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Department of Earth and Environmental Science
Douglas J Jerolmack
Research Interests - Sedimentology on MarsResearch
in this area focuses on interpreting past environmental conditions on
Mars (and potentially other planets) by using sedimentary deposits.
Mars has abundant features attesting to the presence of liquid water:
large valleys carved into bedrock, sandy fans deposited in craters, and
now evaporite minerals preserved in rock. It is not known, however,
whether Mars maintained an early climate that was warm enough to
sustain a hydrologic cycle, or whether it was mostly cold and dry with
short bursts of localized warming - caused, for example, by volcanism
or asteroid impacts. Understanding early climate on Mars has important
implications for understanding planetary formation and evolution, and
also for determining whether conditions ever existed that were
favorable to life. Our group has reconstructed past water and wind
conditions on Mars though use of image and topography data, Earth
analogs and quantitative sediment transport models.
Reconstructing formative conditions of a fluvial fan on Mars
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In
recent years, many depositional fans have been discovered on Mars that
formed (presumably) by fluvial processes. The first and most
well-documented was the Eberswalde Crater fan (originally called Holden
Northeast). The ancient channels (more than 4 billion years old!) are
made of more resistant sandstone, such that erosion of the fluvial
surface by wind has removed the intervening finer-grained material and
exposed the channels as topographic highs. Topography measured from the
Mars Orbiter Laser Altimeter (MOLA) allowed determination of the slope
and volume of the fan, while infrared images from Themis were used to
infer grain size and bedrock exposure. We used an analytical model for
the formation of alluvial fans, and fit the model to the observed
Martian fan profile to compute water and sediment discharges that would
have formed the deposit. The result is that such a fan could have
formed in less than 100 years, and therefore does not require that Mars
was warm and wet for long periods of time. Figure: top left shows
Eberswalde Crater with images from the Mars Orbiter Camera (MOC) and
color indicating elevation as measured by MOLA - the red box shows the
location of the fan; bottom left shows MOC image of the fan; bottom
right shows Themis infrared data draped on the MOC image, where color
correlates with exposure of bedrock; top right shows the edge of the
fan, where arrows indicate the edges or river channels.
Collaborators: Maria Zuber (MIT), David Mohrig (UT-Austin), Shane Byrne (USGS-Flagstaff).
Reconstructing wind conditions on the surface of Mars
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The
Mars Exploration Rovers (MER) have collected unprecedented data of the
surface of Mars. Although the principle objective of MER is to search
for evidence of ancient water, wind-blown sediments and their deposits
were everywhere which contain clues about aeolian (wind) activity
today. The rover Opportunity observed coarse-grained ripples on the
Meridiani Plains, and also the remnants of large dunes preserved in
rock. Our team used grain size data, observations from similar
sedimentary features on Earth, and simple models of sediment transport
to estimate the wind speed currently sculpting the landscape at
Meridiani. Images: top shows Opportunity on the Meridiani Plains and a
vast expanse of coarse-grained ripples; middle images show ancient
aeolian dunes preserved in Burns Cliff at Endurance Crater, and a
close-up image of hematite spherules that compose part of the Meridiani
ripples; botom shows a panoramic view of White Sands National Monument,
New Mexico, where ripples similar in size and composition (right) were
studied.
Collaborators: Part of this research was conducted at the
Jet Propulsion Laboratory with the MER team. Close collaborators are
John Grotzinger (Caltech), David Mohrig (UT-Austin), David Fike
(Washington University) and Wes Watters (MIT).
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Department of Earth and Environmental Science
University of Pennsylvania, 254-b Hayden Hall, 240 South 33rd Street
Philadelphia, PA 19104-6316
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