New data, collected by U.S. National Aeronautics and Space Administration (NASA)'s Juno spacecraft during its first pass over Jupiter's Great Red Spot in July 2017, reveals that the solar system's most famous storm extends far below the clouds.
One of the most basic questions about Jupiter's iconic feature is: how deep are the roots?
"Juno data indicate that the solar system's most famous storm is almost one-and-a-half Earths 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 was quoted as saying in a news release.
Jupiter's Great Red Spot is a giant oval of crimson-colored clouds in Jupiter's southern hemisphere that race counterclockwise around the oval's perimeter with wind speeds greater than any storm on Earth. Measuring 16,000 kilometers in width as of April 3, 2017, the Great Red Spot is 1.3 times as wide as Earth.
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, according to Juno co-investigator Andy 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," said Ingersoll.
The science instrument responsible for this in-depth revelation was Juno's Microwave Radiometer (MWR), which has the "unique capability to peer deep below Jupiter's clouds," said Michael Janssen, Juno co-investigator from NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "It is proving to be an excellent instrument to help us get to the bottom of what makes the Great Red Spot so great."
The findings were announced recently at the annual American Geophysical Union meeting in New Orleans.
"Also detected: A new radiation zone, just above the gas giant's atmosphere, near the equator," the mission team tweeted.
The zone, identified by the Jupiter Energetic Particle Detector Instrument (JEDI) investigation, includes energetic hydrogen, oxygen and sulfur ions moving at almost light speed.
The particles are believed to be derived from energetic neutral atoms, fast-moving ions with no electric charge, created in the gas around the Jupiter moons Io and Europa. The neutral atoms then become ions as their electrons are stripped away by interaction with the upper atmosphere of Jupiter, according to JPL.
"The closer you get to Jupiter, the weirder it gets," said Heidi Becker, Juno's radiation monitoring investigation lead at JPL. "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. 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."
Juno also found signatures of a high-energy heavy ion population within the inner edges of Jupiter's relativistic electron radiation belt, a region dominated by electrons moving close to the speed of light.
The signatures are observed during Juno's high-latitude encounters with the electron belt, in regions never explored by prior spacecraft.
The future of the Great Red Spot is still very much up for debate.
While the storm has been monitored since 1830, it has possibly existed for more than 350 years. In the 19th century, the Great Red Spot was well over two Earths wide. But in modern times, the Great Red Spot appears to be diminishing in size, as measured by Earth-based telescopes and spacecraft.
At the time Voyagers 1 and 2 sped by Jupiter on their way to Saturn and beyond, in 1979, the Great Red Spot was twice Earth's diameter. Today, measurements by Earth-based telescopes indicate the oval that Juno flew over has diminished in width by one-third and height by one-eighth since Voyager times, according to NASA.
Juno's name comes from Roman mythology. The mythical god Jupiter drew a veil of clouds around himself to hide his mischief, and his wife, the goddess Juno, was able to peer through the clouds and reveal Jupiter's true nature.
The spacecraft was launched on Aug. 5, 2011, from Cape Canaveral Air Force Station in Florida, has been orbiting Jupiter since July 4, 2016, and made its first close flyby of the red spot about a year later. Juno's ninth science pass was on Saturday.
During its mission of exploration, Juno soars low over the planet's cloud tops, as close as about 3,400 kilometers. During these flybys, Juno is probing beneath the obscuring cloud cover of Jupiter and studying its auroras to learn more about the planet's origins, structure, atmosphere and magnetosphere.
