Saturday, May 21, 2011

Keeping the Djinn of exploration corked in the bottle of data

One of the interesting problems in trying to use realistic data and a reasonable projection of the future is that, unlike the 2D closed planet we are used to, the amount of data - the number of interesting or strategically significant places we should consider - goes up with the cube of the distance traveled.

The related problem is that space is (effectively, for our purposes) unbounded.  Magellan's expedition sailed for 3 years in as straight a line as they could manage, but they still ended up back in Seville.  Such are globes.  While space may curve on itself over a sufficient distance, for practical purposes if we are going to concern ourselves with individual suns and planets, you have to turn around if you want to get back.

So, lets say we want to take about six months to get to Iota Persei.  Lets also say that for plot reasons we want to have a 30 year old colony there.  That means that we could have data back from expeditions that have traveled at least 15 times as far from Sol.  Since i Persei  is about 10 parsecs away, that means our dataset should carry out 150 parsecs, and we might have some brave souls out as far as 300 parsecs.

The dataset I am currently using extends about 15 parsecs.  This is a volume of 14 thousand cubic parsecs.  Now the catalog I have been playing with has about  a thousand objects, for a density (using less rounded numbers) of 0.701 objects per pc^3.  Projecting that out to 200 parsecs give about 2 million objects.  At 300 parsecs we are talking 8 million.

And its not like we are talking about invisible stuff here.  There are catalogs right now down to an apparent magnitude of +21.  If we consider an M6 at the dimmest star we want to talk about having a planet that's absolute magnitude +12 -- which a catalog down to +21 we could see such a star out to 600 parsecs.  Even M8, which is getting down there, is visible to 100 pc.

So, I want my earth-origin protagonists to have a good sized sandbox to play in; but I need reasonable ways to keep them in the sandbox.  But right now, I need some coffee.


  1. Hey Les, I was reading last week about some exo-planets that have been discovered outside steller systems. Free-floating exo-planets. The ones found are between 10 and 20K LYs from Earth but doesn't mean you can't toss them in as well.

  2. Indeed, it is reasonable to believe that the distribution of bodies goes way below the level which will ignites. I will look at the research, thanks.