Erid

Erid is the home world of Rocky's species, Eridians. It is the first planet in in the 40 Eridani star system, being extremely close to its central star. Erid has approximately 2 times that of Earth gravity, and an extremely high pressure atmosphere composed of mostly ammonia . Erid's strong magnetic field and dense atmosphere block almost all incoming light, including radiation. It is for this reason that Eridians, and presumably other life on Erid, evolved to use echolocation.

## Name

Erid, is the first planet orbiting 40 Eridani A. For reasons Andy dosen't know, astronomers start the naming of planets at “b”. So if they were describing the planet Mercury (the first planet in our system) it would be Sol b. Earth would be Sol d.

Hence the inconvenient name “40 Eridani A b”.

The word “Eridian” was invented by the novel’s protagonist (Ryland Grace) and fashioned after the name of the star. And due to the inconvenient name that humanity has for the homeworld, the protagonist took to calling it “Erid”.

## Properties

Eridani 40 A b really exists and has the following known properties:

·       Mass: 8.47 Me

·       Semimajor Axis: 0.224 au

·       Eccentricity: 0.04

·       Orbital period: 42.245 days

·       Energy Flux from star: 12537 W/m^2

The following are properties that Andy made up, but are not in conflict with any known observations:

·       Composition: Rocky planet with thick atmosphere – high in metals, low in gaseous oxygen

·       Density: 5710 kg/m^3

·       Radius: 12835 km

·       Atmospheric composition: Mostly ammonia (NH3) with trace amounts of other gasses

o  Thermal conductivity at ground level 0.053 W/(m\*K)

·       Surface atmospheric pressure: 28 atm

·       Average surface temperature: 210°C

The following are things that derive from Andy's made up stats

·       Surface gravity: 2.09g (derived from mass and density)

·       Strong magnetic field (otherwise the atmosphere would be gone.)

o  The magnetic field is approximately 25 times Earth’s field strength.

·       Solar day period: 5.1 hours (actually it’s 18397.44 seconds which is 5.1104 hours) (to dynamo-generate that field)

·       Molten metal core (consistent with such a large radius and needed for the field)

·       Tectonic plates and volcanism (because of the magma and core)

·       Liquid water is present on the surface. The high pressure raises water’s bp to above 210°C

## **Ecosphere:**

The planet has a lush, complex ecosystem that Eridians are just one small part of. The bulk of the energy capture for the ecology is done by airborne microbes that live in the higher parts of the atmosphere. They absorb sunlight and consume the gasses in the air to multiply.

Larger microbes eat them, then small animals eat those larger microbes, etc. Similar to Earth’s oceans. There is a “boundary life” layer that is critical to the ecology – they are the creatures that fly, but also come to the ground. Land life preys on those species and fuels the land ecology.

Eridians are the apex predators of the land ecology.

Owing to the thick atmosphere and the sheer volume of microbes and life at various layers, almost no sunlight penetrates all the way to the ground. Again, similar to Earth’s oceans. As a result, the land-based creatures (including Eridians) have no eyes or sense of sight.