  Planets are typically thought to form in protoplanetary disks left over from
protostellar disk of their newly formed host star. However, an additional
planetary formation route may exist in old evolved binary systems. In such
systems stellar evolution could lead to the formation of symbiotic stars, where
mass transferred from the expanding evolved star to its binary companion could
form an accretion disk around it. Such a disk could provide the necessary
environment for the formation of a second generation of planets in both
circumstellar or circumbinary configurations. Pre-existing first generation
planets surviving the post-MS evolution of such systems may serve as seeds for,
and/or interact with, the second generation planets, possibly forming atypical
planetary systems. Second generation planetary systems should be typically
found in white dwarf binary systems, and may show various observational
signatures. Most notably, second generation planets could form in environment
which are inaccessible, or less favorable, for first generation planets. The
orbital phase space available for the second generation planets could be
forbidden (in terms of the system stability) to first generation planets in the
pre-evolved progenitor binaries. In addition planets could form in metal poor
environments such as globular clusters and/or in double compact object
binaries. Observations of planets in such forbidden or unfavorable regions may
serve to uniquely identify their second generation character. Finally, we point
out a few observed candidate second generation planetary systems, including PSR
B1620-26 (in a globular cluster), Gl 86, HD 27442 and all of the currently
observed circumbinary planet candidates. A second generation origin for these
systems could naturally explain their unique configurations.
