Astronomy Department Living in a comet: How to build a Dyson treehouse by Wladimir Lyra | New Mexico State University - BE BOLD. Shape the Future.
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Living in a comet: How to build a Dyson treehouse by Wladimir Lyra

(Originally published in the  Las Cruces Sun News on March 8, 2020 – link)

Green lush gardens, shimmering water shoals, butterflies fluttering by. Looking at the sparse moving clouds that dot the deep azure sky, a wandering voyager could almost feel at home. Except that the sky is strangely close. Through the dense foliage, a window in the shiny metal dome where the sky is projected lets one glimpse a tiny and distant Sun. And that whiff of rotting flesh that they said would be almost imperceptible is pungently all around.

This is not Earth. Our voyager is inside a comet, four billion miles away from the closest dune of earthly sand.

The scenario above was envisioned by the mathematician and physicist Freeman Dyson, who recently passed away at the age of 96. Aside from leaving long-standing contributions to physics, mathematics, and engineering, he also spent a lot of time thinking about the future of humans in space. The concept of a Dyson Sphere is now a staple in science fiction. The solar panels you have on your roof may be collecting enough energy for your house needs, but that’s a tiny fraction of all the energy produced by the Sun. A Dyson sphere is a giant shell that an advanced civilization would construct to capture the totality of the energy output from its star. The concept is completely hypothetical: for all their scanning of the night sky, astronomers have not spotted any unambiguous sign of astro-engineering. Dyson also proposed the idea of a tree environment that could survive in space and support a human colony. These hypothetical trees would be genetically engineered to produce a greenhouse around themselves, and thus be able to maintain a balmy temperature.

The notion is not as crazy as it sounds. In fact some plants on earth already do that. They belong to the rare variety of thermogenic (heat-generating) plants. The skunk cabbage, for instance, is able to heat up to a whopping 60oF above air temperature, melting frozen ground and pollinating earlier than other plants. Other heat-generating plants are the voodoo lily, the dead horse arum, and the carrion flower. Many of these have stinky names because of their unusual reproductive strategy: they emit a scent of decaying flesh to attract carrion-eating insects that then act as pollinators.

A Dyson tree would be genetically engineered out of these plants to withstand the hazards of space. The bark would be made thick and hard to survive the near vacuum, and transparent to allow sunlight in. Glass has the appropriate properties, and the added bonus of being opaque in infrared, trapping the heat. Comets are made of ice, which could be melted to produce water. Seeded on a comet, a full-grown Dyson tree would generate a breathable atmosphere and enough heat to support an ecosystem; the interior of the comet hollowed out to contain the atmosphere. The comet would resemble a huge leafy spaceship, half-natural, half-engineered. A Dyson tree in a comet the size of Manhattan could support a human population of millions.

Comets number in the trillions, and extend through a vast region of the Solar System beyond Neptune dubbed Kuiper belt, after Gerard Kuiper, the Tucson-based Dutch-American astronomer who first suggested its existence – after Clyde Tombaugh discovered Pluto, its largest member. In deep freeze at the far reaches of the Solar System, comets are only visible from Earth when they are tugged from their orbits and plunge inwards, their ices boiling off the surface when they get close enough to the Sun. Covering several comets with Dyson trees would support a civilization in the Kuiper Belt consisting essentially of an archipelago of city states, powered by a Dyson sphere. Like ancient Polynesia, humans would be able to travel from island to island, in propulsion rockets that would not require much fuel to escape the small gravity of their tiny worlds.

Far-fetched? More science fiction than science, yes. Impossible? We can’t say. Jules Verne’s “From the Earth to the Moon” sounded far-fetched to its contemporaries, but barely 100 years later the Apollo 11 followed almost the exact script. Science fuels science fiction, and in turn science fiction inspires a new generation of scientists. In the far future, a tourist in the capital comet of the Kuiper Belt may look back at the writings of our times, now ancient, and staring at the greenery in front of them, no longer a fiction, wonder in awe at the prescience of Freeman Dyson. They may end up loving the visit – if the engineers also find out how to get rid of the funky smell.