Arka means Sūrya (Surya). In Matsyapurāṇa (Matsyapurana), while mentioning the nine planets, Śanigraha (Sanigraha; Saturn) s mentioned as Arkaja. Śanigraha or Śanaiścara(Sanaischara) is Arkaja, since he is born of the womb of Chāyā (Chaya), and sired by Sūrya (Surya).