Jupiter, the largest planet in our solar system, gives us a unique opportunity to learn about planetary formation and structure. One of the leading hypotheses for the formation of Jupiter, referred to as gas accretion, is the focus of a study by Ravit Helled (University of Zurich) and colleagues. This model posits that gas giants like Jupiter initially form in the same way as terrestrial planets like Earth until their cores become sufficiently massive to begin accreting hydrogen and helium, the two lightest and most abundant elements. Hydrogen and helium accumulate slowly as the planet heats up, but eventually the planet reaches a critical mass at which hydrogen and helium accrete rapidly.

The Juno spacecraft, which was launched in 2011 and arrived at Jupiter in 2016, provides gravitational field observations that constrain Jupiter’s internal structure. Helled and colleagues reviewed existing computer simulations of the interior structure of Jupiter that are consistent with the gravitational measurements made by Juno. One commonality among these simulations is a discontinuity in density at approximately half the radius of Jupiter, implying that Jupiter has a “fuzzy” core composed of 65-95% hydrogen and helium and 5-35% heavier elements (by mass). This is in contrast to terrestrial planets, which contain less than 1% hydrogen and helium, and also in contrast to Jupiter’s atmosphere, which contains about 99% hydrogen and helium. Helled and colleagues propose that, during accretion, heavier elements dissolve in the hydrogen and helium and may be enriched by evaporation from the core. Helled and colleagues also suggest that a giant impact may have mixed an original solid core with surrounding hydrogen and helium. Further understanding of the origin of the fuzzy core will assist scientists in learning about the formation of not only our own solar system, but also other systems with giant planets. READ MORE