Kepler’s findings have revealed that our own world sustains life as a mere coincidence. This is unsettling.
While Earth is unique, of course, and arguably rare, it has been discovered, with a fair amount of certainty, that the situation here on Earth, which allowed life as we know it to exist, is not exclusive to our beloved planet. There are at least millions, perhaps trillions—perhaps numbers we haven’t had a reason to name! moles on moles on moles! (or, perhaps just one mole?)—of other planets which exist, did exist, or will exist, which have the potential to support life as we know it.
Life as we know it, specifically, an evolutionary potential toward the sort of life that includes complex beings perhaps similar to ourselves, requires of a planet the simultaneous presence of liquid water, solid land or mass or shallow points in said water, a source of energy (star) and an atmosphere. This situation requires that a planet be within the “habitable zone” of a star, and that the star be large enough such that the planet is not “tidally locked.” Thus, in the case of a red dwarf star, such a planet in the habitable zone would fail to spin, and if any liquid water were present it would only exist along a single line between the hot side facing the star and the frozen side facing away. No life there. (Also, red dwarfs have significantly less energy and burn out much sooner than one such as our sun. We got really lucky.)
Based on our current understanding, the elements necessary for “life” also happen to be those which are most abundant in the universe: Hydrogen, Oxygen, Carbon, Nitrogen. We assume that these are the ingredients necessary for life, of the sort recognizable to us as life, anyway, and so we have focused our attention to that end. I mean, it is possible that other corners of the universe have other elements in surplus (with these particular four in scarcity), and it is also possible that life could have evolved from different materials. There probably exist elements not present from our vantage point, and thus undiscovered by human science entirely. With so much about the universe belonging to the unknown category, at this time it is only useful to search within the known parameters. Also, of course, there is simply so much to look at; we must narrow the focus to draw any conclusions.
This reminder applies to the epitome of all data calculations, the equation we will never be able to solve: accurately and completely mapping the stars.
(Did you know that, even if every resource on our planet were dedicated to a super computer/telescope to solve this equation, there still would not be enough processing power or time to reveal an answer? This is why we begin astronomy by pointing our telescopes in a single direction, looking for something familiar, and seeing what can be learned by looking at the sky only a little bit at a time.)
What is the goal of this search?
There is the unending human curiosity, the pursuit of knowledge. There is the fear of our own mortality. As we learn more about our planet, we have become increasingly aware of its temporal qualities; anthropogenic influences aside, the period in which life can exist on Earth is finite. Even in the most optimistic scenario in which humans are able to maintain existence on the planet, by not destroying themselves either through war or the tapping of resources, our world will still someday reach a point where it becomes inhabitable. The Earth is slowly moving away from the sun (1.5cm/yr), the Earth’s spin is slowing as the moon pulls away, and the Sun’s spin is also slowing as the planets pull on it. One day, maybe the planets and the Sun stop spinning. Maybe over time the Earth moves far too far from the sun and becomes really fucking cold. Maybe the Sun burns out entirely in around billion years. It would be nice to know if any of this is going to happen. Also: when.
At five billion years, the Earth will have moved .0001 times present distance between itself and the Sun; it is likely that Earth will theoretically be habitable until the Sun implodes. Scientists have calculated that Earth is 4.54 billion years old, with an error range of 50 million years. The first humans existed ~1-2 million years ago; the period of our existence can be eclipsed by a rounding error.
It’s uncertain what we can know. There is the hope, the dream, that other intelligent life… well, Mars may well have been inhabited, or at least habitable at some point, simply by the basic principle we know, which is that the universe constantly expands, as does our solar system. At some point Mars was in the habitable zone, that exists between our Sun and the dark of the universe; then, later, Earth moved into this position. By this logic we could infer that Venus has the potential to become inhabitable – we know very little of this planet but that it is gaseous and hot at its surface, and that its crust is actually older than Earth; the one element it lacks is Hydrogen, however it is speculated that, at one point, there did exist water oceans on the surface, which were boiled by the close proximity to the Sun, allowing the Hydrogen to escape into space. Fast-forward a few hundred million years, after Venus has moved further away from the Sun, and, say, a large meteor filled with Hydrogen hits the planet… then, there would exist the potential to terraform Venus into a habitable planet. Further, if we humans are still alive at this time we may be able to speed up, or create, that serendipitous meteoric aftereffect. Ultimately, the theory here is that, potentially, Mars, and Earth, or Venus, when caught at the right time, could sustain life. So, we’re not prisoners to our astronomical good fortune.