How to become a space faring civilisation without leaving the armchair

Give me the place to stand, and I shall move the earth

About 250 million years hence our solar system will pass into a region of space in which stars are far denser than in our present neighbourhood. Although not more than one in ten thousand is likely to possess planets suitable for colonization, it is considered possible that we may pass near enough to one so equipped to allow an attempt at landing. If by that time the entire matter of the planets of our system is under conscious control, the attempt will stand some chance of success.

J. B. S. Haldane, Possible Worlds, The Last Judgement(*)

Beware: This quote is science fiction and was written circa 1927. However, Haldane was a wild imagination. Look:

A recent paper dealing (yes, one more) with the Fermi Paradox model the settlement of our galaxy by space-faring civilisations, taking explicitly into account the effect the motion of stars, which many other works treat as static objects. The authors find that star motions should make it easy for civilisations to spread across the galaxy:

We also include the effect of stellar motions on the long term behavior of the settlement front which adds a diffusive component to its advance. As part of our model we also consider that only a fraction f of planets will have conditions amenable to settlement by the space-faring civilization. The results of these models demonstrate that the Milky Way can be readily ‘filled-in’ with settled stellar systems under conservative assumptions about interstellar spacecraft velocities and launch rates.

Carroll-Nellenback, Jonathan, et al. ‘The Fermi Paradox and the Aurora Effect: Exo-Civilization Settlement, Expansion and Steady States’. ArXiv Preprint ArXiv:1902.04450, 2019.

They also address the question of the galactic steady-state achieved in terms of the fraction of settled planets and conclude that the galaxy might be crowed without us being aware:

These results break the link between Hart’s famous Fact A” (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the galaxy. Explicitly, our solutions admit situations where our current circumstances are consistent with an otherwise settled, steady-state galaxy.

The story goes on, and in another paper, astronomers at the University of Leiden in The Netherlands have simulated the evolution of a cluster of 1,500 stars in the Orion Trapezium star cluster some 1,300 light years away in Orion, of which 500 are orbited by a total of 2,522 planets. Their study focuses on the production of free-floating planets (0.24 to 0.70 free-floating planets per main-sequence star, in line with previous studies). By extrapolation, we conclude that no less than 50 billion planets in the Milky Way are likely to be free-floaters—unbound to any star system:

Our study focuses on the production of free-floating planets. From a total of 2522 planets in the initial conditions of the simulation, a total of 357 become unbound. Of these, 281 leave the cluster within the crossing time-scale of the star cluster, the others remain bound to the cluster as free-floating intra-cluster planets. Five of these free-floating intra-cluster planets are captured at a later time by another star.

The two main mechanisms by which planets are lost from their host star, ejection upon a strong encounter with another star or internal planetary scattering, drive the evaporation independently of planet mass of orbital separation at birth. The effect of small perturbations due to slow changes in the cluster potential are important for the evolution of planetary systems. In addition, the probability for a star losing a planet is independent of the planet mass and independent of its initial orbital separation. As a consequence, the mass-distribution of free-floating planets is indistinguishable from the mass distribution of planets bound to their host star.

Elteren, A. van, et al. ‘Survivability of Planetary Systems in Young and Dense Star Clusters’. Astronomy & Astrophysics, vol. 624, Apr. 2019, p. A120., doi:10.1051/0004-6361/201834641.

We tend to see Earth as a quiet holiday resort in the confines of our galaxy, the Milky Way, but we should take a second look and think of it as the best long term spacecraft we can dream of. In fact, it offers us two options: wait a few hundreds millions years and see (waiting the mountain come to us), or find out how to move it

If only we were able to finally find out where to stand the proverbial Archimedes’ lever 😉


Featured Image: Alone in Space – Astronomers Find New Kind of Planet

(*) About Haldane’s The Last Judgment, in Spanish

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