How many satellites can we safely fit in Earth orbit?

Magnetic Mishaps: Disturbances in the Earth’s Magnetic Field Could Lead Migrating Birds Astray

By measuring the different speeds at which seismic waves penetrate and pass through the Earth's inner core, researchers believe they've documented evidence of a distinct layer inside Earth known as the innermost inner core - a solid 'metallic ball' that sits within the centre of the inner core.

The Seven-Ages of Earth as Seen Through the Continental Lens