docs: def parse_nate_sims(path):
      '''
      parts0.dat) contains the id number, particle fraction (ignore) a, ecc, inc, long. asc., arg. per, and mean anomaly
      for every particle in the simulation at t=0.
      The second (parts3999.dat) contains the same info at t=3.999 Gyrs for these particles.
  
      :return:
      '''
      zerostate = pandas.read_table(path + 'parts0.dat', delim_whitespace=True)
      endstate = pandas.read_table(path + 'parts3999.dat', delim_whitespace=True)
  
      # add perihelion
      zerostate['q'] = zerostate['a'] * (1 - zerostate['e'])
      endstate['q'] = endstate['a'] * (1 - endstate['e'])
  
      return zerostate, endstate