Jupiter's Great Red Spot is Shrinking

[Tormod]

Scientists studying Jupiter’s Great Red Spot have produced the best map ever of the wind speeds on the giant planet, a place where wind gusts are typically 250 miles per hour or higher.

 

The maps consist of tens of millions of velocity measurements and provide a sharp image of what's happening with the Spot.

 

Indeed, according to Xylar Asay-Davis, a scientist at the University of California at Berkeley, these maps represent the highest resolution and highest accuracy full-planet maps ever produced. The Spot is a lozenge-shaped “anti-cyclonic” storm that has been raging on Jupiter for at least three centuries. Like meteorologists who study earthly hurricanes to better understand the behavior of violent storms, planetary astronomers try to record detailed images of the Spot to better to understand weather on Jupiter –a planet with no visible solid surface that is, at least from our point of view, nothing but weather.

 

Detailed images are hard to come by since the Spot is always on the go and must be imaged in a complex dance of movement. First, the planet as a whole is rotating at more than 23,000 miles per hour at its equator, making it the fastest rotating planet in the solar system. Then the Spot is moving along its horizontal band, a cloud band stretching all the way around the planet. Then that band is moving relative to some of the other parallel bands at other latitudes. Furthermore, the Spot is revolving counterclockwise, completing a rotation about once every six Earth-days. Finally, the camera taking pictures, mounted on flyby missions including the Galileo or Cassini spacecraft, are themselves shooting through space at thousands of miles per hour.

 

Asay-Davis says that a further complication in sizing up the Spot is the fact that clouds that are not actually part of the Spot are hovering nearby. Some of these clouds nip off parts of the Spot or are, in their turn, pulled into the Spot. The only true way to measure the extent and motion of the Spot, he says, is to measure planet-wide wind speeds.

 

The high resolution maps created by Asay-Davis and his colleagues draw on data from Galileo, Cassini and observations from the Hubble Space Telescope, and are processed with sophisticated software. From all this number crunching, the team of scientists deduced that the Spot has shrunken over the past dozen years. The Spot has survived for at least 300 years and is in no danger of dissipating, says Asay-Davis. Those nearby clouds, regularly bumping into Spot can subtract or add energy from it.

 

Asay-Davis's reported his findings at a meeting of the American Physical Society’s division of fluid dynamics.

 

Source: Image from HubbleSite, story courtesy of Inside Science News Service, American Institute of Physics