Going by the planet flash order. Which was Mercury, Mars, Reef, Dreadnought/Saturn, Galaxy Edge (lol), and finally Tetras. Dreadnought should be next.

In the last invitation of the nine, the emissary mentions that our fate is a war amidst derelict ships, between two sisters. Obviously means we are going to Saturn’s orbit to help the Queen fight Savathun. The question is when and where in Saturn’s orbit exactly

<Potentially. Still, the Tablets of Ruin, which would allow Savathûn complete control over the Taken as well as the ability to Take herself are in the Dreadnaught. The Distributary is a good goal, but it's good to have a fallback.>