5 février 2015

Titan comme on ne l'avait jamais vue!


Titan ressemble plus à Vénus ou à Mars que ce qui était cru auparavant:

Saturn’s largest moon, Titan, looks more like Venus and Mars than astronomers ever suspected—at least when it comes to suffering a severe strike from the solar wind.

NASA’s Cassini spacecraft made a flyby of Titan in December 2013 that offered a unique opportunity for scientists, in newly reported observations. For the first time, scientists caught a close glimpse of the large moon when it was outside Saturn’s protective magnetic field.

The solar wind, basically fast-flowing charged particles, continually blasts out from the sun and past the entire solar system.

Earth’s magnetic field shields the atmosphere from being stripped away by the solar wind. By studying the solar wind’s impacts on worlds lacking a global magnetic field, like Venus, Mars, and now Titan, scientists learn about their atmospheres and how their chemistry changes under solar assault.

Titan spends about 95 percent of its time around Saturn, within the planet’s strong, protective magnetosphere. So Cassini mission planners were excited to observe the moon exposed and naked in the solar wind during the 2013 flyby. The visit allowed them to see the shock wave produced around Titan as the fast-flowing solar particles slammed directly into the moon’s unprotected atmosphere.

“We observed that Titan interacts with the solar wind very much like Mars, if you moved it to the distance of Saturn,” said Cesar Bertucci of the Institute of Astronomy and Space Physics in Buenos Aires, who led the research with colleagues from the Cassini mission.

Despite the complicated chemistry of thick methane-rich skies, Titan’s atmosphere seems to have responded to the solar wind in essentially the same way as the red planet, which has a much thinner atmosphere than Earth or Saturn's big moon.

“We thought Titan in this state would look different,” Bertucci said. “We certainly were surprised.”

Now researchers believe these new findings suggest that regardless of where unmagnetized planets lie in the solar system, they all interact with the solar wind in the same way.



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