Understanding the New Jupiter: Discoveries of the Juno Mission
By Dr. Scott Bolton, Principal Juno Investigator, Nov. 10, 2021
Summarized by Laurie Averill, Volunteer JPL Solar System Ambassador
New discoveries of the Juno Mission challenge theories about how planets are formed, Jupiter’s weather cycle, and magnetic fields. They also provide insights into Ganymede.
This illustration uses data obtained by NASA’s Juno mission to depict high-altitude electrical storms on Jupiter. Juno’s sensitive Stellar Reference Unit camera detected unusual lightning flashes on Jupiter’s dark side during the spacecraft’s close flybys of the planet. Credits: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt/Heidi N. Becker/Koji Kuramura
Formation of Jupiter
New observations about the structure of Jupiter challenge current theories of planet formation. Jupiter’s core is dilute and made up of hydrogen and helium that is 60 to 70% of the size of the planet at the center of its endless atmosphere. Unlike planets with well-defined cores that current theories indicate were formed by colliding and clumping of materials in the disc left over from the Sun’s formation, a new theory proposes that Jupiter was formed like the Sun by a collapsing interstellar cloud. This insight could help to explain the formation of giant, gaseous exoplanets.
Shallow Lightning and Mushballs
Ammonia is an important component in the generation of lightning and Jupiter’s weather cycle. Shallow lightning occurs above the water ice cloud of the atmosphere of Jupiter, higher than was thought possible, and is not produced by a weather cycle solely dependent upon water. Lightning has been detected on Jupiter in a shallow region above the water ice cloud with the low-light camera: (Watch video: https://youtu.be/tq_6DClZ0Ns). A current model suggests that violent thunderstorms blow water ice crystals over 16 miles up into the Jovian atmosphere above the water clouds. Here ammonia vapor acts as antifreeze, melts the water ice crystals and joins with them to form ammonia-water clouds in the minus 126 degrees Fahrenheit environment. Droplets of falling ammonia-water collide with upwelling water crystals and electrify the clouds to form the lightning. These droplets also seed mushballs, Jovian hail stones. The mushballs grow larger as they are driven up and down through the atmosphere. Ammonia-water mush and, in lower water-cloud levels, water coat the seeds in progressively thicker and heavier layers. When the mushballs are heavy enough, they escape atmospheric currents, and fall deeper into Jupiter’s atmosphere. Jupiter’s atmosphere warms as it nears the core. The ammonia mush eventually heats enough to evaporate and release the ammonia vapor in the deeper levels of the atmosphere. This model explains the weather cycle of Jupiter and why ammonia has been visible to Juno at the top and deep levels of the atmosphere, but disappears in between. Juno can only observe ammonia directly as a vapor. These observations can also help to understand the weather on exoplanets that is driven by the cycling of vapor, liquid, and frozen forms of compounds other than just water.
(continued next page)