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[–] DessertFox 0 points 1 point (+1|-0) ago 

Do you follow (real) exoplanet news? We're just short of 2000 known ones currently. I'm looking forward to the Webb telescope, which should be able to find earth-sized planets.

I anticipate that our solar system is roughly average, and most probably have a few smaller rocky planets. It would be unlikely for us to live in an extremely unusual solar system, so my data based on a sample size of 1 is based on that presumption.

How about you? We live in interesting times.

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[–] TunaAndCucumbers ago  (edited ago)

I'm not the comment OP, but I do love following this stuff.

I would say our planetary system is far from average, mainly due to the fact that we have a comparatively large main sequence star. An average planetary system would most certainly contain a much smaller red dwarf star at the center. I imagine this would decrease the chances of having gas giants (though you might have some ice giants like Neptune and Uranus), since the accretion disk would have much less material for planets to form from.

Overall, it might also decrease the possibility of a stable system, since there would, most likely, be no Jupiter sized planet to shepherd in stray comets and other bits of primordial leftovers. The habitable zone would also be much closer to the star. I'm not sure if this would decrease or increase the chances of impacts to rocky planets. I'm assuming it'd be an increase, since the overall amount of space for these planets to orbit in would be much smaller, but I don't know. Do we have any astronomers in here that can shed some light on this?

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[–] DessertFox 0 points 1 point (+1|-0) ago 

It's hard to disagree with you, but we should note that the habitable zone has been extended to include moons that are heated by tidal forces, or even planets that are heated largely by radioactive decay (like earth is).

The heat inside the planet is great for maintaining liquid states, but sunlight is a better source of usable energy for any life forms. I don't know if there are any life forms that could gain energy only from heat. It's theoretically possible, but the biology would be complex, probably too complex to emerge. Life can probably start with significantly less sunlight than we have. Or, there may be creatures with an entirely passive life, that exert no energy on their own (the biological version of RFID, more or less). That would be very interesting, but very hard to detect; its also debatable if they could be called lifeforms.

By the way, Japan's Akatsuki spacecraft is back on course for Venus orbit. The mission was partially abandoned in 2010 when it couldn't reach its intended orbit, but they are able to use plan B now. It'll start sciencing in December. I love Venus, we've ignored it for too long. It's so like Earth, but very different.