Joss Whedon’s “Firefly” reflects Joss’s disinterest in science in a subtle way. As a series it got so much right, like no noise in space, but it does have a few oddities from the point of view of Hard SF. Aside from that weird space-drive, I mean.
For example, the terraformed moons & planets of the ‘Verse are said to have had their atmospheres and gravity fixed by the terraforming process. Atmosphere is OK (in decades, mind), but gravity?
Here’s a speculative, but hopefully Hard SF take on fixing a planet/moon’s gravity. Question: without adding mass how do you increase a planet’s surface gravity?
Ans: Shrink the planet.
Consider: materials under compression increase in density. Intense gravitational and electromagnetic fields, perhaps even strong nuclear fields, cause materials to compress into denser forms. Some such are metastable, like diamond too, thus remain dense after the pressure subsides. Some fretful types still worry that particle accelerators might create bits of quark matter (strangelets) which can catalyse catastrophic collapse of the Earth to nuclear density. There’s several reasons why that’s unlikely, but what if there was a nuclear process that can collapse a planet’s metallic core and leave the silicate mantle?
The energetics are actually in favour of that occurring since shrinking a mass releases gravitational binding energy. If ‘Verse engineers found a way of shrinking a metallic core to 0.1% of its previous size then a planet would contract and its surface gravity would increase. At the core/mantle boundary the core’s gravity has increased 100-fold, thus enhancing compression of the silicates of the mantle.
How much would gravity increase? To double the surface gravity a spherical body would need to shrink to 70.7% of its previous size. Doesn’t sound like much, but it means the average density increases by sqrt(8)= 2.83. Escape velocity increases by just 19%, but that’s a second-order problem. Earth, so shrunk, would be just 9,010 km across.
One result I can’t parameterize is where the released gravitational energy would end up – some would become heat and probably melt much of the mantle, but that might be needed to create volcanism and revive a magnetic field. The rest would end up in the chemical bonds of the new high density phases of the compressed mantle.
Anyway there’s a new trick to add to fiction: compressed planets. I’m sure someone can imagine a way of limiting strong nuclear material, like quark matter, to just compacting a metallic core in the 500 years between Now and the ‘Verse.
Greetings,
I happen to be interested in the questions of terraforming (I do have an article under: http://www.strolen.com/content.php?node=3638 – it is a roleplaying site, so the science may be more than a little off 😉 ). Kudos for thinking of a solution for this problem!
Of course, the process would be massively destructive for the surface of the planet; forget anything that was there before. A question is, how long would it take until the planet ‘settles down’, and is calm enough to be habitable?
From a literary point of view, it would be interesting if the process were used on a planet, seemed to calm down, became settled… and then slowly began to revert. Geological processes can take quite some time, and not everything compressed will stay so – and the writer (and the poor subjects of his imagination) have a pretty catastrophe on their hands.
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As an aside, I wondered on a different feature of Firefly that looks a little off – it is the surprising number or habitable planets and moons in a single system.
Changing the composition of the atmosphere and other tricks would have an effect, but it still looks quite improbable. Aside from Lagrange points, and more exotic astrophysical constructs; or lots of physical movement – do you have any ideas on how to put plenty of _habitable_ planets in one place?
Hi Manfred
What inspired me to look into the ‘Verse further and fall in love with the series was the theoretical work on the formation of Uranus and Neptune. According to the Oligarchic accretion model dozens of Mars-to-Earth sized planetoids were required to form the Ice Giants – and almost as many scattered far and wide from the Sun.
So there could be plenty of planets in a single system, but a long way out – perhaps 100 – 1000 AU from the central star. Even further out in the case of our system since the Kuiper Belt would’ve been disrupted by near-in Earth-mass planets, but there’s nothing stopping a different outcome in other systems. Perhaps a binary companion confined the scatter to closer to the star? Thus two systems with dozens of planets each.
Also we know that large Jovians can exist in close orbits and remain stable – 47 Ursa Major b & c are perfect examples, or the planets of Upsilon Andromedae, or 55 Cancri. Such Jovians would easily have heavy enough moons to target for terraforming – if Jupiter is any guide then we might reasonably expect 4-5 moons each. In a triple star system with three Jovians per star we’d have perhaps 45 moons suitable for terraforming, plus inner planets, and a cloud of outer worlds perhaps in the hundreds.
Terraforming an Oort Cloud planet might seem incredibly difficult, but orbital fusion-powered ‘stars’ might easily provide enough warmth and energy to sustain a biosphere. If close enough to the central star a giant lens-like soletta might be suspended in the planet’s L1 point with its star thus providing natural light sufficient for life. If wormholes can be created one end might orbit close to the central star and ‘light-pipe’ sunlight directly to the planet.
Thus a few ideas to play with.
I knew half of that! 🙂
But I certainly missed the other half, that there can be a plenty of sufficiently large bodies.
With that in mind, all that is needed is the right temperature:
– the central star could become a red giant, or advance into a similar high-output phase
– multiple stars in a system change the equation as well
– for planets that in fact moons of Jovian planets, there is tidal heating
– conversely, a far/low output star could allow planets to have a thick atmospheric mantle, which would prevent heat loss, and let the natural radioactivity and geology make the rest (see the hypothesis on rogue planets, that could be habitable even in interstellar space: http://en.wikipedia.org/wiki/Rogue_planet#Atmosphere_hypothesis)
…and there’s probably more.
Thanks for the ideas, Adam! Looks like the Firefly setting isn’t impossible after all!
To Crush The Moon by Wil Mccarthy explores just such a scenario — crushing the moon to raise its surface gravity to that of Earth’s. McCarthy writes semi-hard SF – he always makes a great show of how scientific concepts back his ideas, even as the ideas verge on the fantastic. Think Niven. Note that “To Crush the Moon” is actually the third part of a long novel cut into three parts, the first two parts being titled “The Welllstone” and “Lost in Transmission”. All three books are sequels to the much ligherweight “Collapsium” which introduced the ideas that the books explore. All are recommended, but particularly To Crush The Moon, which could be read as a stand-alone novel, if the reader was somewhat tolerant about not quite knowing the full backstory.
Hi Eric
Glad I have good company in my idea – I thought I was going out on a limb, but I really enjoyed Will’s “The Collapsium” (as it was titled here in Oz) – the science glossary at the back was fascinating and entertaining.
To make 1 gee on the Moon needs a “crushing” to 40% of its current size – about 2800 km across in final form. Density, on average, goes up to 49.6 – some of the core will need to be stabilised “quark matter”, but it might catalyze the collapse of the whole too. Will McCarthy probably uses some collapsium. Bob Forward’s old McAndrews tales spoke of high-density degenerate matter as an industrial quantity material, relatively easily handled – compared to “tamed” black holes that is. By 2500 or so perhaps it will be.