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Enjoy the starry night skies
Be a considerate neighbor. Reduce nighttime glare.
Shield your outside lights downward.
Let the stars light up the night.

December 2014 night sky

—Charlie Christmann

Rosetta and Philae at  Churyumov-Gerasimenko

All eyes were on 67P/Churyumov-Gerasimenko as the Rosetta spacecraft sent its lander, named “Philae,” to touchdown on the surface of a comet for the first time. Every planetary body, including Earth, has its own unique hazards when trying to land on its surface from space. Earth has a thick atmosphere that generates tremendous temperatures as a spacecraft approaches. Not many materials can take the heat; any breach in the heat shield could spell disaster as we all saw in the shuttle Columbia breakup in 2003. Mars has a thin atmosphere making it difficult to slow down from orbital velocities to make a soft landing. There is not much Martian air for parachutes to catch. The moon has essentially no atmosphere; slowing down to touchdown takes pure rocket power.

The challenge of landing on a comet generated many more questions than answers. Comets were believed to be big snowballs with some rock thrown in for good measure. Some thought the surface was soft and fluffy. Others thought the comet may be nothing more than a pile of icy rock slightly bound together by gravity. Would there be gas vents to blow the lander off the surface? Could Philae cling to the surface in the low gravity long enough to do something useful? Finally, everything must take place automatically. At 317 million miles from Earth, radio messages are delayed by 28 minutes each way.

Initial images taken by Rosetta revealed 67P to be a world with boulders, towering cliffs and dangerous valleys and pits, with jets of gas and dust streaming from the surface. Landing on the surface would be precarious at best. Philae was released from Rosetta at a height of 14 miles to slowly fall in 67P’s feeble gravity, several hundred thousand times weaker than on Earth. Even after falling that far for about seven hours, the probe hit the surface at just over one mile per hour. The initial touchdown was almost exactly where it was planned. Unfortunately, the surface was harder than expected and the lander bounced twice. Two hours after the initial landing, Philae came to rest next to a vertical wall in the shade with little sunlight hitting its solar cells to recharge its batteries.

“The Philae lander came into contact with a soft layer several centimeters thick. Then, just milliseconds later, the feet encountered a hard, perhaps icy layer on 67P/Churyumov-Gerasimenko,” stated German Space Agency (DLR) researcher Klaus Seidensticker.

After about sixty hours, Philae exhausted its batteries and fell silent. But in that short time, many of the science experiments returned data to keep scientists happy for years.

Preliminary results show the comet has carbon-containing organic molecules. No life, just the building blocks to make life. Mission controllers asked Philae to hammer into the surface of the comet, and found that the comet surface is probably as hard as ice, according to ESA. Not the fluffy snowball they expected. Controllers also commanded Philae to drill into the surface of the comet just after it came to rest, but scientists are not sure how much comet material was collected and analyzed.

Even though the lander is now dormant, European Space Agency officials are hopeful that Philae could come back to life as Comet 67P makes its way around the sun. It’s possible that the sunlight and temperature conditions around the lander could change as the comet gets closer to the sun.

Rosetta is expected to stay with the comet as it makes its closest approach to the sun in August 2015. The orbiter is scheduled to study the comet through at least December 2015. It should be exciting to see 67P come to life as it nears the sun. Unfortunately, the comet is not expected to be visible from Earth without a telescope peaking near magnitude 13 (17 times dimmer than the unaided eye can see).

 
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