Transcript Yung_Parkinson_PSseminar04 - Division of Geological and

Chemical Evolution in the Saturnian System
Yuk L. Yung
C. D. Parkinson
Division of Geological and Planetary Sciences
California Institute of Technology
1/4/2005
Miller/Urey Experiment
By the 1950s, scientists were in hot pursuit of the origin of life. Around the world, the scientific
community was examining what kind of environment would be needed to allow life to begin.
In 1953, Stanley L. Miller and Harold C. Urey, working at the University of Chicago, conducted an
experiment which would change the approach of scientific investigation into the origin of life.
Miller took molecules which were believed to represent the major components of the early Earth's
atmosphere and put them into a closed system
Purines
Pyrimidines
Sugars
Fatty acids
Amino acids
Nucleotides
Lipids
(Membranes)
Proteins
(Catalysts)
Nucleic acids
(Information)
The chiral Molecules of Life
C4H2 + H + M  C4H3 + M
C4H3 + H  2C2H2
QuickTime™ and a
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+
Barrier ~
3.9 kcal
mol-1
Barrier ~
5.0 kcal
mol-1
ΔHrxn ~
-1.6 kcal
mol-1
+
FUSC4_titan_revA_gxz100_vims
3.0
H Ly
Solar reflection X 1/3
NI_1200 x 10
N2_LBH_1380 X 40
Counts s-1 cm-2
2.5
2.0
1.5
1.0
0.5
0.0
-2
-1
0
RT
1
2
Atmospheric Densities
N2 density from mass 28 peak
1500
Fit of the N2 and CH4 INMS densities as analyzed by Roger Yelle
Fit of the N2 and CH4 INMS densities inferred from detectors C1 and C2
1500
ingress data
egress data
best fit densities
Vervack ingress
Vervack egress
1400
1300
ingress data
egress data
best fit densities
Vervack ingress
Vervack egress
1400
errln(N2)=4.977%
errN2=20%
errln(CH4)=1.3845%
1300
errln(CH4)=1.6233%
Altitude (km)
altitude (km)
N2 density from mass 14 peak
1200
1100
1200
1100
N2
N2
1000
1000
CH4
900
7
10
8
9
10
10
density (cm-3)
10
10
11
10
900
CH4
7
10
8
10
9
10
Density (cm-3)
10
10
11
10
INMS Hydrocarbons 1200 km
(preliminary)
•
•
•
•
•
•
•
C2H2 (acetylene)
C2H6 (ethane)
C3H4 (propyne)
C3H8 (propane)
C4H2 (diacetylene)
C2N2 (cyanogen)
C6H6 (benzene)
?
~5000 ppm
~300 ppm
~100 ppm
~30 ppm
(10 ppm)
?
(10 ppm)
?
(10 ppm)
• Nitrogen
Isotopic ratios
– INMS from N2: 14N/15N = 182 (+74, -41)
– Gurwell submillimeter (HCN) = 94+/-13 (T
dependent)
– Jupiter:430 (Owen et al., 2001), HB:320,Terrestrial:272
– HCN enriched relative to N2 in ISM Terzieva&Herbst, 2000
• Carbon
– INMS from CH4: 12C/13C = 93 +/- 1
– ISO(HCN) = 89 +/- 9
– Gurwell submillimeter (HCN) = 130+/-29
– Terrestrial:89
• No evidence of 36Ar ==>less than 10-4
Hydrodynamic Escape from
Planetary Atmospheres
•In Jean’s escape, particles at the
exobase moving in the outward
direction with sufficient velocity (i.e.
high enough kinetic energy) can
escape from the planet…typically the
vertical flow from the atmosphere is
small
•HDE arises when the flow speed
becomes large
•HDE also differs from gas-kinetic
evaporation in that in some
circumstances a substantial fraction of
the entire thermospheric energy budget
is used to power escape of gas from the
atmosphere; it is possible that heavier
species can be “dragged” along during
HDE
•Under this circumstance, it is expected
that atmospheric expansion due to HDE
will be the dominant loss process
•HDE is an important process in atmospheric
evolution of the terrestrial planets and CEGPs
and can change the composition of planetary
atmospheres from primordial values
irreversibly
•hydrogen escape is of particular importance as
it affects the oxidation state of the atmosphere
and because it results in the loss of water
vapour
For Instance…(outstanding problems)
•Did early Venus initially have an ocean?
HDE modelling using a water-rich
atmosphere on Venus can help assess this
problem (Kasting and Pollack, 1983)
•Isotopic ratios (i.e. fractionation: D/H, N,
and noble gases) are very different on
terrestrial planets even though they are
believed to be formed from similar material
(Hunten et al., 1987; Pepin, 1991)
and…
•Greenhouse warming by methane in
the atmosphere of the early Earth?
CH4 density on early Earth dependent
on HDE, strongly influencing its
atmospheric climate and composition,
i.e. (Pavlov et al., 2000; 2001)
•“blow-off” on HD209458b (Osiris)
(Vidal-Madjar et al., 2003; 2004)
Hydrodynamic Escape
By Vidal-Madjar, A.
HD Escape Equations
Some Previous Models
•Watson et al. (1981): shooting method or
trial-and-error method to solve steady state
HDE equation for early Earth and Venus
•Set of solutions at the critical point (exobase)
selected which can match the zero temperature
at infinity and set temperature at the lower
boundary.
•Calculated temperature and density at the
boundary very sensitive to initial settings and I
couldn’t reproduce cases using that method
•Kasting and Pollack (1983) numerically solve
the steady state HDE problem for Venus
•Use an iterative method in which the momentum
and energy equations are simultaneously solved
•Not able to get an exact sol’n at the critical point
obtaining the supersonic solution
•Instead, they obtained subsonic solutions and
argued that the escape flux can be close to the
critical escape flux
•Method included infrared cooling by H2O and
CO2 while only EUV absorption considered by
Watson
•Chassefiere (1996) solves steady state HDE
problem from lower boundary to exobase level
•Position of exobase level is determined when the
mean free path becomes greater than the scale
height
•Outgoing flow at exobase is set to be equivalent
to a modified Jean’s escape (ionization and
interaction between escaping particles and solar
wind considered)
•Application to water-rich early Cytherian
atmosphere
•Using the equations 1, 2, and 3 with
B.C.’s etc, the HD equations can be
solved using 1st order LaxFriedriechs scheme, Godunov
method, or Finite Difference method
since these are linear advection
equations (hyperbolic)
•We use WENO (weighted essentially
non-oscillatory) finite difference
scheme with AMR (adaptive mesh
refinement)
Open Source Ions over Ring
Plane