Cassini sees Titan glow just before destruction


Useful right until the last minute, NASA’s Saturn probe sent data about the planet’s moon just before the end. Andrew Masterson reports.


Once more with feeling: Cassini records Titan just before plunging to its destruction.
Once more with feeling: Cassini records Titan just before plunging to its destruction.
NASA

In its dying hours, as it plunged towards fiery oblivion on Saturn, NASA’s Cassini probe captured the dawn of spring on the moon called Titan.

Research by planetary scientists at the University of Bristol in the UK has used Cassini’s final transmitted images to add valuable data to an emerging picture of seasonality on the moon.

It has long been known that Titan’s poles flare and gutter, behaving as seasonal hot spots. In 2012, however, observers noted a sudden strong cooling on the moon’s southern pole.

In a paper published in the journal Nature Communications, a team led by Nicholas Teanby report that the change was initiated in 2009, when an area of peak warming moved into the northern hemisphere. This caused an atmospheric collapse in the south and the formation of a polar vortex.

Through the next two years, the continuing subsidence caused the emergence of a mid-atmosphere hot spot which, in turn, caused “extreme enrichment” of several types of gas.

In a result described as unexpected, this enrichment dramatically increased the cooling efficiency of the mid-atmosphere strata, initiating a period of cold temperatures.

Teanby and his colleagues note that Titan’s climatic fluctuations are unique in the solar system, because most of the gases which act to cool down the planet are produced by means of photochemical reactions in the upper reaches of the atmosphere

“This does not happen on the other terrestrial planets—Earth, Venus, and Mars—as the major atmospheric cooler on those planets is CO2, which is uniformly mixed so is not enhanced by subsidence at the winter pole,” they write.

Titan’s atmosphere is nothing if not dynamic, however. Based on available data, the scientists predict that its southern polar vortex will continue to evolve and that the cold snap will eventually end.

Indeed, the most recent – and for the time being, last – observations of the moon show that a new hot spot is already forming. Indeed, if we can ascribe for a moment an anthropomorphic element to spacecraft, the promise of warm weather on Titan was the last thing Cassini saw.

“Cassini’s incredible voyage through the Saturnian system ended on 15 September 2017 when it entered Saturn’s atmosphere, making these the last measurements of Titan’s winter pole until another mission can return to the Saturn system,” the scientists note.

  1. https://www.nature.com/articles/doi:10.1038/s41467-017-01839-z
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