Christopher Parkinson: Research Interests
Many environmental processes contribute to the reflected stellar and emitted thermal
spectrum of an extrasolar terrestrial planet, viz., atmospheric radiative transfer, climate,
chemical, geological, exogenic, and biological processes. Given a series of initial
conditions, algorithms can be utilised in a forward time stepping approach to march the
environment toward a plausible equilibrium state which then outputs a final spectrum of
the planet that can be compared with data collected by an instrument such as the
proposed Terrestrial Planet Finder (TPF). Recent advances in modelling and
measurement of climate systems have made understanding the complex behavior
associated with linkages between these processes, considered isolated in the past, an
attainable goal. In my capacity as an astrobiologist with the JPL VPL group, I have been
working on a methodology by which such a synergy can occur. My research group will
work in conjunction with the VPL to apply a hierarchy of models and modern analysis
techniques to investigate the dynamics of biospheres with the ultimate goal of using these
tools to address the problem of planetary habitability and life detection. Each of the core
modules of the VPL requires a high level of sophistication in the individual algorithms
employed, and hence, over the next several years, I am particularly interested in
expanding upon the work I have done with the VPL to solve some specific problems
germane to astrobiology as detailed below. In pursuit of these research topics, I will use
complex numerical models and the research will be guided by and validated with an
increasingly comprehensive range of observations from solar system terrestrial planets.
Part of the focus of my research group will be to continue to integrate, improve and test
existing models, and develop new model components.
Climate Modelling:
A simple climate model is being developed to simulate the thermal structures of
extrasolar terrestrial planetary surfaces and atmospheres. This model employs a 1dimensional radiative convective equilibrium (RCE) model (c.f. Crisp, 1986; 1989) to
simulate the globally-averaged, vertical temperature profile of the atmosphere. This RCE
model is currently being updated to increase its reliability and range of validity. Once
these upgrades are complete, the RCE will be combined with a simple energy balance
climate model (EBCM) to simulate the east-west and pole to equator transport of heat and
moisture, and the pole-to-pole variations in the climate of an extrasolar terrestrial planet.
The RCE model uses explicit time-stepping to solve the thermodynamic energy equation
for a vertically-inhomogeneous planetary atmosphere as an initial value problem. Once
these RCE model upgrades have been completed and validated, we will use this model to
derive the global-averaged net radiative/convective/conducive fluxes, heating rates, and
thermal equilibrium temperatures for a variety of plausible planetary environments.
Christopher Parkinson: Research Interests
The EBCM will then use baroclinic adjustment (c.f. Stone 1978; Stone and Nemet, 1996)
at tropospheric levels and linear diffusion (c.f. North et al. 1981) at higher altitudes to
distribute heat between the soundings. For a specific run, the model is initialized from an
assumed initial state and marched to equilibrium using a simple, explicit forward time
stepping process. This approach has been widely used for studies of the Earth s present
climate, the paleoclimate, and the atmospheres of other planets and I am very interested
in continuing a more detailed study of these problems with Dr. David Crisp and Dr.
Giovanna Tinetti using these tools.
Abiotic Planetary Modelling The Upper and Lower Boundary Condition on the
Atmosphere:
Progress has been made on a number of fronts toward establishing boundary conditions
for planetary atmospheres in the VPL. Of great interest in astrobiology generally and the
VPL is the treatment of hydrodynamic loss processes of chemical constituents from the
upper planetary boundary layer. Although planetary hydrodynamic escape models have
been created in the past (Watson et al., 1981; Kasting and Pollack, 1983; Chassefiere,
1996), the problems were solved by integrating the coupled, time independent mass,
momentum, and energy equations for the escaping gas from the homopause out to
infinity. Solving the one-dimensional, steady state approximation becomes problematic
at the distance where the outflow becomes supersonic. A new technique has been
developed for the treatment of hydrodynamic loss processes from planetary atmospheres
by Parkinson et al. (in preparation) utilising the Godunov method. A detailed description
of a first order Godunov scheme is given by Godunov (1959), Gombosi (1984), and
Leveque (2002). This method overcomes the instabilities inherent in modeling transonic
conditions by solving the coupled, time dependent mass, momentum, and energy
equations, instead of integrating time independent equations. A preliminary model of
hydrodynamic escape has been validated against simple, idealised cases (viz., steady state
and isothermal conditions) showing that a robust solution obtains and then compare to
existing cases in the literature as cited above. I have a strong interest in developing these
general tools in order to apply them to various problems such as the evolution of the early
Earth, Venus, and Martian upper atmospheres (with the view to understanding extrasolar
terrestrial planetary evolution), as well as studying close-in extrasolar gas giant planetary
atmospheres, in close collaboration with Prof. Yung and Richardson at Caltech and Prof.
Kasting at the Penn State Astrobiology Research Center (PSARC).
General geochemical (Yang, Holland and Rye 2002) and Fe isotopic studies of an older
paleosol (2.75 Ga) has provided further understanding of elemental cycling on ancient
Earth. These studies provide empirical constraints for validation runs of the VPL against
Archean Earth. A reactive transport modeling study of a 2.2-2.4 billion year old (Ga)
paleosol has yielded insights into the composition of Earth's atmosphere at that time and
The paleosol modeling study is the first of a series of process driven kinetic models that
will serve to characterize the interactions between atmospheres and planetary surfaces,
and the tools developed in this highly specific model are highly transferable to more
generalized models that are yet to come. I aim to continue working with colleagues to
Christopher Parkinson: Research Interests
develop such lower atmospheric couplings to make the modelling of lower boundary
conditions of the atmosphere more robust.
Christopher Parkinson: Research Interests
Chemistry Models for Extrasolar Planets:
A coupled photochemical-climate model for Earth-like planets, which is an end-to-end
test case for the larger VPL atmosphere model, and chemistry models for extrasolar giant
planets is being developed.
The Photochemical-Climate Model for Earth-Like Planets: This model (J. Kasting) has
been used to model chemically and radiatively self-consistent atmospheres for Earth-like
planets around other stars. Experiments were run (Kasting, Krelove, Segura) for an
"Earth" with oxygen levels from the present atmospheric level (PAL), down to
1/100,000th PAL. This time-stepping model was also run to equilibrium to derive
atmospheres for the planets around F2V, G2V and K2V stars, and to understand
atmospheric conditions during the Earth's Proterozoic period. It was found that as
atmospheric oxygen is removed, the ozone layer descends, and the stratospheric
temperature bulge is reduced (via reduced heating from solar UV absorption by ozone).
However, the ozone column remains appreciable down to 0.01 PAL of oxygen. They
also modelled Earth-like planets orbiting K2V and F2V stars. I would like to conduct an
model validation study comparing their model with the Caltech/JPL KINETICS model
used by the VPL and continue this research and work on similar important problems in
collaboration with Prof. Kasting’s team at PSARC.
Extrasolar Giant Planet Chemistry Models: A 1-D chemical model for close-in
extrasolar giant planets (CEGPs) has been developed (Liang et at., 2003). These planets
are extremely close to their parent stars and experience high temperatures and UV fluxes,
which modify the chemical reactions normally seen in Solar System Jovian planets. For
CEGPs, the formation of hydrocarbons, oxygen chemistry, and hydrodynamical loss are
significantly enhanced due to their environment. Because of enhanced photolysis of
higher order hydrocarbon species, our model is based only on H2, CO, H2O and CH4.
Our two main results are that (a) H is produced largely in the atmosphere through the
reactions of OH radicals, and H2 is not sensitive to the exact abundance of CO, H2O,
and CH4 and (b) H2O acts as a catalyst and can be produced via the reactions of CO and
H2. The modifications to the chemical model to incorporate new chemistry, database
modeling, and to couple it to a hydrodynamic escape code, are directly applicable to
modifications required for the VPL terrestrial planet models and their validation and I am
very interested in continuing this research.