By detecting the distribution and total number of particles hitting detectors on the ground, physicists can infer the energy of the primary particle that began the air shower. For higher-energy cosmic rays, they will detect more particles on the ground, and the spread will be greater. Physicists also can determine the direction the particle was traveling as it entered the atmosphere. The trajectories of lower-energy cosmic rays are greatly influenced by the magnetic fields of our galaxy, so we cannot identify the original direction from which they came (the identity of the particular supernova remnant will probably never be known). Ultra-high-energy cosmic rays, on the other hand, are so powerful that they can traverse our galaxy's magnetic fields largely undeflected. Most scientists presume that these highest-energy cosmic rays come from places beyond our Milky Way galaxy. Air Showers Detector