Thread

We are deviating slightly from what the Dragon Lover's Guide states about the origins of thread.  Thread is NOT from the Oort cloud.  The reasoning for this is stated below.  Thread comes directly from the Red Star.  The parasitic organism actually requires the turbulent atmosphere of Red Star to breed.    While this atmosphere has altered through the changing of Red Star's orbit. The change has actually been benificial to Thread's life cycle.  It no longer 'dies back' out of the atmosphere due to the extreme cold when Red Star receeds from Rukbat.  The Seismic activity of Red Star throws the Thread-pods up into the turbulent upper atmosphere.

Without the trailing cloud, how, then do they get to pern?   Due to the siesmic activity there are many thread spores in the atmosphere.  The gravitational interaction between Pern and the Red Star during passes and as Red Star settles into a close, parallel orbit to Pern will substitute for the interaction witht he Oort cloud, thus spinning the upper level of spores into space and towards the Red Star's gravatic neighbor.

The circumstances to generate such a situation are quite unlikely; however, the premise of this game is that the wildly unlikely has occured, much to everyone's dismay.  Thread began falling on the 16th day of the 9th month of the year 2424 in game.  This is fall in the northern continent and spring in the southern.

The reason for this change is first, to more logically support the premise of the game.  Second, the Oort Cloud is not an origin for short period commets.  It is an origin for long period commets that is situated roughly 50, 000 AU which is roughly 1 lightyear from our sun.   For a planet to actually pass through the Oort cloud would require an orbital path far in excess of anything thus far discovered.  A planet at that distance would be in real danger of breaking away from the solar system entirely.  The commets in the Oort cloud are only rarely sent spinning inward.  This is usualy the result of interstellar gravitational forces and star motion.   Most of this was not really understood when Anne McCaffrey began writing her Pern books.

In our own solar system, the furthest out we have confirmed a planet or planet-like object is Pluto at 39.5 AU.  (1 AU= the distance between Earth and the Sun.)  This is closer to the Kupier Belt which is believed to be the source of short-period commets.  This belt rests at 50-100 AU, closer by nearly 3 orders of magnitude.  Pluto's orbit is roughly 248 earth-years long.   The ratio between Pern and Red Star is almost identical, if you go by a 'normal' pass/interval cycle.  Assuming a simlar length of orbit, and similar origional orbital speed we can assume Red Star cannot go out too much further than Pluto.  It origionally had a much more irratic orbit than Pluto, so it spends at least portion of its year close enough to Rukbat that it is not the frozen chunk of nothing that Pluto is.

Credit for the actual science: The NASA home page
(The extrapolations are my own I'm not going to blame any of my mistakes on them!)