Glossary
Chapter 4
  accelerate increase speed
  assume believe something is true
  astronauts people trained to fly a spacecraft
  breakthrough an advance or discovery
  calculation math
  clever smart
  cosmos everything that is in space
  engineers people who design or construct structures
  exploit use or develop
  fireflies insects that light up
  galaxy a large group of stars and planets
  mass the measure of a solid body
  measure an amount of something
  mere small, only
  paces steps
  pass by go on
  predicted guessed, based on knowledge
  solar probe a small spacecraft sent to study the sun
  speed of light the rate at which light moves
  structure the way parts are put together
  sustained kept up or maintained
  thrust forced
  universe all of space including galaxies, stars, and planets
  unmanned having no crew or passengers
  vast large
  wormholes holes that lead somewhere else in space