# I Disappearing lakes on Titan - seasonal cycles

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#### mfb

Mentor
Earth and Titan are the only objects in the Solar System with stable liquids on its surface. Earth has water oceans, lakes, rivers and rain, Titan has methane/ethane oceans, lakes, rivers and rain. Earth has seasons, and so does Titan. They are just much longer as Saturn's orbital period is 29.5 years.

Studying data from the Cassini mission scientists have found three lakes that were present in winter but disappeared in summer, the first time such a large change has been found. It is expected that evaporation is too slow for the process - the liquid must have gone elsewhere. Studying changes like this will tell us more about the only other system of surface liquids we know.

Press release: Disappearing Lakes Offer Clues to Titan’s Seasonal Cycles

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Dragonfly is a proposed helicopter to explore Titan. The low gravity, slow wind and dense atmosphere make flight very easy (humans could fly with muscle power), the mission could explore many different places on the surface. Even at its slow speed of 10 m/s it can fly 60 km in two hours - farther than any rover ever made it on Moon or Mars (although it might make shorter flights for safety reasons). And it can do that every Titan day, or twice per month! It could launch 2024-2025. More details

Related Astronomy and Astrophysics News on Phys.org

#### Comeback City

I wonder... could this be a result of some sort of tectonic activity? Considering the now-emptied lakes are all within the same general area, that is.

This older NASA article confirms there is tectonic activity on Titan, albeit slightly different from that of Earth.

Thoughts?

#### Zeke137

Gold Member
I'm not an expert in this field, but my understanding of the situation is that the hydrology on Titan is complicated by the fact that both ethane and methane can exist in all three states under the conditions prevailing there, and hence both participate in the hydrologic cycle on Titan. This is in contrast to the hydrology on the present-day Earth, where only water exhibits this behaviour. It's not well understood whether, or to what extent, seasonal variations in temperature or atmospheric pressure on Titan can alter the relative amounts of ethane and methane vapours in the atmosphere.

Ethane and methane have significantly different properties: liquid ethane ($C_2H_6$), with a higher molecular mass than methane ($CH_4$), is less volatile than liquid methane, and is hence less likely to evaporate from an ethane/methane mixture present in a body of liquid on the surface of Titan. So it's possible that lakes and ponds viewed in the northern summer on Titan have different amounts of ethane/methane compared to cooler parts of the seasonal cycle.

Some studies (https://hal.archives-ouvertes.fr/hal-01718104 , https://www.hou.usra.edu/meetings/lpsc2014/pdf/2371.pdf) suggest that karst (dissolution) geological forms exist on Titan, and that ponds and lakes formed in such areas can be subject to slow drainage by solution/percolation into the surrounding (mainly water-ice) rocks. Dissolution rates of substrate may differ between ethane and methane.

So it would seem that at least two mechanisms for shrinkage of ethane/methane lakes and ponds could be present on Titan.

#### mfb

Mentor
Considering the now-emptied lakes are all within the same general area, that is.
That is probably just a selection effect - we don't have the same image quality for the whole planet.

#### Zeke137

Gold Member
Another word on possible karst/dissolution geology on Titan: liquid methane will not dissolve water ice, but it will dissolve organics like solid acetylene which may be bound into the water ice.

"Disappearing lakes on Titan - seasonal cycles"

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