The Long Way Round

At its aphelion, or most extreme orbital limit, the long-period comet C/2032 F3 reaches a distance of more than 3.5 trillion kilometres from the Sun. This is around 23,000 times the distance between the Sun and the Earth, or 770 times the distance between the Sun and Neptune. To a human observer standing on the comet’s surface, the Sun would look much the same as any other star, and the Earth and other planets would be too far away to see with the naked eye. Rather than appearing as part of a larger gravitationally-bound system, C/2032 F3 would seem to rest in the centre of its own, private, star-studded sphere.

To an observer standing on Earth, meanwhile, the comet would be almost totally undetectable, at least with early 21st century technology. 3.5 trillion kilometres is too great a distance for the Sun’s rays to have a meaningful heating effect, and the comet’s surface temperature hovers somewhere in the vicinity of negative 250℃. This means that it lacks a tail, since comet-tails arise when volatiles on the surface sublime in response to solar heating. And, while C/2032 F3 is relatively massive compared to comets in general, it is still too insubstantial to cause readily detectable perturbations in the motions of other celestial bodies.

In terrestrial terms, C/2032 F3 arrives at its aphelion in the year 278,413 BCE. At this time, Earth is home to a multitude of different species, ranging from single-celled organisms with lifespans of under a day, through to clonal tree colonies that cover islands, and can live for millennia. One among the multitude, a relative newcomer, is an unassuming species of ape that will, much later, be granted the designation H. sapiens. There is nothing that marks it as particularly unusual at this time.

Nor is there anything to mark the comet’s aphelion, as C/2032 F3 sweeps calmly past its furthest remove, and begins the long journey sun-ward. It travels quickly, by human standards, with a typical speed of between one and two thousand kilometres per hour. Of course, the environment through which it travels is hardly one where human standards apply, and the comet’s pace pales in comparison to the distances it must cover.

Like many long-period comets, C/2032 F3’s orbit is highly elliptical. It spends almost all of its time beyond the outer planets, in the dark, cold, and overwhelmingly empty expanse known as the Oort Cloud. But for part of each orbit, C/2032 F3 dives towards the inner solar system, eventually coming closer to the Sun than every planet other than Mercury, before careening onwards to repeat the cycle. The aphelion does not mark the beginning of such a dive, exactly, since C/2032 F3 must travel a tremendously long way before it reaches even the outer planets. But it does mark a turning point.

Moving, again, at between one and two thousand kilometres per hour, it takes more than 270,000 years for the comet to reach the very outer limits of the Sun’s planetary system. During all this time, it remains almost entirely unchanged. It does not collide with other Oort Cloud objects, which are vanishingly few and far-between in any case. A layer of frozen dust on the comet’s surface, deposited towards the end of its last solar foray, nearly half a million years earlier, remains essentially undisturbed.

This is not true on Earth. Over the same time period, almost every part of the planet exists in constant motion. Great clouds of water vapour gather and disperse in the lower atmosphere, driven by churning currents of air. Much of the planetary surface is liquid, and consequently pulled and pushed by those same atmospheric currents, as well as heat from the planet below, the movement of ocean-dwelling animals, and the Moon’s gravity. On land, these several hundred millennia see great rainforests spread and then succumb to desertification, new species appear while others pass into extinction, and countless singular moments of pain, joy, and realisation.

For much of this time, humanity remains unremarkable. The species expands beyond its continent of origin, but this is something many other species have accomplished in the past. In some parts of the world, humans have an outsized impact on regional ecologies, and are at least partially responsible for numerous individual extinction events and instances of localised environmental remodelling. Beginning five thousand years ago, in half a dozen places around the globe, groups of humans pass a threshold in their co-operative capabilities, and learn to coordinate on a scale hitherto unknown for large primates. But this, too, is not without precedent in the annals of all life on Earth. 

It is not until much later, around 1750 CE, that genuinely remarkable things begin to happen. C/2032 F3 crosses Neptune’s orbit, thereby entering the planetary solar system. Its pace increases in response to the Sun’s greater proximity, but it remains otherwise unchanged.

On Earth, a cascade of mutually-reinforcing events commences. Humanity develops new techniques for understanding and interacting with the world around it, and the result is a fundamental shift in the planet’s resource economy. Millions of years worth of solar energy, compressed into the ground, is gradually rendered usable. Humanity’s population doubles, then doubles again, all while the energy available on a per-capita basis continues to rise. The sum total of human happiness swells, even while the human capacity for destruction sharpens.

Over the course of two hundred years, humanity, and human industry, come to the boil in ways that are truly unprecedented. Groups of humans, larger and better coordinated than ever before, inflict deep and slow-healing wounds on one another, while at the same time unfurling new and fertile domains of understanding.

By the time the comet passes Uranus, it is moving at more than 70 thousand kilometres per hour. Ultraviolet light from the Sun starts to ionise carbon monoxide on the comet’s surface, blowing the resulting CO+ ions behind it in a pale blue stream. 

Humanity reaches a tentative hand to the heavens. The long-accruing debts of its deal with the Earth begin to come due.

C/2032 F3 becomes visible in the night sky on June 8, 2033. Astronomers have been aware of it since the previous year, but there is nothing to mark it as especially noteworthy from a scientific standpoint. The best predictions of the comet’s trajectory have it safely by-passing Earth. While there is some media coverage of its arrival, few people pay it serious attention. For several days, the comet looks much the same as any other star, if a little smudged around the edges. 

On June 11, as C/2032 F3 passes Saturn, this changes. Already, the comet has a sizable tail of vapour behind it, and now the temperature rises to the point where a range of more exotic chemicals join the fray. These surface chemicals are unusually plentiful, since C/2032 F3 has completed only a handful of circuits around the Sun, meaning there have been precious few previous opportunities for burnoff.

The tail that forms behind it in the June, 2033 passage is a thing of rich beauty. In just a matter of hours, C/2032 F3 becomes the brightest object in the night sky.

In most worlds, this marks the end of the story. For 89 nights, C/2032 F3 hangs in the sky, providing Earth’s 8.5 billion human inhabitants with a sense of cosmic immediacy, and a story to tell their grandchildren. It passes the Earth and Venus, grazes Mercury’s orbit, then continues on its way.

In one world, things unfold differently. A team of scientists notices certain unusual features of the comet’s shape and coloration. They run simulations, and are able to account for the anomalies only by assuming that close to 60% of C/2032 F3’s mass is composed of a particularly rare mineral ore. This ore does not occur naturally on Earth, and represents the rate-limiting resource in a proposed pathway towards efficient fusion energy. In other words, the comet is the cosmic equivalent of walking into an exam room, wildly underprepared, then finding the answers you need written on the ceiling. 

At its perihelion, or closest orbital approach, the long-period comet C/2 2032 F3 would reach a distance of only 60 million kilometres from the Sun. It never gets there. On Earth, a cascade of mutually-reinforcing events commences.
 

A note on the text: 

The EA community spends a lot of energy on existential risk reduction. I think this is basically great. At the same time, ensuring a flourishing future may depend not only on our capacity to safeguard against risks, but also to recognise and make the most of opportunities. My guess is that such opportunities aren’t nearly as significant as the risks, at least as regards their implications for present-day action, but I’d be interested to hear thoughts on this. E.g. Are there plausible ways to fill in the formulation: ‘unless we develop technology X before time Y we miss out on [extremely valuable] opportunity Z’?