Every astronomical body, be it moon, planet, star, or black hole has an invisible line around it called a Roche limit. Inside a body's Roche limit, no object that is held together only by the force of its own gravity can survive. It's torn apart by the object whose Roche limit it has fallen below. It is important to note that the object torn apart is always the less massive of the two, because the more massive object has a larger Roche limit, so it destroys the less massive object before entering the Roche limit of the less massive object.
Io and Europa don't actually pass below the Roche limit of Jupiter, but both of them get close to it at perigee (the closest point to Jupiter in their orbits), then move back away from it until they reach apogee (the furthest point in their orbits). The difference in the stress Jupiter's gravity puts on these two bodies between perigee and apogee is so great that it keeps both bodies warm inside. This process is called tidal heating, and while there are other factors that contribute to the heating of both worlds, they are far less significant than their simple proximity to Jupiter's Roche limit.
This same mechanism could be applied to Mars through two methods. The first is to move Mars close enough to a more massive body that the tidal heating effect kicks in.
There are problems with this approach. The first and most obvious being, how do you move a planet? Well, as it turns out, we happen to know the answer to that. In fact, if you want to get really, really technical about it, we've even done it.
All those probes we've sent to the outer solar system, like Voyager 1 and 2 and Cassini-Huygens have made close flybys of Jupiter. In the process, a tiny amount of the kinetic energy locked up in Jupiter's orbit of the sun was transferred into the spacecraft. The amount of energy involved is so small that our sun will go cold long before the shift in Jupiter's orbit is measurable, but the process scales well. If you were to use a much larger relative mass, and to fly that same mass by over and over again, the gravitational interactions would begin to move Jupiter closer to the sun. Fly the mass by on the other side of the planet, and you transfer the energy into Jupiter, moving it further away from the sun. We know the process worked for two reasons. One, the math involved has been tested repeatedly. Two, the current location of the Jovian planets and the existence of the asteroid belt instead of a fifth terrestrial planet in the inner solar system can only be explained by this process occurring in the early solar system.
Unfortunately, moving Mars would be the simple part, and there are other obstacles that couldn't be overcome. First, there are only two real candidates for where to put Mars, either in Jupiter's or Earth's orbit.
With Jupiter's orbit, in order to get Mars into a position where the tidal heating can occur, you would have to drop it right smack in the middle of Jupiter's radiation belt. Sure, you'd heat the planet up, but you'd also render it completely sterile and incapable of bearing life.
With the Earth's orbit, you'd have to get rid of the Moon and the process would disrupt the oceanic tides and cause all kinds of trouble with earthquakes and disruption of satellite orbits, and just make space near Earth a nightmare to deal with. Not to mention that moving planets in and out of Earth orbit is insanely dangerous.
Then there is the really big problem. In order to put Mars into orbit around another body, you would have to accept a retrograde orbit (Mars would go around the planet in the direction opposite the spin of the planet). Retrograde orbits invariably decay, and since you would have to put Mars close to the Roche limit to begin with, that decay would quickly drag Mars in below its Roche limit which would tear it to pieces, every one of which would eventually fall onto the planet.
In short, moving Mars is out.
That being the case, the only real option for restarting the core of Mars is to build a gravity source to cause the tidal heating. In other words, to build a planet of equal mass, or slightly larger and place it in such a way that Mars regularly makes close approaches to the new planet's Roche limit.
This has several things to recommend it. Because you would be dealing with masses small enough to manipulate directly, you wouldn't be forced to accept a retrograde orbit, so the new body would never fall on Mars. It would also be much faster and safer than trying to move a planet. It would also take considerably less energy.
The process itself is relatively straightforward. There is enough mass in various belts out beyond Neptune to build several planets the size of Mars. In fact, it's highly likely that there are several bodies out there the size of Mars or larger. But it's the smaller bodies that are of interest. They're easier to move, which means they would be easier to drag back to Martian orbit. Mars' existing moons, Deimos and Phobos are both small asteroidal moons that would make the perfect starting place. Phobos needs to be boosted to a higher orbit anyway because it is slowly falling towards the surface of Mars, and it's going to hit eventually.
Again, the process is going to be long, expensive and labor intensive, but it could be done in a few centuries, which is about the same about of time it would take you to cook Mars's atmosphere out of the ground. It also has the added advantage that the same tidal forces which would reheat the interior of Mars would also help build the dynamo which would create a strong Martian magnetic field by stirring the liquid iron core of the planet. In the end, what you would get is a binary planetary system where one of the worlds looked a lot like Earth.
If Mars is that much of a challenge, what about other planets or moons in the solar system?
Mars has one major problem: the lack of internal heat. Venus doesn't have that problem. Venus is extremely geologically active. Venus, however, has three major problems, and in order to explain them, we need to take another brief trip into the distant past.
At some point in the past, and unlike the event which formed the Moon (we have no way to date it) Venus was struck by an object that was close to, if not greater than, Martian mass. Unlike the Earth, however, where the collision was to spinward (i.e. the collision wasn't dead center but off to the side in the direction the planet was spinning), the collision with Venus occurred antispinward (the collision was offset in the direction opposite of the planet's rotation). The collision was so hard, the direction in which Venus spins was reversed. Venus not only spins in the wrong direction, but it takes longer to complete one rotation than it does to complete an orbit around the sun. Because of the incredibly low rate of spin, Venus has no measurable magnetic field. If it has one at all, it is too weak to extend from the core of the planet all the way to the surface.
Venus's second problem is its lack of a moon. If Venus had a moon, than the slow rotation wouldn't be as much of a problem, because the orbit of the moon would perturb the liquid core enough to generate a magnetic field. Venus's third problem is its location. If Venus were where Mars is, it might very well be a garden, but its proximity to the sun killed it over the last billion years or so.
The thing is, a billion years, a billion and a half years ago, Venus probably didn't look that different from Earth. The atmosphere was probably about four times thicker, but very Earthlike. There were oceans, Earth type plate tectonics, and much like Mars, there is a high probability that there was life. Unlike Mars, we'll never know one way or the other because any traces would have been destroyed as Venus has resurfaced itself over the last 50 million years.
But our sun is a main sequence star, and as main sequence stars burn, they swell. Because their energy output is a function of their surface area, over the course of the last billion years, the total solar output has increased by about thirty percent. As that happened, the temperature on Venus began to rise as the greenhouse gasses captured more and more energy. The natural precipitation cycle of water slowed the process down until the planet reached the point where temperatures stopped getting low enough for it to rain. Once that happened, there was no way to remove any of the greenhouse gasses from the atmosphere, and the planet was caught up in the runaway greenhouse effect. The oceans slowly boiled off over several million years and by the time they were a
ll gone, the temperature on the planet began to reach levels where CO2 and water were literally being baked out of the rocks. With the change in the chemical composition of the rocks, the increase in pressure due to the fact that the entire mass of the oceans and a good deal of the mass of the crust had entered the atmosphere, and the incredibly high temperatures, the surface of the planet became soft and somewhat flexible.
To make matters worse, the pressure pushed the water vapor, the lightest of the gases making up the soupy new atmosphere, to the top where it was unprotected by the thick clouds. In the upper reaches of the atmosphere, UV radiation broke the water apart, and without a magnetosphere to shield the planet, the solar wind stripped most of the hydrogen away. The oxygen and what hydrogen was left reacted with the sulfur dioxide to form sulfuric acid, and the planet was slowly transformed into the hell it is today.
Terraforming Venus where it is would require a way to shield it from the sun and the solar wind. If you could accomplish that feat, you would just need to wait until the planet had cooled off significantly, then dump a volume of water approximately equivalent to the entire hydrosphere of Earth into the atmosphere, then wait about three hundred million years while the planet completely resurfaced itself.
Moving Venus to a different location presents the same difficulties as moving Mars would. It can be done. The process is relatively straightforward. The tricky part is that if you did attempt it, you would very likely knock Earth out of its orbit. It's far too dangerous and would result in no tangible benefits. I don't want to say terraforming Venus can't be done, but I will say that we know of no way, based on current science, to terraform Venus in a realistic timeframe.
As to other candidates that have been put forward from time to time, Io sits in the heart of Jupiter's radiation belt and anyone on the surface would receive a lethal dose within minutes. Europa is, despite the tidal heating, insanely cold, so cold that at certain times, liquid oxygen could exist on its surface. It also sits on the edge of Jupiter's radiation belt. The lethal dose would take longer, but the radiation levels are just too high. Titan has the same temperature problems as Europa, without the tidal effects that keep the oceans of Europa liquid.
Which brings us back to Mars.
If we want another planet, Mars is still our best bet. The key is to take a different approach. You won't have any open oceans or wilderness, but what you could have, in fifty to a hundred years from now, are thriving cities, productive farms, parks, pastures, factories and anything else you need. All you have to do is give up the notion of making the entire world habitable at once.
Instead, you build domes and arcologies (cities enclosed in a single building). Build domes twenty miles across and you can make the planet habitable a hundred square miles at a time. If built right, the whole thing would act as a shield against radiation and electromagnetic interference from the sun. The iron and carbon needed to make the domes is readily available on the surface and in the atmosphere. If you don't want to thin out Mars's atmosphere, you can just dig it out of the ground and scrape it off the poles.
It's not as sexy as terraforming. It doesn't capture the imagination the same way the idea of transforming an entire planet does. What it does do is present us with projects that can be completed in a decade or two. It lets the people paying for it, be they investors or taxpayers, see the results of their spending.
Ultimately, I'm in favor of terraforming. I like planets. But realistically, it makes more sense to crawl before we try to run a marathon, and even a relatively simple terraforming project is a marathon. Building domes on Mars, on the other hand, is a simple, practical solution that can be built with today's technology and science. Call it a starter project.
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Salvos against Big Brother: Copyright: How Long Should It Be? by Eric Flint
I ended my last essay by presenting the general principles needed to answer the question, how long should copyright terms last?
For those of you who didn't read or don't remember what I said, here it is:
First, authors need to have enough protection to enable them to be able to make a living as full-time writers.
Second, that protection has to be long enough to provide them with a motivation to write for the public, and see doing so as a possible profession.
But that's it. Those are the only two legitimate concerns. Any term of copyright which exceeds that minimum necessary length, as Macaulay put it in the quote I cited in my last column, has no legitimate purpose. Once you cross that line, a necessary evil has simply become an evil—and the farther past that line you go, the more evil it gets.
Now let's get into the details.
The first thing I need to establish are some facts. I need to do that because I've found that many people, including many authors, have very unrealistic notions about how long copyright actually protects anything. What happens is that they look only at the law—ignoring all social and economic realities—and say to themselves, "Oh, wow, anything that gets written—including anything I write myself—will be protected by copyright for seventy years after I die."
Uh, no. In the real world—except for intellectual property owned by giant corporations—here is what really happens:
The longer copyright lasts, the less likely it is that 99.99% of anything ever written will ever get reissued. What excessively long copyright terms actually do is destroy writing. They don't protect writing, they ravage it.
Why?
Well, it's simple—if you look at writing as a professional craft, subject to economic imperatives like any other form of work, instead of a legal or philosophical abstraction.
Here is the cold, hard reality. I call it the ninety-nine perfect rule:
99% of all writing falls out of print within ten years after it is published. In most cases, within five years. That's because the standard rule of thumb in the publishing industry is that 80% of all sales of a book take place in the first three months after publication. And the remaining 20% usually drops off steeply. Within a few years of a book being published—faster than that, in the case of most shorter pieces of work—it is simply not economically viable for a publisher (or a book distributor or retailer) to keep the book in print any longer.
90% of all writing that falls out of print will never be reissued, under any circumstances—even with good copyright laws. That goes up to 99% with bad laws like the ones we have today.
The reason, again, is economic. For all the paeans of praise showered on "immortal literature," the cold, cruel, hard fact is that the overwhelming majority of writing is pretty ephemeral as far as the public is concerned. This should come as no surprise to anyone, because the fact is that whatever else it may be, fiction writing is first and foremost entertainment—and entertainment, with a few exceptions, has always been subject to the dictate that the public wants novelty. They don't want to hear the same story over and over again; instead—with a few exceptions—they want to keep getting new ones.
For every piece of writing that stays before the public for centuries—such as Cervantes' Don Quixote—there are literally hundreds of thousands of pieces of writing that vanish with the wind. That's even true with books, much less short pieces of writing. Most books—"most," as in 99.999% of them—are not and will never fall into the same tiny category Don Quixote does. They are ephemeral. They will arrive, enjoy their day in the sun—such as it may be, which varies a lot—and then they will pass away. Most of them forever.
That's the reality—and that is the reality which determines the lives of professional authors, as professional authors.
And that's also the reality that should—and did, until fairly recently—determine the length of copyright terms.
So. What shouldbe the length of copyright terms? Let's approach the problem by bracketing it. Ranging shots, so to speak.
The original copyright terms set in the Statute of Anne of 1709 (fourteen years) and the modification
placed in the original U.S. Copyright Act of 1790—which provided for a fourteen year extension after the first fourteen years had elapsed—has turned out to be too short.
Why? you might ask—given that I just got through pointing out myself that 99% of all books will fall out of print before fourteen years elapse, anyway.
Well, it's because averages are only that—averages. Remember that the purpose of copyright is first and foremost to provide a means whereby some authors can become professional authors. So what you now have to do is consider what percentage of writers can ever manage to do that?
And here we run into another ninety-nine percent rule. Or ninety percent rule, at least. The big majority of people who get something published will never be able to make a living as writers. Indeed, most of them won't ever generate a significant income at all from writing, even one that could substantially supplement their income from their principal means of livelihood.
I can't give you exact percentages, because I don't have them. So far as I know, nobody has ever done a systematic survey and study of the issue. What I can do is give you some rough guidelines, based on my own experience as a professional writer and what I've learned from talking to many professional writers, editors and publishers.
As I said in my last essay, writing is very much like acting. It's a profession that has no entry bars of any kind. You do not, as a doctor or lawyer does, need to take any schooling to practice the trade, nor do you need to pass any formal examinations or get any official certificates entitling you to engage in the profession. Furthermore, although certainly not to the same degree as acting, writing is a relatively glamorous profession.
So, lots of people take a crack at it. Lot and lots and lots of people. Of those people who take a stab at it, about 90% never have any success at all.
But some do. Perhaps 10%, sooner or later, will get something published—or, if they're actors (or singers) get a small gig somewhere. But they never manage to do it with any regularity or frequency at all. Eventually, most of them stop trying altogether and move on in their lives to something else.
Jim Baen's Universe Volume 1 Number 3 October 2006 Page 41