Mdthbs

In a certain star system, Star B orbits Star A. Planet C lies in between the two stars and also orbits Star A. Planet C and Star B share an orbital period, and are at roughly the same places in that period. Consequently, there is no night on Planet C. As Star A sets, Star B rises.

Is such a configuration possible (and if so, plausible)? Could such a planet support life, or would the constant exposure on both sides to radiation make the planet too hot?

The short answer is: No.

To have the same orbital period, they would need to be in the same orbit.

If the planet was in L-4 or L-5 (see Wiki: Lagrange Points)of Star B which is orbiting Star A, there would be very little night but there would still be night.

the only way for this to work is for the planet to be in L-1 between the two stars. the problem is that L-1 is not a stable location and the planet would have drifted off of that position and begun a wild ride orbit long before life could have developed.

Also, I can't imagine that L-1 would be in the habitable zone in any case. There may be a way to jigger the star masses to make that work but the planet still wouldn't stay where it belongs.

The only way for it to work is to find a planet that just happens to be in the proper position now but will soon leave it. Not much chance of life there though.

You could try an Earth-like moon orbiting a gas giant. The gas giant may be reflective enough that it will be almost as bright as the direct sunlight.

Edit:

One possible solution is that the two stars are roughly the same mass and the planet orbits the center of mass of the two stars. I still don't think that would work but someone might be able to math that out. It seems to be too much like balancing on a pin.

"Planet C and Star B share an orbital period" - unfortunately, this won't work. The orbital period of an object is proportional to how far away it is from the object it orbits (more specifically, the oribtal period squared is proportional to the cube of the distance). That means if star B is farther away from A than C is, B will orbit more slowly.

Habitability is much more plausible - the habitable zone of a star depends on how bright the star is. If you somehow had a star on each side of the planet, you'd just need the planet to be at the outer edge (or maybe a little outside it) of the what the habitable zone would be for each star by itself. There is some point at which the stars will be far enough away that the planet is kept at an acceptable temperature only because there is no night.

I think yes.

1. Start with Earth (planet C) and sun (star A). You might make Star A a little more massive and move Planet C's orbit out some.




2. Star B is a little star - equal to 75 Jupiters. It is far away, in approximately the orbit of Neptune. It is more massive than a planet and so it can (must) move much faster than Neptune does. Also you need it to move fast to complete its orbit in the time planet C completes its much smaller circle. At the same time you need it to stay far away from Planet C or its proximity is going to perturb the planet's orbit.

A thing to remember about orbits: X does not orbit Y. X and Y orbit their common center of gravity. When X (e.g. star) is of hugely greater mass than Y (e.g. planet) then their center of gravity is usually still within X. But if you have 2 stellar mass objects then the center of mass might not be within one of them.