Scientists analyzing data from NASA’s Cassini spacecraft have found that Titan – the largest moon of Saturn and the only moon in the Solar System with a dense atmosphere – behaves much like Venus, Mars or a comet when exposed to the superfast solar wind.
This image shows conditions observed by Cassini during a flyby on December 1, 2013, when the magnetosphere of Saturn was highly compressed, exposing Titan to the full force of the solar wind. In analyzing data from the encounter, the researchers observed that the moon interacted with the solar wind much like the planets Mars and Venus, or a comet. Specifically, they saw that the solar wind draped itself around Titan, creating a shockwave that formed around Titan where the full-force solar wind rammed into the atmosphere of the moon. Previously, scientists had thought Titan would have a different sort of interaction with the solar wind because of the complex atmospheric chemistry of the moon. Image credit: NASA / JPL-Caltech.
“We observed that Titan interacts with the solar wind very much like Mars, if you moved it to the distance of Saturn. We thought Titan in this state would look different. We certainly were surprised,” said Dr Cesar Bertucci of the Institute of Astronomy and Space Physics in Buenos Aires, the first author on the study published online in the journal Geophysical Review Letters.
Titan is large enough that it could be considered a planet if it orbited the Sun on its own, and a flyby of the giant moon in 2013 simulated that scenario, from Cassini’s vantage point.
The encounter was unique within Cassini’s mission, as it was the only time the space probe has observed the moon in a pristine state, outside the region of space dominated by Saturn’s magnetosphere.
Titan spends about 95 percent of the time within Saturn’s magnetosphere, but during a Cassini flyby on December 1, 2013, the moon happened to be on the sunward side of Saturn when a powerful outburst of solar activity reached the planet.
The strong surge in the solar wind so compressed the Sun-facing side of Saturn’s magnetosphere that the bubble’s outer edge was pushed inside the orbit of Titan.
This left the moon exposed to, and unprotected from, the raging stream of energetic solar particles.
The special circumstance allowed the scientists to study the shockwave that formed around Titan where the full-force solar wind rammed into its atmosphere.
At Earth, our planet’s powerful magnetic field acts as a shield against the solar wind, helping to protect our atmosphere from being stripped away.
In the case of Venus, Mars and comets – none of which is protected by a global magnetic field – the solar wind drapes around the objects themselves, interacting directly with their atmospheres. The researchers saw the same thing at Titan.
Dr Bertucci and his colleagues thought they would have to treat Titan’s response to the solar wind with a unique approach because the chemistry of the hazy moon’s dense atmosphere is highly complex. But Cassini’s observations of a naked Titan hinted at a more elegant solution.
“This could mean we can use the same tools to study how vastly different worlds, in different parts of the Solar System, interact with the wind from the Sun,” Dr Bertucci concluded.
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C. Bertucci et al. Titan’s interaction with the supersonic solar wind. Geophysical Research Letters, published online January 28, 2015; doi: 10.1002/2014GL062106
