by JEFF HECHT
Titan’s atmosphere gives rise to clouds and complex weather IMAGE/NASA/JPL/Space Science Institute
We knew very little about this strange world before NASA’s Cassini spacecraft arrived at Saturn seven years ago. Since then, the ringed planet has completed a quarter of an orbit around the sun and Titan has passed through its spring equinox. In that time, Cassini has swooped by Titan almost 80 times and has released the Huygens lander onto its surface.
Together they have penetrated the haze that hides Titan’s surface to reveal modest mountains, vast fields of sand dunes, rocks, and even streams, lakes and weather.
Titan looks surprisingly familiar, although it is a cold, dimly lit world made from unfamiliar materials, says planetary scientist Elizabeth Turtle of Johns Hopkins University Applied Physics Laboratory in Baltimore, Maryland. “The rocks are water ice and the lakes are methane and light hydrocarbons, yet we see processes very similar to what we see on Earth.”
So far, there are no recognisable signs of organic life. That’s not surprising: by terrestrial standards, Titan is a deep freeze with surface temperatures at a chilly -180°C. Yet Titan is very much alive in the sense that its atmosphere and surface are changing before our eyes. Clouds drift through the haze and rain falls from them to erode stream-like channels draining into shallow lakes. Vast dune fields that look as if they were lifted from the Sahara sprawl along Titan’s equator, yet the dark grains resemble ground asphalt rather than sand. It is a bizarrely different world that looks eerily like home. Or as planetary scientist Ralph Lorenz puts it: “our prototype weird-world exoplanet”.
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