CIRS Objectives and Plans at Jupiter
January 23, 2001
The composite infrared spectrometer (CIRS) on NASA's Cassini spacecraft,
is observing Jupiter, its rings, and the surfaces of its satellites
through "infrared eyes." The observations will allow Cassini scientists
to probe the composition and thermal structure of these objects.
CIRS functions both as a remote-sensing assayer and thermometer. In the
mid-infrared, CIRS measures the abundances and spatial distributions of
various gases, including methane, acetylene, benzene, and other
hydrocarbons, water, and carbon dioxide. The observed distribution will
provide clues to the physical processes active in Jupiter's stratosphere
and at higher altitudes, such as photochemistry, charged particle impacts,
and dynamical transports.
In addition, the temperatures of Jupiter's stratosphere and tropopause
(the region of the temperature minimum just below the stratosphere,
separating it from the troposphere) will be retrieved from the infrared
spectra. From the temperature fields, the strong east-west winds can be
determined, and thermal anomalies associated with atmospheric waves
derived. Variations over periods of hours to months can be monitored with
Besides global observations, CIRS is targeting selected features visible
on Jupiter's cloud tops.
Joint observations with Cassini's visible and infrared mapping
spectrometer, (VIMS), imaging subsystem (ISS), and ultraviolet imaging
spectrograph (UVIS) will be made to characterize regions where Jupiter has
auroras. These measurements can be used to understand the processes that
go on at the altitudes in Jupiter's atmosphere that each instrument is
best suited to measure. CIRS spectra will be particularly sensitive to
the hot spots that are known to exist in the middle and upper stratosphere
over certain longitude ranges at high latitudes.
It has not been possible before to study Jupiter in the far infrared at
the spatial and spectral resolution available with Cassini CIRS. Surveys
of gaseous and condensed ammonia will yield interesting data about
Jupiter's weather in the upper troposphere, just above the visible cloud
deck. Of cosmic importance is the search for deuterium, heavy hydrogen,
in molecules made of one regular hydrogen atom and one deuterium atom.
The ratio of deuterium to hydrogen is an important parameter defining
conditions during the Big Bang formation of the Universe.
Jupiter's moons are receiving attention from CIRS as well. Thermal and
spectral features can be studied in greater detail than was possible with
Voyager's infrared interferometer, spectrometer and radiometer instrument,
and Galileo does not carry a comparable instrument.
The rings surrounding Jupiter will be surveyed for their temperature and
composition. The far infrared offers the opportunity, via a temperature
determination, to infer the sizes of the particles orbiting the planet.
CIRS can search for the spectral feature indicating silicate
(silicon-oxygen compound) minerals, which would constrain ring composition
if it is found.
CIRS Principal Investigator:
Mr. Virgil G. Kunde
NASA/Goddard Space Flight Center
Mail Code 693.2
Greenbelt, MD 20771-0001
Additional information about Cassini-Huygens is online at http://saturn.jpl.nasa.gov.
Cassini passed its closest to Jupiter on Dec. 30, 2000, en route to reach its primary destination, Saturn, in 2004. Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the Cassini and Galileo missions for NASA¿s Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.