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Galactic Settlement by Hitchhiking �Among Passing Star Systems

Brian Tillotson

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Three points about interstellar SF

Interstellar schemes have not been physically plausible

SF can show realistic, affordable interstellar travel if:

Stars move (they do)
We can use comets (we can)

Which gives us:

New stories
Hope—especially outside SF

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Question: How far...

...from our solar system to the nearest solar system?

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Too far!

4.3 light years from our "habitable zone" to alpha Centauri's
40,000 years* with today's best propulsion

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4.3 ly

*big error bars

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This has consequences outside SF

Interstellar travel is seen as fantasy

Faster Than Light (likely impossible)
Or extreme cost & risk

Generation ships
Long sleep
Laser sail
...

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Prominent voices say "We'll never do it"

Alcubierre ship: http://www.nasa.gov/centers/glenn/images/content/101681main_CD1998_76634_1200x900.jpg

This file is in the public domain in the United States because it was solely created by NASA.

Author: Les Bossinas (Cortez III Service Corp.) Artist's depiction of a hypothetical Wormhole Induction Propelled Spacecraft.

Red giant Earth and Moon:

https://commons.wikimedia.org/wiki/File:2,400_Kelvin_and_Counting.jpg.

Kevin M. Gill, title 2,400 Kelvin and Counting, Creative Commons Attribution 2.0 Generic license.

Red giant Earth:

https://commons.wikimedia.org/wiki/File:Red_Giant_Earth_warm.jpg.

Created in Celestia. Prediction of the Earth's appearance in 5-7 billion years when the Sun is a Red Giant.

This work is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or any later version. This work is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. See version 2 and version 3 of the GNU General Public License for more details.

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Two flaws in that argument

4.3 light years is not always true: stars move

It's not even true now: comets shorten the trip

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1. Stars move

Alpha Centauri is getting closer
Others are sometimes very close!

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SF neglects this

2

4

6

0

light years

J2146+3813 98 km/s

−10k

20k

40k

60k

0

years

we are here

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2. Comets shorten the trip

Where can we live in the solar system?
Usual answer: out to the asteroid belt or Jupiter

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Jupiter

Sun

asteroid belt

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But what if we could live in comets?

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credit: Roy Scarfo, from Dandridge Cole's "Beyond Tomorrow"

NASA/Rick Guidice - https://space.nss.org/settlement/nasa/70sArtHiRes/70sArt/art.html (image link)

+

=

NASA / JPL-Caltech / UMD

O'Neill-like space habitat

thousands or millions of people per comet

Comet

+ nuclear power (or fusion)

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If we inhabit comets...

...then habitable zone includes Oort cloud

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trillions

Jupiter zone

credit: NASA / William Crochot

~5 x Sun-Earth distance

credit: Roy Scarfo, from Dandridge Cole's "Beyond Tomorrow"

>1,000,000,000,000 comets

Oort cloud: �~100,000 x Sun-Earth distance (1.5 light years)

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Less than 1 light year between Oort clouds*

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4.3 ly

1.5 l.y.

1.9 l.y.

Sun

alpha Centauri

0.9 ly

*maybe they touch already—edge is ill-defined

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Star motion + Comet living = Short interstellar hops!

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Oort clouds overlap during stars' encounter

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settled after encounter

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Oort clouds overlap during stars' encounter

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settled after encounter

we'll take a closer look here

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First we settle the Sun's Oort cloud...

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× = settled comets

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Then visitor's comets pass through

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× = settled comets

_° = transiting comets (e.g. from α Centauri)

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Many comet-comet pairs have close passes

Some < Earth-Moon distance
Short flight to overtake passing comet

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rendezvous maneuver

"Easy" to cross over during overlap!

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Departing cloud is seeded

Some new comets are settled
Settlements can expand to rest of that cloud

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settled comet

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Hitchhiking the galaxy

Fast-moving stars quickly span the galaxy*
We disperse from those seeds

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*not easy to catch—affects stories

Earth and nearby stars

Now

Earth

formerly nearby stars (5 of many)

1/8 of a galactic orbit from now

Credit: ESO, European Southern Observatory, CCA 4.0

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The future has been happening for 300,000 years

sea level

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For continents or stars, timing matters

expand across Africa

Out of Africa

first modern humans

UPOS J1121,

2.8 ly

Sholz's star, 0.8 ly

α Centauri, 3.1 ly

expand into Oort cloud

J2146+3813,

1.6 ly

span Asia

expand into next Oort cloud

−100 kyr

−300 kyr

−200 kyr

+100 kyr

0

Eurasia to America

Sol to next star?

That's the big scale. For small groups actually doing this, we need a finer look. When we check how often these opportunities come by, we see they roughly match what humans have been doing already.

Our species evolved and began to spread out, but we couldn't leave Africa until the sea level was low, and we couldn't leave Asia until it was even lower. The timing of these events is here along the top, and you can see the passage of nearby stars is similar.

The major steps in human migration happen about as often in the future as in the past.

Mention alternate history: we're ready earlier when Sholz's star comes, or a later star comes about now.

Credit: sea level traced from Root Routledge, created from source information and graphs from James Hansen publications. Root Routledge material is copyrighted, but available for non-commercial distribution.

From https://serc.carleton.edu/integrate/teaching_materials/coastlines/student_materials/901.

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Stories need conflict. There's plenty!

Stay or go?
Race to control
Missing the boat
Lifeboat dramas
Exploration

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Desperate maneuvers
Punctuated social equilibrium
Origin debates
New-settlement politics
We & aliens can't hide

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SF themes

Continuity with pattern of earlier migrations

We're not doomed by Sun's death

We can take other Gaian species

We aren't cancer, we're Earthseed

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J. Patrick Fischer, CC BY-SA 3.0

kallerna, CCA 4.0

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Your thoughts?

I'll see you at the poster
Or email me: brian.j.tillotson@gmail.com

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THE END

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