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

[Frida Space]

If they manage to establish communications with Philae we might get a new CIVA panorama!

[Frida Space]

So, last time we heard from Philae was 20 days ago, and now for 2 weeks Rosetta will be flying over the southern regions where it won't be able to listen to Philae.

[KerikBalm]

Anyway, the point is that the force required to move it is very very small - it may produce a very very very small acceleration for a 100 kg object... but there's plenty of time for it to act.

So anyone talking about a jet moving it should not be imagining some geyser that is producing a blast that could do anything described here:

Wasn't this probe anchored down with its harpoons? Then again, if blasted by a jet, I suppose that could take out a receiver and muck up the solar panels. Yes, bad news. :/

I would guess the force of any jet wouldn't be much more than a few times higher than the ambient surface pressure of the comet....

And that pressure is... well.... We may say Mars is nearly a vacuum, but its got a super dense atmosphere compared to Pluto, and I suspect pluto has really dense atmosphere compared to the density/pressure of these jets.

Lets assume it gets to 0.5 pascal... (pluto's atmosphere is said to be between 0.65 and 2.4 pascal, triton's is between 1.4 to 1.9)

Lets assume the probe has 0.1 square meters of surface area....

0.05 Newtons...

Its said its weight is equal to 0.3 grams on earth... that is 0.0003 kilograms.... that is 0.00294 newtons

0.05/0.003 = 16.67

.5/16.67 = 0.0299

If a jet's pressure even gets to 0.05 pascal (Earth's atmosphere: 101,000 pascals), that probe is gonna go flying...

Didn't they worry about this happening as it gets closer to the sun?

[lajoswinkler]

To make the body move, there needs to be a net positive force acting on it. If all of the surface is exuding gas, the particles go in pretty much all directions. Why would the lander be thrown somewhere by an uniform field of escaping gas?

Also, the shadow of Philae does not exude gas, or does it at a much lower rate. The shade does move, but that means the Sun moves, too. When the shadow is sideways, Sun's rays are delivering way less power per unit of area.

Rotational period of the comet is a bit above 12 h so it means around 6 hours of light.

I'm not convinced.

[rkman]

If all of the surface is exuding gas, the particles go in pretty much all directions. Why would the lander be thrown somewhere by an uniform field of escaping gas?

Why would there be a uniform field of escaping gas? Every indication is that the venting is not uniform.

Wasn't this probe anchored down with its harpoons?

The reason for the mishap with the lander (it bounced and got sort of lost) is that the harpoons did not fire.

Edited July 30, 2015 by rkman

[lajoswinkler]

Why would there be a uniform field of escaping gas? Every indication is that the venting is not uniform.

Do you have any idea how large even the smallest of these jets is compared to a washing machine sized box?

[*Aqua*]

that probe is gonna go flying...

Didn't they worry about this happening as it gets closer to the sun?

Not really. The primary goal was to land on that comet and get as much data as possible until the batteries are drained. That was less and more successful than they hoped.

It was less successful because the landing mechanism was a fail. The screws didn't work and the Philae bounced to somewhere. The thruster which was supposed to help holding it down on the ground failed even before the probe undocked. But on the other hand is was more successful because they got data from each place it bounced off (three IIRC).

It's lucky that Philae is still on the comet and can still send data. If it went down where it was supposed to, it could be blown of into space by now. Ice screws can't survive that heat.

[lajoswinkler]

What heat? The surface of the comet is incredibly cold.

[*Aqua*]

Yeah, it so could that ice vaporizes.

[tater]

He's likely assuming the sublimation that is occurring is from extreme heat, would be my guess, even though it's below the triple point.

[KerikBalm]

Well, in direct sunlight, it should get pretty warm... the Moon certainly does during the day (over 110 C at the equator... well above the boiling point of water at 1 atm)...

But the pressure is certainly well below the triple point, with basically no gravity, its scale height is probably greater than the hill sphere... the gas can't really get to much pressure at all.

So that means that the temperature must be below the triple point, or all the H2O would be gone already.

At low pressure, the ice will sublimate away below 0 C, and the temperature won't rise above the sublimation temperature, just as a block of ice won't go higher than 0C until it has all melted.

That is assuming there are volatiles at the surface, if the crust is thick enough, it could be a bit different.

[rkman]

Do you have any idea how large even the smallest of these jets is compared to a washing machine sized box?

From a large distance only large jets can be seen.

The crevice where Philae ended up is small and features a variation of geology, leading me to think that if venting would take place there it would likely not be uniform around the lander.

[lajoswinkler]

Yeah, it so could that ice vaporizes.

It does not vaporize, it sublimates and it happens because the pressure is incredibly low. Total vacuum for our intents and purposes.

The surface shouldn't get relatively hot (to our human experience) because, among other reasons, the volatiles sublimating are carrying away the heat. Also I'm quite sure the ESA designers thought about those basic requirements. No reason to think Philae might get rekt like that.

From a large distance only large jets can be seen.

The crevice where Philae ended up is small and features a variation of geology, leading me to think that if venting would take place there it would likely not be uniform around the lander.

I've already explained that - if there were such extremely localized jets, the surface would look foggy from far away. It's quite possible you'd barely be able to see the jet if you were standing in it.

It simply isn't active as Hollywood taught you. If it were, the comet would not have existed for billions of years. It would be consumed in decades.

[lajoswinkler]

Philae's view while falling towards Agilkia site.

http://www.esa.int/spaceinimages/Images/2015/07/Descending_to_a_comet

I told you it was not powdery.

[rkman]

It simply isn't active as Hollywood taught you.

Please explain to me again why i would take your word over that of ESA:

The lander is likely situated on uneven terrain, and even a slight change in its position – perhaps triggered by gas emission from the comet – could mean that its antenna position has also now changed with respect to its surroundings.

http://blogs.esa.int/rosetta/2015/07/20/rosetta-and-philae-status-update/

Hint: taking cheap and presumtious shots at someone's sources of knowledge don't do you any good.

Edited July 31, 2015 by rkman

[Aethon]

Twelve days to perihelion.

I can't find my 3D glasses, or my Galactic astronomy book which contained said glasses... I just had it.

http://www.universetoday.com/121664/t-minus-12-days-to-perihelion-rosettas-comet-up-close-and-in-3d/

Edited August 2, 2015 by Aethon

[Aethon]

^^ Found it!

Some interesting 67p science data coming in.

"Sixteen compounds were identified, divided into six classes of organic molecules (alcohols, carbonyls, amines, nitriles, amides and isocyanates). Of these, four were detected for the first time on a comet (methyl isocyanate, acetone, propionaldehyde and acetamide)."

"terrain in the vicinity of Philae's final landing site is dominated by dark clumps that are probably large grains made up of organic compounds. Since cometary material has hardly been altered since its origins, this means that, early in the Solar System's history, organic compounds had already clumped together in the form of grains, and not just as small molecules trapped in the ice as was previously thought."

http://www.sciencedaily.com/releases/2015/07/150730172518.htm

For the purist moneybag.

http://www.sciencemag.org/content/349/6247/aaa9816

http://www.sciencemag.org/content/349/6247/aab0671

http://www.sciencemag.org/content/349/6247/aab0639

http://www.sciencemag.org/content/349/6247/aab0689

[lajoswinkler]

Please explain to me again why i would take your word over that of ESA:

Hint: taking cheap and presumtious shots at someone's sources of knowledge don't do you any good.

ESA mentions possible change in orientation. Nothing about certain blowing off from the surface.

[Aethon]

Comet outburst causes changes in its' magnetic field.

In this sequence of images, the one at left was taken at 8:06 a.m. CDT and doesn’t show any visible signs of the jet. 18 minutes later at 8:24, it’s very bright and distinct (middle image) with only residual traces of activity remaining in the final photo made at 8:42.

The photos were taken from a distance of 116 miles (186 km) from the center of the comet. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The decrease in magnetic field strength measured by Rosetta’s RPC-MAG instrument during the outburst event on July 29, 2015. This is the first time a ‘diamagnetic cavity’ has been detected at Comet 67P/Churyumov–Gerasimenko and is thought to be caused by an outburst of gas temporarily increasing the gas flux in the comet’s coma, and pushing the pressure-balance boundary between it and incoming solar wind farther from the nucleus than expected under ‘normal’ levels of activity. Credit: ESA/Rosetta/RPC/IGEP/IC

The graph shows the relative abundances of various gases after the outburst, compared with the measurements two days earlier. Water remained the same, but CO2 and especially increased dramatically. Copyright: ESA/Rosetta/ROSINA/UBern/ BIRA/LATMOS/LMM/IRAP/MPS/SwRI/TUB/UMich

http://www.universetoday.com/121824/dramatic-outburst-at-rosettas-comet-just-days-before-perihelion/

Edited August 11, 2015 by Aethon

[-ctn-]

Also, from ESA about the same outburst (regarding the argument that a jet didn't/couldn't move Philae):

The images were taken from a distance of 186 km from the centre of the comet. The jet is estimated to have a minimum speed of 10 m/s and originates from a location on the comet’s neck, in the rugged Anuket region.

[rkman]

ESA mentions possible change in orientation. Nothing about certain blowing off from the surface.

I did not claim Philae would be blown off from the surface. It's possible but imo not the most likely.

A change in orientation is more likely caused by non-uniform outflow in the crevice where Philae is (was?) located than by a uniform flow that you claim is more likely.

I suppose the outflows become more uniform at some distance from the surface, but with neither the interior nor the surface of the comet being uniform on the scale of the lander, outflows are not likely to be uniform near the surface where they'd affect the lander.

[Frida Space]

Pieces in the 1-40 (!!) metre size range are starting to fall off the nucleus, according to OSIRIS PI Holger Sierks.

[Streetwind]

Holy moly. Do we get to see the thing collapse live* on camera?

* after processing a series of still images

[Frida Space]

Holy moly. Do we get to see the thing collapse live* on camera?

Tomorrow, Rosetta will be @ 327 kms from the nucleus. If anything happens (although I highly doubt it), it should have a really spectacular, wide-angle point of view.

[Shpaget]

The pictures of the outburst, unless cropped in gradual manner, show the change in orientation.

Could it be a result from the tremors caused by the outburst?