It’s a while since I added to my occasional series concerning the exploration of life on other planets, so here are some thoughts about the giant planets in our solar system. Largest of all is Jupiter, followed by Saturn, then Uranus and Neptune. Each of these has a collection of moons, but I’ll deal with them another day. We also know of a number of exoplanets of this size circling other stars – big planets being easier to detect than smaller ones, other things being equal – but that’ll be the subject for another day.
These large gas giants are characterised by hugely deep atmospheres, in which the pressure rapidly builds to intolerable levels as you drop down through it. It is unclear whether there is a hard surface at any point, or whether the gases of the upper layers simply get progressively denser and more viscous with depth. With no obstructions to stop them, wind currents circle the planet and stir up giant storms that can last for decades. It is not an obvious place for life to thrive.
Science fiction writers have, nevertheless, speculated about life here. Some authors simply ignore what we know (or were writing at a time when much less was known), while others try to weave their stories alongside the facts as we understand them. Typical of the first is EE (Doc) Smith, who was never shy of hypothesising life anywhere, and took great delight in speculating how environmental pressures would shape an alien race’s outlook on life, as well as their physiology. He placed several races on gas giants, including Jupiter. Such races, in his view, would be not only squat and strong – to cope with the gravity – but arrogant and condescending towards the weaklings of other worlds. A large part of Spacehounds of IPC deals with a long-running war between the hexans and the Vorkuls, inhabiting two opposing cities and fighting an impeccable war against each other. The Earthlings help resolve the fight by siding with the more morally upright side – they have little enough in common with either, but the hexans turn out to be unacceptably vicious and ruthless.
Iain M Banks, on the other hand, tried to take a more nuanced view. A couple of his books – including The Algebraist, for example – present life on gas giants as essentially floating, by analogy with oceanic creatures here on Earth. Different kinds of life coexist at different levels of the multi-layered atmosphere. Some of these interact, for better or worse, and others never meet.
Current scientific thinking is less optimistic about life of these giant planets, preferring to think about their moons. That’s a subject for another day. But there was a fascinating piece of analysis I read recently, trying to tackle the question of whether denizens of the gas giants would develop space travel. Basically, the rocket problem is that of managing your fuel. You need a certain amount of fuel to send your object of interest – the payload – up from the surface to orbit. But the payload has a protective casing, which you don’t need in orbit but which weighs something. Then there’s the fuel you’ll burn, and the container holding it… and these also weigh something. So you need more fuel to push up all that lot… and so on. Think back to how small the Apollo moon landers were compared to the entire Saturn V launch system.
The most fuel-efficient way to accomplish this is to have booster stages that are used in the early part of the flight, and then detached when empty to reduce weight for the next stage. Until the advent of reusable vessels like the Space Shuttle, and more recently Elon Musk’s launch vehicles that return to a soft landing, all of these lower stages were single-shot throwaway items. Now, that’s a problem for us here, but in turns out to be a much bigger problem if you are starting from a larger planet. Even one twice Earth’s mass would present difficulties, and Jupiter has about 300 times the mass. Musk’s Falcon Heavy rocket can place about 50 tons of payload into low earth orbit. Taking off from Jupiter, the same rocket could only get 40 kilograms into space. Would a race of beings living on one of these gas giants – even supposing they wanted to look through dense layers of cloud to see what was outside and spark their curiosity – have the resources to embark on space exploration?