This research proposal aims to study the solubility of noble gases like helium, argon, and krypton under the conditions of Titan, Saturn's largest moon, using molecular dynamics simulations. Titan shares similarities with prebiotic Earth but its atmosphere and surface chemistry are not fully understood due to discrepancies in data from previous missions. The researchers hope to provide accurate solubility data through simulations to help constrain Titan's noble gas budget and assist in determining its origin and evolution.

1. SRC 2014 Research Proposal
Solubility of Noble Gases Under Titan Conditions
Mentor: The Miller Lab, California Institute of Technology
Research Participants: Alice Schmitt, Eric Liu
The study of Solar System bodies serves to provide insights and clues to understanding our past. As the
prebiotic (pre-life) version of our planet no longer exists, we must look towards other planetary bodies, such as Titan
(Saturn’s moon), in order to observe processes and phenomena no longer available on Earth. Although Titan is less
than half the diameter of Earth and nearly 10 times farther from the Sun,
it is the only body other than Earth in the Solar System with a dense
atmosphere as well as the only moon with liquid bodies on its surface.3
Furthermore, Titan’s atmosphere consists of dinitrogen gas and
hydrocarbons, primarily methane and ethane.1
Titan, is the second largest
natural satellite (moon) in our solar system and the only one with a
substantial atmosphere featuring complex organic processes.2
Titan’s
atmospheric water is almost completely frozen since its equatorial
surface temperature is 93.7K, so methane may play the role on Titan that
water does on earth, forming clouds, rainfall and lakes.2
In spite of the
much lower temperature in the Saturn system, Titan holds remarkable
similarities to prebiotic Earth as its atmosphere and surface contain
complex organic chemicals in the form of gas, aerosol, and liquid phases.
Also, the processes on its surface point to the possibility of an internal water ocean.1
Further attempts to study Titan, however, are hindered by the lack of a dedicated mission after the Huygens
lander. Additionally, much of the information gathered on the Cassini-Huygens mission varies from previously
projected results.3
Many gases that were thought to be on Titan were discovered to be present in quantities that were
much smaller than previously thought.4
It appears the scaled amount of Argon-36 is much lower than anticipated,
and is nearly 250 times smaller than that of Earth’s.4
Missing gases are speculated to be trapped in the crust of
Titan; dissolution in hydrocarbon lakes and confinement in clathrate hydrate crystals are possible causes.2
Knowing
the solubilities of these gases is vital to constraining the overall noble gas budget of Titan, allowing the effective
employment of modern dating methods based on noble gas isotopic compositions.4
In the past years, teams have investigated free energies of solvation for different substances in methane and
ethane. Our goal is to provide accurate solubility data specifically for noble gases such as helium, argon, and
krypton. We will utilize the NAMD Scalable Molecular Dynamics
software5
in conjunction with the Visual Molecular Dynamics
(VMD) package6
in order to create data points and analyze them.
Molecular dynamics simulations can provide accurate projections
on the behavior of molecules under various conditions and are
more feasible alternatives to direct exploration, because it is not
financially plausible to send more probes to the Saturn system at
this time. The data points provided by the simulations can be
utilized to provide projections of dissolved noble gas
concentrations, constraining the overall budget of such gases on
Titan. Furthermore, the data can be used to assist researchers in
determining the origin and evolution of Titan through methods
such as K-Ar dating.
Under the mentorship of the Miller Lab in Summer Research Connection 2014, we hope not only to
address the data discrepancies between projected and experimental studies, but also to familiarize ourselves with
molecular dynamics simulations and analyze and interpret the resulting data.
1
F. Raulin, C. Brasse, O. Poch, P. Coll. Prebiotic-like chemistry on Titan, Chem. Soc. Rev., 2012, 41, 5380-5393
2
J. Lunine, S. Atreya. The methane cycle on Titan, Nature Geoscience, 2008, 1, 159-164
3
Facts About Titan, ESA, <http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Facts_about_Titan>esa.int., July
8, 2014
4
R. Hodyss, M. Choukroun, C. Sotin, P. Beauchamp. The Solubility of Ar and Kr in liquid hydrocarbons: Implications for
Titan’s geological evolution, Geophysical Research Letters, 2013, 40, 2935-2940
5
Kale, L., et al. ; Skeel, R.; Bhandarkar, M.; Brunner, R.; Gursoy, A; Krawetz, N.; Phillips, J.; Shinozaki, A.; Varadarajan, K.;
Schulten, K.; J Comp Phys 1999, 151, 283.
6
Humphrey, W.; Dalke, A.; Schulten, K. J Mol Graphics 1996, 14, 33.
Figure 1: Artist’s conception of the Huygens Lander
on Titan.2
Figure 2: VMD generated image of an argon atom within
methane molecules.