From the Sun God the Incarnation of Rama, from the Moon that of Krishna, from Mars that of Narasimha, from Mercury that of Buddha, from Jupiter that of Vamana, from Venus that of Parasurama, from Saturn that of Koorma (Tortoise), from Rahu that of Varaha [Boar] and from Ketu that of Matsya occurred. All other incarnations that these are through the Grahas. The beings with more Paramatmamsa [i.e. Rama, Krishna, Narasimha and Varaha] are called divine beings’.
Brihat Parasara Hora Sastra, Translated by R. Santhanam (1984), Chapter 2, Verses 5-7.
Notably, according to the Brihat Parasara Hora Sastra – an important Smriti Sastra or compilation of Indian astrology for prediction (i.e. fortune telling) – although all ten of the Dashavatara have corresponding astrological symbols, only four are considered as divine beings (i.e. Rama, Krishna, Narasimha and Varaha).
The sun is the soul of all. The Moon is the mind. Mars is one’s strength. Mercury is speech-giver while Jupiter confers knowledge and happiness. Venus governs semen (potency) while Saturn denotes grief.
Of royal status are the Sun and the Moon while Mars is the army chief. Prince-apparent in Mercury. The ministerial planets are Jupiter and Venus. Saturn is servant. Rahu and Ketu form the planetary army.
— Brihat Parasara Hora Sastra, Translated by R. Santhanam (1984), Chapter 3, Verses 12-15.
Bengal Institute of Oriental Studies 