A possible Jupiter-sized body may also exist orbiting at Pluto's distance with a period of 170 years. Since then, a second pulsar has been added to the short list of neutron stars with orbiting planets. But how could the devastating supernova explosions that surely accompany the formation of neutron stars have left these planets intact? The orbits also seem to be exceedingly circular, as though not much has happened to disturb them in billions of years, yet the pulsars are probably less than 800 million years old of themselves. The origins of these planets remain very much a mystery today.
If a star looses more than half its mass, a sure bet for most supernovae, any orbiting planets will drift out of the star's gravitational grasp. These orbits should be highly elliptical, which in the case of the actual planets they are not, so this process could not have led to the formation of the planets. The planets could not have formed before the supernova detonation occurred. At the present time, there is no accepted explanation for how these planets formed after the supernova.
This answer was updated in 2011.
See my books:
The Astronomy Cafe (1998) and
Back to the Astronomy Cafe (2003) for more FAQs in printed form. Author: Dr. Sten Odenwald, Copyright 2011
Return to Ask the Astronomer