There has long been a theory that at least some UFOs are craft from one or more alien planets. But which planets? Decades ago it was possible to speculate about Mars and Venus being habitable worlds, but the discoveries of the space age have shown Venus to be a hellish oven of a planet and Mars is a frozen desert with (we are told) an atmosphere that is little more than a vacuum. Aside from the fact that Mars, while certainly cold, dry, and lacking oxygen, may have a denser atmosphere than NASA claims, both these worlds may have been very different in the distant past. Indeed, even NASA believes that Mars once had surface water, including an ocean, and denser air. In a previous print magazine article I wrote about how even Venus may once have been livable until being struck by a massive asteroid. But today most speculation about space visitors focuses on other solar systems.
Despite the vast distances involved, alien civilizations might send unmanned probes perhaps possessing AI (artificial intelligence). Or actual biological entities might arrive after generations on an ark ship with artificial gravity and sunlight and a complete ecosystem aboard, including growing plants. Or there may be some loophole in the laws of physics… perhaps, as some have speculated, spacecraft could be designed that would not accelerate in our space, but could create a sort of bubble of their own space, and then propel the bubble across the light years between the stars. No one has any idea if this is possible or not, or how it might be done.
As to the existence of habitable extra-Solar planets, astronomers estimate that there are anywhere from 100 to 400 billion stars in our galaxy alone. If just one in a thousand was orbited by a planet hosting an advanced species, that would be 100 to 400 million worlds. And we are discovering that most stars do, indeed, have their own planetary systems. But are these habitable?
Most people are not aware that the overwhelming majority of our galaxy’s stars are near the center or in the densely packed globular star clusters. And these are mostly very old stars with low “metallicity,” meaning that they are almost entirely composed of hydrogen, with practically none of the carbon and oxygen needed for life, or the silicon and iron and other elements needed to have solid planets. And where stars are densely packed, any planets would likely suffer relatively frequently from the disastrous effects of nearby supernovae. In fact, with so many nearby stars, many such planets would also suffer from dangerous thermal buildup.
Of the remaining stars out in the more habitable galactic arms, the majority are small red dwarf stars, which remain on the main sequence for a very long time, and which do usually have planets. The problem is that the “Goldilocks zone” for such stars, the region where it is not going to be too hot or too cold, is small and close to the stars. Planets in this zone would be tidally stressed and heated internally, adding to the internal heat produced by the planet itself, causing massive volcanism. Such worlds would be dangerous and unstable and might not even have solid crusts. Eventually the planets would become tide-locked to their stars, with one side baking in the red sunlight and the other enduring a bitterly cold and unending night. Some astronomers have suggested that strong winds would even out the temperatures somewhat, but such winds would themselves make it difficult to establish a civilization. And there would be nothing to prevent all the atmospheric moisture from evaporating from the hot side and falling as snow on the cold side, to remain there permanently. And many of the rocky, solid worlds similar to our home are “super-Earths,” whether orbiting red dwarfs or larger and hotter stars. Everywhere we look, large objects generate proportionately more heat than smaller objects… stars are hotter than planets; massive Jupiter is hotter inside than less massive Earth; and Earth’s core is hotter than our Moon’s. Super Earths would likely be so active volcanically that life could scarcely survive there, let alone civilizations.
Our own solar system, although it may have been very unstable in its early history, with planets like Jupiter drifting closer to the Sun and then further away, seems stable today and designed for life. The big gas giant planets like Jupiter are far from the Sun, unlikely to destabilize our own world’s orbit with their massive gravity. And, nearer the Sun, we have the solid, rocky worlds like Earth, which sits in the middle of the “Goldilocks zone” where a world can have temperatures conducive to life. Earth even has a Moon massive enough to stabilize our axial tilt to some degree. But most other solar systems discovered to date are nothing like our own, with “hot Jupiters,” gas planets close to their parent stars. Either they formed near their stars before the stars began generating massive amounts of energy or they migrated in.
We are assured by astrophysicists that in perhaps five billion years our Sun will leave the “main sequence” of stellar evolution, and, running low on hydrogen fuel, will expand into a red giant star and destroy the Earth. What most people don’t know is that our Sun (according to these same astrophysicists) has been slowly getting hotter since it was formed perhaps 4.6 billion years ago. In as little as half a billion more years it will probably make our world uninhabitable. This means that a civilized species has but a comparatively short window in time to develop spaceflight and, if need be, migrate to safety.
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