Theia (Planet)

This page is about the hypothetical planet-sized object. For the Titaness, see Theia (mythology).

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Basic Information

Per the Giant-impact hypothesis, Theia (sometimes alternately called Orpheus) was the rogue planet, planetoid, planetar, or asteroid that crashed into the Earth 4.5 billion years ago. This collision coated the surface of the earth with lava and debris. It also blasted material into orbit around the Earth, and that material eventually became the Moon.

Prior to the collision, Theia may have been about the same size as Mars.

Prior to 2016, the assumption was that of a glancing blow: Theia had basically bounced off of the Earth and been hurled out of our solar system. Recent advances in seismographic imaging suggest the impact may have been more direct. There are two extremely large (a million times the size of Mount Everest) chunks of rock deep inside the Mantle of the earth that are now believed to be chunks of Theia that were driven deep inside our planet by the force of the impact.

Theia is named for the Titan from Greek Mythology. That titaness Theia was the mother of Selene (the goddess of the moon).



Game and Story Use

  • Deep scans could reveal some sort of mystery in those buried Theia chunks.
    • It seems like a good, though inaccessible, place to put your precursor artifact. It could be a riff on the Gaia Hypothesis, with some sort of ancient precursor supercomputer buried deep in our planet and secretly exerting its influence. What happens if it decides we are a threat?
    • Panspermia theories conject life here began out there. So the Theia chunks could be the habitat of dragons, demons, kaiju, aliens or whatever else is going to eventually emerge from the surface and threaten the world.
    • Or, you know, just like extremophile archaea that are unlikely to have any real impact here on the surface, but could I guess be used as explanation for a plague or pandemic. Not that you need such a justification these days, as our ecosystem is plenty good at trying to kill us with or without alien influence.
    • No doubt a large chunk of Theia also ended up in/as parts of the Moon. Depending on tech level, that may be easier to reach than deep mantle, so you may have some astronaut or space probe discover a thing on the moon that foreshadows the thing beneath the earth.
    • A volcanic eruption or earthquake could bring to the surface a hunk of alien rock with an out of place artifact held within.
  • In a space exploration speculative fiction game, the PCs could be sent to rescue a space colony on a planet that is about to be hit by a rogue planet. Obviously, this would be an Extinction-Level Event, the end of the world as we know it, for anyone left behind on the colony. As they narrowly escape in time, the PCs watch the beautiful and horrifying cosmic forces devastate the world and hurl enough lava into orbit to form a small asteroid belt that it's likely to eventually coalesce into a new moon.
  • Mass Driver or stellar engine technology could theoretically weaponize an entire planet. You wouldn't actually need anything nearly as large as Theia or Mars to bring about an apocalypse, but sufficiently advanced aliens with a flair for the dramatic might do so just to send a message to other civilizations that witness the results.
    • Mess with us, and we'll move the heavens and the earth to wipe your entire planet from the historical record.
      • Actually, that would make some absolutely killer characterization for your Evil Empire in space. Instead of "they've just built a deathstar, and we need to stop them before they use it", you could do "they already have a track record of genocide, here's the list of the 17 homeworlds they've slagged just to earn their street cred".
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