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| Titel |
Constraints from chaotic terrains on the surface temperature of Mars during the Hesperian |
| VerfasserIn |
Sandra Schumacher, Tanja Zegers |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034182
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| Zusammenfassung |
| Introduction: The surface temperature of a planet is an indicator of a planet’s ability to host
life as temperatures well below the freezing point make it difficult for life to develop at or
close to the surface. However, it is no easy task to constrain the surface temperatures of a
planet in the past. For Mars, different studies yield different results as e.g. [1] argue that
surface temperatures on Mars were high enough to allow for liquid water on the surface
during the Hesperian evidencent by the observed drainage patterns in the northern Valles
Marineris region. On the other hand, [2] have analyzed Argon release in Martian meteorites
and conclude that the surface temperatures were well below the freezing point during
the Hesperian. One possible explanation for this apparent contradiction are the
different time scales considered. While for drainage patterns to develop a time span on
the order of ten thousand years is sufficient, the analysis of the meteorites only
constraints the long term surface temperatures in the order of one million years and
upward.
Here we present another way to constrain the long-term surface temperature of Mars
during the Hesperian. Geological analysis of chaotic terrain in Aram Chaos indicates that it
might have formed as the result of a buried ice layer which subsequently melted [3]. As the
melting process depends on the temperature distribution within the subsurface, it also enables
us to constrain the surface temperature which is one boundary condition of the
system.
Model: To derive the surface temperature we use the geometry and scenario for Aram
Chaos as proposed in [3]: The chaotic terrain is situated in a crater partially filled with an ice
layer, covered by an overburden of rock units (sediments). Due to the insulating effect of the
sediment, the ice layer will melt under certain conditions. This may eventually (after maybe
hundreds of millions of years) lead to the collapse of the overburden, associated with a
catastrophic outburst, creating the chaotic terrain. The conditions under which melting takes
place in this scenario are calculated in our numerical model (Figure 1). In this model the
thickness of the sediment cover, the thickness of the initial ice layer, the surface
heat flux, the thermal conductivity of the sediment and the surface temperature are
varied. Geologic analysis of the crater [3] has yielded a possible thickness of the
water layer before the outburst in the range of 700 m to 1500 m. Therefore, we try
to identify the parameter combinations which result in a melt layer of equivalent
thickness.
Results: The results indicate that surface temperatures had to be well below the freezing
point for a prolonged period of time as already surface temperatures of more than - 15Ë C
result in an unrealistic amount of melting for Aram Chaos. However, this finding
does not exclude short periods of higher temperatures as the temperature wave
in such cases does not penetrate deep enough to influence the melting of the ice
significantly.
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References: [1] Mangold N. et al. (2007), JGR 113, E08009, [2] Shuster D.L. and Weiss
B.P., (2005), Science 309, 594-597, [3] Zegers T. et al. (2009), ESLAB 40th, 2009 |
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