Physicist: In theory, there’s nothing standing in the way. In fact by constructing a planet from asteroids, comets, or dust you can expect to get a fair amount of energy back out. Normally, you’d just chuck a bunch of dust, rocks, and ice together (the way God intended), but that releases a whole lot of heat, leaving the planet very molten for a very long time.
If instead you build a massive spherical scaffold around the future location of the planet you could lower new material gently to the surface, and generate power (e.g., tie a rope to the rock, and let it turn a generator as it falls). So, if you do it right the whole thing would be “free” from an energy stand point. In fact, you’d probably need some way to dissipate the extra unused energy. The total energy, E, created by a planet as it coalesces from a dispersed cloud is approximately 
Little history: that “R5” equation was derived to estimate whether or not Santa would destroy the world every year (He doesn’t).
The biggest concerns would be time scale, available materials, and whether or not you should bother.
Magrathea: the world building world.
I won’t even consider the question of engineering topography on the surface of the new world, since it’s not even a problem. According to John Robert McNeill, as early as the 1980’s humankind became the greatest earth-moving force on the planet, surpassing everything else (erosion, volcanism, glaciers and rivers, and even ants and termites) put together. So: shaping every mountain, valley, and ocean basin from the ground up (as it were)? Doable.
Mines are big.
Time scale is a problem, of course, because it’s a big project. The best way to gather materials at the construction site is to use other nearby planets for gravitational assists or “slingshots”. After all, if you want to move a rock the size of a continent from place to place, the last thing you want to do is try to push it yourself with a rocket. Instead you can nudge them slightly in the right direction and, within a couple hundred years, you’ve got your gigantic rock in the right place. Later, when you’ve got enough of the planet built that it has its own gravity, and lowering material gains you plenty of energy, you can afford to attach super rockets to the asteroids and moons you want to include in your new planet. Still, almost any reasonable construction scheme will have a very optimistic lower bound of at least several hundred years.
As for materials, the only information I have comes from our own solar system. The Earth alone has more mass than 200 asteroid belts. The closest source of material, not already in the form of planets and moons in our solar system is the Oort cloud, which (according to the best estimates to date) may contain enough material to make almost half a dozen Earths. However, the Oort cloud is on the order of 10,000 AU away (1AU is the distance between the Earth and the Sun). For comparison, the New Horizons probe, now en route to Pluto, is the fastest object ever made. Despite that, it will still take about nine and a half years to cover the 30 AU out to Pluto (and NASA isn’t even going to have it slow down when it gets there). To make things worse, almost all the mass out there is tiny grit. You wouldn’t be grabbing rocks to send back, you’d be sweeping up fine space-powder and bagging it, one grain at a time.
So, say you don’t want to do that, and you decide to steal moons instead. If you could somehow pull all of the moons of Jupiter out of orbit (using up most or all of your energy budget) you’d have enough material to create about 1/15 of one Earth. The moral of this story is that once a solar system is formed it’s amazingly clean. Other fully-formed star systems seem to be just about as clean.
So you may ask yourself: why bother? Well, you probably shouldn’t bother. Today is the golden age of planetary astronomy (and astronomy in general). Over the past year we’ve found (and verified) about 1 to 2 new planets a week, around other stars. 518 have been found so far, and almost all of those have been within 300 light years. It’s looking like there are hundreds of billions of planets in our galaxy at least, so it’s likely that whatever kind of planet you want, you could probably find it or simply adjust a planet that’s close enough.
The mass and distance for all of the exoplanets found as of Jan. 14, 2011. If this plot included all of the missing planets it would be solid red. Click for full size.
After all, as long as we’re assuming that we can build planets from scratch, we may as well assume that we can just move to a distant star system.
I’m Going to build a planet.
I will help.
In other words, terraforming existing planets within the goldilocks zone is a helluva lot cheaper than building one from scratch.
CURSE YOU TITAN A.E. for giving me unrealistic expectations of building my own planet!
I am sure we’ll one day do this, lol we might be like aliens xD
This is a computer game that I want to play.
Magrathea!
i think it’s impossible!
and we should just clean earth!!!!!!!!!!!!!!!!!!!!!!!!!
we are doomed we can die from moving and building a planet!
Lets build a planet 😀 im only 14 i got years and yeArs of life to help :p
Why build a sphere?
A thin arced surface, perhaps rotating to simulate gravity, seems much more do-able.
Creating a planet wouldn’t be impossible its just that their are a lot of variable to it time and resources being the biggest limit. But like Manual i’m fourteen and have lots and lots of time.
I just feel instead of wasting time building a big planet build a real toy sized one and make stars a lamp we could support life and look like gods. XD
Ok, people. Let me borrow a shovel from my neighbour and I can help build that planet.
A planet, although costly to make artificially, has the advantage of being tough and stable. On the other hand, I like to think of the alternatives. What could start as a platform orbiting the Sun could become a ring and then a huge shell. People could live inside it, enjoying constant sunlight. The rotation of the shell would create artificial gravity that keep people and the atmosphere close to the shell, which would have to be air-tight. I’m not sure I’d like to live there, but it would be a great base for manufacturing galactic fleets. Also, space ships could easily arrive and depart without experiencing the cost, problems, and challenges associated with dealing with the gravity of a planet. This becomes crucial when dealing with huge ships big enough to offer a comfortable trip to another star. Anyways, dream on!
What about from material from the sun? How many earths could you make if you took all the carbon out of it, the amount of carbon in the sun is .40 of it’s mass, and the sun has a mass 330,000 that of the earth so, the amount of carbon 330K x .40%= 1320 times the mass of the earth.
I will help, it’s going to happen one day so lets speed it up a couple a hundred years. Also as ecotricity is the way forward it could just be a planet to generate energy 🙂
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Here [] take a brick.
Brick-by-brick..
building the planet sounds possible but where would the air and water come from? And what about other life forms? Better idea to clean up earth.
Building a new planet is not about replacing Earth. It is about supplementing the Earth and creating new land for life. I wonder if someday, when humanity’s technology is far more advanced, we couldn’t take Mars, Callisto, Ganymede, Europa, Ceres, Vesta, and most of the Solarian Asteroid Belt and use them to create a planet with maybe 0.9 G and very Earthlike potential. Water and oxygen could be gained from the water already on Europa, Ganymede, Callisto, and Ceres. Nitrogen could be take from Titan. Such a planet could occupy Mars’ position in the Solar System and act as a colder Earth analog.
we can just get a lot of comets and use gravity to build an earth sized world. plus we would get a lot of water from the original comets.
Thorium may be the best source for it. I’m 16 and I want to build my planet. So I think I need to work at thorium……
The main steps for building a planet are:
Get three quotes from planet building companies, and choose the one with best value for money, but also providing a comprehensive guarantee and a track record in delivering on time.
Get three quotes from finance companies or banks, and choose the best deal, taking into account upfront fees, interest charges and flexibility of repayments.
While you don’t need any government approval (because no one controls space), you will still need to form an alliance with a government that has a strong military and is willing and able to defend your rights, and can be counted on for the next couple of centuries at least, until you get established. Otherwise, someone might just steal your newly built planet!
I think it would be a cool idea to instead take moons like Europa and Titan, and move them to be by Earth. Then they will be in the Goldilocks zone and have water. This would also provide us with land that we can use to further our reach.
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Dude, building an artificial planet and moving some humans over there could actually solve a lot of problems such as ::
– overpopulation
– water supply
– polution
we could literally start over on a “new earth” and make things cleaner and more advanced. I think that would be pretty cool.
If we created a dense ball of a fair size and cost is it possible that you could use it as artificial gravity to build ships off
We could make several planets and move our entire population there when Earth’s resources are depleted and earthquakes destabilize it. We’d have to develop a just interplanetary system of governance though so the Core planets wouldn’t form an Alliance to usurp the freedoms of the outer planets—let’s call them Rim planets—that would cause Independent thinkers to rise up in rebellion in search of freedom and Serenity. And I’d like a ship capable of interplanetary travel built on the design of a Firefly. I’m 60, so hurry it up Manual, Jay and Vivek. Also, would one of you develop a protocol to increase the average lifespan by 50-60 years so I can live long enough to see this?
I like it, it could be a backup plan if we can’t clean up earth, let us start now!
I am planning on doing this for school work. i just need a spaceship and then everything will be in order.
I will build my own Planet!! This will be my vision for my new aerospace company based in the Philippines called DreamPlanet.