Rosetta's comet mission discussion thread

In summary: The landing is expected to occur on Wednesday, November 12th at 12:35am PST.The Rosetta mission is a European Space Agency (ESA) mission with some US instruments on board. It carries a lander that will descend onto the comet surface, take pictures at the surface, and study the comet. The lander's feet will have to drill into the comet material in order to be anchored firmly, because the gravity is very slight.
  • #106
Although the drill successfully executed its pre-planned procedure, I didn't hear any confirmation that the drill actually made contact with the surface or successfully picked anything up. If it didn't actually pick anything up, the other experiments to analyse the results would probably not be very useful.

It's also unfortunate that the lens cap on the APXS spectrometer apparently failed to open, and again this could only be determined after the experiment was thought to have worked normally according to plan.

I can understand that they want to be as optimistic as possible, reporting "80% of planned science data" was obtained. However, it's still not clear whether that contained anything very useful.
 
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  • #107
OmCheeto said:
But I wonder though, will the comet becomes more active, and would the glow of the coma act as a 24 hour light source? Do we have any comet experts on staff?

My guess is that reflected light from any outgassing or dust would be extremely tenuous (the coma occupies a vast volume of space). Even if the outgassing were very strong (which would probably threaten the stability of the surface) the reflected light would be far weaker than direct sunlight.
 
  • #108
The concern with increased insolation is too much heat, too hot PV's band gap shrinking due to thermal charge carriers.
 
  • #109
Doug Huffman said:
The concern with increased insolation is too much heat, too hot PV's band gap shrinking due to thermal charge carriers.

I wonder how warm it will get.

Rosetta takes comet's temperature
between 13 and 21 July, 2014
...scientists determined that its average surface temperature is about –70ºC.
The comet was roughly [3 AU] from the Sun at the time..., meaning that sunlight is only about a tenth as bright [as on earth].
Although –70ºC may seem rather cold, importantly, it is some 20–30ºC warmer than predicted for a comet at that distance covered exclusively in ice.​

And the batteries have to be warmed up to 0°C to just to start charging.

http://www.spaceflight101.com/play-by-play-philae-landing.html
During hibernation, Philae will dedicate all generated power to keeping its secondary batteries warm as they need to be at a temperature of 0°C to start charging. To achieve that, the lander would need about 50 to 60 Watt-hours of power per day plus the additional power to boot up and initiate communications. This is only possible if the illumination situation improves significantly as the comet moves closer to the sun and the overall geometry enters a more favorable setting – at least that’s the hope, although odds are looking slim.
​
hmmm...

____date___AU from sun
07/17/14_________3.815
11/15/14_________2.967

I think I'll send a tweet to Rosetta to get a new temperature reading. :)
 
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  • #112
enorbet said:
Yes the Lander is asleep but the boys back home certainly are not. If you'd like too see some truly diligent sleuthing results take a peek at this http://blogs.esa.int/rosetta/2014/11/16/philae_spotted_after_first_landing/

I found the following interesting comment within the comments section of the ESA blog:

"The MUPUS instrument was deployed but the surface was so hard that the shaft of its hammer broke as reported in the BBC's "Sky AT Night" special tonight.. The question of, is the surface rock or ice remains an open one, for us at least. The harpoons may have fired as planned, but bounced off the very hard subsurface, the ice screws were deployed but could not dig into the subsurface for the same reason. The plot thickens as they say."

At about the 34:20 mark in this Rosetta mission results video, we hear the OSIRIS Principle Investigator, Holger Sierks, remark upon the color of the comet. He makes the enigmatic statement that although the color is gray, the bright areas look less reddish, and the comet would look red if it weren't so dark.
 
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  • #114
Interesting pictures of Philae after her first landing:

OSIRIS SPOTS PHILAE DRIFTING ACROSS THE COMET
Released 17/11/2014 3:00 pm

They still haven't found her final landing spot.

The following comment has me puzzled:

"The image taken after touchdown, at 15:43 GMT, confirms that the lander was moving east..."
​
How does one decide, which way is north, on a rotating dumbbell?
 
  • #115
BBC reports, http://www.bbc.com/news/science-environment-30083969#

"...data was pulled off the robot just before its sagging energy reserves dropped it into sleep mode.
Little of the results have so far been released by the various instrument teams. The one major exception is MUPUS.

This sensor package from the German space agency's Institute for Planetary Research deployed a thermometer on the end of a hammer.

It retrieved a number of temperature profiles but broke as it tried to burrow its way into the comet's subsurface.

Scientists say this shows the icy material underlying 67P's dust covering to be far harder than anyone anticipated - having the tensile strength of some rocks.

It also helps explain why Philae bounced so high on that first touchdown.

The 4km-wide comet has little gravity, so when key landing systems designed to hold the robot down failed at the crucial moment - the probe would have been relying on thick, soft, compressive layers to absorb its impact.

However much dust it did encounter at that moment, it clearly was not enough to prevent Philae making its giant rebound."

ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) reports,
http://www.igep.tu-bs.de/forschung/weltraumphysik/projekte/rosetta/comet_en.html
http://www.igep.tu-bs.de/forschung/welt ... _ROMAP.pdf
 
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  • #116
OmCheeto said:
How does one decide, which way is north, on a rotating dumbbell?

By the right hand rule, as usual?
 
  • #117
Jonathan Scott said:
By the right hand rule, as usual?
Yes. I know that. But is it magnetic north, or geoorsolarrotationalyaxially north?

Sorry to be too succinct. I'm always assuming. Very bad habit of mine.
 
  • #118
OmCheeto said:
But is it magnetic north, or geoorsolarrotationalyaxially north?

For things like that, north is defined purely by the main rotation axis.
 
  • #119
Jonathan Scott said:
For things like that, north is defined purely by the main rotation axis.
Any idea what the xyz rotation axis is, in relation to our solar system's main "planetary" plane of orbits?

Sorry to speak in such simpleton terms, but it's been 1/3 of a lifetime since I've spoken the language.

hmmm... Never mind. I spend 20 seconds thinking about it, and the math, which I also no longer know, hurt my brain.

I spent at least 30 minutes the other day, relearning geometry, trying to figure out how to physically make an angle of 67.5°.
I eventually did it, but it hurt my brain.

Ugh. Time for a nap.

Don't ever get old, JS. You are our only hope.
 
  • #121
OmCheeto said:
Ugh. Time for a nap.

That and Advil PM, :) old age cure-alls.
 
  • #122
_79110193_79108784.jpg


Beautiful : ^)
 
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  • #123
The progression noted here hints at what may become one of what will likely be many important discoveries and that is the unexpected density of the comet. Someone noted that comets have been characterized as the dirty snow along highways after a few days and it can now be seen that this is not at all accurate, at the very least on this comet but possibly common to many as some fundamental process may be involved in the early solar system of which we presently understand little. I will be watching with great anticipation as that story unfolds.

Please, if you beat me to it, continue to post here on this and any other developments. This could be a year long thread and deserve it.
 
  • #124
I see your point. What if a comet is not a dirty snowball but a rock hard ball of ice? With thin or varying thickness blanket of dust.
Then must it not have gone through a phase change at some time? To get some crystalline hardness?
How could that have happened?

BTW the photo was taken from Rosetta on 11 November at nominal altitude of 10 km. Here is the ESA link to it in case anyone is curious. What I posted has been cropped so it conforms more with the landscape images we are used to. The original at ESA has some sky in it with a few stars or perhaps a planet overhead.
http://www.esa.int/spaceinimages/Images/2014/11/NAVCAM_top_10_at_10_km_8
 
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  • #125
Yay!

Philae Lander On Comet Could Wake Up As It Nears Sun: Scientists
November 18, 2014 02:05pm ET

...Philae's overly shadowed location will be an advantage as Comet 67P approaches the sun in the coming months.

At that point, they said, it is "probable" that the increased doses of solar power will warm the lander, permitting its secondary battery to power up sufficiently to renew communications via the Rosetta spacecraft orbiting overhead.

In response to SpaceNews inquiries, Stephan Ulamec, Philae project manager at the German Aerospace Center, DLR, on Nov. 18 said such a scenario "is very likely to happen. Philae will not overheat on its way to the sun because of its shaded position.
Philae, may have turned a lemon of a parking spot, into lemonade. :DAnd, um, what?
ESA Rosetta managers are debating whether to land Rosetta on Comet 67 at the end of its operational life, but no decision has been made.

That would be cool. I wonder if it could become operational again on its next trip back in 6.45 years?
Solar panels rule!
:)
 
  • #126
Does Rosetta have legs?
 
  • #127
berkeman said:
Does Rosetta have legs?
I don't think so. But, on the surface, it'll only weighs 1/3 of an ounce.
They just need a more controlled landing.

pf.2014.11.18.2028.rosetta.eq.weight.on.comet.67P.jpg
 
  • #129
An earlier posting about the MUPUS results suggested that the surface was too hard to be refrozen ice, but they are now saying it is as hard as solid ice. If that's the case, I think it would be quite understandable; if you add dark dust to an icy surface and perihelion is not much outside Earth's orbit, I'd expect the surface to melt sufficiently to form a slush which would then be much harder on refreezing when it moved further away. (As far as I know, it couldn't actually form puddles of liquid water as it would sublime to vapour instead in the absence of any pressure, but I'm not an expert).
 
  • #130
berkeman said:
Does Rosetta have legs?

I don't think so, but that shouldn't be a problem. NEAR Shoemaker landed on Eros without legs and Philae's legs wasn't very helpful after all.
 
  • #131
Jonathan Scott said:
An earlier posting about the MUPUS results suggested that the surface was too hard to be refrozen ice, but they are now saying it is as hard as solid ice. If that's the case, I think it would be quite understandable; if you add dark dust to an icy surface and perihelion is not much outside Earth's orbit, I'd expect the surface to melt sufficiently to form a slush which would then be much harder on refreezing when it moved further away. (As far as I know, it couldn't actually form puddles of liquid water as it would sublime to vapour instead in the absence of any pressure, but I'm not an expert).

According to my interpretation of the phase diagram of water, you are correct.

phase.jpg


With such a low surface gravity, I seriously doubt the pressure would ever venture much above zero. So I'm going to go out on a limb and state that it's virtually impossible for liquid ice to form on a comet.

I don't think I'd studied the phase diagram, nor understood exactly what it meant, until one day, when Borek asked; "Where is the water in space?"
I thought that was a great question, and didn't know the answer, so I figured it out.

I would do the experiment, and see what happens to water under a complete vacuum, but I don't think I can get my freezer down to 200K.

Also, I just checked, and 200K ≈ -70°C, which was the comets temperature in mid July.
Of course, sections of it must have been at least that warm by June:

ESA
30 June 2014
ESA’s Rosetta spacecraft has found that comet 67P/Churyumov–Gerasimenko is releasing the equivalent of two small glasses of water into space every second, even at a cold 583 million kilometres [3.9 AU] from the Sun.
 
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  • #132
DrStupid said:
I don't think so, but that shouldn't be a problem. NEAR Shoemaker landed on Eros without legs and Philae's legs wasn't very helpful after all.
I didn't want to show how big of a nerd I was yesterday, but, well...

I weighed an unopened roll of aluminum foil yesterday.
≈ 28 ounces
18.5 m2
Rosetta has dimensions roughly 3m x 2m x 2m
Sitting down on her small end, a 4m2 sheet of aluminum foil exerts 17.4 times as much force here on Earth as she does on the comet.

I also calculated the equivalent force in U.S. (new) penny weight.
It came out to 4 pennies.
So, hold a penny in your hand, and imagine flattening it to an area of 1 square meter.

This is when I decided they should land Rosetta on her side, so the solar panels wouldn't act as a cometary ejection seat, as I imagine the rate of sublimation is going to get much worse.
 
  • #133
OmCheeto said:
I didn't want to show how big of a nerd I was yesterday, but, well...

I weighed an unopened roll of aluminum foil yesterday.
≈ 28 ounces
18.5 m2
Rosetta has dimensions roughly 3m x 2m x 2m
Sitting down on her small end, a 4m2 sheet of aluminum foil exerts 17.4 times as much force here on Earth as she does on the comet.

I also calculated the equivalent force in U.S. (new) penny weight.
It came out to 4 pennies.
So, hold a penny in your hand, and imagine flattening it to an area of 1 square meter.

This is when I decided they should land Rosetta on her side, so the solar panels wouldn't act as a cometary ejection seat, as I imagine the rate of sublimation is going to get much worse.
You keep acting like this and your going to get kicked out of the "Dummy" group:D
 
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  • #134
OmCheeto said:
According to my interpretation of the phase diagram of water, you are correct.

Thanks for checking. What I was wondering is whether ice covered in dark dust and exposed to sunlight might be able to get to a partially liquid ("slush") state within the body of the material, even while the surface is "boiling" (actually subliming) away, so when it cools again it could become more like solid ice on each cycle.
 
  • #135
a composite material
 
  • #136
OmCheeto said:
I didn't want to show how big of a nerd I was yesterday, but, well...
I can top that!

The surface is not flat (neither is Rosetta). Rosetta would probably balance on a few (maybe just 3) points. On the positive side, the probe survived ~3g during the launch from Earth, and it can use its thrusters to make a single very soft landing on a suitable spot.Concerning ice/water: the comet does not have pure water. In general, additions to water extend the range of liquid water.
 
  • #137
marcus said:
a composite material
Anyone know how to contact Mr. billiards?

He's my PF go to guy on rock and water composites. :)
 
  • #138
OmCheeto said:
Anyone know how to contact Mr. billiards?

He's my PF go to guy on rock and water composites. :)

(at at least when at high pressure and temperature deep in the earth, he is a geophysics PhD student)

One way to contact him would be to go to his profile page:
https://www.physicsforums.com/members/billiards.59465/

and look down to where it says "start a conversation", and click that, and in effect send a private message to billiards.
If he has arranged to be notified by email when he receives a private message at PF, then he may see the message you send him.

The whole thing impresses me as ready for laboratory experiments in low temperature vacuum chamber set-ups, so we might simply have to wait until people with ideas such as what Jonathan Scott just suggested a few posts ago have done some experiments on putative comet material formation and written some papers. I wouldn't count on there already being answers, although there certainly might be!
 
  • #139
Hits and misses from Rosetta and Philae
http://news.sciencemag.org/europe/2014/11/doomed-comet-lander-delivered-harvest-science

- A rod meant to measure heat flow broke while the lander was attempting to hammer it into the comet’s surprisingly tough surface.

- The shutters to another instrument—one that measures composition by bombarding materials with x-rays—did not open, so the instrument measured mostly the titanium and copper of the shutters.

- And the most sought-after result—an attempt to measure the composition of a subsurface sample obtained by a drill—did not come to pass.

- the orbiter’s camera team presented images that showed arcs of dust emanating from jets—a finding that could help them understand the mechanisms of outgassing.

- ROSINA, a Rosetta instrument that uses spectrometers to measure gas abundances, has obtained a highly sought after result: the so-called deuterium-to-hydrogen ratio of water in the comet’s thin atmosphere, or coma. The measured value for 67P is much higher than the ratio in Earth’s oceans and higher than in other comets

Peculiarities of the drilling fiasco.
http://blogs.esa.int/rosetta/2014/11/19/did-philae-drill-the-comet/
 
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  • #140
marcus said:
...The whole thing impresses me as ready for laboratory experiments in low temperature vacuum chamber set-ups, so we might simply have to wait until people with ideas such as what Jonathan Scott just suggested a few posts ago have done some experiments on putative comet material formation and written some papers. I wouldn't count on there already being answers, although there certainly might be!

Well, I didn't know what "putative" meant, so I started there. (It's related to "reputed", as in; "The comet's reputed composition is...". I think.)

Anyways, after 6 hours of googling and reading and skimming, I decided my background in the areas of Geology and Chemistry were too lacking, and I had no comprehension of what I was reading.

It all started out with someone named Jens Biele. Which I thought was kind of a nice name, as I have relatives living in Bielefeld Germany. And is also probably the only reason I remember his name this morning.

Dr Biele, Philae Lander Payload Manager and Lander System Science, had his name on a couple of papers that I looked at:

44th Lunar and Planetary Science Conference (2013)
PREPARING FOR LANDING ON A COMET – THE ROSETTA LANDER PHILAE​

Which was apparently written for management, as I understood most of what was being said.
The best part of this paper, for me anyways, were the outgassing predictions.

The second paper I looked at, which was about 10 miles long, was, as I said, mostly incomprehensible.

About the only thing I understood, was a single equation.

vg = 3 π vt / 8
where
vt = mean thermal speed at temperature T
vg = the speed at which the molecules leave the surface

Algebra is about the only thing I can comprehend anymore...

And the chemistry? I don't even know how chemistry works on Earth.

How in the world will I figure out exo-chemistry, if I can't figure that out.

interstellar.and.comet.organics.never.mind.jpg


hence, I gave up.
 

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