Any ship entering the Lithuim Nebula has to slow down. The Celsius Nebula has the gas resource availible. When a ship or a defensive structure is in a Celsius Nebula, all supplies are cut off. This makes supplies unavaible and weapons non-functional. Vessels will avoid the anti-matter nebula and a plot courses around the dangerous nebula.
Asteroids provide ore to harvest.
There are three types of asteroid fields and they reflect on how much each of the nuggets provide ore. Large asteroid fields contain large nugget deposits of ore. Medium asteroid fields contain medium sized nuggets of ore. Small asteroid fields contain small nuggets of ore. When the usable ore is taken away by the Harvesters, Siphons, or Galiots, there is unusable asteroids left floating around.