NASA’s Juno Spacecraft Updates Quarter-Century Jupiter Mystery

The spacecraft has been collecting data on the interior of the gas giant since July 2016. Some of its latest findings touch “hot spots” in the planet’s atmosphere.

Twenty-five years ago, NASA sent the first probe in history into the atmosphere of the largest planet in the solar system. But the information returned by the Galileo probe during its descent to Jupiter caused it to scratch its head: the atmosphere it was plunging into was much denser and hotter than scientists expected. New data from NASA’s Juno spacecraft suggests that these “hot spots” are much wider and deeper than anticipated. The findings on Jupiter’s hot spots, along with an update on Jupiter’s polar cyclones, were revealed Dec. 11, during a virtual press conference at the fall conference of the American Geophysical Union.

“Giant planets have deep atmospheres without a solid or liquid base like Earth,” said Scott Bolton, Juno principal investigator at the Southwest Research Institute in San Antonio. “To better understand what is happening in the depths of one of these worlds, it is necessary to look below the cloud layer. Juno, who recently completed his 29th close-up of Jupiter science, it does just that. The spacecraft’s observations are shedding light on old mysteries and raising new questions, not just about Jupiter, but about all gas giant worlds. ”

This time-lapse video clip shows the movement of cyclones at Jupiter’s south pole from February 2017 to November 2020. The data was collected by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard the Juno spacecraft. POT. Image Credit: NASA / JPL-Caltech / SwRI / ASI / INAF / JIRAM

The latest long-standing mystery Juno has tackled stems from 57 minutes and 36 seconds of data that Galileo transmitted on December 7, 1995. When the probe responded by radio that its surroundings were dry and windy, shocked scientists attributed the finding to the fact that the 75 A 34-kilogram probe had descended into the atmosphere within one of Jupiter’s relatively rare hot spots: localized atmospheric “deserts” traversing the gas giant’s northern equatorial region. But results from Juno’s microwave instrument indicate that the entire northern equatorial belt, a broad, brown, cyclonic band that wraps around the planet just above the gas giant’s equator, is generally a very dry region.

The implication is that hotspots may not be isolated “deserts” but rather windows to a vast region in Jupiter’s atmosphere that may be hotter and drier than other areas. High-resolution data from Juno show that these Jovian hotspots are associated with breaks in the planet’s cloud layer, allowing a glimpse of Jupiter’s deep atmosphere. They also show that hot spots, flanked by active clouds and storms, are fueling high-altitude electrical discharges recently discovered by Juno and known as “shallow lightning”. These discharges, which occur in the cold upper reaches of Jupiter’s atmosphere when ammonia mixes with water, are one piece of this puzzle.

“High in the atmosphere, where shallow lightning is seen, water and ammonia combine and become invisible to Juno’s microwave instrument. This is where a special type of hail is forming that we call ‘balls of fungus, ‘”said Tristan Guillot, a Juno member. co-researcher at the Université Côte d’Azur in Nice, France. “These mushroom balls get heavy and fall deep into the atmosphere, creating a large region that is depleted of both ammonia and water. Once the mushroom balls melt and evaporate, the ammonia and water return to a gaseous state and are visible to Juno again. “

This animation takes the viewer into a large storm high in Jupiter’s atmosphere, where a soft particle of water and ammonia (depicted in green) descends through the atmosphere, collecting icy water. The process creates a “mushroom ball”, a special hailstones made from a slurry of water and partially liquid ammonia and a solid crust of water and ice on the outside. In about 10 to 60 minutes (depending on their size), these mushroom balls reach the deepest layers of Jupiter, below the water clouds, where they quickly melt and evaporate. Theoretical models predict that these mushrooms could grow to about 4 inches (10 centimeters) in diameter, weigh up to 2 pounds (1 kilogram), and reach speeds of up to 450 mph (700 kph) during their descent. Image Credit: NASA / JPL-Caltech / SwRI / MSSS / CNRS

Jupiter weather report

Last year, Juno’s team reported on South Pole cyclones. At that time, Juno’s Jovian Infrared Aurora Mapping instrument captured images of a new cyclone that appeared to be attempting to join the five established cyclones circling the massive central cyclone at the south pole.

“That sixth cyclone, the baby of the group, seemed to be changing the geometric configuration at the pole, from a pentagon to a hexagon,” Bolton said. “But unfortunately, the attempt failed; the baby cyclone was ejected, moved away and finally disappeared.”

With three giant swords extending about 20 meters (66 feet) from its six-sided cylindrical body, the Juno spacecraft is a marvel of dynamic engineering, spinning to stay stable while making oval orbits around Jupiter. See the full interactive experience at Eyes on the Solar System.

At present, the team does not have an agreed theory on how these giant polar vortices form, or why some appear stable while others are born, grow, and then die relatively quickly. Work on atmospheric models continues, but at present no model seems to explain everything. How new storms appear, evolve, and are accepted or rejected is key to understanding circumpolar cyclones, which could help explain how the atmospheres of these giant planets work in general.

More about the mission

JPL, a division of Caltech in Pasadena, California, manages the Juno mission for principal investigator Scott Bolton of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is administered at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. Lockheed Martin Space in Denver built and operates the spacecraft.

More information about Juno is available at:

Follow the mission on Facebook and Twitter at:

Contact with the media

DC Agle
Jet Propulsion Laboratory, Pasadena, California.

Gray Hautaluoma / Alana Johnson
NASA Headquarters, Washington
202-358-0668 / 202-358-1501 /

Deb schmid
Southwest Research Institute, San Antonio