Thread (Pern)

Thread is the name of a deadly phenomenon that appears throughout Anne McCaffrey's series of science-fiction novels about the fictional planet Pern. It consists of a rain of threadlike silver filaments of a space-borne mycorrhizoid spore that devours all organic matter that it touches. These filaments bridge the space gap between Pern and their origin, a rogue planet called the Red Star, when the two planets are close enough. The Red Star has a 200 Turn (Pernese year) elliptical orbit around its sun (Rukbat, in the Sagittarian sector). Thread can reach Pern for about 50 Turns while the Red Star is at perihelion.

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 killing any 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 the thread are the dragonriders and their mounts, 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 them with "agenothree" (nitric acid - HNO₃) before they burrow into the soil.

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• Dragonriders of Pern - series overview