APOD: Rosetta Approaches Comet... (2014 Aug 11)

[APOD Robot]

Rosetta Approaches Comet Churyumov-Gerasimenko

Explanation: What does it look like to approach a comet? Early this month humanity received a new rendition as the robotic Rosetta spacecraft went right up to -- and began orbiting -- the nucleus of Comet 67P/Churyumov-Gerasimenko. This approach turned out to be particularly fascinating because the comet nucleus first revealed itself to have an unexpected double structure, and later showed off an unusual and craggily surface. The above 101-frame time-lapse video details the approach of the spacecraft from August 1 through August 6. The icy comet's core is the size of a mountain and rotates every 12.7 hours. Rosetta's images and data may shed light on the origin of comets and the early history of our Solar System. Later this year, Rosetta is scheduled to release the Philae lander, which will attempt to land on Comet Churyumov-Gerasimenko's periphery and harpoon itself to the surface.

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[Kris Kelvin]

Very ugly. I definitely prefer my comets in Middle Ages illustrations...

[Dr. Work]

"Craggily" is not a word. You mean craggy or cragged.

[CURRAHEE CHRIS]

So, is anyone running the odds on the success of the Philae Lander attaching itself to the comet surface??? Anyone heard anything in terms of how long they hope the lander maintains itself on the comet?

[Chris Peterson]

"Craggily" is not a word. You mean craggy or cragged.

Every author of English is afforded the opportunity to create new words, which may or may not enter popular usage. I think "craggily" is a rather nice word.

[Boomer12k]

SO COOL to see the nucleus of a comet...with no out gassing....we always wondered what one really looked like.

I can't wait to see what others look like. Maybe next time around...Halley's Comet....

:---[===] *

[rwlott]

"Craggily" is not a word. You mean craggy or cragged.

Every author of English is afforded the opportunity to create new words, which may or may not enter popular usage. I think "craggily" is a rather nice word.

You're so right, Chris, but not only that, "craggily" IS a word, with a very old history (see http://dictionary.reference.com/browse/craggily). Just because it's in less common usage than craggy or cragged, and flagged in a few computer spell checkers (Starship Asterisk*'s, for example), doesn't mean that it's an invalid word.

Russ

[geckzilla]

Asterisk doesn't have a spellchecker. Any spellchecking done is a native function of whatever browser you are using.

[Chris Peterson]

You're so right, Chris, but not only that, "craggily" IS a word, with a very old history (see http://dictionary.reference.com/browse/craggily). Just because it's in less common usage than craggy or cragged, and flagged in a few computer spell checkers (Starship Asterisk*'s, for example), doesn't mean that it's an invalid word.

So in this case the author is simply "guilty" of using an adverb as an adjective. Also a time honored element of the evolution of English.

[geckzilla]

Guiltily, I think you mean.

[hughhyatt]

"Craggily" is not a word. You mean craggy or cragged.

Every author of English is afforded the opportunity to create new words, which may or may not enter popular usage. I think "craggily" is a rather nice word.

You're so right, Chris, but not only that, "craggily" IS a word, with a very old history (see http://dictionary.reference.com/browse/craggily). Just because it's in less common usage than craggy or cragged, and flagged in a few computer spell checkers (Starship Asterisk*'s, for example), doesn't mean that it's an invalid word.

Russ

You're right: craggily is a word, but an adverb, when what was clearly called for was an adjective. And while it's true that English is a living, evolving language, and that adverbs are sometimes used as adjectives or even eventually BECOME adjectives, it seems clear that this was a mistake, not an attempt to enrich the language. (All of which brings to mind a comment from a former boss: "One of the nice things about the English language is that you can noun any verb.") Just my 3¢ worth.

[MadCat-75]

Hi,

definitively the wrong music...

Blue Danube or Also sprach Zarathrustra "Einleitung" fit much better ^^

[geckzilla]

You are right, Hugh, Comet Cherry Gerry isn't craggily. It's snuggily and wuggily. It just wants to be loved.

[Beyond]

Language is a means of communication, pure and simple. IF an existing word doesn't quite fit what you wish to communicate, then by all means, fold, bend and manipulate until it does. It's not evolution, it's necessity, the mother of invention.

[Remo]

What does "orbiting" mean in the astronomical sense? Revolving around another object under the influence of that objects gravity?

It is my understanding that Rosetta is still using its engines to reconnoiter around the comet in a tetrahedrical pattern before drawing closer and actually inserting itself into orbit. I don't mean to be nitpicking, but does what it is doing now count as orbiting? I am curious if there is a black and white answer, or if this is a grey area definitionally speaking.

[BillBixby]

What does "orbiting" mean in the astronomical sense? Revolving around another object under the influence of that objects gravity?

It is my understanding that Rosetta is still using its engines to reconnoiter around the comet in a tetrahedrical pattern before drawing closer and actually inserting itself into orbit. I don't mean to be nitpicking, but does what it is doing now count as orbiting? I am curious if there is a black and white answer, or if this is a grey area definitionally speaking.

Great question. I, too, would like the answer. How much gravity is required for this comet to acquire a satellite for a moon? The engineers, techs and scientists must think there is enough. What would b the orbit time and distance. I don't imagine it would be a tight orbit but, what are the plans? I missed the answers if they were already given.

Bill

[geckzilla]

You could say that Rosetta is experiencing a series of open orbits but is turned around in time by thrusters to enter a slightly different orbit until finally it enters a closed orbit around the comet.

[rstevenson]

... How much gravity is required for this comet to acquire a satellite for a moon? ...

What gives Rosetta a chance at a closed orbit, as opposed to shooting past, is that it has sufficiently reduced its speed relative to the comet. That's what all the zooming around has been doing for the last several years, getting Rosetta into position to creep up on the comet.

As for orbit time and distance, take yer pick. Faster/closer, slower/farther out. I believe the goal for now is to gradually close in on the comet, allowing plenty of time for mapping the comet visually as well as gravitationally, so they can pick the best spot for the lander.

Rob

[Remo]

How much gravity is required for this comet to acquire a satellite for a moon? ... What would b the orbit time and distance.
Bill

Doesn't take much. It has a pathetically small gravity well. The escape velocity off of Comet Churyumov-Gerasimenko has been estimated to be 1 ft/sec (.3 m/sec), but that is dependent on volume and density and density has yet to be determined (density will be determined experimentally from actual orbital data). However, acquiring is kind'a complicated because you need something to slow down the satellite.

Funny thing though, satellite orbit times scale linearly (i.e., based on diameter). So if you made a scale model of the earth with its same density, satellites will have the same orbital periods as they do now. For example, if we modeled the earth as a ball with a diameter of .5m, then the moon would be 30 m away, and the orbital period would be ~29 days, and a geostationary satellite would be ~1.7 m away from the center of the ball and have an orbit of 24 hours.

An ice ball like Comet Churyumov-Gerasimenko is not going to be too dense, so if we assume a density of 1/8th that of earth, instead of a ball of .5m diameter, we would use a ball of 1m. The position of the geostationary satellite (1.7m) and our moon (30m) would be the same relative to the center of the ball. I suspect that the ESA guys are going to want to position Rosetta as close as possible to the comet without endangering its mission which would probably mean an orbit of some place between 12 and 48 hours.

[DavidLeodis]

You are right, Hugh, Comet Cherry Gerry isn't craggily. It's snuggily and wuggily. It just wants to be loved.

That made me . All it wants is a cuggle.

When I see the name Rosetta it always makes me think of the Georgie Fame and Alan Price 1970s song Rosetta, in which is sung "Rosetta are you better are you well, well, well...".

[Remo]

Great question. I, too, would like the answer. How much gravity is required for this comet to acquire a satellite for a moon? The engineers, techs and scientists must think there is enough. What would b the orbit time and distance. I don't imagine it would be a tight orbit but, what are the plans? I missed the answers if they were already given.

Bill

Last night, while trying to sleep, I listened to a great podcast, Starstuff, put out by the ABC which interviews one of the lead engineers and answers your question about the orbital plans and is available here http://www.abc.net.au/science/audio/201 ... opic=space . I also did some investigation this morning and discovered a great article by the economist which explains the reason for the rather odd way of sidling up to the comet, which is available here: http://www.economist.com/blogs/economis ... explains-4. Both these sites are quite interesting. In short, the plan is to start at a distance of 100 km and start drawing gradually decreasing triangles around Comet Churyumov–Gerasimenko using the spacecraft thrust until the spacecraft is around 30km from the comet where they will try to establish a keplarian orbit. Further maneuvering will eventual decrease the orbit to approximately 10km.

I also did a rough calculation of the orbital period of Rosetta assuming it was 100 km from the comet (which is the planned starting point for the tetrahedron maneuvers). I got an orbital period of 2.3 years with a velocity of 700 m/day. This orbital velocity is far less than Rosetta's actual velocity with respect to the comet. I think a better description is that Rosetta is currently co-orbiting the sun with Comet Churyumov–Gerasimenko and is currently doing maneuvers with the intent to eventually establish a keplarian orbit around Churyumov–Gerasimenko

[DavidLeodis]

I've just noticed that in the description to the video it states "The first image was taken on 1 August at 11:07 UTC (12:07 CEST)" and "The last image was taken 6 August at 06:07 UTC (08:07 CEST)". CEST is likely to be the Central European Summer Time zone, which is 2 hours ahead of UTC. Thus the "6 August at 06:07 UTC (08:07 CEST)" agree. The "1 August at 11:07 UTC (12:07 CEST)" would therefore seem to be an error because if it was 11:07 UTC that should be 13:07 CEST.

[Danejurdad]

Amazing mission but an unfortunate miss for the folks posting this APOD video using Mozart's "Eine Kleine Klank" for background! Why, in Gods name, was Strauss's Blue Danube not used? This waltz, immortalized for any space junky in Stanley Kubrik's "2001 A Space Odyssey", stands alone at the pinnacle of the ethereal!!
For your listening and viewing pleasure (and lest you doubt my words): https://www.youtube.com/watch?v=muPNlnm ... erebusjoey

[Viper]

This comet that Rosetta is looking at would make a great space station. Almost impervius to impacts and protection below its surface from radiation. A wealth of metals and water ice both fuel and water processed from ice. Nudge its orbit a bit and earth has a small moon and a great space station. This one is 4 miles across and would cover LA and 4 miles high.