Is Nava Graha worship a Vedic tradition or a puranic tradition? Are there any references to Nava Graha worship in Vedas?
There are a bunch of Vedic mantras together called as the "Navagraha Suktam" which is considered to be a hymn dedicated to the Navagrahas.
Although it's called the Navagraha Suktam and the mantras are accepted as mantras related to the Navagrahas by authoritative Hindu organizations but the explicit mention of Navagraha is never to be found in that hymn.
In any case,the following are a few mantras from that hymn.
The mantra that is attributed to Surya in that hymn is:
With the Light of Truth in space advancing, determining life and death, borne in his golden chariot he comes, Savitar, God who gazes upon the worlds. (Rig Veda 1.35.2 ; Taitt. Sam.22.214.171.124a)
a̱ gni ṁ d ū ̱ta ṁ v ṛ ̍ ṇ īmahe ̱ hot ā ̍ra ṁ vi ̱śvave ̍dasam | a ̱sya ya ̱jñasya ̍ su ̱kratum ̎ |
We choose Agni as our messenger, the herald, master of all wealth. Well skilled in this our sacrifice. (RigVeda 1.12.1; Taitt. Sam. 126.96.36.199)
ye ṣāmī śe ̍ paśu ̱pati ̍ ḥpa śūn āṁ catu ̍ ṣpad ām uta ca ̍ dvipadām | niṣkrī ̍to ̱’ya ṁ ya ̱jñiya ̍ ṁ bhā ̱game ̍tu r ā ̱yas-poṣā ̱ yaja ̍m ānasya santu ||
Which creatures does the Lord of creatures rule:— both the four footed and birds. May He, being
propitiated, accept His sacrificial share, may abundance of wealth come to the sacrificer. (Taitariya Samhita. 3;1;4d)
Similarly the mantra for Soma(Moon) is :
om aapyaa yasva sametu tay vishvata: soma vrushN iyam | bhavaa
vaajasya sangathay | apsumesomo abraveedantar vish vaani bhesha jaa | agnincha vishvasham bhuvamaapashcha vishva b heshajee: | gouree mimaaya salilaani takshatyeka padee dvipade e saa chatushpadee | ashTaapadee navapadee babhoovushee sahasra aksharaa paramay vyoman || om adhi devataa pratyadhi devataa sahitaaya somaaya nama:
& similar mantras are there for each of the remaining 7 grahas.
This is a partial answer.
There is this passage that talks about ways to keep heavenly bodies pleased.
Grahas in Mahabharata
Markandeya answered, ‘There are three kinds of purity, viz., purity in speech, purity in deed, and purity achieved by use of water. He that has recourse to these three kinds of purity, attains, without doubt, to heaven. That Brahmana who adoreth the goddess Sandhya in the morning and the evening, and who recites meditatively the sacred goddess Gayatri who is the mother of the Vedas, sanctified by the latter, is freed from all his sins. Even if he accepts in gift the entire earth with her oceans, he doth not, on that account, suffer the least unhappiness. And those heavenly bodies in the sky including the sun that may be inauspicious and hostile towards him soon becomes auspicious and favorable towards him in consequence of these acts of his, while those stars that are auspicious and favorable become more auspicious and favorable in consequence of such conduct of his.’
Mahabharata, Vana Parva, Section CLXLIX