Dr. Griffith investigates the chemical, dynamical and thermal structures of planetary atmospheres, using ground-based and spacecraft observations. The data are interpreted with radiative transfer calculations to measure the temperature, composition and dynamical signatures of planetary atmospheres. These results are analyzed with simple chemical, radiative and dynamical models to address questions on atmospheric structure and evolution.
Currently Dr. Griffith is up to her elbows in the analysis of data from the Cassini spacecraft. She is particularly intrigued by Titan, Saturn’s largest moon, which she regards as a deranged version of Earth. On Titan methane acts like water and can exist as a gas in the atmosphere, or as liquid and ice, in rain, snow and lakes. Cassini images of Titan show features near the equator indicative of methane rivers and ancient shorelines reminiscent of Earth, thus suggesting wetter times underneath a cloudless sky. Titan’s methane clouds are found only near the south pole, and, in a narrow band lined up at -40 latitude, like a string of beads. This weather forecast contrasts Earth’s, where with the exception of a few deserts an umbrella may come in handy at any time and season. It is not entirely clear how Titan’s weather works and what created the dry shore lines and extensive rivers that the Cassini Huygens mission witnesses under Titan’s largely clear skies. Dr. Griffith’s present work aims to characterize the clouds, circulation, surface humidity and the stability of the atmosphere to understand the moon’s exotic weather.
Additional efforts aim to quantify the mass and location of organic material that precipitates to the surface from the stratosphere. Surface sediments are produced from byproducts of the photolysis of methane, which depletes the methane inventory fast enough to obliterate the atmospheric supply in 10 million years. The sediments are thus vestiges of the past presence of methane in Titan’s atmosphere. The present lack of oceans or apparent surface liquids suggests that methane is supplied by recent cryo-volcanism. But it is still not clear how long Titan has had methane in its atmosphere. Surface sediments are observed in the form of extensive dunes. Yet, instead of dune-forming particulates, we expected the 80% of the surface sediments to be liquid ethane, the main product of methane photolysis. Recent work by Dr. Griffith suggests that ethane precipitates only in Titan's polar regions. Thus perhaps lack of lakes in Titan's well-imaged tropics occurs because ethane instead accumulates at the poles as lakes or ice caps depending on the polar surface temperatures.
Dr. Griffith has also investigated the atmospheres of Jupiter, Saturn and their cousins, brown dwarfs.
Former Spacecraft Involvement
Current PTYS Graduate Students
- Robert Zellem, 2015 (Ph.D. PTYS)
- Johanna Teske, 2014 (Ph.D. Astronomy)
- Paulo Penteado, 2009 (Ph.D. PTYS)
Complete publications list available from: NASA ADS Author search: Caitlin A. Griffith
Refereed publications (NASA ADS): Calendar Year 2016 through July 2018
Pearson, K. A., Palafox, L., Griffith, C. A. Searching for exoplanets using artificial intelligence 2018MNRAS.474..478P
Chapman, J. W., Zellem, R. T., Line, M. R., Vasisht, G., Bryden, G., Willacy, K., Iyer, A. R., Bean, J., Cowan, N. B., Fortney, J. J., Griffith, C. A., Kataria, T., Kempton, E. M.-R., Kreidberg, L., Moses, J. I., Stevenson, K. B., Swain, M. R. Quantifying the Impact of Spectral Coverage on the Retrieval of Molecular Abundances from Exoplanet Transmission Spectra 2017PASP..129j4402C
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