Which direction is the best way to go if you were to have to leave Sol and travel 500 ly away to find habitable planets to set up long term colonies?

Towards the core through the Orion-Cygnus Arm?
Towards the Carina-Sagitarius Arm?

Is there any difference in the direction?

This takes place in roughly 2300 CE.

We have FTL drive capable of 10c, but it's not used for exploration much. Originally several ships were sent off to check out worlds for habitability near by when FTL became available, but that program ceased/went ignored when we found the first habitable world... which we promptly colonized. All or most ships with FTL mainly do work in the Sol system with some sending colonist to this 2nd world and returning with goods (I think this actually stopped by this time due to other things, but not important here. I forget the exact timeline off the top of my head.)

The FTL Space telescope I asked about in another question would be about 2000 Lightyears out at this point maximum with non-stop flight, so they're probably a little closer in than that.

The colony ship is actually 5 colony ships that want to settle on separate but relatively close by planets ^.^

The trip takes 50 years. They are going the max speed things can go for them. They may have sent "probes" out 5 to 10 years prior.

This isn't an "urgency" thing, but more of a political, get away from the morons thing, They could theoretically last forever out there without landing on a planet, but we like planets so want to colonize new worlds and set up to build a new civilization.

There are supposed danger zones and a "galactic habitable zone". I'm just not sure where they are. They know there are habitable planets out there, but not where they are. Suppose they know what we know more or less, but want to randomly come across these worlds which way would they go? Or is 500 ly not significant enough of a distance to enter a danger zone/exit the habitable zone?

  • $\begingroup$ 1. What knowledge does this civilization already have of its stellar neighbors? 2. How fast can this ship travel, and how many prospects could it survey in, say, a generation? Even with these questions answered, this could use some clarification. In concrete terms, we can't exactly generalize what planets would be like in one zone of the galaxy over another. $\endgroup$
    – Ross
    Commented Sep 14, 2016 at 21:01
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    $\begingroup$ Colonization ships are going to be far too expensive to just send out, you need to have a definite destination in mind. Send small, possibly unmanned, scouts to find likely places, then follow up with more detailed analysis. Then, when you are satisfied, you send the colony. $\endgroup$
    – Seeds
    Commented Sep 14, 2016 at 21:42
  • $\begingroup$ @Seeds that may be the case, but not important. $\endgroup$
    – Durakken
    Commented Sep 14, 2016 at 21:51

3 Answers 3


We don't know yet.

They're going to want to head towards the nearest cluster of five habitable-looking planets. Unfortunately, we can't really say where that cluster is at, given our current technology level. Scanning planets with a telescope will be a MUCH better idea than sending ships off in a hopeful-looking direction, so you'd want to initiate a major star survey to find a cluster of hopeful-looking planets, and then go towards them. There's likely to be habitable (or at least terraformable) planets in all directions, so it will be a matter of which direction has the closest cluster.

Unfortunately, we don't know the answer to that yet. Our ability to analyze exoplanets is still in its infancy, but I suspect that by the time we have FTL drives, we'll have a much better idea of what kind of planets are around us.

  • $\begingroup$ +1... but I believe, in the third sentence of the first paragraph, you meant sending off "ships" rather than "planets". o.O $\endgroup$
    – Ghotir
    Commented Sep 14, 2016 at 22:04
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    $\begingroup$ @Ghotir Well, the phrase is technically correct, you'd rather send telescopes than planets ;) $\endgroup$
    – Oxy
    Commented Sep 15, 2016 at 8:12
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    $\begingroup$ @Ghotir I did mean ships, but come to think of it, sending planets would be a great way to make sure you've got habitable worlds at your destination, provided you've got the engine technology to fly a planet around the galaxy... $\endgroup$
    – ckersch
    Commented Sep 15, 2016 at 19:51
  • $\begingroup$ Except for the fact that it'll freeze and lose all its atmosphere during the journey. You're better off terraforming one that's already there, as planets, in general, are turning out to be anything but rare. $\endgroup$
    – Stephan
    Commented Dec 12, 2017 at 19:18

You should not consider core and rim-ward in this scenario. The Milky Way is around 150 000 light years in diameter. The proposed 500 light year travel is just 1/300th of that. It's like the difference between crossing the US from coast to coast and crossing from the Statue of Liberty in New York over to Central Park.

To boost their chances, the ships could instead aim at dense clusters of stars. The Hyades cluster being the closest at 153 light years. That hopefully let the ships investigate many star systems and even settle in relative vicinity of each other.

Edit: Oops, turn around, turn around! (See Durakken's comment :-)

  • 2
    $\begingroup$ That would be a bad idea as I understand it ^.^ Clusters are full of young unstable stars that likely don't harbor life. $\endgroup$
    – Durakken
    Commented Sep 15, 2016 at 20:28
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    $\begingroup$ Kap obivious here, chill out Abulafia, good proposition. @Durakken there anyway will be no live on a planet, colonists need prepare planet by them self, if they wish a planet base. If you wish to eat ohmnomnom, you have to cook. $\endgroup$
    – MolbOrg
    Commented Sep 15, 2016 at 21:42
  • $\begingroup$ Not going to places with complex local lifeforms already might be a really good idea, if you just want to set up your own colony. $\endgroup$
    – Fhnuzoag
    Commented Sep 18, 2016 at 1:05

They would start with a survey. Look at the much ado about Mars landing sites for an idea of how involved the process is. They won’t be going off into the unknown, picking a direction! They will have targets in mind with some preliminary information about them. They will easily know all about the planetary systems involved, including what can be seen from afar about conditions in the target worlds.

They will list out all the candidates that can be reached, and argue at length over which features are important, which risks are unacceptable. These will be specific worlds and even colony locations within them, not a rough guess of which direction to set off in!

Most stories written prior to the 1990s missed the fact that we can see them from here before going anywhere. Even if that’s more of a stretch with the 500 ly distance, see this question and an article it references where it shows that multiple telescopes placed in the same orbit as the moon (synthetic aperture the half a million miles in radius) can see details 10s of kilometers across on planets 4× farther than what you are interested in.

Even lacking the ability to take a look first, it would be irresponsible not to send probes before the colony ship.

So, the beginning of your novel won’t be concerning which direction to head off with into the unknown, but will be debate on which sites to target based on knowns and unknowns. They will be scattered around in all directions, and if you want to note that they are not uniformly distributed, take a look at a map on that scale to see of the spiral arm or disk thickness is significant.

  • $\begingroup$ Unless they're space vikings and are brave like that. (which the asker seems to imply "eff this place, peace out!") My point being: just because we wouldn't, primarily due to the uncertainty of our technology and the astronomical costs involved (pun intended), doesn't mean that a culture in the future would have the same inhibitions. $\endgroup$
    – Stephan
    Commented Dec 12, 2017 at 19:26

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