Ammonia clouds, jet streams cause Jupiter's swirling colors

Pressurized magnetic fields 1,800 feet below the surface abruptly cut off the planet's jet streams.
By Laurel Kornfeld | Jan 07, 2019
Jupiter's iconic horizontal bands and color swirls are caused by strong jet streams or bands of wind that push colorful ammonia clouds across the planet, according to a new study published in TheAstrophysical Journal.

The horizontal colored bands for which the giant planet is famous are made up of ammonia in Jupiter's upper atmosphere, which gives them a variety of colors, including white, yellow, orange, red, and brown.

Unlike Earth, Jupiter has no known solid surface, resulting in the bands diving deeply into its gaseous subsurface of hydrogen and helium.

According to researcher Navid Constantinou of the Australian National University (ANU) Research School of Earth Sciences, Jupiter's jet streams, which drive the flow of gases around the giant planet's outer atmosphere, are influenced and shaped by magnetized gases far below the planet's surface.

NASA's Juno spacecraft, which has been orbiting Jupiter since July 2016, recently found that the planet's jet streams extend to a depth of 1,800 miles (3,000 km) before coming to a sudden end.

Without solid geography such as mountains and large landmasses, Jupiter's jet streams are never modified and therefore stay straight and regular, as opposed to Earth's jet streams, which are obstructed by surface features that make them wavy and irregular.

Working with Jeff Parker of Lawrence Livermore National Laboratory in Livermore, California, Constantinou created a mathematical model of planetary jet streams based on those of Earth, which drive its climate and weather. They found that Jupiter's atmosphere, which is composed largely of hydrogen and helium, undergoes heavy pressure beneath the surface that strips electrons from hydrogen and helium molecules, generating electric and magnetic fields.

Pressure from these electric and magnetic fields begins approximately 1,800 miles (3,000 km) beneath the surface, exactly where the jet streams abruptly end.

Movements and patterns seen in surface horizontal bands are influenced by these intense subsurface magnetic fields.

"We think our new theory explains why the jet streams go as deep as they do under the gas giant's surface but don't go any deeper," Parker said.

Studying Jupiter's atmosphere gives scientists important insights into the general atmospheric flows of planets, Constantinou noted.

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