In 1802 , shortly after discovering Pallas , Olbers suggested to Herschel that Ceres and Pallas were fragments of a much larger planet that once occupied the Mars -- Jupiter region , this planet having suffered an internal explosion or a cometary impact many million years before .
In 1802 , shortly after discovering Pallas , Heinrich Olbers suggested to William Herschel that Ceres and Pallas were fragments of a much larger planet that once occupied the Mars -- Jupiter region , this planet having suffered an internal explosion or a cometary impact many million years before .