Transcript Venus - Carmenes

The Global Resurfacing of Venus
Marta Lúthien Gutiérrez Albarrán, 2014
Venus:
Topography
Radar mapping (Magellan)
Venus’s atmosphere in UV (Pioneer-12) and
radar mapping (Magellan)
Venus:
Surface features
Global topographic map of Venus (Magellan)
Volcanism
Pancake volcanoes, lava channels and shield plain
Unique surface
features
Arachnoid
Corona
Tectonic activity
Highlands of tesserae terrain and ridge belt
[Computer generated, based on Magellan radar data]
Impact Craters
Sequence of surface units
Resurfacing models: Crater distribution
Turcotte et al. (1998)
Resurfacing models: Mean surface age
Crater frequencies on Venus are
low compared with those on the
surface of the Moon and Mars.
This shows that the surface is
young, perhaps no older than a
mean of 500 Myr (estimates of
the crater production rate predict
ages between 190-800 Myr)
Resurfacing models: Constraints
• The spatial and hypsometric distribution of craters cannot be
distinguished from a random distribution.
• The random crater distribution is independent of size.
• The density of small craters declines with decreasing diameters
due to atmospheric filtering.
• The spectrum of crater modification differs greatly from that of
other planets: 62-84% are pristine, 2.5-4% are embayed by lavas,
aprox. 8.5% are slightly fractured, and only 3.5% (aprox.) are
highly fractured.
• The lava embayed craters are concentrated in zones of recent
volcanism, and the highly fractured craters are associated with the
equatorial rift systems.
[Schaber et al. 1992; Strom et al. 1994]
Resurfacing models: Global vs Regional
• Global resurfacing: Catastrophic burial
associated with instantaneous overturn of
the lithosphere and intense volcanic and
tectonic activity about 300-500 Myr ago
which ended abruptly.
• Regional resurfacing: Progressive burial
of small areas at a time as new volcanic
centers developed. Requires a constant
rate and spatially random distribution of
volcanism. Ultimately, the whole planet
would be resurfaced, albeit over a longer
time period.
Global vs Regional resurfacing: Simulations
Strom et al. 1994
Global vs Regional resurfacing: Simulations
Competing processes of constant rate impact
cratering and volcanism. Initially crater-free
surface.
Resurfacing age uniquely determined by
number of observed surviving and partially
embayed craters.
• Catastrophic, global scenario.
• 950 surviving craters
• 5% partially embayed craters.
• Equilibrium regional scenario.
• 30% partially embayed craters,
substantially greater than
observed. Equilibrium number
significantly less than observed.
Bullock&Grinspoon 1993
Global vs Regional resurfacing: Conclusions
Global resurfacing models are consistent
with:
• The spatially random crater
distribution and its diameter
independence.
• The random hypsometric crater
distribution.
• The very low abundance of embayed
craters and fractured craters.
• The concentration of embayed and
highly fractured craters at zones of
recent volcanism and tectonism.
Objections to regional resurfacing models:
• Simulations result in about 17 times/15%
more embayed craters than observed.
• Simulations result in unobserved
nonrandom crater distributions for
resurfacing areas between 0.03% and
100% of the planet’s surface.
• Models not consistent with the number
and nonrandom distribution of
volcanoes and the nonrandom
distribution of embayed and heavily
fractured craters.
[Bullock&Grinspoon 1993; Strom et al. 1994]
References
•
Basilevsky, A. T. & McGill, G. E. 2013. Surface Evolution of Venus, in Exploring Venus as a Terrestrial
Planet (eds L. W. Esposito, E. R. Stofan and T. E. Cravens), American Geophysical Union, Washington,
D.C.
•
Bullock, M. A., D. H. Grinspoon, & J. W. Head III 1993. Venus resurfacing rates: Constraints provided
by 3-D Monte Carlo simulations, Geophys. Res. Lett., 20(19), 2147–2150.
•
Herrick, Robert R. 1994. Resurfacing history of Venus. Geology, vol. 22, no 8, p. 703-706.
•
Saunders, R. S., Arvidson, R. E., HEAD, J. W., Schaber, G. G., Stofan, E. R., & Solomon, S. C. 1991.
An overview of Venus geology. Science, 252(5003), 249-252.
•
Strom, R. G., G. G. Schaber, & D. D. Dawson 1994. The global resurfacing of Venus, J. Geophys.
Res., 99(E5), 10899–10926.
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http://en.wikipedia.org/wiki/Geology_of_Venus
http://csep10.phys.utk.edu/astr161/lect/venus/surface.html
http://ircamera.as.arizona.edu/NatSci102/NatSci102/text/venusgeol.htm
http://geology.about.com/od/venus/a/aa_venus.htm
http://www.harmonicamundi.org/HGS/atmos_proj/resurfacing.html
http://explanet.info/Chapter07.htm
http://www.geol.umd.edu/~jmerck/geol212/lectures/12.html
http://global.britannica.com/EBchecked/topic/625665/Venus/54191/Interior-structure-and-geologicevolution
http://geology.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn=geology&cdn=education&tm=8923&f=10&tt
=14&bt=8&bts=1&zu=http%3A//www.lpi.usra.edu/publications/slidesets/venus.html
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Thank you!