Cassini Catches Titan Naked in the Solar Wind

Researchers studying data from NASA’s Cassini mission have observed that Saturn’s largest moon, Titan, behaves much like Venus, Mars or a comet when exposed to the raw power of the solar wind. The observations suggest that unmagnetized bodies like Titan might interact with the solar wind in the same basic ways, regardless of their nature or distance from the sun.

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 Dec. 2013 simulated that scenario, from Cassini’s vantage point. The encounter was unique within Cassini’s mission, as it was the only time the spacecraft has observed Titan in a pristine state, outside the region of space dominated by Saturn’s magnetic field, called its magnetosphere.

The solar wind is a fast-flowing gale of charged particles that continually streams outward from the sun, flowing around the planets like islands in a river. Studying the effects of the solar wind at other planets helps scientists understand how the sun’s activity affects their atmospheres. These effects can include modification of an atmosphere’s chemistry as well as its gradual loss to space.

Titan spends about 95 percent of the time within Saturn’s magnetosphere. But during a Cassini flyby on Dec. 1, 2013, the giant 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.

This diagram depicts conditions observed by NASA's Cassini spacecraft during a flyby in Dec. 2013, when Saturn's magnetosphere was highly compressed, exposing Titan to the full force of the solar wind. Image credit: NASA.

This diagram depicts conditions observed by NASA’s Cassini spacecraft during a flyby in Dec. 2013, when Saturn’s magnetosphere was highly compressed, exposing Titan to the full force of the solar wind. Image credit: NASA.

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