Giant planet interiors and Saturn's ring age

7 problems

• How did Jupiter's dilute core form and survive 4.5 billion years?

  Contested

  A giant collision or gradual accretion of rock and ice could have produced a spread-out core. It must also have resisted being mixed away by convection ever since.

• Where and how much does helium rain out inside Jupiter and Saturn?

  Open

  At high pressure, helium may stop mixing with hydrogen and sink as droplets, releasing heat. This could explain why Saturn is warmer than expected and why both atmospheres lack helium.

• What is the radial distribution of heavy elements inside Jupiter?

  Partially resolved

  Juno's gravity measurements show Jupiter's heavy elements are spread out over a large region instead of packed into a small core. The exact profile is still poorly pinned down.

• Why do Jupiter models want fewer heavy elements than its atmosphere shows?

  Open

  The Galileo probe measured an atmosphere enriched in heavy elements, but many interior models that fit Juno's gravity need a less enriched outer layer. Either the models or the assumed relation between pressure, temperature and density of hydrogen-helium (the equation of state) is wrong, or the planet has an unexpected layering.

• How did Saturn's rings form?

  Open

  If the rings are young, something recently broke up a moon or passing body near Saturn. If old, they formed with the planet, and their icy composition needs another explanation.

• Are Saturn's rings young or as old as the solar system?

  Contested

  The rings are almost pure ice even though dust falling from space should have darkened them over billions of years, suggesting they are only a few hundred million years old. Others argue the rings resist or hide this pollution.

• Why does Uranus emit far less internal heat than Neptune?

  Open

  Neptune radiates more than twice the energy it receives from the Sun, while its near twin Uranus radiates only slightly more than it absorbs. Either something inside Uranus traps heat or Uranus lost its heat early.