Archive for May, 2010

Inhabitable Planets…

Posted in Art, Astronomy, SF, Speculation with tags , , , on May 28, 2010 by davidnm2009


Inhabitable planets. Aaah, that phrase.

It’s a phrase that can hide a world of sins. You come across it a lot in science fiction, and it’s turning into one of my pet peeves. Briefly, the ‘consensus’ definition appears to be a planet where an adult human being wouldn’t need a spacesuit. Call this the spacesuit test, if you will!

Presumably, this planet doesn’t make the grade…

But there’s a problem there. That can cover a huge range of environments. Sure enough, you see this in SF, from really well-thought-through and believable worlds all the way to single-biome stereotype-pools.

But it’s worse than that. Even if a planet is technically inhabitable, that doesn’t mean it will be Earthlike. I got to thinking about this in depth a few years ago, during my brief (and wholly-disastrous) experience of GM’ing an RPG campaign. Although the campaign was a trainwreck (I take full responsibility for being useless) and failed after just four sessions, it did get me to thinking about just what exactly you would experience when setting foot on an alien planet. When you have to describe things to people, you really need to think about them first, and it does help if you can create a strong visual image. Let’s take an example.

A terrestrial-mass planet orbiting a red dwarf.

It’s a dwarf and it’s red(ish). They do exactly what they say on the tin…

Red dwarfs are the most common type of star (around 80%, by numbers) and it appears many of them have planets. So they aren’t absurd to pick on. However, unlike our Sun, red dwarfs are very faint (a very bright red dwarf might just scrape up to eight percent the luminosity of our Sun). There isn’t a single one that you can see with the naked eye here on Earth; no-one had any idea they even existed until the invention of the telescope.

So, any planet that could pass the spacesuit test is going to have to orbit close to the star. If it’s as far out as the Earth, it will be a frozen ball of ice and the weather forecast may involve it raining nitrogen – not humanly-convenient, to say the least! In principle, you can snuggle planets up close enough to such stars – we know of red dwarfs with close-in Jovian planets, and even a few terrestrial-mass-range companions.

However, there is a problem. It’s called tidal locking. The star’s tides will, over millions of years, spin the planet down until it completes one rotation in the time it takes one orbit, thus always presenting the same face to the star. One side will be daylight, forever, and the other night, forever. (And this is quite unavoidable for a planet so close in.) It used to be thought that this was a planet-killer; such extreme temperature variations would prevent any kind of life. However, current research suggests that atmospheres can ameliorate the extremes. Even a thin atmosphere should be enough to keep the dayside hot-but-liveable and the nightside cold-but-liveable. Wind – isn’t it great?

Let’s just quickly take stock. We have a planet orbiting a small, reddish sun. Its ‘year’ lasts several terrestrial days to maybe a month at the most. On one side of the planet, the sun never sets. On the other, it never rises. So far, so weird!

On the surface

Red dwarf, strange shoreline.

The planet would be tide-locked, so the sun would never move in the sky*. Plants would presumably grow toward the sun, but unlike Earthly sunflowers, they wouldn’t turn during the day. Also, the vegetation would be rather Goth. It would need to make the most of the weak light, and be particularly good at soaking up the near-infrared. Plants would probably be black rather then green.

The sky would be odd. Our sky is blue due to Rayleigh scattering; short-wavelength photons such as blue light scatter more than longer-wavelength ones. But a red dwarf is brightest in the infrared; they don’t supply much ‘blue’ flux at all**. So without much light to scatter, even during the day the sky will be dark. It will be brightest near the horizon, where you’re looking through the thickest cross-section of air (so more air to scatter the few blue photons). Presumably you would get a sort of turquoise band, that fades rapidly to navy-blue or even black. There’ll probably be another bluer region near the star itself, too. But overhead, inkiness rules. If you shade your eyes from the sun, you could probably see stars, even by daylight.

Also, the sun itself will be odd. It will seem much bigger than ours does, even though M dwarfs are all physically-smaller. A habitable planet around an M dwarf will have to be close. (A terrestrial world around Proxima Centauri, for instance, would have a 7-Earth-day orbit.) Even though the star is smaller than our Sun, the planet will be so much closer, and that will result in a huge, fat-looking sun.

But that sun won’t dazzle you. I mentioned that most of M dwarf flux is in the infrared – you would probably be able to stare right at the star, even by daylight. It would be bright, yes, but it won’t blind you. What you would notice, though, would be the heat. It would be something like standing next to a baker’s oven with the door open. Human skin can register infrared, and there is a lot of IR coming off this thing.

The point I’m trying to make is, this planet might be inhabitable, but it wouldn’t be Earthlike.

*Or at least, not much. Libration and obliquity would complicate this picture, and also any eccentricity in the orbit. However, you wouldn’t expect much of either obliquity or eccentricity this deep in a star’s gravity well, so although I’m wrong, I’m not too wrong here.
**B-R > 1.0, if I recall correctly. Or to put it another, non-logarithmic way, the ‘blue’ band (B) has less than half the amount of flux as the ‘red’ band (R).



Posted in Speculation with tags on May 11, 2010 by davidnm2009

I’ve been doing some thinking about what we can possibly ‘reasonably expect’ from the next 100 years. Bear in mind these are not predictions, just speculation. Attempts to ‘accurately’ predict the future are almost certainly doomed to failure. Nonetheless, some thoughts…

  • Global warming will carry on. If anything serious was going to get done about it, it would probably already have started. Sadly, I think we can honestly say that the Kyoto Protocol really hasn’t been very effective – all it’s really managed to do is get people talking about the issue. I suppose that’s something, but it’s not really enough!
  • This implies new land rushes. Once the ice-cap is gone, Greenland will be a lot more habitable. Extensive human population there is hardly absurd, in fact there is historical precedent.
  • Depending on how far temperatures rise, one might even imagine an Antarctic land rush, although if this does happen, the population centres will presumably be in East Antarctica, where most of the land would be.
  • Major worldwide economic problems when the oil runs out.
  • A global subsistence crisis will likely be part of the above. Consider: the Earth has enough arable land mass for 2 bn people, using conventional agriculture. Petrochemical-derived fertilisers allow us to squeeze more energy out of those square miles of ground, which is why a population of ~7 bn can currently (just barely) be fed. However, when the oil starts running out, so will said fertilisers, and also it will be harder to physically-transport them to the places where they’re needed…
  • One way or another, I strongly suspect that the world population in 2110 will be lower than the population in 2010. Climate change plus tropical diseases moving north/south plus oil crisis plus too many hungry mouths doesn’t make for a pretty combination. If I had to guess, I’d say 1 – 2 billion rather than 9 – 10 billion.
  • On the other hand, economic and political turmoil on Earth perhaps make space colonisation more likely. It’s hard to imagine running a colony set-up at a conventional corporate-style profit, but the cost/benefits analysis looks rather different if you’re fleeing social meltdown back home.
  • If colonisation does happen, then I suspect Mars is a more likely target than the Moon. Mars has comparatively-abundant water and more favourable gravity, even if the Moon isn’t quite as bone dry as we once thought.
  • Or, in fact, oddly enough, Venus might also be a good bet. There’s a layer in its atmosphere with Earthlike temperatures and pressures, P&T conditions similar to those atop Mauna Kea (not entirely pleasant, but humanly bearable – I can say that from experience!), and solar energy would be abundant. One can imagine balloon cities, drifting above the Venusian clouds – Buckminster Fuller has seriously proposed engineering along those lines, so it’s actually less mad then it sounds.
  • Back on Earth, America will cease to have any significance at around the time the oil wells start coughing up dry. It’s economy is utterly dependent on cheap oil, American politics is strongly in hoc to the oil companies so there’s no dynamism for adjustment and there’s no pressure for change from much of the American public, either. With that combination, complete failure is the only option. The country itself may – may! – survive the transition, but its superpower status won’t.
  • Call me cynical, but I suspect the European Union won’t manage much better. Scandinavia tends to weather crises well, and the Germans are notoriously resilient, but some of the rest of us seem a bit too self-absorbed, apathetic and unwilling to face the serious change that would be necessary to adapt. (Sorry; small disgruntled liberal moment there. It’ll pass. Eventually.)
  • Somewhat more optimistically, by the middle of the century astronomy will be a different place. We will very likely have spectra of Earth-mass exoplanets, and will certainly have some idea of the mass distribution of super-Earths. (I can say that with confidence … it’s already possible to put bounds on the upper limits.) We will also have a clearer idea of whether this planet is a flukish outlier, or if the Galaxy is littered with them.
  • Will there be a First Contact by 2110? I don’t know. My intuitive feeling is ‘no’; personally I suspect that civilisations are thinly spread both in space and time. However, that is just a personal feeling, and may be utterly baseless. We don’t even know for a fact if there are inhabitable planets around Alpha Centauri A or B yet, so in principle, there could still be a civilisation ‘next door’.
  • What will actually happen is probably lots of stuff that I haven’t thought of here, and very little of what I have…

The First – And the Only?

Posted in SETI, Speculation with tags , on May 9, 2010 by davidnm2009

When I was in Tesco’s today, for no apparent reason, half the lights suddenly went out. It was a bit startling, albeit otherwise inconsequential. But it did get me to thinking about energy crises.

Energy crises have been a major factor in technological development. The Industrial Revolution was arguably first foreshadowed when late-Elizabethan England began to run out of wood. Trees burn far faster then they grow – by the end of the 17th Century, London had eaten all the woodland for miles around. People had to move to burning coal for heating and industry. Only there was a problem – the easy-to-get-at coal quickly ran out. Mines had to start digging deeper – except they had this awkward habit of flooding. Obviously it’s a bit hard to run a profit when all your miners keep drowning!

Enter the pump. Only, the problem was, horse-drawn pumps didn’t really run well enough. They were inefficient and required a lot of horses – and horses are expensive. They need feed, they need stables, they need rest. So when the first steam boilers arrived, in the early 18th Century, it was a godsend for the mines. Steam pumps don’t need hay or stables. So the mines could go deeper and deeper.

But this has led me to an odd thought. Suppose we haven’t quite got it right. Suppose there’s just something basically wrong in the way we’ve organised our economy or our society. It wouldn’t be the first time – a professional civil service is obvious in hindsight, but Rome’s republic never thought of it. Tax farming is a very bad idea, but the French monarchy carried on with it until the bitter end. Organising all your neighbours into a vast series of heavily-armed alliances is grist to the mill for security dilemmas – but that didn’t stop the continental alliance system breaking horrifically in World War One.

Suppose, then, that we go down, for whatever reason. Maybe the seas rise and flood all our ports, disrupting trade. Maybe a bacterium figures out how to eat plastic. Maybe the markets set the world up the bomb so badly that no amount of bail-outs can reverse a catastrophic decline in economic activity, leading to truly mass unemployment, hunger, riots, instability, civil wars and worldwide collapse. (In which case, in respect of moron bankers, there will be at least a shred of poetic justice. To quote what Jared Diamond had to say about the Norse Greenlandic elite, ‘..the only privilege they earned themselves was to be the last to starve.’)

Anyway, in this cheery scenario, what happens in 500-5,000 years’ time? Will we be the Atlantis or the fallen Rome to some successor-civilisation? Will English be preserved for centuries as the language of scholarship and the arts, much as Latin was in the West? Will distant-future tourists gape at the ruins of half-sunken skyscrapers and artists make charcoal sketches from the shade afforded by fallen concrete slabs?

Simple answer: no.

Why do I say no? Because I don’t think anyone will follow us. It comes back to the energy crises I mentioned above. You see, we’ve chopped down all the forests and dug up all the easily-accessible coal. Yes, trees will grow back eventually, climate allowing, but once coal or oil are burnt, they’re gone. There is very little left near the Earth’s surface that any putative successor-civilisation could use to advance itself. And it’s not just coal or oil – copper, iron, lots of other valuable metals all fall under the same category. (Smelting down all the Roadmakers’ abandoned cars is a non-starter, too – you need coal to get the kind of heat required to do that properly.)

Any successors to us are probably limited to windmills and water-driven wood-frame devices. It’s hard to see an industrial technological path that doesn’t involve petrochemicals. (And there’s a SETI thought – oil beds don’t form that easily, and accessible ones are even rarer. And how many other planets have had a Carboniferous-analogue?) Our successors will have wood, wind and water. And that is all they will ever have.

If I have a point with all of this, it’s this. We have an advanced, industrial civilisation. Yes, it’s a mess and yes, it has problems – but it’s a lot better then any of the alternatives. Back to nature *sounds* great, but I have hayfever, so I prefer my outdoors in moderate doses only. And anyway, to make it work, you’d somehow have to make more than 6,500 million people vanish. I can’t imagine they’d like that much.

You see, as we developed, we lifted the ladder up with us. We can’t climb down to the lower floors, but we can fall – and if we do, we’re staying down there. For a while as we lie injured on the floor, we’ll still be able to see the ladder, up above us, but it will remain forever out of reach. Basically, folks, our choice is simple.

We have to find some way to make this society work. Or it won’t.