The Juno spacecraft updates the mystery of Jupiter in the quarter century

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 spacecraft during its descent into Jupiter caused scratches on its head: the atmosphere in which it sank was much denser and hotter than scientists expected. New data from NASA’s Juno spacecraft suggest that these “hotspots” are much wider and deeper than anticipated. The discoveries about Jupiter’s hot spots, along with an update of Jupiter’s polar cyclones, were unveiled on December 11, during a virtual press briefing at the American Geophysical Union’s fall conference.

“Huge planets have deep atmospheres without a solid or liquid base like Earth,” said Scott Bolton, Juno’s principal investigator at the Southwest Research Institute in San Antonio. “To better understand what is going on deep in one of these worlds, you have to look under the layer of clouds. Juno, which recently completed the 29th scientific step on Jupiter, does just that. The spacecraft’s observations shed light on old mysteries and new questions – not just about Jupiter, but about all the giant gas worlds. “

The last long-running mystery Juno tackled came from 57 minutes, 36 seconds of data that Galileo transmitted back on December 7, 1995. Surprised scientists attributed the discovery that the probe (34 kilograms) descended into the atmosphere in one of the relatively rare hot spots of Jupiter – localized atmospheric “deserts” that cross the northern equatorial region of the gas giant. But the results of 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 the hotspots may not be isolated “deserts”, but rather open up to a vast region of Jupiter’s atmosphere that may be hotter and drier than other areas. Juno’s high-resolution data shows that these Jovian hotspots are associated with breaks in the planet’s cloud deck, providing a glimpse into Jupiter’s deep atmosphere. They also show hot spots, flanked by clouds and active storms, fueling high-altitude electrical discharges recently discovered by Juno and known as “surface lightning”. These discharges, which occur in the cold upper areas of Jupiter’s atmosphere when ammonia mixes with water, are a piece of this puzzle.

“Up in the atmosphere, where shallow lightning is observed, water and ammonia are combined and become invisible to Juno’s microwave instrument. A special type of hail is formed here, which we call ‘mushrooms,'” he said. Tristan Guillot, a Juno co-investigator at the Université Côte d’Azur in Nice, France. “These fungi harden and fall deep into the atmosphere, creating a large region that is depleted of both ammonia and water. Once the mushrooms melt and evaporate, the ammonia and water change back to a gaseous state and are visible. again for Juno. “

Jupiter weather report

Last year, the Juno team reported on South Pole cyclones. During that period, Juno’s Jovian Infrared Auroral Mapper captured images of a new cyclone that appears to be trying to join the five established cyclones that revolve around the central massive cyclone at the South Pole.

“The sixth cyclone, the baby of the group, seemed to change the geometric configuration at the pole – from a pentagon to a hexagon,” Bolton said. “But, unfortunately, the attempt failed; the baby cyclone was thrown out, removed and eventually disappeared.”

Currently, the team does not have an agreed theory about how these giant polar vortices form – or why some seem stable while others are born, grow and then die relatively quickly. Work is continuing on atmospheric models, but currently there is no model to explain everything. The way new storms appear, evolve and are either accepted or rejected is the key to understanding circumpolar cyclones, which could help explain how the atmospheres of such huge planets generally work.

---

---