The Verse as an Engineered System


Years ago, when the 1970s “Battlestar Galactica” was the pinnacle of TV Sci-Fi in a 10 year old’s imagination, I wondered at the nature of the 12 Colonies of Man, which all seemed to be in the same star system. The old BSG was a bit confused about “star systems” vs “galaxies” so much so that the interstellar nature of the Colonies and their systems had to wait for the 2004 reboot to be made explicit. Yet the idea stuck with me – could a system have 12 habitable planets? I knew about binary and trinary star systems as well as the possibility of Gas Giant moons being habitable (something I imagined as a child, only to have confirmed by the discovery of habitable zone Gas Giants over the last 19 years.)

Then along came “Firefly” and its Verse, which is in a multiple planet, multiple star, yet single system. Dozens of planets! Could that be possible?

Planet-formation Guru, Sean Raymond, has wondered the same thing and has now posted a series of blog-posts which have made the imagining more concretely physics based.

The discussion begins here: Build a better Solar System, a post in which Raymond ponders how our Solar System could be improved by rearranging the known bodies – he concludes we could have 7 habitable ‘planets’ though several would orbit a more Sunwards Jupiter.

Leaving our Solar System behind, he ponders the “Ultimate Solar System”, which squeezes the maximum number of planets into orbit around the best kind of star (an M0-M1 star at about 0.5 Solar Masses probably.)

Ultimate Solar System, Prelude: Building the ultimate Solar System

Ultimate Solar System, Part 1: Building the ultimate Solar System part 1: choosing the right star

As mentioned the right star is an M star, but not one that is too small, as smaller stars mean planets are subject to much higher tidal forces. For example, the strength of tides varies with the inverse cube power of the orbital radius, while the luminosity of stars varies with the 4th-3rd powers. For a 0.5 Solar mass star, the luminosity is about (0.5)^4 = 0.0625 times the Sun, so the habitable radius is at about 0.25 AU, but the tidal forces are ~(0.5)*(1/0.25)^4 times what Earth experiences from the Sun i.e. 32 times stronger. Meaning instead of half metre tides, the planet might get 16 metre tides, though it’d also be rotating slower due to more tidal-braking.

Ultimate Solar System, Part 2: Building the ultimate Solar System part 2: choosing the right planets

Naturally enough, since we’ve picked a long-living star, we want long-living planets – not too small, else they’ll lose their atmospheres. However, since we’re engineering things, selecting a low-EUV activity star will aid in keeping the atmosphere. Another concern is the inexorable decline in geological activity. Bigger planets last longer.

Ultimate Solar System, Part 3: Building the ultimate Solar System part 3: choosing the planets’ orbits

Raymond discusses habitable zone orbits and orbital stability – spaced properly and the system is stable against mutual perturbations for aeons, at least.

Ultimate Solar System, Part 4: Building the ultimate Solar System part 4: two ninja moves — moons and co-orbital planets

This is where the real innovation appears – firstly, twin planets – equal mass planets orbitting each other; then two pairs sharing an orbit 60 degrees apart. This allows 24 planets to be squeezed in, on six mutually stable orbits. Alternatively there could be four Gas Giants in 3/2 resonance orbits, each with five habitable moons, and each Gas Giant with two Trojan pairs in the L4/5 positions, thus 9 habitable planets per orbit for a total of 36.

Ultimate Solar System, Part 5: Building the ultimate Solar System part 5: putting the pieces together

Finally the Ultimate System is a Binary – one with the double Trojan Pairs in six orbits (24 total) and the other with Gas Giants and their retinues of Trojans and Moons – for a Grand Total of 60 habitable planets. The binary stars are at least 100 AU apart, to avoid exciting each other’s systems into too much Chaos. Of course we know of widely separated stellar systems with higher multiplicity. We could have two 100-AU apart binaries, themselves orbitting another binary at a distance of ~2,000 AU. Now that’d be a setting for some cool SF!

Lockstep Empire


Karl Schroeder’s imaginary “Lockstep” Civilization or Empire is a group of thousands of human-inhabited planets which periodically go into synchronous suspended animation for 30 years at a time, then revive for a month – a ratio of 360:1. This conserves resources and allows them to travel ‘quickly’ (from a subjective point-of-view) between worlds. Intriguing the planets are those possibly thousands which are sprinkled through the dark void between every star. The suggested number is ~hundreds of thousands of Pluto-to-Moon sized objects and thousands of Earth-sized objects for every star in the sky. A vast territory, all within a few light-years at most.

The Lockstep Empire is a reasonable solution to the problem of interstellar travel & communications – if we can’t develop warp-drive. It’s also a good exposition of the inter-stellar (“between the stars”) territory that civilizations could access and populate. Schroeder has rightly noted that many thousands of large objects probably exist between the stars, though maybe not so many Neptune to Jupiter sized ones, however, as WISE has demonstrated there seem to be fewer brown-dwarfs and super-Jovians Out There.

Here’s a short-story set in the Lockstep universe, from Tor: Jubilee, by Karl Schroeder

The kind of materials captured by the small denizens of inter-stellar space depends on how they formed. Two main options: via direct collapse out of protostellar nebulas or via scattering from forming planetary systems. In either scenario they might capture large amounts of the primordial nebula’s hydrogen/helium gas, along with ices, silicates and metals. One could have a large population of “micro-Neptunes” – Mars-to-Earth mass objects with gas-planet atmospheres. Internal geothermal heat will make it very hard for such objects to condense their helium atmospheres, but hydrogen might cool sufficiently to form oceans and ice-caps. Imagine such dark, eerie oceans of ultra-cold liquid, lit by stars twinkling through helium atmospheres…


Marshall Eubanks notes in the the comments:

In a short submission to Nature in 1999 (, David Stevenson pointed out that an Earth-like nomadic planet in deep space, with an Earth-like amount of radioactive heating, could have a thick hydrogen-helium atmosphere and a surface temperature high enough to support liquid water on the surface, even though there was no Sun and the planet would appear to have a temperature (as seen from the outside) of only 35 K. So, there might be “dark, eerie oceans” of regular old water on some dark Earths, oceans we might conceivably be able to sail without much protection, although we would need some sort of breathing apparatus.

Stevenson’s paper is available here, slightly longer than the “Nature” edit, on the author’s web-site: Interstellar Planets

Helium Planet?

Somewhere between 100-200 times Astronomical Units (AU) from the Sun, planets get COLD enough for hydrogen to begin condensing, as the surface temperature drops below the hydrogen critical point (~33.2 K, 13 atm) and then triple point (~20.6 K, 0.07 atm). Raw hydrogen is unlikely to be present without helium – both were ~99% of the mass of the Solar Nebula that the planets formed out of. Helium, in the form of its stable isotopes helium-4 and helium-3, doesn’t condense until much, much further from the Sun and inside the Galaxy might be too hot for it to condense at all.

The recent study, blogged here, which computed primordial H2/He atmospheres would resist being eroded from Super-Earths by their stars’ early high levels of soft x-rays (“XUV”), also computed significant H2/He atmospheres would be captured by planets from Mars-size and upwards. If such an object was driven out of the Inner System, or from near the Gas Giants, then it might’ve retained its primordial atmosphere and found orbital stability in the region beyond Neptune. Several such objects may exist, for there’s reason to think the Gas Giants formed from Mars-size “planetary embryos”, but such would be undetectable by astronomers due to their slow orbits and dimness… all, except the inner-most, which may explain the curious orbits of objects like Sedna and 2012 VP133, as reported recently:

Solar System’s edge redefined

Dwarf planet ‘Biden’ identified in an unlikely region of our solar system

Of course, being Crowlspace, our take is the implications of a planet with a condense hydrogen surface (oceans?) and an atmosphere of high-purity helium. Helium-3 is an advanced fusion fuel and, once we have reactors up to the task, highly desirable. With a solar abundance of 4E-4 (i.e. 1/2500) relative to Helium-4, that might sound a bit scarce, but it’s immensely more than what we can scrape together here on Earth. A “Super-Mars” (~0.5 Earth masses) with a primordial atmosphere might have captured anything from 4.7 bars to 772 bars of atmosphere according to this reference:

Origin and Loss of nebula-captured hydrogen envelopes from “sub”- to “super-Earths” in the habitable zone of Sun-like stars

Let’s assume a neat 100 bars. A 0.5 Earth-mass planet, of Earth composition, would have a radius of (0.5)^0.3 ~ 0.81 times Earth and thus a surface gravity of (0.5)^0.4 ~ 0.76 times Earth, with a column mass of ~1,350 tonnes, of which 75% is hydrogen. Thus 336.4 tonnes of helium for every square metre of planet and ~100 kg of that would be helium-3. Total supply would be ~3.8E+16 kg. Interestingly the primordial deuterium/hydrogen ratio is 1/40,000, meaning that the condensed hydrogen would supply 50 kg/square metre of deuterium. A stoichometric mixture of D/He3 for fusion would be 50/75 or 125 kg/square metre of planet – 4.2E+16 kg or 42 trillion tonnes. One could fuel up 840 million “Daedalus” class starships. For the same fuel mass, 50,000 tonnes per ship, one could send 50,000 tonnes of payload (a small space-colony) to the stars at 0.012 c and slow it down at the destination. With a mass allotment of ~50 tonnes per person, the total travelling population would be ~840 billion people…

Wonder Material, Part 3 – By Macron Beam to the Stars!

We’ve discussed the potential boost that quarter-wave sails made of Carbon Nano-Tubes (CNTs) might achieve from being pushed by the Sun. Dropping to 0.019 AU, the final velocity is 0.056c – dropping to 0.00465 AU (skimming the photosphere) would allow a speed of over 0.11c, but the material might not be up to the beating. Crewed vehicles would not endure the extreme acceleration – 84,000 gee at peak – so the speeds that might be achieved by solar-sailing star-travellers would be limited to 1,000 year flights to Alpha Centauri, with just 17 gee peak acceleration (as described in papers by Matloff).

Yet there is another option. Given a supply of small sails, carefully aimed or with some guidance, then why not use them as the momentum transfer system for a crewed starship? Greg Matloff explored the “macron beam” option in his discussion of non-nuclear starship propulsion in the early 1980s, but AFAIK didn’t suggest using mini-sails to accelerate larger starships. Jordin Kare proposed micro-sails pushed by laser to use as a momentum beam, but what I am suggesting is using very rugged solar-sails for boosting manned vehicles to higher speeds than their ‘natural’ acceleration limits would allow.

If CNT quarter-wave sails prove as agile as Christensen, Zubrin & Spieth have described, able to accelerate at 18 m/s2 at Earth’s orbit, thus having a thrust/mass ratio of ~3,000, then they could form the basis of a naturally energised “Sail-Beam” or “Macron Beam”. The most energy efficient ratio of macron-particle to space-vehicle velocity is 2:1, which allows a macron beam total mass of 1/2 the space-vehicle to be used. If the peak speed is limited to 0.056 c, then the most efficient starship speed is 0.028 c. But we can go faster if we have plenty of sails, approaching the macron beam speed asymptotically. In theory a Macron Beam of mini-sails could push an Icarus Probe, with a payload of 150 tonnes, to the preferred mission speed of ~0.045 c.


I’ve derived a proof of the most efficient ratio, using an equation originally derived by Matloff – the proof is available here: Maximum Mass-Beam Efficiency

The basic equation is:

dV/V = 2.e.(Mp/Ms)/[1 + 2.e.(Mp/Ms)]

…where dV is the velocity change, V the macron beam speed, e the momentum transfer efficiency, Mp the total particle mass, and Ms the vehicle mass. If we rearrange it to find the ratio Mp/Ms, we get:

Mp/Ms = (dV/V)/[2.e.(1-dV/V)]

If we assume a perfect reflection (e = 1), then double the mass of the vehicle in Macron Beam mini-sails is needed to get to 0.045 c, with a Macron Beam speed of 0.056 c. As the mini-sail approaches the ship it’s zapped by a laser tuned to a frequency at which it absorbs strongly, quickly blasting it into plasma. Alternatively it is heated by smashing into the vehicle’s magnetic field at a high relative speed. Then the plasma is reflected from a magnetic mirror arrangement on the starship. Some will stream forward at the centre of the magnetic mirror, reducing the reflection efficiency slightly.

If the starship accelerates at 1 m/s2 then it’ll need a final mass-flow of ~0.03 kg/s to push a 200 tonne starship. This doesn’t seem onerous. To reach 0.045 c will need 13,500,000 seconds – just over 156 days. The real trick is keeping the sails on course over ~600 AU when the acceleration finishes.

Water-rich gem points to vast ‘oceans’ beneath the Earth

Water-rich gem points to vast ‘oceans’ beneath the Earth.

A fortuitous sample from the Transition Zone in the Mantle has demonstrated the long suspected presence of Ringwoodite and its water-rich properties, confirming the idea of buried oceans deep within the Earth. Crustal slabs are believed to carry water into the mantle as they subduct. Such water returns to the crust as water-enabled melts like the granite ‘balloons’ (batholiths) which float up through ‘solid’ rock and lift up the terrain. This new evidence confirms that there’s water down there already, possibly several oceans worth.

The “Nature” paper is: Hydrous mantle transition zone indicated by ringwoodite included within diamond

The SF implications of all that water have not remained unexplored – Stephen Baxter flooded the Earth with mantle water in his tale “Flood” (one-word titles are a favourite of Baxter’s). Of course, Flood-believers posit that at least some of the waters of the Noachic Flood came from the mantle and then returned, but – unlike SF-writers – they’re obliged to explain the mechanism aside from a wave of God’s magic-wand.

At least one Super-Earth around every M dwarf


Every red dwarf star has at least one planet

The news is that every M dwarf probably has at least 1 planet, if not more, which is good news when looking for cosmic real estate. The bad news – as blogged here previously – is that exoplanets bigger than Earth, or even Earth-sized and unlucky, are unable to rid themselves of the primordial H/He atmosphere they capture while forming. Too big means the planet becomes a mini-Neptune.

The relevant preprint is here: Bayesian search for low-mass planets around nearby M dwarfs: Estimates for occurrence rate based on global detectability statistics

One of the systems identified is a two-planet system around the star GJ 682. The planets are Super-Earths, though the uncertainty range goes as low as 2 Earth-masses for the habitable zone planet. Being radial velocity measurements, the odds are it’s a Sub-Neptune massing ~4 Earths. Intriguingly GJ 682 is only 16.6 ly away, so we should probably add the planet to the list of “Nearby Habitable Zone Planets” even if it is a sub-Neptune.

An atmosphere of H/He can be an asset for an anoxic (oxygen-less) biosphere for planets further out from their stars, though too much primordial atmosphere means a very large greenhouse effect trapping geothermal heat in. For example, Earth emits ~0.08 W per square metre, on average. Thus, with no stellar input, its equilibrium temperature is ~34.5 K. With an adiabatic atmosphere holding the heat in, and a photospheric temperature of 34.5 K, then the critical point of water (647.3 K) is exceeded at a surface pressure of ~5742 bar. A convenient measure of total H/He is “Earth Ocean Equivalents (Hydrogen)” (EOEH) – in Earth’s case there’s 1.5E+20 kg of hydrogen in our oceans, the equivalent of 29.4 bar surface pressure. Thus >200 EOEHs would mean no liquid water is possible. Bigger planets would have higher radiogenic and cosmogonic heat-fluxes, roughly increasing with the 1/2 root of the mass. A 10 Earth-mass planet would have a photospheric temperature of ~46 K, but it’d also have a higher gravity, but a higher surface area to spread a given mass of atmosphere over too. For Super-Earths the surface pressure produced by a given atmosphere mass at the surface of the solid core decreases slowly with planet mass (a ~-0.1 power, roughly). So >90 EOEHs would broil a 10 Earth-mass Super-Earth.

Sounds like a lot, but even 200 EOEHs is only 0.5% the mass of the Earth. Not a lot of hydrogen, by proportion, will mean death for an otherwise Earth-like planet.



Super-Earths might be Dead from Gas…

Origin and loss of nebula-captured hydrogen envelopes from ‘sub’- to ‘super-Earths’ in the habitable zone of Sun-like stars

…rather surprising study of hydrogen-capture and loss from planets near Earth’s mass and orbit. Planets bigger than 0.1 Earth masses (i.e. Mars size and up) will capture the hydrogen-helium gas (H2/He) from the nebula that forms around young stars. The XUV (“soft x-rays”) light from young stars is enough to drive the primordial atmosphere away – but critical to future life on such planets, enough must escape to allow a secondary atmosphere, of heavier gases, to form. Below about 1.5 Earth masses, the planets can lose the primordial H2/He. Above that mass not enough is driven away to produce an “Earth-like” planet. Instead a “mini-Neptune” forms, with a deep H2/He atmosphere over a hot, rocky core.

But it’s not all bad news – small planets that were ejected from close to their stars by migrating gas giants, might retain sufficient H2/He to remain warm enough for liquid water, far from their original orbit. Such objects might be sprinkled through interstellar space, awaiting discovery.

Antimatter at Hand?

Marshall Eubanks has posited the presence of million tonne masses of stable quark matter inside solar system objects – potentially both matter and antimatter forms of it, with the antimatter version protected from annihilation by a 100 MeV Colour-Force potential well.

Powering Starships with Compact Condensed Quark Matter

While pure antimatter/matter propulsion promises high exhaust velocities (~c) the difficulties of achieving that ultimate performance are considerable. But what if we use something else for reaction mass and use antimatter to energise that? And, instead of using it in a rocket, we use a magnetic scoop to draw in reaction mass from the interstellar medium? This is the Ram-Augmented Interstellar ‘Rocket’ – though technically a rocket carries all its reaction mass – and it promises high performance without all the disadvantages of exponentially rising mass-ratios. Mixing 1% antimatter into the matter flow could, in theory, produce an exhaust velocity of ~0.2 c. Scooping and energising the equivalent mass of ~100 times the mass of the starship would allow a top-speed of 0.999999996 c to be achieved, before braking to a halt using half that mass. This would allow, at 1 gee acceleration, a journey of ~20,000 light-years. The nearby stars would be accessible at a much lower antimatter budget.

Quark Matter in the Solar System : Evidence for a Game-Changing Space Resource

Very Rapid Rotating asteroids might be held together by the additional gravity of a mm-sized million tonne quark nugget.

Primordial Capture of Dark Matter in the Formation of Planetary Systems

Evidence for Condensed Quark Matter in the Solar System

Observational Constraints on Ultra-Dense Dark Matter

Such quark nuggets would be made in the Big Bang potentially, if antimatter is squirrelled away in such a form, the explanation of the observed lack of free-antimatter in the Universe. The abundance of such ultra-dense tiny specks, to be compatible with microlensing observations, would be in the ‘interesting’ mass-range suggested by the Solar System evidence.

More Harold “Sonny” White Papers & Presentations Online

IXS Enterprise 2
Sonny presented at the Icarus Interstellar “Starship Congress 2013″ in Texas. His talk starts at 13:20 and ends 58:00 at Icarus Interstellar’s YouTube video of the event: Day Three of Starship Congress 2013. Note the interesting discussion of Q-Thrusters for interstellar missions (30 years to Alpha Centauri) and the “warp-drive” illustrations.

Sonny’s discussion of Metric Engineering began with a 2003 paper on the implications of the Alcubierre Metric, here in abstract: A Discussion of Space-Time Metric Engineering. A search on Google will find it at the publisher’s web-site for about $40 US, but a reformatted reprint (White 2003) might be found.

A citation search of the above paper presents two interesting derivative papers:

Artificial gravity field Which is a discussion of how one might use Metric Engineering to generate SF-style artificial gravity. Not easy, but intriguing nonetheless.

Conformal Gravity and the Alcubierre Warp Drive Metric explores an alternative formulation of gravity’s implications for the Alcubierre Metric and the feasibility of warp-drive. Conformal gravity offers the tantalising possibility of warp-drive without the need for NET amounts of negative energy/pressure.

Harold also collaborated with Eric Davis, an exotic propulsion Guru, to discuss the Higher-Dimensional version of the Alcubierre Metric: The Alcubierre Warp Drive in Higher Dimensional Spacetime. The work Harold did for this paper fed into the more recent series of papers on optimising the Warp-Drive’s properties to minimise the energy required. See the previous Crowlspace blog-post for details.

Wikipedia covers the Interferometer Test for space warps in the lab here: White–Juday warp-field interferometer. Present status of the experiment is encouraging, but not conclusive. Sources of noise need to be pinned down and minimised or analysed and removed via post-data analysis.

Recently (last month, almost in time for Christmas) this intriguing paper discussing Sonny’s 2003 paper appeared: The Alcubierre Warp Drive using Lorentz Boosts according to the Harold White Spacetime Metric potential ?. Fernando Loup and Daniel Rocha are warp-drive enthusiasts, not mainstream Relativists, but have produced interesting bodies of work over time. Best read critically.

Finally I should mention the EMDrive controversy and its possible relevance to the Q-Thruster. A patent lawyer, Robert Shawyer, has developed and promoted a propellantless drive based on the behaviour of microwaves in a convergent reflective cavity. He believes it provides thrust without propellant being expelled – its claimed thrust level is much too high for it to be a radio “photon-rocket” (unlike some supposedly propellantless drives that have appeared over the years). Shawyer has claimed interest and experimental validation from Chinese researchers, even though many mainstream physicists (including Greg Egan, the Australian SF writer who is a mathematician by training) have computed the relevant fields of the microwave cavity to demonstrate NO net thrust.

However, there may be a theoretical “out”, which might apply further to other proposed Thrusters. Fernando Minotti discusses one version of gravitation theory in which such thrusts might be produced: Scalar-tensor theories and asymmetric resonant cavities. While the EMDrive probably doesn’t work, another Thruster concept, developed by Cannae, might. Unfortunately their web-site is down so I can’t direct you to their rather interesting material. Whether it’ll produce real results in proper testing conditions *might* come from work at Sonny’s Eagleworks Lab.