Rosetta's comet mission discussion thread

[RonL]

Ugh. Time for a nap.

That and Advil PM, :) old age cure-alls.

 

[marcus]

Beautiful : ^)

 

[enorbet]

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.

 

[marcus]

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

 

[OmCheeto]

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!
:)

 

[berkeman]

Does Rosetta have legs?

 

[OmCheeto]

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.

 

[Dotini]

This ESA Rosetta blog from Tuesday has some information and preliminary analysis to consider. Note the diagram which focuses on MUPUS. I do not understand how this device was able to operate with the craft supposedly on its side and untethered.
http://blogs.esa.int/rosetta/2014/11/18/philae-settles-in-dust-covered-ice/

 

[Jonathan Scott]

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).

 

[DrStupid]

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.

 

[OmCheeto]

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.

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.

 

[OmCheeto]

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.

 

[RonL]

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

 

[Jonathan Scott]

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.

 

[marcus]

a composite material

 

[mfb]

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.

 

[OmCheeto]

a composite material

Anyone know how to contact Mr. billiards?

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

 

[marcus]

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!

 

[Dotini]

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/

 

[OmCheeto]

...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.

Origin and Early Evolution of Comet Nuclei (2008)​

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

v_g = 3 π v_t / 8
where
v_t = mean thermal speed at temperature T
v_g = 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.

hence, I gave up.

 

[Borg]

Get out your 3D glasses. From the APOD. Today's picture is 67P in 3D.

 

[Dotini]

http://deepimpact.umd.edu/gallery/jpg/313_635_F3.jpg

 

[Dotini]

The above image is from http://deepimpact.umd.edu/gallery/313_635_F3.html

"We have found extremely high-temperature minerals coming from the coldest place."
Early analysis revealed minerals that included magnesium iron silicate, known as olivine, or, in its gem-quality variety, peridot; magnesium aluminum oxide, also called spinel; and titanium nitride. Brownlee said all these form at temperatures of at least 2,000 degrees Fahrenheit.
http://www.washingtonpost.com/wp-dyn/content/article/2006/03/13/AR2006031301670.html

 

[RonL]

So much slick surface area makes it look like a gold nugget from a river bed oo)

 

[Dotini]

Unfortunately, the image posted is not yet an official true color image. The official one will be released Dec 15, supposedly.

It seems the instrument makers have the rights to all their data for the first 6 months.

http://www.dailymail.co.uk/sciencetech/ ... black.html

 

[Dotini]

Now we are starting to get some important science discovery news.
http://www.bbc.com/news/science-environment-30414519#
http://www.dailymail.co.uk/sciencet...ta-results-deepen-mystery-oceans-arrived.html
http://blogs.esa.int/rosetta/2014/12/10/rosetta-fuels-debate-on-origin-of-Earth's-oceans/
https://agu.confex.com/data/abstract/agu/fm14/5/9/Paper_22395_abstract_18425_0.png

 

[Jonathan Scott]

I would have thought that the make-up of gases near the surface would be very strongly affected by their volatility, in that even slightly lighter molecules would have greater velocity for the same energy and hence would be likely to escape more rapidly than heavier ones, altering the concentrations of what was left. On that basis, one would expect normal water molecules to escape slightly more easily than heavy ones, potentially increasing the deuterium ratio in what was left later on the warming side of the orbit.

So unless I've missed something, I don't see any good reason to believe that the deuterium ratio near the surface is likely to give a fair indication of the deuterium ratio within the body of the ice. The latter would be much more interesting and convincing.

 

[mfb]

The escape velocity is of the order of 1 m/s - well below the thermal motion of molecules (even at 3 K). Only chemical bonds keep them on the asteroid, so binding energy is relevant. Is that different for heavy water? It has a slightly higher melting and boiling point at standard pressure, but that difference is small.

 

[Jonathan Scott]

The escape velocity is of the order of 1 m/s - well below the thermal motion of molecules (even at 3 K). Only chemical bonds keep them on the asteroid, so binding energy is relevant. Is that different for heavy water? It has a slightly higher melting and boiling point at standard pressure, but that difference is small.

Good point - this is not like an atmosphere situation.

The Wikipedia entry on deuterium has this to say (unfortunately with no good references as far as I can see):

However, different astronomical bodies are found to have different ratios of deuterium to hydrogen-1, and this is thought to be as a result of natural isotope separation processes that occur from solar heating of ices in comets. Like the water-cycle in Earth's weather, such heating processes may enrich deuterium with respect to protium.

 

[Dotini]

There are no large water ice patches detected on 67P.
http://rosetta.jpl.nasa.gov/news/na...an- spacecraft -returns-first-science-results

http://www.sciencemag.org/content/early/2014/12/09/science.1261952
The provenance of water and organic compounds on the Earth and other terrestrial planets has been discussed for a long time without reaching a consensus. One of the best means to distinguish between different scenarios is by determining the D/H ratios in the reservoirs for comets and the Earth’s oceans. Here we report the direct in situ measurement of the D/H ratio in the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA mass spectrometer aboard ESA’s Rosetta spacecraft , which is found to be (5.3 ± 0.7) × 10−4, that is, ~3 times the terrestrial value. Previous cometary measurements and our new finding suggest a wide range of D/H ratios in the water within Jupiter family objects and preclude the idea that this reservoir is solely composed of Earth ocean-like water.

A NY Times science writer, citing a few papers, helpfully suggests Earth may have been wet from (almost) the beginning.
http://www.nytimes.com/2014/12/11/s...omets-as-a-source-for-Earth's-water.html?_r=0