Originally posted by sonhouse
Yeah, I read that about Eridani, there was an article in Scientific American a few years back analyzing the orbits of the three stars in Alpha Centuari and the conclusion was the orbits of planets similar to ours would not be in danger of being slung about by either star in the system that is basically a binary with a distant dwarf star way too far away to ...[text shortened]... giants so close to its primary would cause havoc on tiny planets like Venus, Earth and Mars.
Well the thing about our current detection methods for planets is that they are naturally much more sensitive to
so called 'hot Jupiter's' as the Doppler wobble from a close in gas giant is much easier to detect and the dimming
from a hot Jupiter passing in front of its star is bigger and more frequent than that of a small planet farther out
meaning that they are the first things likely to be found. So there is a significant selection bias.
Also these methods are tuned to detect planets that are orbiting edge on or close to edge on to us.
If the planets are orbiting perpendicular to us then they wont eclipse their star and there will be no Doppler wobble
we can detect.
As we are not currently looking with anything that can really see planets directly even at 4 years out we are reliant on
the solar system being edge on to us.
Statistically this means that the likelihood of any given star system appearing to us to have planets is significantly reduced
Due to the relatively small proportion of solar planes we can detect.
This is why our planet hunting techniques involve looking at large numbers of stars simultaneously over a large proportion
of the sky in the hope that we catch a few with planets. Which has to date been very successful.
However if you are interested in finding an earth like object in space then I wouldn't rule out close in gas giants just yet.
If a gas giant is sitting in a stars habitable zone it might well be a better bet for finding life than a solitary rocky planet
in the same orbit.
The reason being that if gas giants in other solar systems are anything like ours they will have dozens of moons.
some perhaps even bigger than the earth.
And given that one of the problems with small rocky planets (or moons) is that they cool down too fast and lose there
magnetic field and volcanism before life can really develop much there is even more hope with gas giant moons because its
perfectly possible for the gas giant to keep the moon hot with tidal stressing.
Also one of the plus points of the earth is that our moon keeps our axis tilt stable again promoting conditions for life (as well
as on the early earth providing massive tides that are thought to be crucial (or at least very beneficial) for early life development)
and a moon orbiting a gas giant gets it's axial tilt stabilised by the gas giant in exactly the same way.
So a gas giant orbiting in it's stars habitable zone might very well be a better bet for life hunting than a solitary planet.
And due to the ease of panspermia between moons it might well be that if you have one life bearing moon around a gas giant
you would probably have several.