B3, page 64 in the MEPAG “Mars Science Goals, Objectives, Investigations, and Priorities, 2020 Version” document.

Mars weather monitoring is a science objective
that supplements those of current mission. It is also
an “exploration science/reconnaissance” objective,
precursor of future operational weather forecasting
missions in support of human exploration. It is particularly well suited for a satellite constellation to be
launched in the current decade, in parallel with the
Martian Moons eXploration (MMX) and International-Mars Ice Mapper (I-MIM) missions as well as
the Mars Sample Return (MSR) program (it should
be noted that the future of I-MIM is uncertain at the
time of writing, after the recent NASA’s announcement that financial support to the development of
this mission is terminated).
Areostationary Satellite Constellation:
As it happened for the study of meteorology on
Earth in the 1970s, when geostationary satellites
started to be launched in addition to platforms in low
Earth orbit, the study of Martian meteorology could
thrive at the turn of this decade by putting a constellation of satellites with weather-focused payloads in
novel areosynchronous or areostationary orbits, in
addition to platforms in low Mars polar or nearlypolar orbits. An areostationary orbit is circular,
equatorial, Mars-synchronous, at 17,031.5 km altitude. Platforms located in such orbits would be able
to provide an unequalled view of the evolution of
meteorological phenomena in the horizontal dimensions, although limited in the vertical dimension.
The periareion of the “Hope” spacecraft is very close
to the areostationary altitude, and its inclination is
only 25°. This platform, when it orbits near its periapsis, provides the current best example of the type
of weather observations that can be obtained by a
single areostationary satellite.
The Approach for Weather Monitoring:
The MSR program will require a large part of
NASA’s and ESA’s resources devoted to Mars science and exploration in the current decade. The other studied or planned Mars missions (including
JAXA’s Martian Moons eXploration –MMX- and
the currently uncertain I-MIM and ExoMars rover)
could take further resources. A low-cost approach to
weather monitoring is, therefore, appropriate, if not
necessary, in order to launch a satellite constellation
in parallel with these missions.
Bottom-up approach. It is convenient to think
about the minimum configuration and payload for a
weather-monitoring satellite constellation, and build
it up considering constraints (budgetary, programmatic, etc.) and available opportunities. Fig. 1 shows
a possible minimum configuration.

Figure 1: Minimum configuration for a weathermonitoring satellite constellation.

Three satellites in areostationary (or at least areosynchronous) orbits, with nadir-viewing payloads
including at least a visible multi-colour camera (spatial resolution < 5 km) and a thermal infrared multiwavelength imager (spatial resolution < 60 km), are
required as a threshold to monitor the Martian
weather quasi-globally, continuously, and simultaneously, although with limitations in the vertical
dimension. This is a common outcome of a few mission concepts involving areostationary satellites that
have been studied in the past five years in the USA
and Europe [1, 2, 3, 4, and 5]. However, several options for enhancing the scientific return and/or the
applications exist. In terms of payload, the addition
of an ultraviolet camera and a near-infrared imager
would allow extending the wavelength range to respectively refine the retrievals of dust and clouds
and enable the retrieval of surface pressure. In terms
of number of platforms, the addition of a fourth satellite in areostationary orbit would allow introduction of stereo view capabilities, improving the spatial
coverage, and providing redundancy (see Figs. 2, 3).
Further, in terms of science objectives and applications, areostationary satellites are also ideal platforms for space weather monitoring as well as communication/navigation applications, which are currently under study by various space agencies (see [3,
6] for detailed analyses of all benefits and applications of the areostationary orbit).

Figure 2: Mars views from a three-platform areostationary
constellation. Dark grey areas are never observed, light
grey areas are observed at the edge of the field-of-view
(they correspond to emission angles larger than ~70°). The
longitude-latitude grid is 10° x 10°. Views are centred at
120°W, 0°, 120°E for convenience. Colour scale and con-

tours represent topography.

Figure 3: Mars views from a four-platform areostationary
constellation. Views are centred at 180°W, 90°W, 0°, 90°E
for convenience (stable and unstable longitudes are shifted
by ~12°-18° westward, e.g., 17.92°W is a stable longitude).

In terms of synergy with other types of satellite
orbits/payloads, the concurrent presence of limbscanning instruments aboard satellites in low polar
orbit would allow aerosol and water vapour profiling, extension of the vertical range of temperature
information into the middle atmosphere, and coverage of the polar regions, thus achieving global threedimensional, continuous and simultaneous weather
monitoring. If more than one polar orbiter is deployed, for instance at two or three additional longitudinal nodes, vertical profiles at several local times
at once could be obtained [2, 7]. Finally, if a payload
including a sub-mm sounder and/or a Doppler nearinfrared LIDAR is added aboard one of the polar
orbiters, access to wind measurements (either lineof-sight winds or wind components) in the respective ranges of 0-40 km and ~10-100 km altitude becomes possible [8, 9].
Modular approach. The ultimate weathermonitoring constellation does not necessarily need to
be launched all at once. The platforms listed above
can be added and/or replaced over time. Provided
the minimum configuration is in place, for instance,
a fourth areostationary satellite or further polar orbiters could be launched separately. More capable
platforms could replace initial ones.
SmallSat approach. Another way to reduce the
cost of a constellation is to “think light, small, and
simple”. In other words, use low-mass/small-volume
payloads with as much heritage as possible, simplify
the concept of operations, use on-board autonomy
for operations and science, and accept lower reliability of single platforms, possibly compensated by
redundancy in their number. Note that there are
long-term cost savings in autonomous systems, but
there is an up-front cost to their development. Therefore, the use of such systems is compatible with a
low-cost mission only if the mission has not to bear
the cost of the autonomy development, or if there is

a long-term plan.
International collaboration. Given the international nature of MSR (as well as MMX, I-MIM and
ExoMars), it is conceivable and desirable that a
weather-monitoring constellation develop as an international, coordinated endeavour. Even if single
platforms might be low-cost, the cost of the full constellation is likely going to be too high for a single
entity in the current decade. International collaboration allows sharing of the costs and risks, while increasing benefits for all partners (access to Mars,
development of national space exploration programs,
technological and scientific breakthroughs, commercial involvement, public engagement, etc.). The ExoMars mission and the I-MIM concept clearly show
that international collaboration has its own risks, but
a bottom-up, modular, low-cost SmallSat approach
can efficiently reduce them. Multiple, focused
SmallSats are more easily entirely contributed by
small entities, such as ESA member-state space
agencies, other small space agencies, university consortia, commercial entities, etc. This increases the
resilience to possible collaboration break up with
respect to the case of a larger spacecraft requiring
multiple contributions.
Use of available opportunities. Using platforms
and instruments that require only minor or moderate
modifications, and finding rideshare or piggyback
launch opportunities are other ways to reduce the
cost of building up a weather-monitoring constellation at Mars. Last but not least, joining forces with
missions with compatible objectives could open opportunities to put weather-focused payloads in orbit
around Mars. This might be the case for I-MIM,
which is currently planned to be in a low, near-polar
orbit, or for an ESA communication/navigation constellation concept in areosynchronous orbit (MARs
COmmunication and Navigation Infrastructure –
MARCONI- see [3] for the general concept).
About a surface weather station network:
This abstract is focused on Mars weather monitoring from orbit. We recognize the importance of
having a scattered network of weather monitoring
stations on the surface of Mars for carrying out
measurements near the ground and in the boundary
layer. An orbital constellation and a surface network
are complementary and both essential to ultimately
monitor and forecast the weather evolution, as the
Earth example clearly points out.
However, on Earth, the surface network was introduced before the orbital component because we
were already living on the planet, while landing on
Mars is still a big (and costly) challenge compared to
putting a satellite into orbit. Building up an orbital
constellation at Mars could be currently done faster
and at lower cost than a surface network. Therefore,
while looking for ways to reduce the cost of multiple

landing, we should focus on the orbital component
within the current decade.
All landers and rovers that are already planned to
be sent to Mars in the forthcoming future should
carry meteorological instruments to contribute to the
currently available surface network.
References:
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Abstract 2083,
https://www.hou.usra.edu/meetings/lpsc2018/pdf/25
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[4] Montabone, L. et al. (2021), EPSC 2021,
625, https://doi.org/10.5194/epsc2021-625
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2/pdf/5013.pdf
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[9] Tamppari, L. K. et al. (2022), Low-Cost Science Mission Concepts Workshop, Abstract 5020,
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