Recent observations suggest that many planetary-mass objects may be present
in the outer solar system between the Kuiper belt and the Oort cloud.
Gravitational perturbations may occasionally bring them into the inner solar
system. Their passage near Earth could have generated gigantic tidal waves,
large volcanic eruptions, sea regressions, large meteoritic impacts and drastic
changes in global climate. They could have caused the major biological mass
extinctions in the past 600 My as documented in the geological records
