When ESA's Huygens probe passed through Titan's atmosphere on its way to a successful landing, it was buffeted by turbulence unexpected by scientists. Very little was known about Titan's atmosphere before Huygen's landing because the moon is shrouded by a thick hydrocarbon haze. Huygens found that the upper atmosphere was much thicker than expected, and broken up into several distinct layers. The probe also discovered possible evidence of lightning strikes around it.