[LINK] "Prisoners of Gravity"

[rfmcdonald]

Could high escape velocities on super-Earths help explain the apparent absence of radio-transmitting extraterrestrial civilizations? Certainly it's a less depressing possibility than others. Andrew Barton argues at Acts of Minor Treason that many of the (broadly defined) Earth-like worlds so far discovered would have very high gravities. He uses Gliuese 581d, a planet that Barton calculates has nearly three times' Earth's gravity, as an example.

Local life forms would be short and bulky - in that kind of gravity, there's nothing to be gained by going up. Without the high mountains that lower gravity makes possible, land would tend to be lower and more eroded - conceivably, there could be high-gravity archipelago worlds. If you're interested, Extraterrestrials: A Field Guide for Earthlings by Terence Dickinson and Adolf Schaller goes into a bit more detail.

That's just biology - I'm more interested in technology. There's nothing about a high-gravity planet that fundamentally prevents an intelligent civilization from arising there, but one that did would face far greater challenges in some respects than we do. Culturally, it could theoretically have the deck stacked against it from the beginning. On a high-g planet, very few things fly and falls are exceedingly dangerous even from what we'd think of as trivial heights. That sort of environment could easily breed what would be, by human standards, an intensely conservative mindset - something like that, introduced early enough and reinforced enough by the environment, could put serious brakes on any kind of serious technological development, or perhaps just leave the people there in a long Bronze Age.

But let's look at Earthissimo. The people there have struggled against the chains of gravity enough to build a technological civilization that we might recognize in the broad strokes - details, of course, would differ immensely. The important issue, however, is access to space - without that, there's no chance of aliens coming to us. It's with access to space that the real challenges lie.

While it's certainly difficult to get to Earth orbit or beyond, it's certainly doable - a big part of the problem is that there aren't yet any economies of scale in the space industries, but even then you've still got to deal with accelerating to 9.4 kilometers per second even to reach the 300-kilometer altitude of the International Space Station. If you're leaving Earth entirely, escape velocity is 11.2 kilometers per second.

How envious the space freaks of Earthissimo would be of us. With all that extra mass pulling things down, it's not easy to get to orbit - Earthissimo's to-orbit velocity would be 44.91 kilometers per second, and if you want to escape entirely, you'll need to have a ship that can accelerate to 63.5 kilometers per second. The problem is that chemical rockets, such as the ones we used as we began to claw our way into the heavens, are insufficiently beefy. Rocket launches from Earthissimo would be incredibly complex and incredibly expensive - enough so that it's easy to imagine that the people there just wouldn't bother with it at all. Hell, we're having enough trouble getting it off the ground here!