Envisat captures a cluster of aircraft condensation trails, or 'contrails', over southern Italy, the Adriatic Sea and parts of Croatia.
Exhaust emissions from jet aircraft contain large amounts of water vapour that mixes with the atmosphere, which under certain atmospheric conditions has much lower vapour pressure and temperature than the exhaust emissions, causing the water vapour to condense to form ice crystals.
These ice crystals act as condensation nuclei around which even more water vapour in the surrounding air condenses. The result is the formation of an elongated cloud-like condensation trail in the sky.
Contrails can last anywhere from a few minutes to hours. They can also grow to form persistent artificial cirrus clouds that can last for days or weeks. Contrails and cirrus clouds could potentially have an impact on the Earth's climate by trapping the Earth's heat in our atmosphere in a similar way to greenhouse gases.
Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument acquired this image on 1 September 2008, working in Full Resolution mode to provide a spatial resolution of 300 metres.