The Kitty Comet will appear on a very rare occurence. There will be a massive meteor shower that will rain down comet kitties from space. While these comets cause a lot of damage, they also leave the rare comet Kitty behind.
Comet Kitties can be tamed just as one might tame an Ocelot. Comet Kitties are completely resistant to fire damage (able to survive in Lava) and scare Creepers away - as Ocelots do. They are also stronger than Ocelots. Comet Kitties have space helmets from traveling from outer space. They can be bred with other cats.
Dying to a Comet Kitty crashing can result in a loss of gear, because the crash is an explosion and can destroy floating items.