Vrishchika is the eighth rashi, the Vedic sign of the scorpion, corresponding to Scorpio. In classical jyotisha it is ruled by Mars (Mangala), which owns it as the night house of Mars; the modern outer planet Pluto has no place in the traditional scheme. Its quality is fixed (sthira), and its element is water (jala tattva). Jyotisha reads Vrishchika through Mars's intensity turned inward and the scorpion's sting: depth, secrecy, transformation, and the drive that works beneath the surface. As a sidereal sign it is fixed to the stars and runs about 24 degrees behind tropical Scorpio; the red star Antares, the scorpion's heart, falls within it. It is also the sign of the Moon's debilitation in the shared dignity scheme, where the Moon is held weakest.
Vrishchika, scorpion, is a direct translation of the Greek skorpios, carried into Sanskrit through the Yavanajataka, a versification of a Greek astrological text of roughly the second through fourth centuries CE, itself resting on the twelve equal signs Babylonian celestial divination had fixed by the fifth or fourth century BCE, with no comparable twelve-sign scheme anywhere in the older Vedic corpus. Mars's rulership of Vrishchika and the Moon's debilitation here, dignities shared with the equivalent tropical Scorpio, belong to a later classical layer, standardly credited to compilations such as the Brihat Parashara Hora Shastra of roughly the seventh or eighth century CE; the outer planet Pluto, given rulership of Scorpio in much twentieth-century Western practice, has no place whatsoever in this classical scheme, which jyotisha has never revised to include it.
Sources Brihat Parashara Hora ShastraSage Parashara (attributed) with The Yavanajataka of SphujidhvajaDavid Pingree, Jyotihsastra: Astral and Mathematical LiteratureDavid Pingree