Drifting Free


The attraction of a rogue planet, no matter how inhospitable.  This edition published by Corgi Books 1973.  Cover illustration by Bruce Pennington.

Free-floating, or so-called “rogue” planets, not bound to any star but drifting alone in the depths of space, may be more common in our Galaxy than previously expected.  Our current theories of planet formation are fairly conclusive that such worlds can be ejected from their parent star systems and, although some statistical studies suggest that they could be rare, the recent detection of two such bodies by Prezemek Mróz of the University of Warsaw and his colleagues may indicate otherwise.

In Two new free-floating planet candidates from microlensing (published online in arXiv, 1 November 2018), they detected the worlds during gravitational microlensing events.  Even though the planets emit little or no light, and so cannot be viewed directly, they can be identified when their gravity warps the light from distant stars beyond them.  One of them is considerably larger than Jupiter, and the other more like the mass of the Earth though again much larger than our own home world.

The team concludes that these detections are consistent with low-mass planets in very wide orbits, or unbound to any star, which may be even more common than stars in the Milky Way.  There could be a lot of them about, and some might even be habitable due to heat from the planets’ interiors being kept in by heavy atmospheres.  Their skies, though, would be permanently very, very dark.

In Rogue Planet, a 2002 episode of Star Trek: Enterprise, our heroes come across such a planet which has broken free from its original system, and find that animal life still exists in places where heat is escaping from below.  Otherwise, the landscape is dark and frozen, as one might expect.  But even then, some aliens with an entirely less altruistic mission have also arrived on the scene.  On the other hand, the Soviet science fiction writer Georgy Gurevich raised the possibility of life existing in the deep oceans of a possible free-floating world in his 1961 short story Infra Draconis.

The science fiction author Poul Anderson described a visit to a rogue planet in his 1968 novel Satan’s World, which features the irrepressible merchant adventurer David Falkayn, who appears along with his exotic alien colleagues in many of Anderson’s tales of the interstellar traders of the future Polesotechnic League.  A planet which has been drifting in space since its formation, its surface having lain for aeons at a temperature not far above absolute zero, has been discovered.

This remote planet is now approaching the blue giant B-type star Beta Crucis – an event which is rare for any wandering world – yet it won’t be captured since the hyperbola of its orbit will take it out into interstellar space again before long.  But while it’s there, the frozen surface starts to melt and vaporize, releasing minerals in the depths for the first time in its history, and providing an ideal location for an industry for transmutation of the rare materials essential to this future civilization.

Whoever claims it first could turn a sizeable profit, and become very, very rich.  But then there are commercial competitors who are also very interested in the lucrative prospects, and others who are willing to take an even more aggressive approach to dominating this potential market.

For us, a profit motive may not be the main attraction of rogue planets, but they are still intriguing.  And, if they are abundant in the Galaxy, some might be fairly close to us.  Perhaps even close enough to warrant expeditions in the foreseeable future – after all, if travel to the outer Kuiper Belt or even the Oort Cloud, stretching more than a light year from our Sun, is seen as feasible, then nearby free-floating worlds could be within our reach.  However, even in the universe of Anderson’s novel where “sunless planets are common”, astronomical distances are still so vast that explorers don’t come across many of them in interstellar space.  We’d still need to know where they are in the first place.


Richard Hayes, Assistant Editor (Odyssey)

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