Another puzzle arising from the newly discovered planets is the origin of planets with elliptical (elongated) orbits.

Some planetary systems may form with several very massive Jupiter-like objects. The gravitational attraction of these planets would perturb their orbits, and they would eventually suffer a very close passage. One planet would be flung out of the planetary system while the other would be re-directed inward (with an elliptical orbit like that found in 16 Cyg B).

The repeated passage of a Jupiter-sized object through the inner portion of the planetary system would result in the gravitational ejection of any smaller, terrestrial planets.

It may require somewhat special conditions in the disk for Earth-like planets to survive processes involving unstable orbits of the gas giants.