Two T-type planets in the habitable zone?

[BlackBat242]

So ERB was correct... he just was talking about a parallel reality?

The two series starring Carson of Venus and John Carter of Mars, for those who haven't read anything by Edgar Rice Burroughs other than Tarzan.

 

[Horatius]

As long as you can fine tune the numbers in a Titus-Bode equation and the Bolometric correction, you can easily put two habitable worlds in a system. It all depends on your precise definition of habitable.

THeres no reason two bodies, with exactly the same orbital parameters couldn't exist 180 degrees offset from one another. Or even two bodies in mutual orbit in the same orbital path (Think Pluto/ Charon). Or one of the bodies as a captured body in a radically inclined orbit.

If only someone had a spreadsheet that made these calculations for you...

I built one in Excel, and Heaven and Earth will let you fudge some of the numbers. Using the Excel sheet, my personal record is 3 habitable worlds in a system with an F5III star.

 

[Fords of Isen]

Gliese 581, a type M2.5V star, may have two (possibly) habitable planets; tidally locked but habitable. http://fr.arxiv.org/PS_cache/arxiv/pdf/0710/0710.5294v3.pdf They suspect one - the innermost of course - is like Venus but it still might be inhabitable, at least one side. The other has a much greater chance. Both are "super earths". It appears quite possible for a system to have two habitable worlds; rare, perhaps in the extreme, but possible.

 

[Anders]

ATHeres no reason two bodies, with exactly the same orbital parameters couldn't exist 180 degrees offset from one another.

Yes, there is a strong reason: it is not stable (technically, the third Lagrange point is an unstable equilibrium). Imagine one body being pushed outwards a tiny amount by a small meteorite or some other disturbance. Now it would experience slightly less gravitational pull from the sun and the other body, and would go into a slightly higher, slower orbit - which would bring it out of alignment after a while, leading to stronger tangential forces from the other body, accelerating the destabilisation. Same thing for being pushed inwards. Counter-Earth won't work.

Or even two bodies in mutual orbit in the same orbital path (Think Pluto/ Charon). Or one of the bodies as a captured body in a radically inclined orbit.

This works better. Pluto/Charon form a double system like the Earth/Moon, and one could have two terrestrial worlds orbiting each other the same way. If the first body is much more massive than the second one, the second could hang around the fourth and fifth Lagrange points (like the Trojan astroids do with Jupiter). It doesn't have to be exact, you can get halo orbits that circulate around them. Even more fun, two planets or moons can be co-orbital like the Saturn moons Epimetheus and Janus: their gravitational interplay keeps them from colliding.

My own favorite way to have several habitable worlds is to make them moons around a warm jupiter in the habitable zone. Note that this actually extends the habitable zone a bit, since they get infrared heat from the giant in addition to the sun. The main drawback is that the close moons are likely tidally locked to the planet and will hence have very long days, but they become rather interesting places and will be close together.

 

[Peter Schutze]

Consider this as well - If Venus was where Mars is, it would have held on to enough atmosphere <snip>. You could, just barely, have 3 habitable planets in a system, much less two. <snip>

venus and mars are just on the borders of a G2v habitable zone so the slightly larger zone of a g0v in some sysgen rules while fiddling the rest minimally and that's quite possibly the result

 

[Maccat]

Agree with the gas giant, again not necessarily tidal locked, or a planet and a really big "moon", where they orbit in essence each other in addition to around the sun. Also the inner edge of habitable and outer would work, same with a captured which could be anywhere.
Only other thing i can think of is there are some asteroids that orbit, *in* earths orbit, only the orbit is like tracing inside and outside capital letter C with earth in the gap. Not sure what the upper mass limit is on an orbit like that. Read about them on the near earth asteroids site somewhere, that tracks all the asteroids, forget the name of the orbit type as well (sigh: need more coffee!).
Lets hear what you work up when you've decided!

 

[spank]

Orbit Name

It's called by a few different names, The one I recall is a Kidney Bean orbit.