In the Dragonriders of Pern series there is an extraterrestrial substance known as Thread. This Thread is nasty stuff that is introduced to the planet of Pern by a rogue planetoid moving close enough to the planet, that Pern's gravity pulls Thread from the rogue planetoid into the atmosphere of Pern, which then falls to the ground and proceeds to eat any carbon based anything it comes into contact with. For more information see the links.
My question is, Is a substance such as Thread theoretically or scientifically possible?