Download Venus Isotopes

Evolution/Alteration of Venus
Isotope Ratios in the Venusian Atmosphere
(A Wish List…)
The Many Morphings of Venus
•
The terrestrial planets likely formed in similar conditions, yet today they
look very different.
•
The evolution of Venus must have been very different than that of Earth:
- No global magnetic field (but likely in the past)
- No plate tectonics (also likely in the past)
- Enormous surface pressure and temperature (94 bar, 700K)
- Atmosphere almost entirely CO2
- Incredibly dry atmosphere (water content 1000x below Earth)
•
One way to understand this evolution is through studying isotopes..
Isotopes as a Tracer of Evolution
McKeegan et al. (2011)
Isotopes as a Tracer of Evolution
δ H218O(‰)
Lee et al. (2005)
Cias et al. (1995)
D/H - Did Venus Have an Ocean?
•
D/H ratio is a tracer of planetary water loss.
H
—Out to Space—
D
H 2O
HDO
O
•
—Down into Crust(?)—
O
Venus’ atmospheric D/H ratio is very high (~250x Earth)
-
At one point, Venus was wet. But how wet?
Owen, Tobias, et al. (2001)
D/H - Did Venus Have an Ocean?
•
To find out how much water was present, you need:
-
Current D/H Ratio
-
Primordial D/H Ratio
•
-
Fractionation factor
•
-
Same as Earth? Same as Comets?
Relative efficiency of H and D loss
Current Absolute Abundance
•
H2O and H2 are fairly well measured
Current calculations give a global
ocean depth of 5-500 meters.
Owen, Tobias, et al. (2001)
D/H - Did Venus Have an Ocean?
•
To find out how much water was present, you need:
-
Current D/H Ratio
-
Primordial D/H Ratio
•
-
Fractionation factor
•
-
Same as Earth? Same as Comets?
Relative efficiency of H and D loss
Current Absolute Abundance
•
H2O and H2 are fairly well measured
Current calculations give a global
ocean depth of 5-500 meters.
Owen, Tobias, et al. (2001)
Atmospheric Escape - Nitrogen
Owen, Tobias, et al. (2001)
Atmospheric Escape - Nitrogen
Stronger escape on
Mars due to low gravity
Owen, Tobias, et al. (2001)
Atmospheric Escape - Nitrogen
Stronger escape on
Mars due to low gravity
Jupiter system formed
from a different source
Owen, Tobias, et al. (2001)
Atmospheric Escape - Nitrogen
Stronger escape on
Mars due to low gravity
What about Venus?
Jupiter system formed
from a different source
Owen, Tobias, et al. (2001)
Atmospheric Replenishment - Ar and Ne
•
The strength of degassing processes is a clue to geologic activity.
•
Argon
- 40Ar is produced radiogenically from 40K, while 36Ar is primordial.
Turcotte and
Schubert (1988)
- Low 40Ar/36Ar indicates low level of current outgassing.
Less active geology.
•
Helium
- 4He produced radiogenically, 3He primordial.
- Currently no accurate measurements of He isotopes.
Current Geological Processes
•
33S/32S
and 34S/32S are good tracers of volcanic processes.
•
Isotope ratios are largely determined
in planetary interiors and volcanism.
•
They therefore are a clue to the
current state of geologic activity.
•
Deviations from the average level
inform you of both surface chemistry and the atmospheric sulfur cycle
δ
34S(‰)
Measurements at ~1% accuracy are needed to provide useful constraints on atmospheric chemistry
Thode, H.G. (1991)
Questions?
References
•
Baines, Kevin H., et al. "Experiencing Venus: Clues to the Origin, Evolution, and Chemistry of Terrestrial Planets
Via In‐Situ Exploration of Our Sister World." Exploring Venus as a Terrestrial Planet (2007): 171-189.
•
Baines, Kevin H., et al. "The Atmospheres of the Terrestrial Planets: Clues to the Origins and Early Evolution of
Venus, Earth, and Mars." Comparative Climatology of Terrestrial Planets 137 (2014).
•
Ciais, P., et al. "A large northern hemisphere terrestrial CO2 sink indicated by the 13C/12C ratio of atmospheric
CO2." SCIENCE-NEW YORK THEN WASHINGTON- (1995): 1098-1098.
•
Donahue, T. M., and C. T. Russell. "The Venus atmosphere and ionosphere and their interaction with the solar
wind: An overview." Venus II (1997): 3-31.
•
Farquhar, James, and Boswell A. Wing. "Multiple sulfur isotopes and the evolution of the atmosphere." Earth and
Planetary Science Letters 213.1 (2003): 1-13.
•
Fedorova, A., et al. "HDO and H2O vertical distributions and isotopic ratio in the Venus mesosphere by Solar
Occultation at Infrared spectrometer on board Venus Express." Journal of Geophysical Research: Planets (1991–
2012) 113.E5 (2008).
•
Owen, Tobias, et al. "Protosolar nitrogen." The Astrophysical Journal Letters 553.1 (2001): L77.
•
Thode, H. G. Sulphur isotopes in nature and the environment: an overview. Wiley, 1991.
•
Turcotte, D. L., and G. Schubert. "Tectonic implications of radiogenic noble gases in planetary atmospheres."
Icarus 74.1 (1988): 36-46.