Our solar system is in no way typical of the diversity out there.
The number of known planets orbiting other stars now stands at more than 200. (The Kepler satellite has identified some 3,000 planet candidates awaiting confirmation).
Some exoplanets are weirdly unlike any in our solar system. The mass of exoplanet HD149026b, for instance, is 20% greater than Saturn but its radius is 22% smaller, which implies that it contains more heavy elements than can be found on all eight of the full-fledged planets circling our sun, according to David S. Spiegel and co-authors.
Some are gas giants similar to Jupiter except they’ve ballooned in size beyond what planetary scientists expected from models of planet formation based on our solar system.
The first figure compares planets by radius (relative to that of Jupiter) and the rate of energy received from the star they orbit, often 10,000 times greater than the solar energy reaching Earth.
The second figure compares planets by radius and mass, which ranges from less than Earth’s to more than 10 times that of Jupiter.
- Colored circles = confirmed exoplanets
- Small white circles = candidate planets identified by the Kepler mission (KOI)
- Red stars = the eight planets of our solar system
The figures are from Structure of exoplanets by David S. Spiegel, Jonathan J. Fortney, and Christophe Sotin, PNAS (2014)]