rfmcdonald | [LINK] "New Debate over Volcanoes on Titan" (Reply)

Shifting from the too-mundane realm of Canadian politics to the wonders of the universe beyond Earth, Centauri Dreams reports on the ongoing debate about Titan and its geological (titanological?) activity. Is it an active world, with ice volcanoes? Or, is it a basically dead world, with only the atmosphere distinguishing it from Jupiter's Callisto?

Back in December, scientists from the Cassini team presented evidence for ice volcanoes on Titan, looking at a region called Sotra Facula, which bears some resemblance to volcanoes on Earth like Mt. Etna in Italy and Laki in Iceland. An ice volcano, also known as a cryovolcano, would draw on geological activity beneath the surface that warms and melts parts of the interior and sends icy materials through a surface opening. Sotra Facula’s two 1000-meter peaks combine what appear to be deep volcanic craters with finger-like flows of material, a kind of surface sculpting that could explain some of the processes occurring on other ice-rich moons.

But work like this is part of an ongoing dialogue testing various hypotheses, and the latest round takes us in a sharply different direction. In a new paper in Icarus, Jeff Moore (NASA Ames) and Robert Pappalardo (JPL) argue that Titan is in fact much less geologically active than some have thought. A cool and dormant interior would be incapable of producing active ice volcanoes:

“It would be fantastic to find strong evidence that clearly shows Titan has an internal heat source that causes ice volcanoes and lava flows to form,” adds Moore. “But we find that the evidence presented to date is unconvincing, and recent studies of Titan’s interior conducted by geophysicists and gravity experts also weaken the possibility of volcanoes there.”

The new work looks at Titan in light of what we see on Callisto, which Moore sees as analogous to Titan ‘if Callisto had weather.’ And indeed, the two moons are roughly the same size, with Callisto’s cratered surface solely the result of impact events rather than internal heating. In the new paper, Moore and Pappalardo see Titan’s surface as explicable entirely from external processes like wind, rain and impacts. These we see in profusion — lakes of liquid methane and ethane, valleys carved by rivers, craters — through infrared and radar instrumentation, but the debate now moves to whether all surface features can be explained in the same way.

Titan’s atmosphere may remain the focus of debate between those who believe the moon is geologically dormant and the ice volcano theorists. The atmosphere is primarily nitrogen, with a few percent methane, and the Sotra Facula analysis, presented at the American Geophysical Union meeting in San Francisco last December, focused partially on that mix. Thus Linda Spilker (JPL):

“Cryovolcanoes help explain the geological forces sculpting some of these exotic places in our solar system. At Titan, for instance, they explain how methane can be continually replenished in the atmosphere when the sun is constantly breaking that molecule down.”

Myself, I'd love Titan to be geologically active, but that's just my prejudice. As the first commenter said, we need another and better Titan probe to settle this.