Recent space missions have raised some interesting ideas about exobiology for me. The Galileo and Cassini results on Europa and Enceladus, respectively have revealed evidence for liquid water oceans under their surface ice, providing a remarkably clement environment for life to originate and evolve, perhaps. And exoplanet surveys have found a lot of terrestrial worlds larger than the Earth that may well possess habitable atmospheres, while smaller worlds might have such thin atmospheres that they couldn’t very well have life on them.
It raises an interesting speculative thought for me: what if there really is something very odd about the Earth?
Astronomically, the Earth has one really weird feature, which is our large Moon. This was created by a bizarre collision during the Earth’s formation. And it has probably influenced the evolution of the Earth, through tidal effects. Planets with such large and influential moons are probably very rare.
Some people have suggested that the reason the modern Earth has as thin an atmosphere as it does is because of the Moon.
Sometimes this theory is used to suggest that the Earth is the only (or one of the VERY few) worlds to produce life. Maybe that’s the “great filter”, they argue (that explains “Fermi’s Paradox” — or “why hasn’t anyone visited us already?”).
But what if it turns out that most worlds with life fall into a few categories of worlds very different from the Earth?
- Earth-size to Super-Earth-size worlds with THICK atmospheres and heavy cloud decks, large greenhouse effect — but further from the star, so that the effect balances out.
Ice-ball moons like Europa and Enceladus where tidal heating maintains a clement liquid ocean under the ice.
We know the latter kind of world must be very common, just from the fact that there’s more than one in our own star system. The former sounds a bit like some of the worlds that have shown up in the Kepler survey.
Both kinds of worlds have interesting problems for development of spaceflight, let alone interstellar flight or even communications.
The heavy gravity of super-earths makes developing launch vehicles (a task we barely succeeded at) very VERY hard.
For the moon-ocean-dwellers, the problem is that they have to get through the ice to reach space.
But more importantly, neither of these worlds even allow their inhabitants to SEE space.
For thousands of years, humans believed the world was flat and even when they became convinced it was round, they believed it was the whole universe, with the sky some kind of dome or sphere attached to it (and very close).
It was the behavior of the stars and planets in the sky (and the Moon) that clued ancient humans in that something more interesting was going on and that the universe was a lot bigger than they had imagined.
Basically, we had the cheatbook staring us right in the face.
That gave us the ambition. And eventually we developed the technology to follow it.
Even there, though, the universe was very kind to us — providing us with a very tantalizing target in the Moon. And beyond that, Mars is a beckoning, earthlike world, compared to most of the worlds we know.
Biologically, also — we are adapted to live in a thin atmosphere. We have senses that don’t depend on the presence of air and use light, which travels just fine through a vacuum. The ocean-dwellers might well be echo-locators, since they presumably live in a very dark ocean. Even if they were to get through the ice and emerge into the vacuum on the other side, what would they make of it? They couldn’t naturally see the stars — and what would give them the idea to build instruments to see them?
What would give them the idea that the universe had anything to offer above the ice sheet (except a quick death)?
Imagine that someday humans make contact with such species. What would they think of us? We’d seem like being peculiarly-blessed with an affinity for life in space — adapted to a thin light air supply, able to withstand both strong gee forces and microgravity, with senses capable of perceiving other star systems and worlds at EXTREME distances, ranging from millions of kilometers to light years.
We’d seem like creatures bizarrely adapted for life in space.