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Sublimating gas molecules scatter off of the surface of an icy body in thesame manner as photons. This means that for every photon-driven body force,there should be a sublimation-driven analogue that affects icy bodies. Thermalphotons emitted from the surfaces of asymmetrically shaped bodies in the SolarSystem generate net torques that change the spin rates of these bodies overtime. The long-term averaging of this torque is called the YORP effect. Here wepropose a sublimation-driven analogue to the YORP effect (SYORP), in whichsublimating gas molecules emitted from the surfaces of icy bodies also generatenet torques on the bodies. However, sublimating molecules carry momentum awayfrom the body at a rate ~10^4-10^5 greater than thermal photons, resulting inmuch greater body torques. While previous studies of sublimative torquesfocused on emissions from highly localized sources on the surfaces of JupiterFamily Comet nuclei, SYORP applies to non-localized emissions across the entirebody, which likely dominates sublimation-drive torques on small icy chunks andDynamically Young Comets, and can therefore be applied without high-resolutionspacecraft observations of their surfaces. Instead, we repurpose the equationsof the YORP effect to account for sublimation-driven torques. We show how anSYORP-driven mechanism best matches observations of the Sun-oriented lineaments(striae) of comet tails, whose formation mechanism has remained enigmatic fordecades. The SYORP effect explains why striae are observed betweennear-perihelion and ~1 AU from the Sun for comets with perihelia less than 0.6AU, and solves longstanding problems with moving enough material into thecometary tail to form visible striae. We show that SYORP can form striae thatmatch those of Comet West, and produce a power-law size frequency distributionof their parent chunks with an index of -1.4 (-1.1- 2).

The Formation of Striae within Cometary Dust Tails by a Sublimation-Driven YORP-like Effect