Downloads the Planck Collaboration (2013) dust map, placing it in the
    default ``dustmaps`` data directory.

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)