Mangala, Mars, is the third graha. Its presiding deity is Kartikeya (Skanda), the war-god, its gemstone is red coral, its element is fire, and its Vimshottari period is seven years. In jyotisha Mangala signifies energy, courage, aggression, competition, siblings (especially brothers), and physical drive. It is classed as a natural malefic, capable of cutting and harming as well as protecting. Mangala rules two signs, Mesha (Aries) and Vrishchika (Scorpio), and is exalted in Makara (Capricorn). The tradition pays close attention to an affliction called Mangal dosha or Kuja dosha, in which Mars in certain houses is held to trouble marriage, and which is weighed carefully in match-making. These are the interpretive conventions of jyotisha; the underlying body is the fourth planet from the Sun, whose reddish colour anchors the coral and fire associations.
The nine grahas of jyotisha take their name from the Sanskrit root grah-, to seize or grasp, a name that reflects the class's defining trait, a grip on the nativity, rather than physical status as a body; Mangala is unambiguously a planet in the modern sense, but two of his eight companions, Rahu and Ketu, are calculated points rather than bodies and belong to the same class purely by that grip. Mars's place in the ninefold system reached Sanskrit astrology from Greek horoscopy through the Yavanajataka, a versification of a Greek text of roughly the second to fourth centuries CE, which brought the apparatus of dignity and exaltation to astronomical knowledge India already possessed. The gemstone and Vimshottari period length now attached to Mangala belong to a later layer, codified in compilations such as the Brihat Parashara Hora Shastra of roughly the seventh or eighth century CE.
Sources Brihat Parashara Hora ShastraSage Parashara (attributed) with Jyotihsastra: Astral and Mathematical LiteratureDavid Pingree, The Yavanajataka of SphujidhvajaDavid Pingree