Jupiter’s Great Red Spot is a monster storm and the biggest in the Solar System. The gas giant’s swirling storm is the size of the whole Earth.

The Great Red Spot has been in existence for more than 150 years.

NASA’s Juno probe discovered that the storm system extends down at least 350km (200 miles) into the atmosphere.

“Juno data indicate that the solar system’s most famous storm is almost one-and-a-half Earth’s wide, and has roots that penetrate about 200 miles [300 kilometers] into the planet’s atmosphere,” Juno principal investigator Scott Bolton, of the Southwest Research Institute in San Antonio, said in a statement.

A wind-movement model animates a mosaic image of Jupiter’s Great Red Spot made from JunoCam images. Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Justin Cowart

The famous storm is slowly shrinking. In 1979, NASA’s Voyager 1 and 2 spacecraft found that the spot stretched well over two Earths wide. But Earth-based measurements today put the spot at only a third of the size measured by the Voyager probes.

The winds there, move at more than 120m/second – getting on for 300mph. So, this is basically faster than anything we see here on Earth.

Juno’s Instrument

Since its arrival at Jupiter on July 4, 2016, Juno spacecraft has made eight flybys over the gas giant. A ninth one will happen this Saturday (Dec. 16).

The spacecraft investigates the gas giant with its Microwave Radiometer instrument. However, the 350km that Juno probed, is just the limit of what the spacecraft’s Microwave Radiometer can sense. The spacecraft’s instrument tracks the warmth in the atmosphere associated with the storm. But Juno might also detect mass movements connected with the spot down at over 1,000km below the planet’s cloud tops.

“Precisely how deep the roots go is still to be determined. But the warmth we see at depth is consistent with the winds we measure at the top of the atmosphere,” said Prof Andrew Ingersoll, from the California Institute of Technology.

“Juno found that the Great Red Spot’s roots go 50 to 100 times deeper than Earth’s oceans and are warmer at the base than they are at the top,” said Ingersoll.

“Winds are associated with differences in temperature, and the warmth of the spot’s base explains the ferocious winds we see at the top of the atmosphere.”

Juno also found two new radiation bands. One lies just above the equator of the gas giant’s atmosphere. It includes hydrogen, oxygen and sulfur ions moving at near light speed.

“We knew the radiation would probably surprise us, but we didn’t think we’d find a new radiation zone, that close to the planet,” said Heidi Becker, Juno’s radiation monitoring investigation lead at NASA’s Jet Propulsion Laboratory. “We only found it because Juno’s unique orbit around Jupiter allows it to get really close to the cloud tops during science collection flybys, and we literally flew through it.”

However, while Juno is probing the gas giant, scientists hope to better understand the planet’s origins.

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Thumbnail image: Red spot. The Voyager spacecraft took the image on March 5, 1979. Credit: NASA’s Goddard Space Flight Center. Video and images courtesy of NASA/JPL