APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

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APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by APOD Robot » Wed Nov 18, 2015 5:12 am

Image A Sudden Jet on Comet 67P

Explanation: There she blows! A dramatic demonstration of how short-lived some comet jets can be was documented in late July by the robotic Rosetta spacecraft orbiting the nucleus of Comet 67P/Churyumov-Gerasimenko. The featured animation depicts changes in the rotating comet with three illuminating stills. Although the first frame shows nothing unusual, the second frame shows a sudden strong jet shooting off the 67P's surface only 20 minutes later, while the third frame -- taken 20 minutes after that -- shows but a slight remnant of the once-active jet. As comets near the Sun, they can produce long and beautiful tails that stream across the inner Solar System. How comet jets produce these tails is a topic of research -- helped by images like this. Another recent Rosetta measurement indicates that the water on Earth could not have come from comets like 67P because of significant differences in impurities. Comet 67P spans about four kilometers, orbits the Sun between Earth and Jupiter, and has been the home for ESA's Rosetta spaceship since 2014 August. Rosetta is currently scheduled to make a slow crash onto Comet 67P's surface in late 2016.

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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by jimwillemin » Wed Nov 18, 2015 12:49 pm

How do terrestrial geochemical and tectonic processes affect the D/H ratio? In particular, I know evaporation affects 18O/16O ratios, leaving the oceans relatively rich in 18O and presumably deuterium. Thus, the water hydrating minerals in sea-floor weathering should be relatively D rich; at least some of this water will get translated into the upper mantle via subduction or otherwise sequestered in rocks. Is four billion years of active subduction enough to change the D/H ratios of the world ocean? Since Mars shows no sign of subduction past or present, what is the D/H ratio in Martian surface ice?

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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by Bellerophon » Wed Nov 18, 2015 2:45 pm

These images make me imagine a pocket of partly melted ice either achieving high enough gas pressure to burst out through a weak spot, or a weak spot forming due to ablation of the surface or some other process, or both. The jet continues until it loses pressure due to a combination of fluid being expended and cooling due to free expansion. So what makes the pockets form beneath the surface, where it should be cooler? Is there more volatile material there that has already evaporated from the ice nearer the surface? I know Rosetta has found CO, CO2, CH4, etc. in the coma of 67P.

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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by Ron-Astro Pharmacist » Wed Nov 18, 2015 2:49 pm

jimwillemin wrote:How do terrestrial geochemical and tectonic processes affect the D/H ratio? In particular, I know evaporation affects 18O/16O ratios, leaving the oceans relatively rich in 18O and presumably deuterium. Thus, the water hydrating minerals in sea-floor weathering should be relatively D rich; at least some of this water will get translated into the upper mantle via subduction or otherwise sequestered in rocks. Is four billion years of active subduction enough to change the D/H ratios of the world ocean? Since Mars shows no sign of subduction past or present, what is the D/H ratio in Martian surface ice?
I am not a chemistry wiz but a quick search gives a little background.

As far as this comet goes – one needs to pay for the privilege of satisfying that curiosity.

Sounds like an ongoing debate. Not debatable is today's APOD. Very nice!
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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by neufer » Wed Nov 18, 2015 3:24 pm

https://en.wikipedia.org/wiki/Spit-take wrote:
<<A spit-take is a comic technique in which someone spits a beverage out of his or her mouth when he or she reacts to a statement. In this context, the word "take" is used in the sense of taking in information. It is similar in construction to the phrase "double-take." Spit take made it into the Oxford Dictionary, not to be confused with the Oxford English Dictionary, in a 2014 update. Danny Thomas sometimes is credited with popularizing its use in comedy. Albert Brooks' short film, The Famous Comedians School, features a workshop on spit takes.>>
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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by dergolem » Wed Nov 18, 2015 4:08 pm

Maybe it's a stray pod from the Eighth Dimension?
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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by Ann » Wed Nov 18, 2015 4:10 pm

neufer wrote:
https://en.wikipedia.org/wiki/Spit-take wrote:
<<A spit-take is a comic technique in which someone spits a beverage out of his or her mouth when he or she reacts to a statement. In this context, the word "take" is used in the sense of taking in information. It is similar in construction to the phrase "double-take." Spit take made it into the Oxford Dictionary, not to be confused with the Oxford English Dictionary, in a 2014 update. Danny Thomas sometimes is credited with popularizing its use in comedy. Albert Brooks' short film, The Famous Comedians School, features a workshop on spit takes.>>
There should be a word for actors who typically launch large gobs of spit when they deliver their lines.

The most (in)famous Swedish spitting actor was Ernst-Hugo Järegård. I have personally been spat on by Järegård during one of his performances (unintentionally, I'm going to assume).

Järegård is most famous for playing a Swedish doctor working in the biggest hospital in Copenhagen, Denmark. His character likes to stand on the roof of the hospital and look longingly at the (now closed) nuclear power plant of Barsebäck in Sweden through his binoculars, while shouting "Danskjävlar!!!" This expletive might be loosely translated as "You f---ing Danes!!!"
Click to play embedded YouTube video.
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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by Boomer12k » Wed Nov 18, 2015 4:33 pm

The differences in the water impurities points to ASTEROIDS as the source of at least the majority of our water. Planets would be gathered up ASTEROIDS for the most part. (protoplanets, planetesimals, that then collided.) As material gathered, and enlarged by collision, more and more would be added. Earth got a vast amount, and in its orbit, was suitable for liquid water.

Interesting article... "Origin of water on Earth"....

Lucky us...

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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by neufer » Wed Nov 18, 2015 5:10 pm

Ann wrote:
Click to play embedded YouTube video.
The most (in)famous Swedish spitting actor was Ernst-Hugo Järegård. I have personally been spat on by Järegård during one of his performances (unintentionally, I'm going to assume).

Järegård is most famous for playing a Swedish doctor working in the biggest hospital in Copenhagen, Denmark. His character likes to stand on the roof of the hospital and look longingly at the (now closed) nuclear power plant of Barsebäck in Sweden through his binoculars, while shouting "Danskjävlar!!!"
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Re: APOD: A Sudden Jet on Comet 67P (2015 Nov 18)

Post by neufer » Thu Nov 19, 2015 2:38 pm

Click to play embedded YouTube video.
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