Jupiter is in the class of planets known as gas giants—those planets primarily made from hydrogen and helium gas, which, under gravitational compression, become metallic fluids. It’s the most massive planet in our solar system—so massive that it influences everything else, including the delivery of material to Earth. Jupiter is also thought to have formed first among the planets, perhaps a few million years after a cloud of gas and dust from the interstellar medium collapsed and led to our solar system 4.6 billion years ago. That influence means that we need to understand the planet’s composition and structure to understand how the solar system came into being.
Through its program of deep space missions, NASA has long recognized the importance of Jupiter. But the planet remains mysterious. Does it have a core? What is the nature of its magnetic field? How do the deep atmosphere and strong winds behave? How much water does it have? To answer those questions, one must visit the planet. For that job, a billion-dollar New Frontiers mission spacecraft named Juno was chosen in 2003, launched in 2011, and went into Jovian orbit on 4 July 2016. The mission, led by Scott Bolton of the Southwest Research Institute, is still collecting data. But it’s already made some important measurements. This Quick Study outlines three types: The first has to do with gravity; the second, with the magnetic field; and the third, with passive radiation from inside the planet.

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