This image was captured on 19 October 2014 and looks across the neck from the comet’s small lobe in the foreground to the large lobe in the background. Parts of the Anuket and Serqet regions are visible in the foreground and a portion of Hapi is present at centre-left, with the dramatic cliff edge in Seth in the background. There are significant variations in the distances between Rosetta and different parts of the comet in the foreground and background, but the average scale in the image is approximately 77 cm/pixel, yielding a frame width of 785m. The image has been contrast enhanced. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.
Today perhaps the most anticipated set of NAVCAM images of Comet 67P/Churyumov-Gerasimenko have been released by the Rosetta Downlink & Archive Team via the Archive Image Browser and ESA’s Planetary Sciences Archive.
The 1776 images cover the period between 23 September and 21 November 2014, corresponding to Rosetta’s close study of the comet down to distances of just 10 km from the comet centre – 8 km from the surface – and the images taken during and immediately following the landing of Philae on the comet.
An animation illustrating Rosetta’s trajectory around this period can be found here, providing context for the range of distances covered by the images in this release. Because of the spacecraft’s proximity to the comet during much of this period, the nucleus overfilled the NAVCAM field of view, and therefore the majority of images are in 2 x 2 rasters to cover the whole comet.
The single frames can certainly be admired individually (see the example above), but they can also be stitched together to create stunning mosaics, as we featured in many of our CometWatch releases from that period. We’re always impressed with the scenes that the image processing fans among you create, and we look forward to seeing what you generate from this release.
In addition to images from the close orbit phase, there are some great gems in this release, such as the NAVCAM’s view of lander Philae shortly after separating from Rosetta on 12 November (below). Although not as detailed as the images captured by Rosetta’s scientific camera OSIRIS, Philae’s body and its three legs can still be made out in a number of NAVCAM images as the lander falls towards the comet.
Philae, seen in Rosetta’s NAVCAM at 10:30, 11:30, 13:30 and 14:30 UT (on-board spacecraft time). The lander is in the top left of the field of view. Philae separated from Rosetta at 08:35 UT and made its first touchdown at 15:34 UT. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.
The NAVCAM also captured some wonderful views of Hatmehit, the large, 1 km-wide depression on the comet’s small lobe, around the time of the landing.
The first image in the sequence below includes the first touchdown point, Agilkia, at the bottom left of the frame. Philae subsequently took flight across the surface of the comet and came to rest elsewhere – a site now known as Abydos – nearly two hours later.
The Hatmehit region on the small lobe of Comet 67P/Churyumov-Gerasimenko as seen by NAVCAM around the time of Philae’s first touchdown, flight over the comet, and final landing at 15:35, 16:35 and 17:35 UT (on-board spacecraft time) on 12 November 2014. The distance between the spacecraft and comet centre over this period was between 17.4 and 17.8 km; apparent changes in the image scale are due to projection effects as the comet rotated underneath the spacecraft. The first landing site can be found in the first image, in the bottom left corner of the frame. The image has been contrast enhanced but vignetting has not been removed. Credits: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0
The next NAVCAM archive release is planned for end June and will cover the period 21 November to 19 December 2014.
Discussion: 33 comments
I’m still waiting for:
A) images of nozzle-shaped vents needed to produce jets from sublimation
B) abundant patches of ice and snow
C) acknowledgement that the dirty snowball hypothesis and sublimation mechanism are WAY off
ad A) There are several approaches to explain collimated jets. This is one of the more recent ones: https://www.lpi.usra.edu/meetings/lpsc2012/pdf/2548.pdf
Another approach: https://www.sciencedirect.com/science/article/pii/0032063394901260
Since Rosetta provides the best-ever observation of an active cometary nucleus, refined models will be defined.
ad B) Surface water ice is rather instable in the vacuum at temperatures above about 200 K. Hence those patches are short-lived in illuminated areas.
ad C) The “dirty snowball” model has been revised in 2005 to “icy dirtball”: 12 October 2005
Observations of Comet 9P/Tempel 1 made by ESA’s Rosetta spacecraft after the Deep Impact collision suggest that comets are ‘icy dirtballs’, rather than ‘dirty snowballs’ as previously believed.
The first 2015 refinement for 67P/C-G is “‘icy dirtball’ covered in ‘goose bumps’”:
https://www3.open.ac.uk/media/fullstory.aspx?id=28503
As for the collimated jets, this will be further refined with new data. The sublimation / clathrate decomposition mechanisms are the only reasonable family of outgassing mechanisms I can see thus far.
The first link you provided is appreciated, it’s one of the better papers I’ve read regarding the jets. However, they make a number of extraordinary assumptions in their methodology and experimental surface. Their data showed collimation exceeding escape velocities, but cometary jets exceed 300 times the escape velocity, where the paper says scaling up their experiment would decollimate the stream.
Observations of Tempel1 showed that the surface is very hard since x-rays were produced in the impact. This is not evidence of ice, only that their prediction is wrong. In fact, the crater was so small they postulated that the dust most have gone up and come back down to partially fill the depression. You choose to modify the theory, I call it a failure.
The streams also bend along the magnetic field, something never predicted by neutral gasses traveling 300 m/s. All predictions of comets were of an icy or snowy surface… remember that Philae had ice screws for a reason. The ice is not there because it never was.
Regarding the jets, we need to distinguish between the velocity of the gasses and the velocity of dust grains. The gasses are at about 700 m/s. Depending on the desity of the gas and the size, shape and density of the dust/sand grains / pebbles etc. those velocities may be anywhere between zero and 700 m/s. GIADA data – as far as published – say dust has been slower than about 10 m/s.
The 700 m/s are probably derived from 3x the speed of sound of the respective gas at the temperature on the surface of the comet. That’s the velocity of the faster individual molecules of a gas exposed to the vacuum.
‘Bend along magnetic field lines’?
The fields at nT, incredibly tiny, and since when is the dust ferromagnetic anyway? Rock, ice, dust etc are not deflected by magnetic fields; are you proposing the dust is iron filings?
The comet has been explicitly shown not to have a field of its own; it’s just the interaction of the photionised plasma with the interplanetary magnetic field. These fields are of order tens of thousands of times weaker than the earth’s field.
Whatever is going on with dust in the jets, it for absolute certain has nothing to do with magnetic fields.
Ross: Why do you say there is no evidence of ice on Tempel 1 because of the impactor? Here is what Wikipedia says:
“The probe’s spectrometer instrument detected dust particles finer than human hair, and discovered the presence of silicates, carbonates, smectite, metal sulfides (like fool’s gold), amorphous carbon and polycyclic aromatic hydrocarbons. Water ice was detected in the ejecta. The water ice came from 1 meter below the surface crust.”
Gerald, I mean wow. The first paragraph of your first linked paper is an eye opener. They out and out say that jets via nozzles has been disproven. And I’m with Ross in that the alternative mechanisms for explaining the jets proposed in the paper, while quite fanciful, are so highly presumptuous and speculative as to stretch credibility beyond recognition.
Sovereign Slave: The authors of the paper at the link provided by Gerald (which you refer to) only say:
“Contemporary models postulate that these jets are
collimated when the expanding gas and dust pass escape
through a physical aperture or nozzle. However, recent high-resolution spacecraft observations fail to detect such
apertures on cometary surfaces.”
They do not say that jets via nozzles are disproven, they construct an alternate “sieve” model and do some simulations to see if it is feasible. They do not say that sieves have been observed.
Well, here’s the paragraph in full. Seems pretty clear jets were there, nozzles weren’t (hence the need to create a new, “novel” approach). Interesting that high-resolution observations revealed this, same thing no doubt that the Osiris images are showing about P67. Truth is, there are no credible models explaining the jets via sublimation. And in the meantime, there is an ever growing list of surprises with each new Rosetta discovery that don’t seem to be supporting sublimation theory either.
Here’s the first paragraph from the paper:
Introduction: Recent high-resolution images of comet nuclei reveal that the gas and dust expelled by the comet is organized into narrow plumes or jets. Contemporary models postulate that these jets are collimated when the expanding gas and dust passes through a physical aperture or nozzle [1]. However, recent high-resolution spacecraft observations fail to detect such apertures on cometary surfaces [2]. Fur- thermore, these models do not explain why cometary jets appear to be directed normal to the local gravita- tional potential [2][5][6]. This is especially puzzling because the jet velocity, typically 300 m/sec far from the comet, greatly exceeds the escape velocity of only about 1 m/sec.
Here we describe a simplified computer model of jets emanating from Comet Tempel 1. Our novel mechanism is based on the occurrence of fluidized flow through the surfaces of comets…
Kamal,
About a couple of months back on this blog, I think at a time when the nozzle model was being discussed, the sieve model was ruled out because it could not construct the columated Jets Sorry I have looked but cant find it.
i think its fair to say that the evidence for how the jets form into columns and accelerate off the surface is not known. this must be taxing the team, there are plenty of theories on the blog but no data to do more than theorize.
Its still ambiguous as to whats happening.
regards
Ongoing research regarding the jets, just an excerpt:
https://www.researchgate.net/publication/258732059_3D_modeling_of_cometary_dust_jets_from_the_nucleus_surface_to_infinity
https://adsabs.harvard.edu/abs/2013AGUFM.P31B1807L
https://adsabs.harvard.edu/abs/2010Icar..210..881B
https://adsabs.harvard.edu/abs/2009DPS….41.3715M
https://adsabs.harvard.edu/abs/2014acm..conf..228I
Some hyperlinnks are incomplete; copy the whole respective line as URL to your browser.
For anyone who likes to see stereo images of 67P/C-G here an attempt to obtain a crossed-eyes and an anaglyph version composed of two roughly matching 2×2 Navcam rasters:
https://i.imgur.com/17CNYNC.jpg
https://i.imgur.com/ZsRZB3S.jpg
Starting from FITS images provided on the site
https://imagearchives.esac.esa.int/index.php?/category/64
I’ve used the ESA/ESO/NASA FITS Liberator 3 to store the 8 fits images as tiff, then used Hugin to stitch each of the two 2×2 rasters, then PhotoScape to rotate the stitches appropriately and to save them as png, then Microsoft’s Paint to register and crop the images, then StereoPhoto Maker 4.40 to properly align the images and to save them as stereo images, then again PhotoScape for annotating and conversion to jpg (quality 98%).
Link to license text: https://creativecommons.org/licenses/by-sa/3.0/igo/legalcode
Sorry, saving as png did Hugin already for me.
… If you stretch the brightness of the stitched image, you may see plume-like features. Those are most likely spurious stitching artifacts, since absent in the source images.
Thanks, Gerald. Amazingly complex geology. It’s an electrifying landscape 😉
Did you find the lander on the surface of the comet? Did i miss something?
Beautifull photo’s of the comet. Strange to look at another world so far away from ours!
Greetings from Almere, the Netherlands
Hi Ries, no you didn’t miss anything – Rosetta watched Philae land the first time, but its final landing site is still to be determined. For background you might like to read this post: https://blogs.esa.int/rosetta/2015/01/30/where-is-philae-when-will-it-wake-up/
Best wishes,
Emily
What Ross Said!
And I’d love to see these rocks that have a density of 470 kg/m^3! Are they like the ones we used to see on the original series of Star Trek? Made of polystyrene, perhaps?
I’d love to see the evidence of all this electrical activity that Rosetta has spectacularly failed to observe. Et boring cetera.
presumably Ian,
You would also like to see some Ice with the same density.
The indirect evidence of the existence of ice is completely overwhelming.
Comets produce huge amounts of water. Not only Rosetta but previous Kuipervtelescope measurements are of H2O, water molecules, not as is frequently asserted ‘just’ OH.
These tons of water have to come from somewhere.
The claims the hydrogen comes from the solar wind do not bear a moments calculation; they are numerically ludicrous. On top of which proton sputter yields at these energies are only low percent, and where does the silicon go, and how do you form water molecules in this very low collision rate environment?
The ice is well hidden – not entirely surprising, ‘refractory’ material is concentrated on the surface. The jets are a weird mystery in several ways.
But ice there must be, given the comet produces large amounts of water and is well below freezing! No other *remotely credible* mechanism has been proposed.
Harvey, you have repeated this mantra about the ice many times, The indirect evidence is strong, but we still have to find it!
If the Rosetta mission ends and we have not found it, or what should be icy lumps on the surface are not shown to be sublimating down to a pile of dust, then it would be a massive disappointment!
If after all the successes of the mission we are still left with conflicting theories about were the ice is and how its breaking down and forming jets, then it will be devastating and will mean we need a new comet mission.
Its an issue that should not be left open.
Regards
Harvey: Instead of ices of H2O, CO, CO2, could one have in the interior ices of hydrocarbons which match the density requirements? If so, one could think of the solar heating as doing two things: ejecting some sublimated gas components like H2O, CO, CO2 out into the coma in the form of jets and leaving (falling) behind them a heavily hydrocarbon-based residue of dust on the surface. Thus the comet nucleus turns itself inside out, so to speak.
Dave, if there actually are nozzles, I can hardly imagine, that OSIRIS wouldn’t be able to see them, with a spacial resolution of a few 10s of centimeters.
The ongoing observations should be able to narrow down the possible models quite a bit. It would be really strange, if not.
Kamal. You could match the density with hydrocarbons I guess.
But comets degas large amounts of molecular water. Despite what others here claim, it is not only observed indirectly as OH, but directly at molecular H2O, seen by Kuiper in the infrared and MIRO at high microwave frequencies. Despite assertions to the contrary, there is no mechanism to get water from silicates and hydrocarbons, even with the solar wind. (I think ‘exothermic self sustaining reaction’ was the phrase; no such reaction exists.) if there were, presumably we should be seeing a silicon surface comet!
At the moment, the only scientifically viable source of that water is sub surface water ice. It amuses me I’m repeatedly accused of being ‘closed minded’ on this. The only reason I know about the EU stuff is I was interested to see if a viable alternative existed. I’d love to have an alternative, but at the moment there simply isn’t one.
The ‘solar wind’ origin has more holes in it than the average sieve. It simply does not work.
So find an explanation which fits the laws of physics and experimental evidence and I’m more than happy to entertain it!
Dave. Nothing guarantees we will see the ice, and yes the evidence is indirect.
To what extent is that unsatisfactory, how much one should spend to get direct evidence, as opposed to indirect, is a matter of scientific politics and philosophy.
There are many, many things in science for which we only have indirect evidence, but it’s so overwhelming and consistent we accept it as proof. Does anyone really doubt the basics of the internal structure of the earth? It’s all indirect, seismic waves, magnetic fields – we’ve never been there and seen it. We’ve never ‘directly seen’ almost any of the sub atomic particle zoo, we just see their decay products and infer they exist.
Comets degas vast amounts of water, carbon dioxide etc; the evidence of that is overwhelming; where does it come from?
The simple fact is we have no other *scientifically viable* theory other than sub surface ice, carbon dioxide etc. The so called solar wind and hydrocarbon theory break multiple laws of physics and are excluded by multiple observations. They aren’t real theories as they are entirely non-quantitative. No ‘real scientist’ would argue with that for a moment.
If a *real, viable, sensible* alternative were proposed, there would be very, very strong argument for a ‘decide between them’ mission. But right now that’s not the case. If no viable alternative is proposed – and it seems unlikely – it will be about further unravelling the detail and surprises, which will be a harder ‘sell’ I suspect.
Hi Dave, agree.
Most abundant substance Alice is seeing is molecular water, at least on the UV spectra. Or don’t believe in Alice.
https://blogs.esa.int/rosetta/2015/06/02/ultraviolet-study-reveals-surprises-in-comet-coma/
The point is: Want to see placid rivers of crystalline waters? Or pure ice crowned mountains?
In spite of the beauty and the incredible landscapes seen on these images, I can’t help but notice that this is yet another release of Navcam images and Osiris images are nowhere to be seen.
I should be in awe and because of all this mess, I am kind of disgusted. When do we get the Osiris images the taxpayers have paid for ??
thank you very much
These pictures are so much sharper than what I first saw of the moon orbits (and the backside of the moon) in the 1960s (there were Russian craft too at the time. And then I wish we could do the same with … exoplanets and … the bottom of our oceans which are more of a terra incognita still than some of our nearest objects in space …
It’s amazing to me that there is not a redo, or at least major revision of a 40+ year old theory about the dirty snowball theory. This is not science, it is a belief. Stardust mission revealed the presence of both olivine and cubinite which are not formed in the same temperature environments, unless there was very rapid and extreme surface heating which can’t be explained under the current models. The origin of comets has not been explained, and the Ort cloud theory fails in this one observation of mineralogical data. It’s time for a redo!
Hi Kurt. Sure a redo is happening right now. This is becoming a saga of phenomena. Cometary science has re-birth in just a year. [Maybe not exactly the same that each of us was expecting].
Minds, specially those experienced ones who had to build theories based on drops of data, are still digesting this truck load. Their comments are going to be the most important 🙂
Coraline’s Core Material born from Growth, not Accretion processes.
The physics present [or better said: the relative absence of physical perturbations] at 67P’s nursery favored the geometric, ‘labyrinthine drawings’ in the structure of the Material.
This is Cometary Fiction.