Rosetta, Philae and Comet 67P/Churyumov-Gerasimenko.

[Kryten]

Can you provide a mechanism by which the comet could change in shape so dramatically without an obvious outburst?

[Aningaaq]

That was the original plan: even with Philae sitting in a well-lit spot, the sunlight wouldn't suffice anymore when the distance is greater than 2AU.

With where it's actually sitting, it should have enough sunlight to operate once it gets closer to the sun. However, for this to work the battery has to become warm enough; and without electrical heating, this, too, has to happen by sunlight. As I understand it, there's little doubt about having enough light for electricity generation in a few weeks' time; the question is whether the lander becomes warm enough so that the electricity may be used. If that happens, the probe can be powered up and will remain powered up until (duration of sunlight per day * intensity) falls below the threshold again.

If they can't find a way of shifting it's position, the final poweroff will happen a lot sooner than at 2AU.

What I read is that the surface will be too hot at 2 AU and destroy Philae's circuits

Can you provide a mechanism by which the comet could change in shape so dramatically without an obvious outburst?

Perhaps an internal fracture that splits the comet in half. That could be possible maybe.

[Motokid600]

I'd guess a collision, but... Could something like that happen without us knowing? Because we've been observing 67p for so long...

[KerikBalm]

I am having a hard time taking you serious when you make these kinds of strong stances without much definitive evidence. We know so little about comets, how they work and how they vary from one comet to the next. This is the very reason we went there.

I've noticed he's mostly right (or at least taking a position that has a very high probability of being right, given the evidence), but often weighs in on more absolute terms than may be proper.

On occassion, he can be absolutely and undeniably wrong. The case I'm thinking of is him claiming in absolute terms that plants do not hydrolyse water, and the O2 they emit is taken from the 2 Os in CO2. He never admitted he was wrong in that instance, but he did stop arguing that his statements were true. While he was still arguing it, his citation was his own memory+a college education...so I understand what you are talking about... but kyrten has a good point:

Can you provide a mechanism by which the comet could change in shape so dramatically without an obvious outburst?

We may not have much in the way of cometary observation, but we know the relevant physics pretty well.

a spheriod would be a lower energy conformation than this bi-lobed conformation.

I could imagine it going from the current conformation to a single ball, in a sort of very low velocity "avalanche" as all the mass falls toward the barycenter.

(although this sort of we ignores the spin)

but the otherway..... that would require some energy input, to start the comet rotating - a collision could do this, but it should have been evident.

Or if you want to say it was mass loss from the neck, we can calculate the mass that would be lost, and the amount of energy needed to vaporize it/eject it.

I suspect that energy will fall fall short of the energy of solar irradience in that time period.

Thermodynamics should tell us that it won't spontaneously change like that, and we have no evidence to suggest something else would have altered it.

[Aningaaq]

Another "Ask Me Anything" opportunity:

A team of engineers from RAL Space will be here to talk about their involvement with Rosetta!

Amongst many accomplishments, they helped build PTOLEMY -- an instrument used to analyze the gases surrounding the comet 67P/C-G.

The AMA is scheduled to start Tuesday, Nov. 25 at 12:00 GMT, 07:00 EST, 04:00 PST. Please come prepared with questions!

Visit http://www.reddit.com/r/space for more details

Please post any answers you may get here or any other relevant answers!

[Aningaaq]

Another interesting article: http://blogs.esa.int/rosetta/2014/11/21/homing-in-on-philaes-final-landing-site/

But CONSERT is also being used to help identify the location of the lander, in combination with work performed by ESOC Flight Dynamics, the Philae lander team, the ESA Rosetta Science Ground Segment, and the OSIRIS camera team.

These two sites have been narrowed down using CONSERT data. The blue area is using the standard shape model and the second site (green) accounts for a deviation from the shape model.

I believe this is the shape model they are using:

It is a chimeric model based on two other shape models. Hopefully they can pin down exactly where Philae is because as I suspected, the CONSERT team needs to know exactly where Philae is in order to accurately analyze their data.

Edit: The shape model photo I posted could be an older model(but it is the most recent I could find in my collection of research papers). The shape model in the first photo looks visibly accurate but I don't know if it that is what CONSERT is actually using.

[Aethon]

The sound of a comet landing.

http://www.nasa.gov/jpl/rosetta-comet-landing-in-thud-and-3d/index.html#.VHNqzYvF-Yf

[Aethon]

Umm. I don't know. It's definitely something.

[Aethon]

[h=1]Philae’s Wild Comet Landing: Crater Grazing, Spinning And Landing In Parts Unknown[/h]

http://www.universetoday.com/116927/philaes-wild-comet-landing-crater-grazing-spinning-and-landing-in-parts-unknown/

[Aethon]

Results from ROSINA instrument indicate that Earths' oceans were not supplied by comets like Cherry Jerry.

http://www.nasa.gov/jpl/rosetta-instrument-reignites-debate-on-earths-oceans/index.html#.VIjKATHF-Yc

[sndrtj]

Results from ROSINA instrument indicate that Earths' oceans were not supplied by comets like Cherry Jerry.

http://www.nasa.gov/jpl/rosetta-instrument-reignites-debate-on-earths-oceans/index.html#.VIjKATHF-Yc

Damn! So... where the hell do we get our water from?

[lajoswinkler]

Damn! So... where the hell do we get our water from?

It was already there. Earth is just one more lump of matter in the Solar system. It's not "special".

[Camacha]

It was already there. Earth is just one more lump of matter in the Solar system. It's not "special".

Did you read the article? There are a couple of other suspects. More questions instead of answers,, but that is to be expected - of course it wasn't going to be the answer we put our money on

[lajoswinkler]

Did you read the article? There are a couple of other suspects. More questions instead of answers,, but that is to be expected - of course it wasn't going to be the answer we put our money on

Yes. I don't think anyone was seriously considering comets to be the main source of our water.

[Luis]

Yes. I don't think anyone was seriously considering comets to be the main source of our water.

Actually, I think that has been the concensus for the last decade at least.

[AbhChallenger]

Good science always raises more questions than answers.

[lajoswinkler]

Actually, I think that has been the concensus for the last decade at least.

Geologists wouldn't agree. There must be an incredible amount of water in Earth. It's not stored as free water, but it's there in the mineral compounds stuffed in magma. There is no reason to think all that water should've been expelled from the planet long time ago, and the amounts we're talking about are absolutely enormous compared to the realistic amounts of comets in the past.

Most people think about pools of water but that's not how water hides. It reacts and forms compounds, not just by complexing with metal ions.

[Camacha]

Good science always raises more questions than answers.

Like I said before, the best discoveries are generally those where someone looks at the data and goes Huh. That's funny.

Geologists wouldn't agree.

I am not sure whether the geologists view of the formation of Earth is much different from that of the rest of science, but there certainly is a gap in our knowledge. Earth contains more water than the other rocky planets and we are still not really sure why. It also seems that early Earth had unfavourable conditions for the retention of a lot of water. If the current water present turns out to have always been here if would certainly mean an adjustment to our understanding of the processes involved.

Of course, the answer could also turn out to be that water was already present and that Earth collected it from space through comets and asteroids, since nothing forbids water to collect on Earth from a number of sources. Whatever the case, comets have been on the table for a while now as a serious contender.

Edited December 11, 2014 by Camacha

[KerikBalm]

Well, we've learned mars has more water than initially suspected, in undersurface ice deposits.

And for retaining water, Earth is the largest of the rocky planets, the only one that still has a significant magnetic field, and isn't as warm as the two which generally lack water (mercury has some ice in polar craters, it seems)

[Camacha]

What surprised me was that ROSINA was not only able to measure greases used in the construction of Rosetta (which is a whole interesting subject on its own, as going to space complicates even something as simple as a lubricant), but also the ongoing out-gassing of water onboard the craft. I would have said that must have boiled off into space years ago, but apparently the instruments are just that sensitive. Pretty amazing, if you ask me.

When Rosetta first emerged from hibernation, ROSINA was able to detect low levels of water still evaporating off the spacecraft 10 years after it left Earth, along with a bit of propellant and some of the grease used on the hardware.

Source.

[Aethon]

From the article :

"Researchers agree that water must have been delivered to Earth by small bodies at a later stage of the planet’s evolution. It is, however, not clear which family of small bodies is responsible. There are three possibilities: asteroid-like small bodies from the region of Jupiter; Oort cloud comets formed inside of Neptune's orbit; and Kuiper Belt comets formed outside of Neptune's orbit."

"The value for the D/H ratio on the comet (Cherry Jerry) is more than three times the terrestrial value. This is among the highest-ever-measured values in the solar system. That means it is very unlikely that comets like 67P/Churyumov-Gerasimenko are responsible for the terrestrial water."

"Almost 30 years ago (1986) the mass spectrometers on board the European Giotto mission to comet Halley could, for the first time, determine D/H ratio in a comet. It turned out to be twice the terrestrial ratio. The conclusion at that time was that Oort cloud comets, of which Halley is a member, cannot be the responsible reservoir for our water."

"This changed when, thanks to the European Space Agency's Herschel spacecraft, the D/H ratio was determined in comet Hartley 2, which is believed to be a Kuiper Belt comet. The D/H ratio found was very close to our terrestrial value -- which was not really expected. Most models on the early solar system claim that Kuiper Belt comets should have an even higher D/H ratio than Oort cloud comets because Kuiper Belt objects formed in a colder region than Oort cloud comets."

"The new findings of the Rosetta mission make it more likely that Earth got its water from asteroid-like bodies closer to our orbit and/or that Earth could actually preserve at least some of its original water in minerals and at the poles."

[lajoswinkler]

And we have the first colour image released to the public.

Red, green and blue filters. Image was taken on August 6th this year at 120 km distance.

So it's gray. I've tried to boost the saturation, but this is a JPEG so not much can be accomplished. It might have a light green hue, although it's probably just gray to our eyes.

[Scotius]

Yeah, it's gray If more comets are like this, space agencies can save money not bothering to send color cameras on future missions

[Aethon]

Damn! So... where the hell do we get our water from?

From what I've read, results of the 2011 D(euterium) to H(ydrogen) ratio from comet Hartley 2 ( a Kupier belt comet ) closely matched that of Earths oceans, however 67p, from probably the same region of space, has a different ratio. This shows that Jupiter family comets are more diverse than first thought.

In the early solar system, the sun was dimmer, and the asteroids had more water than they do today. The theory is that Jupiter chucked a bunch of these water rich asteroids Sunward, a few impacting the Earth during the late heavy bombardment.

http://www.space.com/27991-rosetta-comet-water-earth-implications.html

[m4v]

http://blogs.esa.int/rosetta/2014/12/12/comet-67pc-g-in-living-colour/

As it turns out, 67P/C-G looks dark grey, in reality almost as black as coal

I don't get it, so it is grey or black?