http://www.msnbc.com/news/934038.asp?0cv=CB20
BACKGROUND:
Many astronomers believe that if not for Jupiter, life on Earth would have died out long ago. Jupiter is so massive that it has sucked up many of the asteroids and comets that would otherwise have been bombarding the Earth for millions of years. Thus, it's logical to conclude that having a big gas giant in your solar system can be good for a stable ecology.
But that's not Jupiter's only important advantage. Many of the extrasolar gas giants that we've found have highly eliptical orbits. If Jupiter had such an orbit, it would have disturbed all the little rocky planets of the inner solar system (Mercury, Venus, Earth, Mars). But Jupiter's orbit is also so circular that Earth can sustain a stable climate.
Another problem would be a gas giant in the inner solar system. If Jupiter orbitted near Venus, its gravity might again disturb the Earth. But HD 70642 has its big gas giant in the outer solar system.
All of this makes HD 70642 more like our solar system than any other we've discovered so far, at least in these life-related aspects. It could harbor a habitable planet! It probably doesn't, but if your story needs a nearby star with a habitable planet, HD 70642 is a great candidate.
[This message has been edited by Doc Brown (edited July 07, 2003).]
Because of the arguments Doc has listed, such a system would be more likely to have a habitable planet anyway. So those arguments are good ones to keep in mind when world-builiding.
Thanks, Doc.
As to the issues raised on this thread:
Actually, I wouldn't at all restrict the habitable solar systems of the universe to requiring a large mass planet, in terms of a "mirror Jupiter".
It would be horribly limiting to think in terms of life existing only in familar niches in familar environmental conditions. If the past 20-30 years are anything to go by, that's precisely the way we *shouldn't* be thinking. Deep sea explorations have shown that life can exist on sulphur or methane based energy cycles, rather than solar/photosynthesis based one, not to mention a range of bacteria that can live in the coldest regions of Antartica, to the bubbly calderas of active volcanoes.
There is especially no reason to presume that our solar system presents any particularly strict and exclusive model for the emergence of life - any more than people from Norway should assume that human life on earth is *only* possible when surrounded by fir-lined hills, freezing lakes, and a midnight sun.
Life always shows diversity, the ability to explore every expression, under every condition. The modern SF writer, although perhaps should be very aware of movements in science, should never limit themselves to them. After all, neither does science. Perhaps it could be argued that the true purpose of science fiction is to be specualtive beyond the present limits of science. And if you're wrong there's no great loss - after all, you're writing fiction.
[This message has been edited by Chronicles_of_Empire (edited July 09, 2003).]
I never said that life was restricted to this type of solar system. Even on Earth we've got extremophiles that could live on planets that would kill us, or make us wish we were dead. I expect that even more extreme organisms are possible, and they might even be intelligent.
Some day we might find a comfortable planet orbiting a blue giant star, or a white dwarf star, or a star with a gas giant in the inner solar system. But for my money a sun-like star with a Jupiter-like gas giant is the best place to look.
Given current and foreseeable technology, it would take many generations to send a colony to another planet. All the original crew would probably be dead, and the later crew would have been born and raise in a completely artificial environment traveling in deep space.
Why on Earth (or off it) would such people want to live on a planet at all?
http://www.astronexus.com/eos/index.html
Yeah, there is definately an idea out there about how those who go extra solar to colonize won't really need to look for a planet. They'll probably already have been a couple of generations on a space colony orbiting Jupiter.
quote:
Why on Earth (or off it) would such people want to live on a planet at all?
Because the colony ship would probably be quite limiting in terms of population size. And populations (almost) always want to expand.
But I suspect you're right. A lot of the colonists might stay on the ship and just leave half of their number on a suitable planet in order to allow themselves more space to reproduce.
But how would the ones to be marooned be chosen? Would they immediately set about building themselves a new colony ship? How long would it take them?
Hmmm... that could be interesting...
:-)
quote:
Why on Earth (or off it) would such people want to live on a planet at all?
In which case, they could probably realistically have the capability of expanding their environmental systems and habitat space...it would be a lot easier than learning to live on a planet without any technological infrastructure (for any of you that haven't tried this, I recommend it). And this all assumes that the planet is "habitable". There is simply no way we would know that prior to sending the mission. The mission would necessarily involve a factor of terraforming to insure that the planet could be made habitable.
Do you have any idea how much easier it is to build additional habitat in an environment that you are familiar with than to completely transform the ecology of an alien planet in a controlled manner? I'm telling you that the one is actually much more difficult than the other, and the other is the one I mentioned first 
Kidding aside, best laid plans go astray, Murphy's Law plays havoc, human error surfaces, and who can really anticipate everything -- especially when there's no one who's been there/done that to confirm preparations, particularly for the long haul, and there's no going back for what you forgot or miscalculated?There's also the purpose of the mission. I doubt they set out to live on a ship forever. Consequently, the ship would not (could not, really) have been built with immortality in mind. Wild durability, maybe, but not immortality.
Sooner or later, they're going to need an influx of raw materials. I'm thinking more in terms of metals, but I'm open to suggestions. Maybe radiation/space dust/fill in the blank will erode the entire hull sooner than expected -- or the trip is far longer than expected -- and there's no way to replace such huge, critical portions of the ship all at once.
Colonizing planets, I'd agree, wouldn't be for the faint of heart, but if that was the plan....
a) forseeable technology
b) our Sun is stable
However, if either of those changed it seems perfectly logical that we would seek planets to colonize.
Given forseeable technology, the colonists should have known exactly what they were in for before they left. Astronmers and robotic probes will have determined much.
I'm not a big fan of human terraforming teams. If you want to terraform a distant planet, send some robots a few centuries ahead of the humans.