PV Gap

Luis Said:

another kind of solar system?

We Answered:

I doubt such a system could actually exist for very long. Having planets crossing each others' orbits without a resonance (very unlikely with anything massive) is just asking for disaster (gravitational interactions will cause the planets to scatter each other into different orbits).

Two suns also causes problems though it is possible. Either they have to be close in with the planets orbiting the centre of mass of the two or far enough apart that they don't each perturb the habitable zone of the other.

Having a blue and red sun also seems unlikely to me since blue stars don't last very long (not long enough for intelligent life to evolve) and red stars are either really dim (though very long lived) with narrow habitable zones, tidal locking of any planets orbiting (which means that one side would be always day and the other always night) and a lot of flare activity (good at sterilising any life) or they are gigantic stars at the end of their life which don't have long left before they completely die (and they'll have sterilised any planets still left when they become giants).

If I were redesigning the system I'd swap one of the stars for a nice Yellow star (say G type (sol is G2) although late F and early K would do, in fact with the fifth planet being habitable I'd probably go for a brighter F type star, an F7 should do) and put a red dwarf (M type) orbiting the primary at significant distance (say about 7 or 8 AU) so that it won't screw up the orbit of any planets. I'd also stop having planets cross each others orbits though having a dwarf planet in a resonance with a larger one is fine (just like Pluto is in 3:2 resonance with Neptune).

Calculating the year length is just Newtonian mechanics provided you know the mass of the star and the semi-major axis of the planet's orbit (I wouldn't be making anything habitable have a very eccentric orbit, though you could if you wanted the seasons to be the same in both hemispheres).

Paul Said:

How do we know if any form of life is active on extra-solar planet?

We Answered:

we don't, and Carl will live forever