Thread (Pern)

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Thread is the name of a deadly phenomenon that appears throughout Anne McCaffrey's series of science-fiction novels about the fictional planet Pern. A Threadfall consists of a rain of threadlike silver filaments of a space-borne mycorrhizoid spore that devours all organic matter that it touches. In its elliptic orbit, the Red Star picks up Thread from space and when it gets close enough to the planet some of the thread falls on Pern. The Red Star has a 250 Turn (Pernese year) elliptic orbit around its sun (Rukbat, in the Sagittarian sector). Threadfalls occur on Pern for about 50 Turns while the Red Star is at perihelion; this is called a 'Pass', while the 200 Thread-Free Turns during which the Red Star is farther away are called an 'Interval'.

Thread is dormant in the extreme cold of outer space, but reactivated by passage through the atmosphere. When it lands on a solid surface it burrows into it, multiplying extremely rapidly and consuming any organic substance (including living organisms) that it touches. A burn caused by Thread is called "threadscore".

Although deadly, Thread is not indestructible. The primary means of defense against Thread are the dragonriders and their dragons, who flame the Thread in midair before it can land. Thread drowns if it lands in a body of water, and it can be destroyed by spraying with "agenothree" (silver nitrate - AgNO₃) or fire before it burrows into the soil.

See also

• Dragonriders of Pern - series overview