1994: Investigation of Stratospheric Aerosols in the Atmosphere of Jupiter

As early as the 1930s investigators were beginning to determine the chemical composition of the atmosphere of Jupiter through the analysis of reflected solar spectra. These ground-based telescopic observations identified gaseous methane and ammonia as components of the Jovian atmosphere. The Pioneer and Voyager missions confirmed the earlier ground-based measurements and provided additional support for the hypothesis that the atmosphere of Jupiter was similar in composition to the Sun. Analysis of the Pioneer and Voyager data also provided detailed information on the thermal structure of the Jovian atmosphere. Nevertheless, while these spacecraft missions to Jupiter have greatly increased our understanding of the Jovian atmosphere, a number of questions remained unanswered.

Both spacecraft and ground-based data indicate that clouds and aerosols are present in the atmosphere of Jupiter. Theoretical calculations (computer simulations), performed assuming the spacecraft retrieved thermal structure and a sun-like composition, indicate that three cloud layers should be present in the Jovian atmosphere. Analysis of the Pioneer and Voyager data have confirmed the presence of these three discrete cloud layers, which based on location, bulk composition of Jupiter and the height-dependent profiles of the condensable (cloud-forming) species, are composed of water ice, ammonia hydrosulfide (a mixture of hydrogen sulfide and ammonia) ice, and ammonia ice.

These clouds are located in a region of the atmosphere where the temperature decreases with height called the troposphere. Above the ammonia cloud top is the tropopause or temperature minimum which marks the transition between the troposphere and the stratosphere where the temperature increases with height. Theoretical models of the Jovian thermal structure which include all known opacity sources are unable to reproduce the warm temperatures found in the Jovian stratosphere. An additional absorber must be present. Ultra-violet measurements, which are most sensitive to the stratospheric region on Jupiter, also suggest the presence of an absorbing aerosol.

While there is widespread agreement that aerosols are indeed present in the Jovian stratosphere, their chemical composition and spatial distribution remains unknown. Photochemical models suggest either methane- or ammonia-based compounds are likely. In most models, these stratospheric aerosols are assumed to be well-mixed, i.e. uniformly distributed, however, images of Jupiter at ultra-violet wavelengths suggest that the aerosols are more abundant in the polar regions and above the Great Red Spot. The purpose of this investigation is to examine Hubble Space Telescope data along with Voyager data to determine whether or not the aerosols in the polar regions are the same as those found above the Great Red Spot. In addition, we will seek to determine the composition of these aerosols which will provide some constraints on their origin.

Research Tasks and Scientific Questions

Become familiar with the specific data set that will be used for the investigation. For the Hubble Space Telescope (HST) data, this involves being able to load and display images. For the Voyager IRIS data, this involves being able to read and plot the data.(2 weeks)

Survey the data that will be used for the investigation. Plot the data that will be used. Describe why this data has been chosen for the specific investigation and whether or not this data will be sufficient to address basic research questions. (1 week)

Analyze of the data. Researchers using the HST data will examine different ways to enhance the image contrast in order to look for the signature of clouds. Those working with the Voyager IRIS will plot the data as a function of latitude, longitude and emission angle, examining ratio spectra and performing some simple radiative transfer model calculations. (5 weeks)

1. Can we identify the spectral signature (characteristics) of the stratospheric aerosols?
2. Is the aerosol composition globally uniform?
3. Do the aerosols serve as a tracer of the stratospheric dynamics?
4. Where are the aerosols produced?

Summarize research results.

1. Do the stratospheric aerosols have an identifiable spectral signature?
2. Is additional data required?
3. Are the stratospheric aerosols in the polar regions unique?
4. Are the aerosols above the Great Red Spot related to the polar aerosols?
5. Do they have the same spectral dependence?

Key Concepts

1. Electromagnetic Spectrum
   1. Differences and similarities between solar and thermal radiation
   2. Absorption vs. emission
2. Jupiter Planetary Science
   1. Chemical composition
   2. Atmospheric Structure: thermal structure and cloud structure
   3. Large-scale organization
3. Aerosols
   1. Radiative impact
   2. How to determine composition
4. Data
   1. How to access and display data
   2. How to assess data quality and utility