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Last update: January 2018

My specific research experience with Jupiter's clouds---and the gases that form them---also relates to conditions in the early protoplanetary disk and dynamics of giant planet atmospheres. Understanding the diversity among our own planetary atmospheres is key to understanding fresh observations of the staggering number of newly-discovered exoplanets, each unique.

The talks below organize my research into overarching themes in the science of planetary atmospheres. The talks can be geared towards audiences at the levels of Jupiter specialists to the general public.



Time-domain data — distinct from spatial-domain imaging data or from spectral-domain data — provides a whole new approach for making discoveries about how the atmospheres of the outer planets function. Key areas of study are heat transport, atmospheric structure and evolution, composition, the formation of clouds and hazes, impact processes, and impactor populations. My talks focus on several recent time-variable phenomena and investigations:

  • In 2014, we started the Outer Planet Atmospheres Legacy (OPAL) program with Hubble. Once a year, this program images each of our four outer planets, producing a pair of global maps. Using OPAL data, we have discovered new waves and vortices, and studied the evolution of climate and weather systems in Jupiter, Uranus, and Neptune. Saturn data are planned for 2018, now that the Cassini mission is over.
  • The first OPAL Neptune data revealed a new dark vortex. The dark spot has been tracked by Hubble as it drifted slowly toward the south pole. By late 2017 the spot, which we call SDS-2015, had almost faded from view.
  • After the color change of Oval BA, discovered by collaborator and amateur astronomer Chris Go in the Philippines, we used data from Hubble, Cassini, and Keck to make several discoveries about vortices on Jupiter.
  • The Shoemaker-Levy 9 (SL-9) collision with Jupiter in 1994 was unique in that the impacts were predicted well in advance. But three impact events discovered in 2009 and 2010 were discovered live, or within one Jupiter rotation after the impact had taken place. In both 1994 and 2009, the Hubble Space Telescope had just been refitted with new cameras, and Hubble data played a major role in showing how the impact debris in Jupiter's atmosphere evolved over time.
  • In 2008, while helping ESO's Very Large Telescope team to test its multi-conjugate adaptive optics system on a solar system target, we discovered that Jupiter's haze belt at the equator had shifted. We are conducting studies to determine whether the shifted haze is a mist of fine cloud particles lofted up from below, or a frozen smog produced by solar UV rays.



This talk is structured around the exploration of several intimately related questions concerning water and other volatiles in giant planets:
  • Can we use giant planet volatile abundances to constrain how the planets formed, and also characterize the icy planetesimals that contributed to their formation?
  • What is the cloud structure in the giant planets?
  • What did the Galileo Probe Mass Spectrometer find out about water on Jupiter?
  • Have remote sensing efforts measured water in the giant planets? Will remote sensing succeed in the future?
  • Can the abundances of other volatiles indirectly tell us about water?
  • How do volatile abundances compare among the giant planets?
  • What do the densities of giant planet moons tell us about their origins?



Three different gases condense in Jupiter's troposphere, resulting in a complex vertical distribution of clouds. Water forms the deepest of these clouds, but water clouds are usually obscured by overlying cloud layers. The layer above, probably composed of ammonium hydrosulfide, results when highly toxic ammonia and hydrogen sulfide gases react to form a solid. The chemistry of this strange cloud layer is poorly understood, partly because of the hazards of working with these gases in the laboratory.

Ammonia condenses as the highest cloud layer in Jupiter's cold upper troposphere, yet the distinct spectral signatures of ammonia ice are surprisingly uncommon. Small ammonia cloud particles may be wafted upward to contribute to the thin haze that blankets the planet above the clouds. Since cloud heights, cloud thicknesses, and ammonia gas concentration are variable on Jupiter, we use them to trace dynamic processes in the atmosphere.

The elements N and S (and probably O) in Jupiter's cloud-forming gases are about four times more enriched (with respect to hydrogen) than in a protosolar composition gas. Carbon and noble gases are also enriched. It is generally believed that these elements were enriched when Jupiter accumulated icy planetesimals during its formation, but planetesimals with the necessary abundance ratios have never been observed. The origin of these planetesimals (and therefore Jupiter itself) is still a mystery.