A Crude Guide To Solar Energy Levels in The Solar System
(This is background information only - you do not need to know this to play "6 Billion™")
The main purpose of this article is to explode some of the popular myths surrounding solar energy levels in our own Solar System, to reveal the true nature of those solar energy levels, and to speculate on the future use of those solar energy levels by space-faring life in the coming centuries. A secondary purpose is to illustrate how easy it is for a non-scientist (such as me) to explore original and fun ideas with just a little mathematics and some imagination. I hope non-scientific readers may be encouraged to try something similar themselves.
In writing about solar energy, please note that I do not exclude the future development and usefulness of other forms of energy such as anti-matter, or fusion.
In reading this article, you will have to think in 3 spatial dimensions, and there will be some basic mathematics involved (done in 15 minutes on my AUD $ 5.00 calculator). There will be no getting away from 2 basic formulae
My calculations are mostly rounded up or down, and only crudely at that (but good enough to prove my points). I choose to do this to show that even a non-scientist (such as me) can do some basic science, and then think about the results for himself or herself. Plus, rough figures are perfectly OK to test a theory.
How to calculate the surface of a sphere (r = radius)
4 x pi x r2
Example: A sphere with a radius of 3m has a surface area = 4 x pi x 32 = 113.14m2
How the Inverse Square Law applies to sunlight (r = radius)
This basic law of physics actually applies to gravity, light, or even an electrical charge attraction/repulsion between two objects. For this article, I am only interested in the effect on light.
For example, tells us is that if you double your distance from the Sun, the light is only 1/4 as intense.
See Educator's Guide to The Inverse Square Law for more.
Some figures relating to our Solar System
Planet Mean Distance (millions of KM) Mean Distance
Surface Area (AU2) of sphere at this distance Solar Intensity
(relative to Earth)
Mercury 57.9 0.387 1.88 AU2 6.67 Venus 108.2 0.724 6.59 AU2 1.91 Earth 149.6 1 12.57 AU2 1 Mars 227.9 1.523 29.16 AU2 0.43 Jupiter 778 5.200 339.93 AU2 0.037 Saturn 1427 9.539 1143.91 AU2 0.011 Uranus 2870 19.184 4626.61 AU2 0.0027 Neptune 4497 30.060 11359.59 AU2 0.0011 Pluto* 5900 39.439 19554.04 AU2 0.00064
Note: AU = Astronomical Unit (the distance of the Earth from the Sun). * = recently reclassified as a dwarf planet.
This table tells us what we expect to be told, namely that Solar Intensity tails off pretty rapidly as you leave the inner solar system. Also, space is big. Imagine a sphere with a surface area of 19,554.04 AU2 surrounding the Sun at the same mean orbital distance as Pluto!
The amount of solar energy is the same at any distance throughout the Solar System
You don't believe me? Try this - multiply the Solar Intensity by the spherical Surface Area for each of the planet rows. Can't be bothered? Well, I've done it for you:
Planet Total Solar Energy Mercury 12.54 Venus 12.59 Earth 12.57 Mars 12.53 Jupiter 12.58 Saturn 12.58 Uranus 12.49 Neptune 12.49 Pluto 12.51
(Note: these calculations ignore any 'shadows' caused by planets, asteroids or comets. Pretend they are not there!)
The results show that the resultant figure is always roughly the same (from 12.49 to 12.59), which can only mean that the same amount of solar energy is available at any distance throughout the Solar System. The only reason the figures differ at all is because of my crude rounding.
It doesn't matter what the 12.49 or 12.59 result means (12.49 "what"?). I am confident that other measurement scales, if used, would give the same significant result - namely, that the same amount of solar energy is available at any distance throughout the Solar System.
The scientists out there have probably got bored by now, wondering where all this basic science is going. Read on - I have a little something for you too.
The reasons that non-scientific people think there is less solar energy at a distance of Pluto, compared to Earth, are:
- per square metre, there is less solar energy out at Pluto compared to Earth (per square metre, Earth gets over 1,500 times the energy that Pluto gets).
- people think in the ecliptic plane (the imaginary disc which roughly includes the orbits of all the planets)
- people think we have to live on planets ("planetary chauvinism")
There is no scientific reason (given careful planning) why a solar panel array couldn't orbit the Sun at the same distance as the Earth , but on a perpendicular plane to Earth's orbit. Or, solar panel arrays could be positioned in orbits around the Sun at the same distance as Earth, but preceding or trailing the Earth-Moon system (think of Jupiter's Trojan asteroids). To coin a phrase, think outside the sphere that you live in - Earth! Then, think outside the disc that you live in - the ecliptic!
Some Common Sense
Think of a light bulb in an opaque box 1 cubic metre in size - no light escapes. Similarly, the same light bulb enclosed in an opaque sphere 5 metres in radius will also trap all the light. But the energy output of the light blub is constant, so both the close-range box and larger (and more distant), sphere will trap the same amount of energy.
Hence, the same amount of solar energy is available at any distance throughout the Solar System (just imagine a very big opaque sphere enclosing a large light bulb - all the original energy is trapped, regardless of the radius of the enclosing sphere).
The reason why my assertion (that the same amount of solar energy is available at any distance throughout the Solar System) is true is because you must take into account all the energy at the same distance from the Sun. The further from the Sun you get, the more space there is for that energy to be spread out.
Dyson Sphere - Kardashev Level Two
Hence, as Freeman Dyson suggested long ago, a sphere constructed at a suitable distance from the Sun would be an extremely efficient way for a space-faring civilisation to achieve Kardashev Level Two (utilise all the resources of the home solar system).
Or, as Dyson has recently suggested (1999, "The Sun, The Genome ,and The Internet") if you have sufficiently large solar energy collectors (and we still have to improve the efficiency of the ones we currently have), you could support a colony of humans at any distance within the Solar System. They might have to think about living in space, instead of on the surface of a planet or moon. Otherwise, you constantly waste energy getting out of the gravity well of your home world. Dyson suggests the Kuiper Belt over the more commonly suggested Asteroid Belt - more ice, and slower delta V (less energy) required for manoeuvring to or from the more slowly orbiting comets.
If this is the first that you've heard of Nanotechnology then start by reading "Engines Of Creation" by K. Eric Drexler. What follows is an exploration of solar energy usage through advanced nanotechnology. Note that humanity's future colonisation of the solar system does not depend upon such technology. Rather, humanity's future colonisation of the solar system depends upon the efficient extraction and harnessing of solar energy.
Nanotechnology is concerned with building things at the molecular level - the scale is 1 billionth of a meter. However, building at this level does not restrict you to building small objects, as nicely demonstrated by Robert Bradbury in his article Nanoassembly Of An Aircraft Carrier.
The expectations of this emerging technology are that self-assembling replicators will produce a range of 'smart' materials which could empower human directed evolution and re-shape our environment here on Earth and in space.
In Chapter 6 (The World Beyond Earth) of Engines Of Creation, Eric Drexler quite rightly extols the advantages of living in space over living on planets. Part of the chapter features a discussion on the abundance of solar energy.
Imagine a square metre of nano-material, capable of acting as a solar energy collector. To keep the wording simple, let's call this device a Nano Cell. Suppose you have a design requirement to build a Nano Cell which can collect a Standard Charge at any distance from the Sun up to Pluto. The amount of energy collected by a Nano Cell at a distance of Mercury from the Sun is defined as a Standard Charge. It is unlikely that a Nano Cell would be restricted to just "light" (as humans see it), but then again it is unlikely it would be able to collect energy from the full electro-magnetic range. So, let us assume it collects a broader spectrum of energy than humans can see (but not the whole spectrum).
Close to the sun, the Nano Cell would be a small, thick slab. At greater radii, it would flatten into a larger, thinner sheet. Hence, if it wanted twice the power (a Double Charge) at the same distance, it could double its size. But, if it wanted the Standard Charge at twice the distance, it would have to quadruple its size (refer Inverse Square Law).
Hence, a 'smart' Nano Cell might be engineered which could operate from Mercury to Pluto by adjusting its size to fit its position in the Solar System. Out at Pluto, the Nano Cell would have to be over 1500 times larger.
I am not aware of other proposals for a Nano Cell, so I'm hoping it's an original idea.
Most people are familiar with the lightsail. If you are not familiar, Eric Drexler explains how they work in Chapter 6 (The World Beyond Earth) of Engines Of Creation.
Imagine again a square metre of nano-material, this time operating as a lightsail. Let's call this device a Nano Sail. As with our Nano Cell, the Nano Sail is required to be able to operate with a Standard Charge, though this time we are not converting sunlight into electricity. The Nano Sail uses solar light pressure to accelerate itself.
As with a Nano Cell, a 'smart' Nano Sail might be engineered which could operate from Mercury to Pluto by adjusting its size to fit its position in the Solar System. It would be capable of constant acceleration (reversing direction and deceleration would be the same as for a light-sail - tricky, but possible). If a small capacitor was thrown in, any extra charge gained in the inner Solar System could be used for other purposes or simply as an energy reserve. The minimum design requirement is that, fully stretched, it can operate out at Pluto - everything else is a bonus.
Put enough Nano Sails together and you have a Nano Sailing Ship (possibly furling its sails when close to a planet). Electricity could be supplied via a number of Nano Cells.
I am not aware of other proposals for a Nano Sail, so again I'm hoping it's an original idea.
Now imagine a Nano Cell which can transmute itself (or part of itself) into a Nano Sail. Suppose it could also transmute itself (or part of itself) back again, at will. Or it might be a Nano Cell joined to a Nano Sail, for a total of two square metres. Add a small nano-computer for some intelligence, and you have a life form capable of "living" at any distance within the Solar System. From what I've read of nanotechnology, I can't see why this wouldn't be possible. If you disagree then I'm happy to listen.
Their only problem, as far as I can see, is that to replicate they initially might be restricted to obtaining material from places with micro gravity and no atmosphere, such as The Asteroid Belt or the Kuiper Belt. By simply "seeding" an asteroid, or comet, with a replicator they could convert it into heliovores.
I am not aware of other proposals for a hybrid Nano Cell / Nano Sail, so yet again I'm hoping it's an original idea. Is "heliovore" too clumsy a term? They feed off the Sun's energy, and "helios" is Greek for Sun. Whilst not literally eating the Sun, they need not be limited to being "photovores"...
If they could get over the replication problem it would qualify as a von Neumann machine, but so do lots of other suggested new life-forms. I'm looking for something both unique and suitable. Perhaps Heliophage? I don't know. So, if you have any genuine suggestions for a suitable name I'd like to hear from you. If not, then heliovore it is.
'Dumb' heliovores could also be envisaged, built without using nanotechnology and perhaps not even endowed with artificial intelligence. However, these "archaic" life forms would be at a distinct disadvantage to their smarter cousins.
Now imagine an entire hollow sphere, like a Dyson Sphere, made from nano-material. This might require Planetary Disassembly, as proposed by Robert Bradbury, if you want a large sphere. It could also be extremely intelligent as suggested by Robert Bradbury in his article on Matrioshka Brains.
Anyway, now imagine that our heliovores have learnt to replicate. There might be billions of them, ranging from a metre square to kilometres square. Perhaps there might be enough of them to actually facilitate planetary disassembly on their own. After all, they would collectively be capable of collecting vast amounts of energy. I'm sure they could also think of a way of focussing that energy, collectively. Or, they might "seed" each planet with Heliovore replicators (consideration would then have to be given to escaping the planet's gravity, which would then decrease over time). Slowly then, one way or another, they could "consume" all the planets to provide material for more heliovores.
Now, all you have left is a swarm of intelligent heliovores swarming in a sphere around the Sun - a Nanosphere.
In Chapter 11 (Engines Of Destruction) of Engines Of Creation, Eric Drexler introduces the concept of "gray goo". The idea is that uncontrolled replicators could be capable of consuming all matter, living or otherwise, on Earth in 48 hours. This is an extreme example, much played down these days, of the potential hazards of nanotechnology to life on Earth.
The heliovores are similar concept on the scale of an entire solar system.
Of course, it could also be possible for humanity to use the heliovores to our own advantage. This might require us to form a co-operative relationship with the heliovores, so they might have to get something out of it too. Or, we might design a creature which feeds on heliovores (and poses no threat to us).
I won't speculate here on what nanotechnology might do for humanity, let alone "to" humanity. But it's always possible we can be a part of any future we care to imagine, heliovores or no heliovores. The boardgame 6 Billion™ was designed from an optimistic point of view, and assumes that we survive the challenges ahead.
Apart from Freeman Dyson, others have speculated about the massive human populations which could be supported using solar energy alone (see Bibliography below). So far, nobody has stated that it is not possible, and in fact the scientific consensus is that it is possible, feasible and desirable.
Precedents (added 27 Feb, 2001)
I have since been informed that TimeLife(?) space exploration series (c.1987) illustrates the application of molecular nanotechnology (MNT) to telescopy: A replicator seed is fired from a mass driver towards the asteroid belt. En route, it transforms into a solar sail. Hard-landing on a carboniferous asteroid, it proceeds to transform it into a million-kilometre reflector telescope.
Also, Robert L Forward has written articles pertaining to Solar Sails and more , though the links were broken when I tried them.
From what I can gather, it still seems that my ideas for Nano Cells, Nano Sails and Heliovores are unique. Also, given the private feedback from scientists who read Nanodot.org, my ideas appear to be as reasonable a proposal as any other advanced MNT device.
Bibliography (pertaining to solar energy and the populations that can be supported)
"The Millennial Project" - Marshall T. Savage
"Mining The Sky" - John S. Lewis
"The Case For Mars" - Robert Zubrin
"Engines Of Creation" - K. Eric Drexler
"Remaking Eden: Cloning and Beyond in a Brave New World" - Lee M. Silver"
The Sun, The Genome & The Internet" - Freeman J. Dyson
"Our Cosmic Future" - Nikos Pranztos
"The High Frontier" - Gerard O'Neill
"The Road To The Stars" - Iain Nicolson
"Pale Blue Dot" - Carl Sagan
"Islands In The Sky" - Edited by Stanley Schmidt and Robert Zubrin
"The Giant Leap: Mankind Heads For The Stars" - Adrian Berry
For an idea of the sort of populations being visualised, read my article Design & Production of 6 Billion . With typical end-game populations in the low trillions, 6 Billion™ itself is far more modest in its proposals.
Those highlighted in bold are the most explicit in terms of timeline, location(s) and population levels.
To get an idea of the likely travel times in the Solar System in the Third Millennium, read my Crude Guide To Travel Times In The Solar System
For a list of articles by me, see the Articles page.
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