“Juno: Revealing the Mysteries of Jupiter” with Ravit Helled (University of Zurich, Switzerland)

Juno was launched in August 2011 to arrive at Jupiter almost five years later. Juno is the first Jupiter mission on a polar orbit. It is a NASA New Frontiers mission and its goals are to understand the origin and the evolution of the planet, to study Jupiter’s interior structure, in particular look for evidence for a heavy-element core and determining its bulk composition, map the gravity and magnetic fields of the planet and map the magnetosphere, measure water and ammonia in the planet’s deep atmosphere, and observe auroras. The mission is ongoing and scheduled to end by having Juno deorbit and dive into Jupiter’s atmosphere in July next year where the spacecraft would be destroyed. Juno’s orbit has a large eccentricity and thus the mission is particularly suited to explore the planet’s magnetosphere and gravity field. Juno is the first mission to Jupiter that relies solely on solar energy thanks to its orbit. The orbit is also well suited to deal with the strong radiation level around the planet.

The question of heavy-element cores in giant planets is one of long-standing interest in planetary science due to its direct connection to planet formation theory. Before the Juno mission, some models of the interior structure allowed cores of masses of several times the Earth’s mass (or even larger), while other models concluded that a core is not necessary to explain the planet’s gravity field features. Juno gravity data imply that Jupiter’s interior is inhomogeneous in composition, and that it is likely to have a “fuzzy” core.

Another question of long-standing interest is the origin of Jupiter’s magnetic field. It is undisputed that a dynamo is at work – in some way similar to the dynamo that generates the Earth’s magnetic field in its core. But the dynamo is not located in Jupiter’s core but at depths where hydrogen becomes metallic and behaves like a metal. It is also still unknown how the dynamo is powered. Accurately mapping Jupiter’s magnetic field helps to understand the dynamo mechanism and can also be used to further constrain the internal structure.

The Juno spacecraft carries a plaque remembering Galileo Galilei and three mini Lego figures (but made of aluminum rather than plastic because of the more challenging space environment) representing Galileo and the roman gods Jupiter and Juno.

Prof. Ravit Helled is professor at the Center for Theoretical Astrophysics and Cosmology of the Institute for Computational Science at the University of Zurich. She is a member of the Juno science team and a highly cited and respected expert for the interior structure of giant planets and their formation in the solar system and beyond.

This Seminar was recorded on September 10, 2020