sentences:  It was detected with the Spitzer Space Telescope,
  
  Current triaxial measurements of Iapetus give it radial dimensions of , with a mean radius of .However, these measurements may be inaccurate on the kilometer scale as Iapetus's entire surface has not yet been imaged in high enough resolution.The observed oblateness corresponds to a rotational period of approximately 16 hours, not to the current 79 days.