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.[1] We present the first experimental results on the evaporation of liquid CH 4 under simulated Titan surface conditions similar to those observed at the Huygens landing site. An average evaporation rate of (3.1 AE 0.6) Â 10 À4 kg s À1 m À2 at 94 K and 1.5 bar was measured. While our results are generally higher than previous models based on energy balance, they show an excellent match with a theoretical mass transfer approach. Indeed, we find that evaporation in the Titan environmental chamber is predominantly diffusion driven and affected by the buoyancy of lighter CH 4 in the heavier N 2 atmosphere. After correcting for the difference in gravity of Earth and Titan, the resulting evaporation rate is (1.6 AE 0.3) Â 10 À4 kg s À1 m À2 (or 1.13 AE 0.3 mm hr À1 ). Using our experimental evaporation rates, we determine that the low-latitude storm recently observed by Cassini ISS would have resulted in a maximum evaporated mass of (5.4 AE 1.2) Â 10 10 kg of CH 4 equivalent to a 2.4 AE 0.5 m thick layer over 80 days. Based on our results, a sufficient amount of CH 4 can accumulate in the otherwise arid equatorial regions to produce transient ponds and liquid flows.

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