World turtle immobilised part 2

Further exploration of the thought experiment in which we have a world carried on the back of a turtle crash into a spherical one.  This time, the landscape underneath the turtle.

In this post I talked about a full-sized globe planet which has had a second planet, a flat one carried on the back of a juvenile world-turtle, land on its surface with minimal damage.  (IE. we still have two worlds, but they're not in great shape.)  Generations have passed, civilisation has more or less recovered from the turmoil and they're in a position to start looking around and wondering what actually happened.

What's known is that the weather is wetter, there are vast salt marshes forming to the East where the a new geographical feature blots out the sun for half the morning, and strange new animals have been seen in those regions.  And the sages, who have read the antique writings, say the winters are now milder, the summers are hotter and the year is two days shorter than it used to be.  Gods were probably involved, but there's no consensus on who they were punishing or for what.

Expeditions sent by the new empire to explore the area don't actually see the turtle with any kind of clarity.  It's too vast.  On a clear day, from a hundred miles away, you might see a hint of a head or a flipper, with a titanic disc above.  The water pouring off the disc falls into vacuum, which instantly converts it to a fog.  It drifts down, where the jet stream helps by pushing it away to the West.  There's still enough water in the air around the turtle to surround it with clouds.  They figure out it's turtle-shaped by mapping it.  On horseback by land, and by ship where its hindquarters overlap the ocean.  In the process they discover The Bite and the curious effect the blood which is still oozing from it has had on the local wildlife, but that's for a later post.

(I did a back-of-the-envelope calculation of how much water is pouring off the disc if it has the same flow rate as Niagara Falls.  Then I decided that that magic which recycles that water back onto the disc is still working — otherwise it would have doubled the amount of water on the planet's surface in the first five minutes.)

What the explorers actually see is cloud-covered lands with a strange top-heavy mountain at the centre.  It's never truly dark here  There's a bright point in the fog, lighting it from the inside.  Sometimes it's above the mountain, far away and dim, sometimes it's close and the cloud glows with a diffuse light.  (One explorer described it as 'akin to being shrunk down and standing at the centre of a cold candle flame'.)

The turtle is ringed with concentric circles of volcanic chasms because it's slowly crushing the continental plate under it (its magical nature gives it some buoyancy even in death, otherwise there'd be no slowly about it). If you remember the first post, the turtle world is the size of Ceres, which is shown on the left here compared to Earth. Its weight has created a depression around it which has filled with brine, making an inland sea a few dozen miles wide.

The area around the turtle was damaged so badly in the cataclysm that none of its life survived. The landscape is slowly being recolonised by hardy plants and a few animals that would be equally at home in a desert. The only intelligent life is a few small, migratory clans of orcs and gnolls.

World turtle immobilised

Picture a world-carrying turtle. Four elephants on its shell, and a flat planet on their backs.  We want the turtle to be visible from the edge of the world, so have the turtle's length overlap the planet's by about an eighth at front and back.  That should give us a bit of flipper and a head to look at if we're peering down from the very edge, where the ocean turns into a waterfall that tumbles endlessly into space.  For the planet to have the same surface area as the Earth, that would make it about 19,000 Km or very roughly 12,000 miles across.  Big.

We want it to be smaller, because we're about to crash it into an inhabited world.  Let's make it a baby, only about the size of Japan.  That gives us 1,200 Km (750 Mi) of turtle, and makes the world on its back 900 Km (560 Mi) across.  Still big.  If we take a Loggerhead turtle as our template, it's a turtle the size of Ceres, the largest asteroid ever discovered.  It's not a dinosaur killer, it's more like the school bully that beats up dinosaur killers and steals their lunch money.  So instead it makes a semi-controlled landing and immediately dies because something much larger than it is has taken a bite out of its side.

(Sages of the day recorded that something whale-shaped blotted out constellations over several nights, other mystics point out that it had a triangular fin on its back.  Educated men know the world is round and can use parallax measurements to estimate the creature's size, but they quickly run out of beads on their abacus in the attempt.)

Even a controlled landing by a 1,200 Km turtle is going to mess up your planet.  First there's the noise, the loudest ever heard.  Birds are knocked out of the air by the pressure of the sound wave.  Then there's the hurricane of displaced air, tearing up forests and stripping fields.  The impact (no more than a kiss, really) sends millions of tons of soil and rocks billowing into the atmosphere, blotting out the sun.  All across your continent, dormant volcanoes erupt back into life, spewing magma and toxic gas.  Earthquakes shiver your cities apart.  The first of the great forests far enough from the crash site to have survived begins to burn.  Rocks the size of houses crash down, entire countries distant.

A third of your population dies in the first few hours.  Half that number again starve as crops fail and the landscape plunges into a winter that will last three years.  More are killed by bandits and wandering companies of looting deserters during the civil war that follows, or forced to flee into the wastes as refugees.  It takes a while for civilisation to re-emerge, establish a government and rule of law, and solve enough of its ongoing problems to think about sending an expedition to the site of the impact to see what the hell happened.  Two generations doesn't seem like an unreasonable length of time.

In the meantime, strange rumours have been filtering out of the East (which is arbitrarily where our turtle landed in relation to the new centres of government).  Never-ending salty rain.  An inland sea where none existed before.  Oddly symmetrical mountains on the horizons.  A shining globe above those mountains, half-hidden by a haze of distance.  Enormous, glowing spheres crashing across the landscape.  Strange, savage animals and plants.

It would be a whole new world, within reach of the recovering old world.  I think I could make a campaign out of that.