Free Republic

Meanwhile, the Doppler discovery of extrasolar planets orbiting very close to their parent stars has raised a different problem. Many of the planets are so close to their stars (<0.1 AU), and so hot, that they cannot be supposed to have formed where we now observe them. By inference, they could have formed at larger distances (several AU) and then migrated inwards. What would cause this inward migration? As with the solar system case, the root cause may be an exchange of angular momentum with material surrounding the planets at their formation. In particular, if the extrasolar planets formed in...

Clandestine comets found in main asteroid belt 19:00 23 March 2006 NewScientist.com news service Kimm Groshong You do not have to look to the outer edges of the solar system, or even out beyond Neptune to observe a reservoir of comets. A bevy of the ice-containing bodies lies disguised as main-belt asteroids between Mars and Jupiter, claim astronomers from the University of Hawaii, US. David Jewitt and Henry Hsieh have dubbed the new population "main belt comets". They describe three objects with near circular, flat orbits in the asteroid belt that stream volatile materials, producing an observable tail for weeks...