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  Night Sky

Turn off or shield your outside lights downward. 
Unshielded, they ruin the night sky, annoy your neighbors, and don’t help with crime.
Keep the starry skies available to everyone.

November 2016 night sky

—Charlie Christmann

Good bye Rosetta:

Nearing the end of its fuel supply and the limit of its solar panels to produce electricity, the Rosetta spacecraft team commanded the probe to crash land onto the surface of comet 67P/Churyumov-Gerasimenko. Its last transmission back to earth happened just seconds before contact on September 30, 2016. It is joined there by its lander Philae that was released soon after the arrival of Rosetta; its mission to touchdown and study the surface. In the seventeen months it orbited the comet, Rosetta has taught us much about comets and the origins of our solar system.

Launched on March 2, 2004, the European Space Agency launched Rosetta, and its attached companion Philae, to chase down and catch a comet. Comet 67P was the perfect target since it orbits between Jupiter and Earth with a period of six years and 5.25 months. The idea was to catch 67P before it started outgassing, and then follow it as it approached the sun and headed back toward the neighborhood of Jupiter. To get an extra boost in speed, Rosetta passed Mars on February 25, 2007, at a distance of only 160 miles. It finally caught up with 67P and began a year-and-a-half orbit on August 6, 2014.

Hello 67P/Churymov-Gerasimenko:

Since its initial discovery by astronomers Klim Churyumov and Svetlana Gerasimenko in 1969, the comet has rounded the sun eight times. The latest perihelion (its closest approach) was August 13, 2015, at a distance of 120 million miles from the sun with Rosetta in orbit.

Astronomers studying its orbit found the comet is a relative newcomer to this neighborhood. Until 1840, the comet came no closer to the sun than 370 million miles, not close enough to form a comet. But, in 1840, Jupiter kicked 67P into an orbit closer to the sun.

Then in 1959, another encounter with Jupiter placed it in its current orbit. Tracing back even farther in time, Scientists believe 67P is an escapee of the Kuiper belt and originally resided some five billion miles from the sun, until something nudged it toward the inner solar system. By about four hundred thousand years ago, it orbited between Pluto and Uranus. Sixty thousand years ago, it had moved to an orbit between Neptune and Saturn. So 67P is a recent visitor to our part of the solar system and likely contains materials from the original formation of the planets and sun.

There were many surprises discovered by Rosetta. First, scientists had expected a potato-shaped object. To their surprise, they saw an object that looked like a rubber ducky with a larger body section, a neck, and smaller head section, making a complete rotation every 12.4 hours.

The lander, Philae, hit the surface of the comet on November 12, 2014, but could not stick the landing. It bounced twice in the low gravity before ending up beside a steep cliff in the shade. Its batteries only lasted a couple of days. The science team expected the lander to find organics, just not in the quantities it did. Sixteen different compounds important for life were discovered, including four not known to exist on a comet before.

Rosetta itself was also busy discovering and photographing the comet as it approached, rounded, and departed the sun. The images show a surprising diversity of landscapes, including steep cliffs, “sand” dunes, and boulders. The surface color is described as black, darker than charcoal. One of the biggest findings is that there is molecular oxygen (the same as we breath here on Earth) coming off the comet. No one expected to find free oxygen since it tends to react with other molecules and should be mostly bound up in water.

As the comet approached the sun, outgassing increased. The amount of water escaping from 67P when Rosetta arrived was around 110,000 pounds per day. Just after perihelion, that had increased to 220 million pounds per day. 67P is expected to shrink in circumference by an average of ten to 15 feet on this trip around the sun. In the 17 months Rosetta observed outgassing, more than 14 billion pounds of water have been lost.

While Rosetta joined Philae on the cold, black surface of 67P/Churyumov-Gerasimenko to rest for the remaining life of the comet, much of the data collected is yet to be analyzed in detail. Many discoveries are waiting to be found in the reams of information from their spectrometers, radars, and imagers. Though the future of 67P is not clear (interactions with Jupiter could again change its orbit in unknown ways), its song, captured by receivers onboard Rosetta (go to youtube/8YkL6bMVXjY), will continue to haunt the solar system for many millennia of years to come. Nice work, Rosetta. Rest in peace.

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