Is There a Starship in Your future: Ask first, Do You Live in a Gravity Well?

Is There a Starship in Your future?

Before you buy a starship, you have to be able to get off the ground. Ever wonder what eventually would determine if an intelligent civilization could become a spacefaring civilization? It has to do with the size of their planet. Before becoming spacefaring, you have to be able to fly heavier than air aircraft and be able to leave the atmosphere and get into orbit around the planet, which requires rocket power. There are plenty of rocky earths out there in our galaxy in Goldilocks zones with the potential for liquid water and the creation of life. The catch is what is the diameter of that rocky planet. Take a look at the cartoon I'm holding of the Earth and a Super Earth. On the left is our Earth. I call it "Roundland" because our low gravity allows us to stand up and build tall structures; there are mountains; and the surface is obviously curved. On the right is a Super Earth which I call, "Flatland." There, high gravity keeps everything flat; even living things will be built close to the ground like my cartoon flat creature; mountains will be molehills. On a super earth about 3 times bigger in diameter than the Earth, the surface gravity would be about 3 times that on earth. That is the result of Newton's Law of Gravitation and some simple math:

F = G m₁m_2 / r²

Where F is the force of attraction between two bodies, G is the universal gravitational constant, m₁and m₂ are the respective masses of two bodies, and r is the distance between the centers of gravity of the two bodies.

The mass of a planet is roughly proportional the cube of its radius, r³. The distance from its center of gravity to the surface is its radius, r. The force of gravity is proportional to its mass, which is a function of the cube of its radius, r³, and inversely proportional the square of its radius, r². So, the gravitational force at the surface is proportional to the radius cubed, r³, divided by the radius squared, r², which is proportional to the radius, r. At a radius three times that of earth, your 200-pound body would weigh 600-pounds. At ten earth diameters, you would weigh a ton or 2000-pounds. Humans on Earth have evolved to stand and walk upright. We can do the high jump and pole vault. We fly airplanes and shoot rockets into space propelled by the brute force (acting over a period of a few minutes) of chemical combustion of fuels and oxidants. That rocket propulsion technology is not powerful enough to reach orbital speeds and space at much higher surface gravities than Earth. I'm logically assuming that the development of chemical propulsion rocket technology will proceed any kind of advanced (sophisticated, probably lower thrust, accelerating and braking over a period of a year) nuclear propulsion capability for interstellar space travel. The aliens living there are stuck in a gravity well, too deep to get out of. They are not going to get into space, far less, buy a starship.

Some of the biggest fish and mammals that ever lived thrive in our oceans. On a super earth, the offsetting effect of buoyancy on gravity would probably allow the evolution of life in their oceans. Whales are comfortable in the water but are unable to breath and suffocate from the effect of gravity on their organs when stranded on the beach. On land, the effect of high gravity would probably result in the evolution of flat low to the ground species like alligators that slither and drag their bellies on the ground. Even on Earth, it takes much effort for them raise themselves up and run short distances. High gravity would also create crushing atmospheric pressures and, I would guess, potentially high surface temperatures due to the higher concentration of greenhouse gases. One could imagine bacterial life existing in cooler clouds at high altitudes.

Although smaller and harder to find with present optical telescopes and techniques like gravitational wobbling and dimming of the parent star when transiting in front of the star, smaller earth size and smaller planets offer a better chance of intelligent life becoming spacefaring. There is probably a limit on the size of smaller planets in terms of ability to hold an atmosphere. We are indeed lucky here on earth, as long as we don't continue to foul our atmosphere with higher levels of greenhouse gases, carbon dioxide from burning fossil fuels and higher methane levels from leaking wells and pipelines and rotting arctic permafrost due to global warming. At least, most of the sane people have gotten the message and will do something about it. If Earth does overheat or some other space born disaster befalls our Earth or solar system, you can be happy that someone does invent a starship to escape this place.