An international team of astronomers, led by Yamila Miguel (SRON/Leiden Observatory), has discovered that Jupiter’s gas envelope does not have a homogeneous distribution. The inner part has more metals than the outer parts, amounting to a total of between 11 and 30 Earth masses, representing 3-9% of the total mass of Jupiter. This is a metallicity high enough to conclude that bodies the size of a kilometer – planetesimals – must have played a role in the formation of Jupiter. It will be published on June 8 in Astronomy and Astrophysics †
When NASA’s Juno space mission arrived at Jupiter in 2016, we glimpsed the remarkable beauty of the largest planet in our solar system. In addition to the famous Great Red Spot, Jupiter turns out to be dotted with hurricanes, giving it almost the look and mystique of a Van Gogh painting. However, the planet’s envelope beneath the thin visible layer is not immediately visible. Still, Juno can paint a picture for us by feeling gravity over several locations on Jupiter. This gives astronomers information about the composition of the interior, which is nothing like what we see on the surface.
An international team of astronomers, led by Yamila Miguel (SRON/Leiden Observatory), now found that the gaseous envelope is not as homogeneous and well mixed as previously thought. Instead, it has a higher contraction of metals — elements heavier than hydrogen and helium — toward the center of the planet. To arrive at their conclusions, the team built a number of theoretical models that meet the observational limitations measured by Juno.
The team studied the distribution of metals because it gives them information about how Jupiter formed. The metals do not appear to be homogeneously distributed over the shell, with more in the inner part than in the outer part. The total amounts to between 11 and 30 Earth masses of metals. Miguel: “There are two mechanisms for a gas giant like Jupiter to acquire metals during its formation: through the accretion of small pebbles or larger planetesimals. We know that once a baby planet is large enough, it starts pushing out pebbles. “The metals in Jupiter that we see now are impossible to reach for that. So we can rule out the scenario with only pebbles as solids during Jupiter’s formation. Planetesimals are too large to be blocked, so they must have played a role.”
The finding that the inner portion of the shell contains more heavy elements than the outer portion means that the abundance decreases outwardly with a gradient, rather than there being homogeneous mixing across the shell. “We used to think that Jupiter has convection, like boiling water, which makes it completely mixed,” Miguel says. “But our finding shows otherwise.”
Provided by SRON Netherlands Institute for Space Research
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