Atmosphere
Atmospheric Composition and origins of Jupiter
In Jupiter's atmosphere, the spectrometer detected surprisingly high
concentrations of argon, krypton and xenon. These three chemical elements,
are called noble gases because they are very independent and don't combine
with other chemicals. Tiny traces of these gases are found in the air
we breathe on Earth, and argon is sometimes used like neon in advertising
signs.
The discovery of these gases in such high quantities in Jupiter's atmosphere
raises questions about how they got there. Prof. Tobias Owen, a member
of the Juno Science Team said, " order to catch these gases, Jupiter
had to trap them physically by condensation or freezing. This process,
he said, requires extremely cold temperatures of about -240 degrees
Celsius (-400 degrees Fahrenheit), colder than the surface of Pluto,
the planet farthest from the Sun. Planetesimals (small objects orbiting
the Sun) in the Kuiper Belt beyond Pluto would be this cold, but Jupiter
is more than six times closer to the Sun and thus is much warmer. For
this reason, Jupiter could not have been the site where the three noble
gases were originally trapped."
"This raises some intriguing possibilities," Owen said. "One
explanation suggests that Jupiter was formed out in the area around
the Kuiper Belt and was dragged inward to its present location. Another
possibility is that the solar nebula, a huge cloud of gas and dust from
which our solar system formed, was much colder than scientists believe.
A third hypothesis proposes that the solid materials that brought these
noble gases to Jupiter began forming in the original huge, interstellar
cloud of gas and dust even before it collapsed to form the solar nebula.
That would make these icy materials older and more primitive than we
had expected."
According to Owen, "If either of the last two hypotheses turns
out to be correct, it would suggest that giant planets can form closer
to their stars than current theories predict. This could help explain
the new observations of planetary systems around other stars, in which
such close-in giant planets are relatively common."
(Source: http://www2.jpl.nasa.gov/galileo/news/release/press991117.html)
Atmospheric Circulation
Jupiter's atmosphere is primarily hydrogen and helium. However, unlike
Neptune or Uranus, its visual appearance is dominated by clouds of ammonia
and other compounds. Galileo observed the clouds and since then cloud
features have been used as tracers of the atmospheric circulation of
Jupiter. The circulation of Jupiter is broken into a series of easterlies
and westerlies from pole to pole in alternating bands, much like the
clouds, which are traditionally described as light zones and dark belts.
The surprising fact about Jupiter is that over two hundred years since
visual observations have been recorded, the banded appearance of Jupiter
has been observed to change over time the in intensity of their colors
and latitudinal widths, yet the observed circulation has changed only
in the magnitude of the peak jets, their locations pretty much fixed.
From the Voyager imaging data, the average zonal circulation was measured
with a very high latitudinal resolution with an accuracy of better than
2 m/s. The measured profile is shown below:
(adapted
from Limaye, Icarus, 1984)Deep Circulation on Jupiter
How deep do these winds persist? The Galileo Probe provided some new information on this question. The probe returned data from a depth of about 22 bars, approximately 156 km (97 miles) below the cloud level where the winds from Voyager were determined.
- Why are the deep winds significant?
- How will Juno determine the deep circulation?
The winds in the deep atmosphere reflect the gravity field in the interior of Jupiter, and hence are a key piece in the puzzle regarding the internal structure of Jupiter.
The Microwave Radiometer (MWR) on Juno will determine the deep atmospheric thermal structure of Jupiter from its radio emissions (thermal).
