Distance from Sol to Altair
Originally named Osiris, the planet is a rocky world occupying the first orbit of the star Altair. Osiris originally had a thick atmosphere composed mostly of nitrogen, argon, and carbon dioxide; the atmosphere protected the planet from the fury of its star, named Sopdu to keep with the Egyptian theme of the system. Apophis orbits 3.4 AU from Sopdu – 508 million kilometers, or 316 million miles. This puts Apophis comfortably in Sopdu’s “Goldilocks zone,” an area that’s not quite too hot, and not quite too cold, so that water can exist as a liquid. However, when the gamma-ray burst swept through the system, it blasted away Osiris’s atmosphere and subjected the planet to the severe solar wind of Altair. The few small lakes around the planet’s equator evaporated away into space, leaving the planet a rocky, sterile husk. Upon arriving at the decimated planet, as a sick joke, the colonists began to call the planet and their colony Apophis, who is the Egyptian god of chaos. The name stuck.
Apophis has no moon. It is approximately 96% the size of Earth, with gravity being 4% less than a normal Earth gee. Its elemental composition is similar to both Earth and Mars, being a differentiated planet: it has a small core made up of metallic iron and nickel, with a less dense crust of silicates. However, Apophis’s core is not spinning, meaning the planet has a very weak and insubstantial protective magnetic field, which causes even more problems for the hopeful colonists after the GRB.
Altair, or Sopdu, is the brightest star in the Earth constellation Aquila, and the twelfth brightest star as seen from Earth. The star is approximately 16.73 light-years from Home System. Sopdu is a Class A7 V main sequence star, about 1.7 times the mass of Sol and nearly 11 times brighter in the visible spectrum. Sopdu is a variable star, meaning it periodically becomes brighter for a time, before dimming again, its apparent magnitude (the brightness as seen from Earth) fluctuating. Sopdu rotates extremely rapidly, causing the star to oblate – meaning the equator bulges significantly. In fact, the width of the star’s equator is 14% wider than the star is tall (from pole to pole).
Sopdu has very high metallicity and a great abundance of iron. Metallicity refers to the amount of metals in a star – a “metal” is considered to be anything heavier than hydrogen and helium. In this classification, oxygen counts as a metal. Stars with high metallicity nearly presuppose rocky inner planets.
In ancient Egyptian astronomy, Altair was part of the constellation of a mummified falcon, representing the god Sopdu, a sky god, a god of war, and a god that offered protection to the inhabitants of eastern Egypt. Sopdu is associated with Horus, also being the son of Osiris. This connection is the reason the Apophis’s original name was to be Osiris.