178 Encyclopedia of the Solar System
especially with respect to their vertical structure beneath
the cloud tops, provides its own set of difficulties.
3.5 Ironic Unpredictability—an Anecdote
The fickleness of Earth’s weather compared to that of the
other planets provides many fascinating scientific problems
for meteorologists. Trying to live on such a planet presents
Earth’s inhabitants with practical problems as well. On the
lighthearted side, there are common bromides such as “If
you don’t like the weather, wait 15 minutes,” and “Every-
body complains about the weather, but nobody does any-
thing about it.” On the serious side, lightning storms and
tornados wreak havoc every year, and before the advent of
weather satellites, hurricanes once struck populated coast-
lines without warning, causing terrible loss of life.
Even now, the tracks of hurricanes are notoriously diffi-
cult to predict. The point is best made with an example, and
the following is a lighthearted anecdote from the first au-
thor’s personal experience: Perhaps he should have known
better than to leave the windows of his apartment open
on such a warm, breezy morning in the summer of 1991,
but the apartment needed airing out, and the author was
preoccupied with a desire to come up with a good way to
illustrate to a group of distinguished terrestrial meteorolo-
gists that the weather on Jupiter is more predictable than
the weather on Earth. And so, he left the windows open,
locked the door, and headed out to Boston’s Logan Airport
to begin a 10 day trip to a symposium on “Vortex Dynam-
ics in the Atmosphere and Ocean,” which was being held
in Vienna. His preoccupation was not helped by the use of
the singular “atmosphere” in the symposium’s title, which,
one could argue, should have been written with the plu-
ral “atmospheres.” To be sure, Earth has its great vortices,
like Gulf Stream rings, Mediterranean salt lenses, and at-
mospheric blocking highs, and even more powerful storms,
like hurricanes, which are driven by moist thermodynamics
(in fact, Hurricane Bob was at that moment slowly heading
toward the Carolina coast). Yet Jupiter’s Great Red Spot
and the hundreds of other long-lived vortices found on the
gas giant planets are in many ways simpler systems to study,
and we have excellent observations of them from spacecraft
likeVoyager,Galileo, andCassini.
After arriving at the conference, the author decided to
make his case by pointing out that aVoyager-style mis-
sion to track hurricanes on Earth would most likely end
in failure. This is because theVoyagercameras had to be
choreographed 30 days in advance of each encounter to
give the flight engineers time to sort through the conflict-
ing requests of the various scientists and time to program
the onboard computer. For the atmospheric working group,
this constraint meant that success or failure depended on
the accuracy of 30-day weather forecasts for the precise lo-
cations of the drifting Great Red Spot and other targeted
features. On Earth, storms rarely last 30 days, and much
less do they end up where they are predicted to be going
a month in advance. The fact that theVoyagermissions
to Jupiter were a complete success, as were the subsequent
Saturn, Uranus, and Neptune missions, illustrates in a prac-
tical way the remarkable predictability of the weather on
the gas giant planets relative to on Earth. [SeePlanetary
Exploration Missions.]
Having made his point, on the road back to the
Vienna Airport after the conference the author was getting
accustomed to the fact that taxis in German-speaking coun-
tries are Mercedes, when the driver explained that the an-
nouncer on the radio was saying that there had been a coup
in Moscow. This left him worried about his Russian col-
leagues, several of whom he had just met in the preceding
week. On the flight back across the Atlantic, he was think-
ing about this when the Lufthansa pilot announced, with
resignation in his voice, that because of thunderstorms the
plane could not land in Boston and was being redirected to
Montreal. After about 2 hours in Montreal, where the plane
was nestled between several other waylaid international
planes that were littered across the tarmac, the go-ahead
was given to finish the trip to Boston. The landing was
bumpy, and the skyline was disturbingly dark, but there
was a beautiful sunset that was framed with orange, red,
and black clouds. It was only after getting off the plane
that the author first learned that Hurricane Bob had just hit
Boston. Boston? Wasn’t Bob supposed to hit the Carolina
coast? It was difficult not to take this egregious forecasting
error personally. On returning home, jet-lagged, the author
discovered that his apartment was dark, the electricity was
out, the windows were of course still open, the curtains,
carpet, and furniture were soaked, and wall hangings and
broken glass were strewn about the floor. The irony of the
situation is not hard to grasp.Voyagerwould have returned
beautiful, fair weather images of North Carolina and South
Carolina, and would have completely missed the hurricane,
which ended up passing through this author’s apartment
1000 km north of the previous week’s prediction.4. Oceans
Earth is the only planet in the solar system with a global
ocean at the surface. The oceans have an average thick-
ness of 3.7 km and cover 71% of Earth’s area; the greatest
thickness is 10.9 km, which occurs at the Marianas Trench.
The total oceanic mass—1.4× 1021 kg—exceeds the at-
mosphere mass of 5× 1018 kg by nearly a factor of 300,
implying that the oceans dominate Earth’s surface inven-
tory of volatiles. (One way of visualizing this fact is to re-
alize that, if Earth’s entire atmosphere condensed as ices
on the surface, it would form a layer only∼10 m thick.)
The Earth therefore sports a greater abundance of fluid
volatiles at its surface than any other solid body in the solar
system. Even Venus’ 90 bar CO 2 atmosphere contains only