Vision and Voyages for Planetary Science in the - Solar System ...

Future Directions for Investigations and Measurements
To address these key questions a set of investigations achievable in the next decade have been
identified that relate to the atmosphere, upper atmosphere and surface volatiles. These investigations
include detection and mapping possible trace gases and key isotopes, with the highest sensitivity
achievable, as a window into underlying geological and possible biological activity. This will be
addressed by the ESA-NASA Trace Gas Orbiter now under development. Fundamental advances in our
understanding of modern climate would come from a complete determination of the three-dimensional
structure of the martian atmosphere from the surface boundary layer to the exosphere. This should be
performed globally, ideally by combining wind, surface pressure and accurate temperature measurements
from landed and orbital payloads. Surface measurements are required to complement these measurements
and to characterize the boundary layer and monitor accurately the long-term evolution of the atmospheric
mass. On a global scale, a network of at least 16 meteorological stations would be ideal. and carrying
capable a meteorological payload to measure surface pressure, temperature, electrical fields, and winds on
all future landed missions would provide an excellent start to developing such a network. These
investigations should be complemented by systematically monitoring the three-dimensional fields of
water vapor, clouds, and surface frosts. Isotopic signatures of volatiles (such as HDO) should also be
monitored to investigate the signature of ancient reservoirs and study fractionation processes (e.g., clouds
microphysics). Finally, research and analysis should continue to improve the numerical climate modelling
of the key atmospheric processes and to support laboratory research, notably in relation to the properties
of carbon dioxide ice and its behaviour under martian conditions.
Characterize Mars’s Ancient Climate and Climate Processes
Recent analyses of the geomorphology and surface composition of ancient terrains have
confirmed that the early Mars climate system was very different and that the global environment varied
throughout this early period. 41 Reconstructing early martian climates remains a challenge. Whether
liquid water occurred episodically or persisted over geological time scales remains debated. Solar
luminosity was 25 percent lower in early martian history than today, and climate modellers have difficulty
understanding how Mars’s atmosphere greenhouse effect could have allowed sustained liquid water and
precipitation consistent with the geological records, 42 although volcanic greenhouse gases 43 or clouds 44 or
impact-induced warming 45 have been suggested.
Important Questions
Some important questions concerning Mars’s ancient climate and climate processes include the
following:
• What was the nature of the early martian climate? Were the conditions suitable for liquid
water episodic or stable on longer time scales? What processes enabled such conditions?
• How and why did the atmosphere evolve? Which process did and still do control the escape
and the outgassing of the atmosphere?
Future Directions for Investigations and Measurements
Major progress in understanding the ancient martian climate can come from determining the rates
of escape and outgassing of key species from the martian atmosphere, their variability and the processes
at work. It will also be crucial to investigate the physical and chemical record constraining past climates
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