The Dark Planets

An article appeared today on about the detection of “free-floating planets.” These planets may have formed around a central star, like the planets in our Solar System did, but due to some gravitational interaction during their star system’s formation the planets escaped their stars. These Jovian planets, which may outnumber stars in our galaxy, are now doomed to endlessly wander the cosmos under perpetual starry night skies.

Naturally, this notion tripped my sci-fi circuits.


This artist's conception illustrates a Jupiter-like planet alone in the dark of space, floating freely without a parent star. Image credit: NASA/JPL-Caltech

We live in an age in which new planetary systems are being discovered at an incredible rate. We are getting closer and closer to the ability to detect other Earth-like worlds around other stars. In fact, just a few days ago a study found that certain climate models of Gliese 581d (that would be potential-planet Zarmina‘s until-now-slightly-less-sexy sister) may support a liquid water cycle.

So what would it take for one of these free-flying, starless planets to be habitable?

The immediate answer that may come to you, the average person, is, “Joe, you are crazy.” But wait a moment!

All life requires is an energy input and certain chemicals, right? Well, all sorts of chemicals exist in gas planets. And there are plenty of possible energy inputs from the gas dynamics going on in their atmospheres – not to mention magnetic fields and other esoteric stuff like that that Earth life generally doesn’t incorporate into its metabolism.

But forget gas-giant balloon-life. Suppose we constrain our notion of habitability to the usual anthropocentric meaning: liquid water on a rocky surface.

In order for a rocky planet to have liquid surface water, it needs two things: heat and pressure. (Pressure so that the water doesn’t just sublimate or boil off into space, and heat so that it doesn’t freeze.) The “pressure” part we can take care of by giving our rocky world an atmosphere. However, we need a heat source – not only to keep the water from freezing, but to keep the atmosphere itself from freezing onto the planet, too. How do we get this heat source? Radioactive heating from the planet interior isn’t going to warm the surface to 273 K. Stars are all going to be too far from these planets to do any good. Emission nebulae are way too cold and rarified, even if the planet is right in the middle of them. The planet is going to pretty efficiently radiate away any heat inputs before that energy goes into heating ice to make water. (I suppose we could stick the planet right in the way of a black hole’s polar jet or some other source of hard radiation for our energy source – but then we’re back to getting really alien alien life. Fun to think about! And what happens to those alien civilizations that thrive on a dark planet bathed in X rays when their planet finishes traversing the zone of hard radiation?!)

I’m pretty convinced that liquid surface water is not going to appear on any free-flying rocky planets. Unless…

Suppose, when a Jovian planet got ejected from its birth star system, it carried its moon system away with it. Maybe some heat can come off of that gas giant and hit the moon! It’s not going to be reflected light, though, because there’s no star to provide bright enough light. No, the energy will have to come from the Jovian itself. This condition means that we’ll have to look at something like brown dwarfs: astronomical bodies that are just slightly too small to ignite under their internal pressure and turn into the hydrogen fusion furnaces that are stars. But they do have some fusion going on in their dense cores.

Take Teide 1, the first brown dwarf to have its existence confirmed. It has a surface temperature of around 2500 K, a luminosity of about 0.001 Lsun, and a radius around 0.1 Rsun. Suppose that a rocky (Earth-density) satellite orbits Teide 1 at its Roche limit, the closest orbital radius it can have without tides tearing the moon apart into a pretty but uninhabitable ring. (By a quick calculation, I get about 337,000 km for Teide 1 – coincidentally close to the Earth-Moon distance.) At that distance, the moon would receive around 1 million watts per square meter from the Jovian. If that’s the input power, the Stefan-Boltzmann law gives the output radiation of the planet in equilibrium. With a couple assumptions about albedo (Earthlike) and assuming that the moon receives incoming radiation over its cross-sectional area but radiates out over its entire surface (and that it’s the size of Earth’s Moon), my quick hand scratchings give a surface temperature near 50 K. Hmm…no liquid surface water there.

But there’s another possible heat input to a moon around a gas giant: the tides of the Jovian world.

Consider Jupiter: it has four big moons, and Jupiter raises such huge tides on these moons that the rocky mini-worlds actually flex, generating heat from friction. On Europa, this tidal heating in its central rocky part is sufficient to melt the inner bit of its water-ice coating into an ocean. Heck, scientists combing Galileo probe data just determined that tidal heating is sufficient to keep pretty much all of Io’s interior molten. That world is made of lava, with a thin crusty shell. And it’s all because the moon orbits a gas giant in a resonance with some other moons. the interaction between their orbits keeps the tidal energy coming.

So let’s give our moon some companions and an orbital resonance. Solar radiation is negligible compared to tidal heating even for Jupiter, so we know that that could give our moon liquid water…at least under the surface, like Europa.

But add an atmosphere, and you get an insulating blanket around the moon’s surface. More internal heat stays trapped on the moon’s surface instead of radiating away into space. I haven’t done the calculations, but if tidal heating can liquify rock on Io I bet it could be enough to melt Europa’s ice layer all the way through for slightly different orbital parameters. And with an atmosphere, the moon gets pressure to keep that liquid water from boiling. Like Titan. Put Titan where Io is…and what do you get? I’m not sure, but it would be really interesting. And it wouldn’t require the Sun.

Cool, huh? It certainly hasn’t been confirmed, and I don’t have a detailed model, of course, but I think the theoretical grounds exist for these free-flying dark planets to have liquid-water surfaces. Imagine vacationing on a beach next to a steaming ocean that is basically a global-scale hot spring, where it’s perpetual night and every couple (Earth) days you see the shadowy form of the gas giant loom overhead, visible more because of the stars it blocks out than from any external light source, except for the occasional immense spark of lightning through its clouds…

The Drive

Imagine, if you will, that a US government agency invented the automobile.

And for forty-five years, nobody else but the National Automobile Sales Agency produces any cars in this country. Not because of any particular regulation, you see – but because cars are complex machines that require precision workings and careful construction. They are expensive and require a significant investment in infrastructure. So, not everybody has a car, though plenty of people out there want one. And those people have to buy the cars developed by the US Car Program. Imagine. If you will.

Now suppose that the first batch of cars that the National Automobile Sales Agency were some real hot rods. They could tear all over the place, they looked downright sexy, and they inspired envy in all but the most curmudgeonly of observers. These cars were a source of national pride. People would travel from far and wide just to get a look at a Car Program showroom – or even just to meet those test drivers who shook down the cars on the federal test tracks.

But then, about thirty years ago (15-odd years after the car’s introduction to American drivers), the government decided that just blasting all over the roads wasn’t a great use of this invention. So the National Automobile Sales Agency set out to design a car that could be a workhorse for people. Suppose they rolled out something like those late-’80s-and-early-’90s Ford Taurus wagons that used to be all over the place. Functional, not that stylish. They can do a lot of things that you need. However, for the sake of this argument, let’s suppose that these wagons weren’t all that reliable. Or, at least, they worked long enough for all your errands and trips – but after each trip, you had to take it to the shop to get it looked at. This became so commonplace that everyone with one of these wagons just built a trip to their favorite Car Program mechanic into their travel itineraries, and the mechanics all did the same overhaul on every wagon that rolled into their shops. All this got built into the expense of owning an automobile, which climbed far above the initial sticker prices.

For some people, business was great.

And this went on for thirty years.

Then, forty-five years after the first National Automobile Sales Agency hot rods burned up their desert test tracks, an American start-up company unveils…oh, let’s say the Tesla Roadster. They plan to start marketing them as soon as they can, and they get initial support from the Car Agency, but they’re mostly on their own so it’s tough to get going.

But they do. After a couple test drives, they even win a highly publicized performance award. And then they start taking pre-orders.

Meanwhile, another American start-up company is working on prototypes. Their progress is less meteoric than Tesla’s, and they suffer some initial setbacks that make them something of a temporary laughingstock in the automotive enthusiast community. But then they roll out a model that has a couple reeeeeal good test drives. It’s something small, kinda sporty, useful, and most importantly, it comes at a fraction of the price that the Car Agency’s wagons have gotten to. Let’s say it’s a Honda Civic. But this company isn’t done shaking up the automotive community! Immediately after sales start on the Civic, this company announces that it plans to develop…hmmm…I know, the Subaru Outback! It’s comparable in functionality to the National Automobile Sales Agency wagon, but promises higher reliability and low, low prices. What’s more, this company has some additional plans – for a massive thing they call the “pickup truck.”

Now, the National Automobile Sales Agency is at a crossroads. It has big plans and big ideas. It hasn’t spent those thirty years with the wagon idling…but there are issues of cost, and infrastructure. If it had a much more economical way to get access to cars, it could get some sweet road trips going. So it starts thinking about ending production of the venerable, respectable old wagons. Instead, it would just buy some Civics and Outbacks and…”trucks” (when they come along) from this company. With all the extra cash it saved from buying those cars instead of building its own wagons (which, really, are far too expensive to keep on the road at this point and are old enough for antique plates in some states), the Car Program will purchase the infrastructure it needs to set up things like highways and bridges and interstates – things that will really enable Car Program drivers to go far, and go see the sights, and visit just about anywhere in the country. You know – the things that all Americans imagined the Car Program would be doing, before those wagons became so darned expensive and the ordinary citizens stopped paying attention to them.

Because, you see, the National Automobile Sales Agency gets its mandate and direction from Congress. Some Congressmen and -women come from districts that have profited extensively from the Car Program. Members of their districts are the mechanics who service all those wagons, keeping them on the road. Members of their districts are the gas station attendants fueling up those wagons. And members of their districts are the National Automobile Sales Agency employees building and selling those wagons.

(Well, actually, that’s not quite correct. I should have said, “and members of their districts are employees of large automotive corporations that have been subcontracted by the National Automotive Sales Agency to build and sell those wagons under the Agency banner,” but that sounds less appealing and doesn’t work as well for these Congressmen and -women when they are going for political soundbites.)

So, to Congress, the Car Program represents jobs. And, unlike many programs designed to stimulate the economy and create work for citizens, the Car Program is popular. People remember what those hot rods could do, and the mystique of those first test drivers still lingers throughout the country. Despite the promise that exists if the Car Program stops making its own wagons and contracts out for newer cars, Congress punts and punts, trying to keep the wagons on the road.

(Again, that sentence is not quite right. It’s not so much that the Car Program would “stop making its own wagons” and instead buy them from someone else. It’s more like the program would switch subcontractors – to one which offers a more competitive product.)

Eventually, they grudgingly decide that the Car Program does need something new, but instead of telling the Program to do the procurement and design work on their own, they direct the Agency to develop a hot-rod-pickup-truck-sedan-RV-Ferrari-flatbed. (That’s what kind of car design I imagine would come out of a Congressional subcommittee.) And they make sure to apportion parts of this work out to as many states as they can.

But still, some politicians decry this move. They are afraid of all the Taurus wagon jobs that will be lost if the Agency moves to something new. So, despite the facts that the wagons are thirty years old, they are unsustainably expensive to operate, they aren’t taking the Car Program to all the places it could (or should want to) go, and that the Outbacks made by the start-up company have pretty much already obsoleted the hot-rod-pickup-truck-sedan-RV-Ferrari-flatbed (not to mention the older Taurus wagons), these politicians argue that the wagons should be kept on the road artificially. Just to keep the wagon-related jobs going. (For a truly ironic twist, a lot of these politicians are Republican.)

And I sit here and think, “But I want to drive on the highway. I don’t want to pay very much, but I still want to see the Grand Canyon. I want other people to do the same. And I think the Car Program could get back to its roots, and really push the boundaries of what we can do with cars – if it isn’t saddled with the burden of having to re-think all the same problems of wheels and engines. If it just buys perfectly good (and inexpensive!) cars from this start-up company, it will free up resources to develop all those bridges and ferries and tunnels that can take cars places that they’ve never been able to go before. Because the strong suit of the National Automobile Sales Agency isn’t that of being an entrenched bureaucracy full of sinecure positions – it’s of taking the big risks that the private companies never will and thus giving our entire society the big benefits of those long shots.”

In case you haven’t guessed it, I didn’t give the Car Agency the acronym “N. A. S. A.” for nothing.

You see, it’s the day that the Space Shuttle Endeavour – my favorite space shuttle, the only one I got to see launch in person – took flight for the last time. And the headlining articles about the launch were things like this: “Workers Left Rattled By Final Shuttle Launches.” The biggest concerns: Where will all the Shuttle Program jobs go when the Shuttle stops flying?

In that article, one Space Coast resident is actually quoted as calling the retirement of the 30-year-old Shuttle program “insane.”

I sympathize with the human aspect of the story, but at the same time…”insane?” I think not. To me, the most important thing about the space program is the space travel. I think it would be insane to keep the Shuttles flying for much longer. I wasn’t stretching the truth much in my little scenario – in some states, the Space Shuttles could have antique license plates. If they were cars. The Space Shuttle Program is older than I am. Okay, Congress, I grew up steeped in space enthusiasm, got a physics degree, got a Ph.D. in spacecraft engineering, and now I’m ready to push the boundaries of space exploration all the way to – oh, what? You want NASA to keep doing the same thing it was doing before I was born, just to keep certain specific jobs safe? No, thanks. Suddenly the “Space Age” really does look forty years old to me.

What strikes me as really insane is the Congressional shortsightedness that has kept NASA from following through on a coherent vision to replace the Space Shuttles. I had no problem with President Obama’s plans – look at the numbers: SpaceX developed a rocket just as capable as Ares I, but SpaceX managed to leapfrog the Constellation schedule and blow the Constellation program budget out of the water. I can totally understand pointing at the Falcon launch vehicle and Dragon capsule and telling NASA, “Hey, um, how about you just buy some of those?” It just makes good business sense. And it would let NASA spend its valuable time and resources on doing the things that I really would like to see the agency do. The things I know it could be capable of, because it once was. Like go to Mars, or put an way station in deep space, or send robots to sail the seas of Titan, or build self-sustaining habitats so that people can really live and work in space. As if directing NASA to do those things won’t create tons of high-paying jobs to replace or exceed the losses!

But instead, Congress fought tooth and nail for an extra Shuttle launch and ordered up the hot-rod-pickup-truck-sedan-RV-Ferrari-flatbed. And they have no idea where that clunker-to-be is supposed to be going. It’s pretty much set up to fail, and I am completely convinced that the Virgin Galactics, SpaceXs, and other new-space companies of the country (and the world) are going to be light-years ahead NASA in the coming decades unless Congress gets some long-term thinking going in its science and space committees.

These last Space Shuttle launches are bittersweet events – as is the end of any program marked by eye-opening achievements. The last launches were always going to be bittersweet – especially for idealists like me.

But there is a right way to do this. As I said, if there’s some long-term thinking in Congress again – giving NASA lofty missions and appropriate resources, without designing its hardware by committee – we could do this the correct way. The way we used to do it.

You see, Gemini XII was the final flight of the Gemini program. No more Gemini were launched after that. The spacecraft were grounded, retired, and mothballed to museums. But that final flight wasn’t so bittersweet.

Because less than a year after Gemini XII, the first Saturn V rumbled skyward, and less than a year after that, astronauts on board Apollo 7 gazed down at the Earth.


A friend who – allegedly – hates puns inadvertently reminded me that I let Star Wars day go by uncelebrated on May the 4th (be with you). Fortunately, last week I also got into a discussion with some of my new coworkers in which that classic get-to-know-people question came up: if you had three wishes, what would they be?

My first two are no-brainers. For me, at least. One: no more diabetes.

Two: Millennium Falcon.


She's the fastest hunk of junk in the Galaxy. She may not look like much, but she's got it where it counts.

I think having the Millennium Falcon at my disposal would actually keep me pretty much set without spending the third wish. Just think of all the problems I could solve if I had the Falcon!

It’s a mobile home. It’s fast transportation. It’s a thrill ride. It’s a utility vehicle. It comes with built-in security systems. I could have fame and fortune or solitude as I desire. It has little dangling masks that let people breathe in space. It’s got extremely capable long-range scanners. It has a landing claw that lets it stick to Star Destroyers.

Problem: Only twelve humans have ever set foot on another planet, and I am not one of them. Solution: She’ll make point-five past lightspeed!

Problem: I have never been to Barbados. Solution: The Falcon flies just as well in atmosphere as in space! And I don’t have to book a hotel, either!

Problem: people are nosy. Solution: pop-out blaster turrets!

Problem: my hand fell off. Solution: Stick my arm in this tube in the medical bay!

Problem: I keep losing my Lando Calrissian. Solution: the Falcon comes with clips!

Problem: NASA moves too slowly/has no money. Solution: Heck, I’d take planetary scientists to other worlds for ten bucks.

Just about the only thing it can’t do is escape a tractor beam. I won't get too close to any small moons. Just in case.

Yes; by three units

The Bad Astronomer has been experiencing some angst over unit systems.

Almost anyone in a technical profession can provide all sorts of complaints about systems of measurement. (I once put a notice on a lab whiteboard that read, “English units suck.”) To me, the oddest thing about all this is exactly the problem at Phil identified: intuition.

I have no everyday intuition for the metric system. I don’t have a good feel for how hot it is in Celsius; nor can I picture the difference between someone 1.4 m tall and 1.8 m tall. I don’t know how much heft a kilogram has if I pick it up in one hand. I don’t know how fast a moving car goes in kph, and I couldn’t deliver a 10 N push.

But, on the other hand, I have no intuition for English/Imperial/US units in a technical context!

I discovered this while spending a summer working for NASA. The Constellation Program, at the time, was officially on English units of measure, and I realized that I had no idea how big things were or what size forces they were experiencing or anything like that. It was a strange inversion of my everyday experience. But then – having been educated in a wonderfully self-consistent system of units, by professors who had synchronized notations – I encountered the horror of a unit that is the “pound mass.” I can understand the desire to try and match the English unit of mass (slugs) to what we usually experience in terms of force and weight, but the real kicker was that as I dug into the “lbm” I encountered inconsistent definitions of the unit. Ack! I ended up just converting everything I was given to metric, doing all the work I needed to do, and then converting it all to English when I finished.

Things were much better that way. And so one of the first things I did in Matlab at my new job was write a bunch of unit-conversion functions.