3 goldilocks zone planets around 1 star:

http://phys.org/news/2016-05-years-earth-planets-host-life.html

Pretty close too, 40 light years, only ten times further than Alpha Centauri A, B, and C.

I still think AC is the place to go to first when we get propulsion that allows 0.9 C or so. 0.9999 would be great. At least, good for the crew🙂

Go to that 40 light year star, it would take about 1/2 year for the crew, and back 1 year, spend 5 years there, 6 years total for crew, 86 odd years passes by on Earth.

Originally posted by sonhouse
http://phys.org/news/2016-05-years-earth-planets-host-life.html

Pretty close too, 40 light years, only ten times further than Alpha Centauri A, B, and C.

I still think AC is the place to go to first when we get propulsion that allows 0.9 C or so. 0.9999 would be great. At least, good for the crew🙂

Go to that 40 light year star, it would take ab ...[text shortened]... , and back 1 year, spend 5 years there, 6 years total for crew, 86 odd years passes by on Earth.

I think it's a little optimistic to hope to detect life on these things, it is a brown dwarf and barely a star.

Where are you going to get the energy from to get to a large fraction of the speed of light? As a hack's argument to get to 0.866c you need to supply the rest mass of the space ship in energy. This is an unbelievably huge amount of energy, to get to 0.9999c you need 70x the rest mass.

If there turns out to be evidence of life on these planets, which molecular oxygen lines would be evidence for, we could try sending a signal, but if there is life there I doubt we'll be able to detect it as photosynthesis seems unlikely given the star "shines" in the infrared.

Originally posted by sonhouse
I still think AC is the place to go to first when we get propulsion that allows 0.9 C or so. 0.9999 would be great. At least, good for the crew🙂

And I think robotic missions should always precede human missions. There is simply no good reason for a human return mission to a neighbouring star.

I actually think that permanently habitable spaceships will come before near light speed travel, in which case leaving the solar system will be largely unnecessary.

Originally posted by DeepThought
If there turns out to be evidence of life on these planets, which molecular oxygen lines would be evidence for, we could try sending a signal, but if there is life there I doubt we'll be able to detect it as photosynthesis seems unlikely given the star "shines" in the infrared.

I see no reason to think the exact same chemistry would be used. Photosynthesis evolved to use visible light because visible light is the brightest section of the spectrum our star emits. There are at least two variations on photosynthesis on earth using different parts of the spectrum, there is no reason to think there couldn't be more.
Also, life on earth took a very long time to come up with photosynthesis, so there is a good argument to be made that other planets have life forms without it or an equivalent and stick to earth bound energy sources.

Originally posted by twhitehead
And I think robotic missions should always precede human missions. There is simply no good reason for a human return mission to a neighbouring star.

I actually think that permanently habitable spaceships will come before near light speed travel, in which case leaving the solar system will be largely unnecessary.

How would humans protect against cosmic radiation?

Originally posted by whodey
How would humans protect against cosmic radiation?

There are a variety of ways, a strong magnetic field possibly being one of the best, but I haven't studied the problem. If there was an easy solution we would have done it already. It remains the case that long term habitable spaceships will probably be viable before fast interstellar travel is, and habitation on local planets and moons probably before that. It will be a very very long time before there is any rational reason to try and send humans to a nearby star system and a return mission will probably never make any kind of sense.

Originally posted by twhitehead
I see no reason to think the exact same chemistry would be used. Photosynthesis evolved to use visible light because visible light is the brightest section of the spectrum our star emits. There are at least two variations on photosynthesis on earth using different parts of the spectrum, there is no reason to think there couldn't be more.
Also, life on ea ...[text shortened]... her planets have life forms without it or an equivalent and stick to earth bound energy sources.

The frequency of light depends on the pigment, I agree, but I doubt that infra-red can support photosynthesis, as there needs to be enough energy per photon to start an electron transport chain. In green plants the photon has to have enough punch to knock an electron out of the chlorophyll molecule. So in an infrared world you'd need a molecule that loses electrons to infrared (which may exist) or some two photon process, which may be possible (I don't know) but it seems unlikely to me.

It's not a question of whether life is there, but whether we can detect life if it's there. Free oxygen is a clear signature. Whereas it's not obvious how one would go about detecting anaerobic life at a range of 12 parsecs.

Possibly of interest:
http://www.astrobio.net/news-exclusive/infrared-photosynthesis-a-potential-power-source-for-alien-life-in-sunless-places/

http://www.wired.com/2010/08/infrared-chlorophyl/

Originally posted by twhitehead
And I think robotic missions should always precede human missions. There is simply no good reason for a human return mission to a neighbouring star.

I actually think that permanently habitable spaceships will come before near light speed travel, in which case leaving the solar system will be largely unnecessary.

The reason you leave the solar system is to avoid getting caught out in a nearby supernova which will ruin your day.

I think you need to have established colonies about 500 light years apart to avoid that catastrophe, which is a very tall order for any civilization.

Obviously a spaceship based colony could repopulate Earth if it got whacked by an asteroid so a lot of civilization killers would be avoided but not all of them.

To avoid all the dangers the universe has to offer you would need to be many light years apart.

In a situation unlikely to happen, suppose that powerhouse star Sirius went nova, at 8 ly away, the whole solar system would be fried. Life under the oceans on Europa or some such would survive but humans would go extinct.

Originally posted by sonhouse
The reason you leave the solar system is to avoid getting caught out in a nearby supernova which will ruin your day.

So, no need for a return mission.

Originally posted by sonhouse
The reason you leave the solar system is to avoid getting caught out in a nearby supernova which will ruin your day.

I think you need to have established colonies about 500 light years apart to avoid that catastrophe, which is a very tall order for any civilization.

Obviously a spaceship based colony could repopulate Earth if it got whacked by an ast ...[text shortened]... e fried. Life under the oceans on Europa or some such would survive but humans would go extinct.

It's basically impossible in the next trillion years or so. Just a point, a nova is the sudden brightening of a star, and is different from a supernova. Sirius A is too small to supernova, it's only twice the mass of the Sun. When it becomes a red giant it is unlikely it's radius will be large enough for Sirius B to start accreting much material. So it probably won't even generate nova flashes, there's almost no chance of a supernova. What could happen is that gravitational radiation will cause their orbits to decay and the two remnant white dwarfs will collide and supernova, but that won't happen for many times the current age of the universe.

Originally posted by DeepThought
It's basically impossible in the next trillion years or so. Just a point, a nova is the sudden brightening of a star, and is different from a supernova. Sirius A is too small to supernova, it's only twice the mass of the Sun. When it becomes a red giant it is unlikely it's radius will be large enough for Sirius B to start accreting much material. So ...[text shortened]... ill collide and supernova, but that won't happen for many times the current age of the universe.

It's basically impossible in the next trillion years or so.

So many orders of magnitude of wrongness... 😛

There is nothing near to us right now that will go supernova any-time soon...

But everything in the galaxy is orbiting at different speeds and so what is near-by
changes, and will change many many many times over the next ~100 times the age of
the universe... Andromeda will hit before that for starters.

As it stands I think we can only confidently state that we will definitely not suffer a
supernova at close range for something of the order of thousands~tens of thousands
of years... Certainly less than 1 million years... And an unfortunately aimed Gamma Ray Burst
could fry us from the other side of the galaxy at any time.

Sirius is indeed not big enough to supernova, and moreover, by the time it reaches the end
of it's life it will be nowhere near us for us to care.

Which brings up the other point about spreading out to avoid supernova...
You don't have to travel hundreds of LY to spread out... Go to the next nearest suitable and
then wait for stellar drift to do the spreading out.

Originally posted by googlefudge

It's basically impossible in the next trillion years or so.

So many orders of magnitude of wrongness... 😛

There is nothing near to us right now that will go supernova any-time soon...

But everything in the galaxy is orbiting at different speeds and so what is near-by
changes, and will change many many many times over the next ...[text shortened]... ut... Go to the next nearest suitable and
then wait for stellar drift to do the spreading out.

Well, I was only considering Sirius, not other stars. Since the only way it can generate a supernova is by orbital decay of what will by then be two white dwarfs, or even black dwarfs, and the current separation is of the order of at least 8 astronomical units, my guess that the orbits won't have decayed enough for that to happen in a trillion years probably isn't wrong. Interactions with other stars could change that outcome, and yes the Sun may come closer to some real supernova candidates, but the main purpose of my post was to point out that Sirius isn't a supernova candidate in the likely life-time of our species, or for that matter planet.

Originally posted by DeepThought
Well, I was only considering Sirius, not other stars. Since the only way it can generate a supernova is by orbital decay of what will by then be two white dwarfs, or even black dwarfs, and the current separation is of the order of at least 8 astronomical units, my guess that the orbits won't have decayed enough for that to happen in a trillion ye ...[text shortened]... s isn't a supernova candidate in the likely life-time of our species, or for that matter planet.

Well the most likely significant disruption of the orbits would be when the stars blow off their outer
layers. The question being how much drag that induces on the two cores.

But yes, that is not anything we need worry about.

Originally posted by DeepThought
Well, I was only considering Sirius, not other stars. Since the only way it can generate a supernova is by orbital decay of what will by then be two white dwarfs, or even black dwarfs, and the current separation is of the order of at least 8 astronomical units, my guess that the orbits won't have decayed enough for that to happen in a trillion ye ...[text shortened]... s isn't a supernova candidate in the likely life-time of our species, or for that matter planet.

I know it is an unlikely candidate for nova much less super, just using that as an example.

I wonder if any star twice the mass of Sol would also put out 25 times the light?

It seems weird there are these stars almost as big as our whole solar system or bigger and yet are still stars. Mind boggling.

http://earthsky.org/space/how-big-is-the-biggest-monster-star

The star shown in the image makes our sun look like Mercury in comparison.

Then there is this: A shock wave in a galactic cluster collision:

Imagine a shock wave going 2000 km per second bigger than galaxies:

http://phys.org/news/2016-05-strongest-merging-galaxy-clusters.html