Tag Archives: alien seas

The lakes and seas of Titan

Chapter 8 of the book “Alien Seas” presents the current understanding of Titan’s lakes and seas after the Huygens and Cassini missions.

Bodies of liquid on Titan are identified from their morphology and their radar reflection properties. The liquid on Titan is not water but a mixture of methane (CH4) and ethane (C2H6). In Chapter 4 of Alien Skies, we considered the seas of Titan in their relation with the atmosphere.

In Alien Seas we learn that the largest sea of Titan, beautifully named Kraken Mare, is about the size of the Black Sea. Titan has other large seas, and a large number of smaller lakes. The seas have rugged shorelines with fjord-like edges, typical of rapidly changing levels, suggesting that seasonal variations in methane rainfall and evaporation constantly change their size. Some seas have indeed been observed to vary in shape during the Cassini mission itself (see receding shorelines on Titan).

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The smaller lakes have more rounded shapes than the seas, reminiscent of “karstic” lakes on Earth, i.e. lakes were water sinks into the underground.

Titan’s seas are thought to consist of a mixture of ethane and methane (present measurements do not allow us to measure their composition), but the balance of the two components will depend on how much liquid sinks into the ground.

Lakes on Titan, radar image [NASA/JPL]

“Alien Seas” book

“Alien seas” is a recent Springer book, edited by Michael Carroll and Rosaly Lopes, with a title that resonates with “Alien skies”.

AlienSeasCover

The topics covered by Alien Seas are more varied than the title suggests since the term “seas” is defined in a wide sense as anything large and liquid, including the molten inside of planets, and even sand dune fields as “sand seas”. Here are the topics:

– the (possible) oceans of Venus

– the (probable) oceans of Mars

– volcanism in the solar system (“oceans of lava”)

– the sub-surface oceans of Ganymede, Europa and Callisto

– ice volcanoes and geyser in smaller moons (like Enceladus)

– sand fields on Mars, Venus and Titan

– the seas of hydrocarbons on Titan

– the interior of Saturn

– “alien” seas on Earth, e.g. salt ponds and under-ice lakes

– exoplanets

The books ends on a fantastic gallery of alien landscapes by different artists.

Each chapter is written by a renown experts in their field, which ensures the quality and reliability of the whole.

See here for a post about the chapter on Venus. The chapter on Saturn consist mainly of a sci-fi style description of a mining operation for diamond and Helium-3 into the depth of the planet in the far future. More directly related to the topic of Alien Skies, it also mentions the storm of Saturn, see this post.

The Lost Oceans of Venus

“Is it deranged to build a good part of a career studying something that may or may not have been?” asks David Grinspoon at the beginning of the chapter 2 of “Alien Seas”, the one about the oceans of Venus.

Grinspoon is the author of “Venus revealed”, a book about the scientific exploration of Venus, and “Lonely Planets”, about the possibility of alien life.

His chapter in Alien Seas explains the two main pieces of evidence of oceans on Venus in the past, namely

– the excess of deuterium in the present atmosphere, that implies that a lot of water, at least in vapour form, was present  in the early atmosphere of Venus (now bone-dry)

– the more circumstantial evidence from our improved understanding of how planets form. We expect the surface early Venus to have been water-rich, like Earth, given how violent and random is the formation of small rocky planets.

Neither argument is entirely fool-proof.  We are like detectives who arrive at the crime scene years after the events, and have no direct clue to work with, only a senile eyewitness with severe memory lapses and the charred remains of a burned note left by the victim.

David Grinspoon makes three points: the first is that Earth-style life could have developed in Venus’s atmosphere, because conditions were very similar to early Earth, with water oceans, volcanoes to provide the carbon and lightnings to provide the energy. The second is that Earth’s version of life could even be Venusian, or the other way around, because exchange of flying rocks was frequent between the planets in the turbulent early days of the Solar System (rocks from Mars still regularly reach Earth today). The third is that Venusian life could have migrated in the cloudtop when the atmosphere got caught in runaway greenhouse and evolved into the present hellish conditions.

You can see a webcast of the talk of David Grinspoon on the topic at Exoclimes 2010 here.

A possible timeline for Venus according to D. Grinspoon, with a long-lasting ocean (blue). [Figure 8.7 of Alien Skies]
A possible timeline for Venus according to D. Grinspoon, with a long-lasting ocean (blue). [Figure 8.7 of Alien Skies]