For most people, Jupiter's most recognizable-and mysterious-
feature is the Great Red Spot. For centuries, astronomers
have watched the storm spin across the giant world's face.
But for planetary scientists, Jupiter's most distinctive
mystery may be what's called the "energy crisis" of its upper
atmosphere: how do temperatures average about as warm as Earth's
even though the enormous planet is more than five times further
away from the sun?
All the sun's giant planets display this energy crisis, and
those in chilly orbits around other stars probably have it,
too. So where does the energy to heat their upper atmospheres
come from?
According to a new study, the energy must originate within the
giants, get transported upward and become amplified by turbulent
storms. The finding appears in the journal Nature. [James
O'Donoghue et al., Heating of Jupiter's upper atmosphere above
the Great Red Spot]
This offers a new window into Jupiter's depths, and should allow
researchers to better understand gas-giant atmospheres throughout
the universe. And it's all connected to the Great Red Spot.
Astronomers have long known that auroral displays can heat
Jupiter's poles, where charged particles trapped in the planet's
intense magnetic field slam into its upper atmosphere. Some
theorists thought this auroral heating could flow toward the
equator to warm the planet's mid-latitudes. So, using NASA's
Infrared Telescope Facility, astronomers observed Jupiter for
nine hours, looking for these flows as thermal fluctuations in
the planet's upper atmosphere.
But they saw none.
Instead, in Jupiter's mid-latitudes they spied a thermal spike
800 kilometers above the Great Red Spot, where temperatures
soared hundreds of degrees higher than the surroundings. The
best way to explain this spike is from the swirling maelstrom
below, where turbulent atmospheric waves must generate heat by
crashing together like breakers on a windy beach shore. Though
this must be a planet-wide phenomenon, it is most obvious directly
over Jupiter's largest, most powerful storm.
As alien as it seems, scientists have seen the same behavior on
much smaller, gentler scales here on Earth, when thunderheads
rising over mountain ranges create rippling waves that heat the
air above.