Basically I want to create a 'physically-realistic' binary planet system orbiting a star in such a way that the two planets are tidally locked, but their period about the barycenter is say, equal to earth's period, completing one revolution every 24 hours. The two planets could be similar in size (like earth and venus) or they could be considerably different (like earth and mars...keeping in mind that if they are too different in size you simply get a natural satellite orbiting the larger planet). Essentially I want to fine-tune these fictional planets to provide similar earth-like conditions, while keeping the two of them tidally locked. Is this getting too complicated? My worry is that I am going to create two planets that simply couldn't exist, because they are too close at too slow a period as to provide the necessary centripetal force to prevent them from simply colliding into one another. Or perhaps such a system cannot exist because inevitably the larger planet would accumulate all the volatile gases, essentially stealing the atmosphere of the small planet. Am I asking too much?
