The upper atmosphere above Jupiter’s Great Red Spot – the largest storm in the Solar System – is hundreds of degrees hotter than anywhere else on the gas giant, according to a team of planetary scientists led by Boston University researcher Dr. James O’Donoghue.
Artist’s concept of the mechanism of heating from the Great Red Spot. Turbulent atmospheric flows above the storm produce both gravity waves and acoustic waves. Gravity waves are much like how a guitar string moves when plucked, while acoustic waves are compressions of the air (sound waves). Heating in the upper atmosphere 500 miles (805 km) above the storm is thought to be caused by a combination of these two wave types ‘crashing’ like ocean waves on a beach. Image credit: Karen Teramura, University of Hawaii at Manoa / James O’Donoghue, Boston University.
Sunlight reaching Earth efficiently heats the terrestrial atmosphere at altitudes well above the surface. Jupiter is over five times more distant from the Sun, and yet its upper atmosphere has temperatures, on average, comparable to those found at Earth.
The sources of the non-solar energy responsible for this extra heating have remained elusive to planetary researchers studying processes in the outer Solar System.
“With solar heating from above ruled out, we designed observations to map the heat distribution over the entire planet in search for any temperature anomalies that might yield clues as to where the energy is coming from,” said Dr. O’Donoghue, first author of a paper reporting the findings in the journal Nature.
Scientists measure the temperature of a planet by observing the non-visible, infrared (IR) light it emits.
The visible cloud tops we see at Jupiter are about 30 miles (48 km) above its rim; the IR emissions used by the team came from heights about 500 miles (805 km) higher.
When Dr. O’Donoghue and co-authors looked at their results, they found high altitude temperatures much larger than anticipated whenever their telescope looked at certain latitudes and longitudes in the planet’s southern hemisphere.
“We could see almost immediately that our maximum temperatures at high altitudes were above the Great Red Spot far below,” Dr. O’Donoghue said.
“The Great Red Spot is a terrific source of energy to heat the upper atmosphere at Jupiter, but we had no prior evidence of its actual effects upon observed temperatures at high altitudes,” said co-author Dr. Luke Moore, also from Boston University.
Artist’s concept of the mechanism of heating from the Great Red Spot. Turbulent atmospheric flows above the storm produce both gravity waves and acoustic waves. Gravity waves are much like how a guitar string moves when plucked, while acoustic waves are compressions of the air (sound waves). Heating in the upper atmosphere 500 miles (805 km) above the storm is thought to be caused by a combination of these two wave types ‘crashing’ like ocean waves on a beach. Image credit: Karen Teramura, University of Hawaii at Manoa / James O’Donoghue, Boston University.
Solving an ‘energy crisis’ on a distant planet has implications within our Solar System, as well as for planets orbiting other stars.
As the team points out, the unusually high temperatures far above Jupiter’s visible disk is not a unique aspect of the Solar System.
The dilemma also occurs at Saturn, Uranus and Neptune, and probably for all giant exoplanets outside the Solar System.
“Energy transfer to the upper atmosphere from below has been simulated for planetary atmospheres, but not yet backed up by observations,” Dr. O’Donoghue said.
“The extremely high temperatures observed above the storm appear to be the ‘smoking gun’ of this energy transfer, indicating that planet-wide heating is a plausible explanation for the energy crisis.”
_____
J. O’Donoghue et al. Heating of Jupiter’s upper atmosphere above the Great Red Spot. Nature, published online July 27, 2016; doi: 10.1038/nature18940
