Transcript Solar System Exploration: Space Science Highlight

Solar System Exploration: Space Science Highlight
Polygonal Plains on Venus Linked
to Global Climate Change
Featuring the Research of
Suzanne E. Smrekar, Pierre Moreels, and Brenda J. Franklin
To be published in the Journal of Geophysical Research: JGR Planets
Characterization and Formation of Polygonal Fractures on Venus
Contact:
[email protected]
Solar System Exploration: Space Science Highlight
Planetary Scientists are exploring Venus today
By examining radar image mapping sent back by
NASA’s Magellan Mission nearly a decade ago…
What can we learn about Earth
by exploring Venus?
Greenhouse effects of global warming
occur on both planets.
Interplay between the atmosphere and lithosphere can
stabilize--or destabilize-- global climate change
over multimillion year time scales…
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Space Science Highlight prepared by Richard Shope
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Solar System Exploration: Space Science Highlight
Solving the Mystery of the Polygons of Venus
What play of forces best explains the magnitude and
uniformity of polygon size at over 200 sites?
Global Climate Change Model Fits Best!
Polygons average ~2 km across.
Are polygons stratigraphic markers?
Solar System Exploration: Space Science Highlight
Did Giants form these polygons on Earth…?
Giant’s Causeway…Ireland
Polygons formed from cooling of volcanic lava flow
Diameter measured in meters
Venus Polygons…
Diameter measured
In thousands of meters
Typically ~2 kilometers
http://www.giantscauseway
officialguide.com
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Solar System Exploration: Space Science Highlight
Venusian Polygons…What titanic forces caused them to form?
Volcanism?
Subsurface Heating?
Global Climate Change?
Evidence:
Uniform size ~ 2km across
Global distribution ~ 200 sites
Fits Global Climate Change Model
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Solar System Exploration: Space Science Highlight
Venusian polygons have average diameter of 1.8 ± 0.9 km
Example of gradation in
size from large to small.
Polygons in this region
range from 6 km near
top to 1 km near bottom.
(Fmap 35S253,
Figure 1 in Smrekar et. al.
JGR-Planets, to be
published.)
Several orders of
magnitude
larger than on
Earth
82 km
Solar System Exploration: Space Science Highlight
SIGNIFICANT RESULTS
Polygonal fractures on Venus indicate Global Climate Change process
Global Distribution of Polygons on Venus
Model validated by new study: Anderson and Smrekar (1999) proposed Global Climate Change
Model as mechanism of formation of polygonal terrain: global warming following by gradual cooling
produces sufficient thermal stresses to produce strains on surface and observed fracture spacing.
Solar System Exploration: Space Science Highlight
Tectonic Effects of Global Climate Change on Venus
S
u
r
f
a
c
e
T
e 900˚K
m
p
e
r 800˚K
a
t
u
r 700˚K
e
Time0
~ 750 Million
years ago
Rapid
Cooling
Causes
Contraction
To depth:
of ~20 km
Volatiles release,
clouds form
H
escapes
H2O
SO2
Climate stabilizes
Clouds reduce
100 Million Years
Reheating
Causes
Expansion
100 Million Years
100 Million Years
Gradual
Cooling
Results in
Additional
Extensions
Solar System Exploration: Space Science Highlight
TALKING POINTS FOLLOW
FROM THIS POINT
Solar System Exploration: Space Science Highlight
Venus Polygons How did they form?
THREE Proposed formation mechanisms
1.
Volcanism: Cooling following lava flow emplacement
•
Why?
– Polygons typically found on surface of slowly cooled lava flows
•
Why NOT?
– To obtain large size, would need to be a lava flow 20 km thick
2.
Lithospheric heating
•
Why?
• Local heating events consistent with lithospheric cooling
•
Why NOT?
•
Inconsistent with variable size and pattern of diminishing size
moving away from center of heating
3. Global Climate Change…
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Solar System Exploration: Space Science Highlight
SIGNIFICANT RESULTS
Features Best Explained by Atmospheric and Surface Interaction
Observations tend to validate global climate change model
Anderson and Smrekar (1999) propose Global Climate Change Model as
mechanism of formation of polygonal terrain: global warming following
by gradual cooling produces sufficient thermal stresses to produce
strains on surface and the observed fracture spacing. Builds on work of
Bullock and Grinspoon (1996, 2001):
1.
Resurfacing event ~750 M years ago triggers volatile outgassing of H2O
and SO2, which form clouds leading to a temperature rise of 90º-200º.
2.
Exospheric escape of H2O and reaction w/surface minerals causes
reduction in cloud cover leading to cooling.
3.
Over time atmospheric albdeo and opacity return to normal and
temperature equilibrates. The whole cycle lasts 300 million years.
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Solar System Exploration: Space Science Highlight
Polygon Plains are found at 204 sites all over Venus
• Nathan Bridges
has mapped
Venusian
geologic regions
• About 50% of
polygons are
near shield
volcanoes
• About 50% of
polygons are in
regions of varied
terrain
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Space Science Highlight prepared by Richard Shope
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Solar System Exploration: Space Science Highlight
Future Mapping May Reveal Polygons as Stratigraphic Markers
Venus appears to have
experienced a period of
high resurfacing rate
consistent with volcanic
outgassing capable of
producing global climate
change--if all polygons
formed in same period,
mapping efforts could
explore whether
polygons are
stratigraphic markers.
Section of Fmap
77N355, with a size of 66
x 53 km.
Locations “a” show
polygons crossing an
apparent flow boundary.
At “b” a younger
volcano covers
preexisting polygons.
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Solar System Exploration: Space Science Highlight
Lower Right
Related Papers
Anderson, F.S. and S.E. Smrekar, Tectonic effects of climate change
on Venus, J. Geophys. Res, 104, 30, 743-30, 756, 1999.
Bullock, M. A., and D.H. Grinspoon, The stability of climate on
Venus, J. Geophys. Res., 101, 7521-7529, 1996.
Bullock, M. A., and D.H. Grinspoon, The recent evolution of climate
on Venus, Icarus, 150, 19-37, 2001.
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