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D.P. Hamilton, M.C. Miller (U. Maryland)
The first extrasolar planets were discovered in 1992 around the millisecond pulsar PSR~1257+12. Interestingly, the eight other isolated pulsars in the Galactic disk are devoid of orbiting masses larger than asteroids(Wolszczan 1999), which argues that pulsar planets likely form in probabilistic events. Our favored mechanism is the immediate recoil of a neutron star through a close companion, a process that occurs in a few percent of supernovae. We show that the amount of mass captured during passage through the companion, despite being primarily Hydrogen and Helium, is sufficient to form rocky Earth-mass objects. We rule out most alternate formation scenarios with the strong constraints that the existence of the innermost planet provides. Finally, we show that recent developments in the study of accretion onto magnetized stars suggest that the pulsar was born with approximately its current rotation frequency and magnetic moment. If so, this suggests that some and perhaps all isolated millisecond pulsars may have been born with high spin rates and low magnetic fields instead of having been recycled by accretion.