Architectures of planetary systems

4 problems

• Why does the Solar System lack close-in super-Earths?

  Open

  Roughly a third of Sun-like stars have planets one to four times Earth's size orbiting closer than Venus, yet the Solar System has none inside Mercury. Something about how our system formed, possibly an early Jupiter blocking inflowing solids, prevented them.

• Are planet sizes and spacings within a system truly correlated?

  Contested

  Planets in the same system often look alike in size and are evenly spaced, like peas in a pod. Some argue the pattern is real and records how they formed, others that it comes from which planets telescopes can detect.

• Why are most compact multiplanet systems not in orbital resonance?

  Open

  Planets migrating through a gas disk tend to lock into resonances, where their orbital periods form simple ratios such as 3:2. Yet most observed multiplanet systems are not in resonance, so most chains must later break apart, and models do not break enough of them.

• Do inner super-Earths and outer cold Jupiters tend to occur together?

  Contested

  Whether stars with close-in super-Earths are more or less likely to also have a Jupiter-like planet far out tells whether giant planets help or block the formation of inner small planets. Different surveys disagree.