docs: def fetch():
      """
      Downloads the Planck Collaboration (2013) dust map, placing it in the
      default ``dustmaps`` data directory.
      """
      url = 'http://pla.esac.esa.int/pla/aio/product-action?MAP.MAP_ID=HFI_CompMap_ThermalDustModel_2048_R1.20.fits'
      md5 = '8d804f4e64e709f476a63f0dfed1fd11'
      fname = os.path.join(
          data_dir(),
          'planck',
          'HFI_CompMap_ThermalDustModel_2048_R1.20.fits')
      fetch_utils.download_and_verify(url, md5, fname=fname)