Comets in ancient India

The Indo-aryans of ancient India observed stars and constellations for ascertaining auspicious times in order to conduct sacrificial rites ordained by vedas. It is but natural that they would have recounted in the vedic texts about comets. In Rigveda ($\sim $ 1700 - 1500 BC) and Atharvaveda ($\sim $ 1150 BC), there are references to dhumaketus and ketus, which stand for comets in Sanskrit. Rigveda mentions a fig tree with roots held up in the sky (Parpola 2009, 2010). Could it have been inspired by the hirsute appearance of a comet's tail? Similarly, could `Ketu' (the torso or the tail part of Rahu) be a Dravidian loan word, since `kottu', an old Tamil word, is associated with scorpion's sting and top tuft of hair? Varahamihira in 550 AD and Ballal Sena ($\sim $ 1100 - 1200 AD) have described a large number of comets recorded by ancient seers such as Parashara, Vriddha Garga, Narada, Garga, etc. In this article, I conjecture that an episode narrated in Mahabharata of a radiant king, Nahusha, ruling the heavens, and later turning into a serpent after he had kicked the seer Agastya (also the star Canopus), is a mythological retelling of a cometary event.