Has an alien comet infiltrated the solar system? - space - 02 December 2008 - New Scientist

"An extrasolar origin makes it easy to explain the composition - of course we d expect everything to be different " Schleicher told New Scientist. "Here three molecules with carbon are all depleted so maybe carbon is depleted across the board That sounds to me as if it came from somewhere else and is not just an oddball from our solar system." Astronomers expect some comets to be hurled out of their stellar systems by the gravity of giant planets. In theory they should be wandering around out there and sometimes come flying though our system - although no comet has yet been found moving fast enough to be identified as an extrasolar interloper. If Machholz 1 did fly in from interstellar space a chance encounter with Jupiter could have made it a captive of our solar system. This would be an extraordinary discovery but much more evidence is needed before the alien origin is any more than a hypothesis. Fortunately Machholz 1 will be close to the Sun again in 2012 when astronomers can study its bright coma of gases again.

via Has an alien comet infiltrated the solar system? - space - 02 December 2008 - New Scientist.