PLANET FORMATION, EXOPLANET, HABITABILITY AND MORE

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Now just past its closest approach to the Sun, Comet C/2013 US10 Catalina is entering the northern sky and is climbing into the predawn sky. Over the coming month, its highly-inclined orbit will take it north of the plane of the solar system, where skywatchers may be able to follow it, appearing as a fuzzy blob as it moves through the stars of the constellations Virgo the Maidenand Bootes the Herdsman through the end of 2015 and into January 2016, passing the bright star Arcturus on New Year’s Day.

First thought to be an asteroid when it was discovered in 2013 by the University of Arizona’s Catalina Sky Survey, the object was designated US10, but further observations helped refine its orbital characteristics, and astronomers have established that it as it swung around the Sun, making its closest approach on November 15, it attained escape velocity—the speed at which it will be able to escape the Sun’s gravitational pull. This will result in its being ejected from the solar system, making this appearance our first and only opportunity to observe this frozen visitor from deep space.

Although some astronomers have forecast that the comet’s brightness may peak in late November, becoming visible to the naked eye, no one is certain as to how bright it will become, and observers would be wise to keep in mind the wisdom of famed comet-hunter David Levy, who has discovered a total of 22 comets: “Comets are like cats. They have tails, and they do precisely what they want.” –Bing Quock

Onset of Winter on Titan’s South Pole

The south pole of Saturn’s moon Titan is just entering winter, and it’s a harsh beginning to the very cold season. NASA scientists estimate that temperatures there likely reach a bone-chilling -238° Fahrenheit (–150° Celsius). And while earthlings may think winter seems to last forever here on our planet, each season on Titan lasts about seven-and-a-half Earth years, so spring is a long way away for the south pole.

Scientists started observing seasonal changes on Titan when the Cassini spacecraft first arrived at Saturn in 2004. At the time, it was mid-winter at Titan’s north pole (and summer in the south). Cassini’s camera and infrared instrument (CIRS) have been tracking seasonal ice clouds disappearing in the north pole and forming in the south pole of the moon ever since.

The size, altitude, and composition of these polar ice clouds help scientists understand the nature and severity of Titan’s winter. CIRS data shows that the ice particles in the clouds are made up of a variety of compounds containing hydrogen, carbon and nitrogen, and that they were weaker in the north pole than they currently are in the south. A new detection, announced last week at 47th Meeting of the American Astronomical Society (AAS) Division for Planetary Sciences (DPS), has found a massive ice cloud system in the south which supports the idea that the onset of winter is much harsher than the end.

“When we looked at the infrared data, this ice cloud stood out like nothing we’ve ever seen before,” says Carrie Anderson of NASA’s Goddard Space Flight Center. “It practically smacked us in the face.”

“The opportunity to see the early stages of winter on Titan is very exciting,” saysRobert Samuelson, a Goddard researcher working with Anderson. “Everything we are finding at the south pole tells us that the onset of southern winter is much more severe than the late stages of Titan’s northern winter.”

Cassini will continue to observe the seasonal changes on Titan and its south pole until the mission’s end in 2017. –Molly Michelson

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