Outer planet atmospheres: seasons on Titan observed by Cassini and
ALMA
Supervisors
Main supervisor: Doctor Nicholas Teanby (University of Bristol)
Project enquiries - Email: [email protected] Contact number: +44 (0) 0117 3315006
Host Institution: University of Bristol
Project description
Titan is Saturn’s largest moon and is the only moon in our Solar System to have a substantial atmosphere composed of nitrogen, methane, and a large array of organic compounds. Titan has many similar atmospheric
processes to Earth, such as clouds, rain, global meridional circulation, and polar vortices. Titan thus provides
the best example of an Earth like planet in the cold outer Solar System and a test case for our understanding of
atmospheric physics under different conditions. By comparing the similarities and differences between Titan
and Earth's atmospheres, we will learn about Titan and also increase our understanding of atmospheres in
general.
This project will study aspects of Titan’s complex atmosphere based on infrared data from the Cassini
spacecraft and the new Atacama Large Millimeter/Submillimeter Array (ALMA). NASA's Cassini-Huygens
mission to the Saturn system has been returning data since orbital insertion in July 2004. During the PhD
Cassini will end its mission in 2017 by plummeting into Saturn's atmosphere and burning up to prevent
potential contamination of Saturn's icy moons. This will leave a unique 13 year dataset with exceptional spatial
and temporal coverage of Titan's atmosphere during almost half a Saturnian year (29.5 years long). Titan
passed northern spring equinox in 2009 and has now entered a time of great atmospheric change, including
destabilisation/reversal of the current atmospheric circulation and formation of a south polar vortex. The project
will focus on data from Cassini’s Composite InfraRed Spectrometer (CIRS), Visual and Infrared Mapping
Spectrometer (VIMS), and Imaging Science Sub-system (ISS). These instruments are sensitive to stratospheric
composition/temperature, tropospheric composition/clouds, and hazes. In addition, ALMA, a new ground based
radio telescope with exceptional spatial and spectral resolution, has recently started to be used for studying
Titan, which will be explored further during the project.
The bulk of the project will be based around analysis of infrared spectra. These spectra will be studied using
radiative transfer calculations, inverse theory, and other remote sensing techniques in order to determine
atmospheric structure and composition. This will involve handling large digital datasets and developing new
analysis algorithms. The derived atmospheric composition could provide the basic input for photochemical
models or could be used to probe atmospheric circulation by using gases as tracers. Comparisons with the
Earth's atmosphere will then be possible.
The successful applicant should have a strong background in physics or the physical sciences, preferably to
MSc/MSci level. A strong interest in planetary science, atmospheres, and numerical analysis techniques is
essential. Familiarity with scientific computing/programming would be an advantage, as the project will
involve significant data analysis. The student will be expected to present results at national and international
conferences and instrument team meetings and publish findings in international journals, which will require
excellent communication and written skills.
Mission Information Links:
http://saturn.jpl.nasa.gov/index.cfm
https://almascience.eso.org
References:
Cordiner, M. A. et al. (2015). "Ethyl cyanide on Titan: spectroscopic detection and mapping using ALMA",
Ap. J. Lett., 800, L14.
de Kok, R., Teanby, N. A. et al. (2014). "HCN ice in Titan’s high-altitude southern polar cloud", Nature, 514,
65-68.
Hanel, R.A., Conrath, B.J., Jennings, D.E., and Samuelson, R.E. (2003). "Exploration of the Solar System by
Infrared Remote Sensing" (2nd Ed.), Cambridge University Press.
Teanby, N.A. et al. (2012). "Active upper-atmosphere chemistry and dynamics from polar circulation reversal
on Titan", Nature, 491, 732-735.
Tobie, G., Teanby, N.A., et al. (2014). "Science goals and mission concept for the future exploration of Titan
and Enceladus", Plan & Space Sci., 104, 59-77.
Figure 1: Cassini images of Titan. (a) Titan's hazy atmosphere contains complex organic
molecules and simpler hydrocarbons and nitriles that can be used to map the circulation. South
polar vortex is visible in the centre of the disc. (b) Reflection of sunlight off Titan's hydrocarbon
seas seen through the murky atmosphere. Image credits NASA/JPL-Caltech/Space Science
Institute.
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