They say "...the first images from this sequence will be received on Earth several hours after separation." To me, this does not mean that all the descent images will be sent before landing, only "the first images" of the sequence. The first images of the descent and the landing panorama are specifically mentioned but not the late descent images. I suspect that late in the descent, all systems will be devoted to a safe landing and none to transmitting images (those of the late stages of descent).

When the late descent images will be transmitted is just not addressed at all.

(edit: Well, it looks like my speculations were unnecessary. )

I can't find anywhere a downloadable 3d model of rosetta spaecraft! Is going on something like pathfinder/sojourner copyright thing, which prevented downloading its model for 20 years?!?

there is a Blender ".blend " file on the NASA 3d mesh site
666669main_Rosetta.zip

what do you know they removed it
http://www.nasa.gov/multimedia/3d_resources/index.html
---- MOVED ---
http://nasa3d.arc.nasa.gov/models#R

http://nasa3d.arc.nasa.gov/detail/eoss-rosetta
Click to view attachment

New navcam images today:
http://blogs.esa.int/rosetta/2014/10/17/cometwatch-at-10-km/

That's one of ours - it's from the Eyes on the Solar System team. Word of warning - as with almost every spacecraft we make - we had nothing in terms of good reference material. Infact, less than ususal because it's an ESA mission. It looks OK - but do not expect it to be especially accurate. We did our best, but we really had little to go on.

My take on the mosaic of 15 October, at 7.9 km from the surface!

Another four image mosaic:
http://blogs.esa.int/rosetta/2014/10/20/co...tch-18-october/
Amazing how the ripples on the 'saddle' (bottom left) resemble the ones we've seen on Mars so many times, though they're not made of even remotely the same materials...

This is one of the best NavCam shot we saw !! But I admit the choice for a "best of" is not easy.

The material is compositionally completly different from martian sand, but it could still be a granular material (loose or solid) that forms ripple due to some kind of shaking...

If there is fine-grained loose material on the surface of the comet, could the gases ejected around perihelion act as a kind of "wind", moving the grains around and shaping them into ripples?

Thanks Charborob : this is a very good question indeed... I had the same in my mind 5 minutes ago when I saw the pictures !

Hello everyone !

I didn't stopped imagery processing, because I'm playing with the astounding images that Rosetta are sending us.

The last one was amazing, but very hard to processe. Here is the result

(Check out the bottom)

Great mosaic Ant103!


there was already a discussion of very speculative wind-like formed ridges and ripples few posts ago. Question remain whether the smooth material is hard (e.g., duricrust) or loose.

Nice to see you're still around Damia
The crack on the right end side of the neck is clearly visible. Hope C-G will stay together. If not, the GC will change...

Thank you, Damia. Astonishing work as always!

Those features on the 'sand' really do look like dunes. I agree with charborob's 'vent wind' conjecture as well. In fact, such 'winds' would presumably have a major role in distributing the fine material in the first place.

Lots of interesting questions arise here. What is the composition of the fines? Can we measure the rate of vent outflow to determine how much force was exerted to form the dunes, thereby setting constraints on both grain size & composition? How exactly was the fine material even formed in the first place?

I'm highly sceptical on this. Dune or ripple formation as we understand it involves gravity controlled saltation and a reasonably steady horizontal wind. Saltating grains on the comet would have to be moving extremely slowly to avoid being blown away altogether. 'Winds' associated with cometary activity are presumably highly variable throughout each orbit and, on the evidence of the jets we see here, near vertical in direction. I agree the visual similarity to Martian dunes is uncanny and may well indicate some underlying connection at a mathematical level, but I think the physical process is likely to be very different.

I think these two are taking 'Extreme Ironing' a bit far!



Click to view attachment

Excellent work, Damia! I can't tell, of course, how much of this might be some kind of image artifacting, but in this image you posted it almost looks like sheets of dust are being ejected -- very fine sheets.

It's a real imaging challenge to show the surface details of the nucleus and also see the jet and dust action. You *really* captured that with this one!

-the other Doug (With my shield, not yet upon it)

It is amazing how much this looks like snow to my eyes, particularly given its bright contrast in the black and white photos and the way it seems to drape over the landscape. Not knowing enough about the physics/physical chemistry involved, i would be interested to know if is there any possibility that a volatile substance (as opposed to a "dust") could be emitted and subsequently deposited (or perhaps directly sprayed onto the landscape, or recaptured by the comet's gravity) and survive any sublimation into "free" space?

It looks like snow because the contrast in the images has been stretched -- there is an excellent blog post on the ESA website about this. The comet is actually extremely dark, about 5% reflective, darker than charcoal. Its surface is definitely covered in dust (that's an early reported result of the mission) and much of the surface is actually too warm for water to be stable, though it's much much colder just below the surface (as reported by Sam Gulkis to the NASA Social held at JPL last week).

Thank you, Emily.

Thanks a lot Damia !
It really looks like a view that could have inspired a painting from Chesley Bonestell...
Enjoy !
Click to view attachment

Oct 18th Navcam 4 frames from http://blogs.esa.int/rosetta/2014/10/22/co...ops-neighbours/

Nice work!

Some of these structures are reminiscent of fumaroles, with encrustations around the edges.

BTW has anyone spotted any potential impact structures yet?

There was one way back during the first big OSIRIS release. It was a small dust-covered bowl (a third of the way down here: http://www.planetary.org/blogs/emily-lakda...around-cg.html).

Nothing confirmed, of course.

Ed:Fixed misplaced bracket...

Edit: To add the pertinent image from Explorer1's link to Emily's blog.
Click to view attachment

And a crop from that image. That crater sits in the center of a raised mound. Coincidence?
Click to view attachment

My stitch of the recent mosaic: http://www.pictureshack.us/images/49436_ES...1018_stitch.jpg

I think those round features are sublimation sites rather than impact craters.

I'm leaning that way as well. The odd rims look as if they may be encrusted with material, perhaps precipitates from volatilized material abruptly re-freezing.

they do

but
if a low speed impact happened then the material around the crater would be of higher density , and have a higher temp of evaporation
that might leave the area around it but allow the surrounding area to evaporate .
Click to view attachment

http://blogs.esa.int/rosetta/2014/10/23/co...n-the-increase/

As the URL says, comet activity is on the increase. Also, it's stinky:

http://blogs.esa.int/rosetta/2014/10/23/th...fume-of-67pc-g/

Phil

John W's suggested mechanism sounds like one that could apply not only to low-speed impacts into ice and snow, but also to higher-speed impacts into sand, dust, or rocky material. But have we seen similar structures forming elsewhere? I am trying to think of other examples on earth or extraterrestrial bodies where an impact "shell" survives as the surrounding material erodes away. For instance, sometimes when a big, isolated raindrop lands on sand and then evaporates, it can leave a cup-shaped structure behind, but this is a poor example because no actual melting is involved.

Maybe the experimental types who create controlled impacts by firing projectiles in the lab could tell us more about when a fused shell structure is likely to remain behind.

In the third image down I like the appearance of shadowing onto the jets. Helps to give some 3-D perspective.

Look at all those organic molecules.

If comets like this crashed into a young Earth, they could have kick-started organic chemistry.

Nice Miller-Urey-like cocktail.
I'm feeling somehow, that this list will grow much longer at higher temperatures.

The point of origin of the jets isn't obvious yet, at least to me. Are they really caused by matter spewing out through identifiable vents, or is it just a general sublimation of the surface? I hope it is one question that will find an answer as the mission advances and as the comet activity increases.

Yes stinky indeed, it's a solar system leftover that's been left basking in the sun for a handful of billion years. So of course it is stinky! =)

In the Comet Activity is on the Increase blog entry, they include two WAC exposures.

Over the dark region in the overexposed image (18.45 second exposure), there are long, faint lines (almost horizontal, tilted with the left side up). Could these be grains floating by, as had been mentioned in the blog a couple times?

Does anyone want to make a guess about their size and distance from Rosetta?

Since the lines are roughly parallel, CRs are almost ruled out. They are not perfectly parallel, and a bit random, hence camera artifacts are unlikely.
Therefore I'm sharing your suggestions, that grains are a good explanation.
The short exposure image contains at least one such line (near pixel pos (1440;400) with (0;0) as the (left;top) corner).
This one line is statistically questionable in terms of length, but it may be taken as a hint for the angular velocity of the supposed dust particle. The line is about 35 pixels long; this corresponds to 0.2 degrees for WAC, using 20.5 arcsec / pixel.
The longest line I could find in the long-exposure image is about 230 pixels, or 1.3 degrees; that's only about 6.5-times the length of the short-exposure line, less than the 18-fold, as would be expected due to the more than 18-fold exposure time. This provides a hint, that some of the long-exposure lines show the respective particle along all the path it's visible for the camera.
Statistics is poor with only one grain in the low-exposure image, but it might provide a hint, that some of the grains even float into the shadow of the camera or the probe, with a very low relative velocity of roughly between one mm to one cm / second.
The size would be in the order of a few micrometers.

Four new navcam images today. On one of the images, we can see scallop-shaped features (see arrows). Sublimation zones?
Click to view attachment

... Hipass-filtering, brightness stretching, rgb-channel combine, closer inspection, and annotation connects the two OSIRIS WAC images:

At least four grains can be identified in both images. This reveals the longest line in the low-exposure image as an outlier in terms of angular velocity, and hence weakens the constraints for distance, grain size and relative velocity by discarding the shadowing hypothesis.

"On one of the images, we can see scallop-shaped features (see arrows). Sublimation zones?"

I had been thinking of these as avalanche scars, places where a patch of the dusty surface slipped and fell off the nearby cliff.

Phil

Although I'm inclined to sublimation (cf. 10/20/14), the lobate piles(?) of stuff on the floor below(?) support your theory.

Notice that the rocks near these features have 'dust' tails, as if there was a prevailing wind blowing from the left. I would interpret these as gas-scoured areas, and the venting is happening from inside the adjoining 'canyon'.

I was skeptical at first (as always), but linking several streaks in the two frames appears to be fairly convincing, and they may indeed be real snowflakes/particles.

In terms of determining sizes/distances, I would say some estimate of the expected relative velocities would be our best bet, as I described in this post. (In that post I was considering dots, not streaks, so only talked about putting limits on distances, but the same idea applies with streaks, where, up to geometrical factors, you could actually estimate the distance.)

I have to keep reminding myself that the nucleus has very low albedo, and these images are very stretched. Has there been mention of any actual high albedo areas being identified?

According to the ESA blog the exposure time for the high-exposure image has been 18.45 seconds.
The estimated 1.3 degrees streak should have been caused by a dust grain, which would have needed about 18.45s / 2 tan 0.65° = 18.45s * 44.07 = 813s = 13.6 min to overcome a distance the same as from the grain to the camera, simplified assuming it has been moving perpendicular to the pointing of the camera. With a more realistic assumption of 45° trajectory it would have been 9.58 min for the same distance.

For a grain at 10 meters distance its relative velocity would have been rougly 10m/600s = 1.6 cm/s. Distance assumption and relative velocity assumption are proportional.

The brightness of the streak in the short-exposure image is about 1/100 that of the brightest features on the comet, assuming a 2.2-gamma corrected image, grey values of 26/255 for the grain pixels and a grey value 213/255 for the brightest parts of the comet ((26/213)^2.2 = 1/102). The length of the streak is about 10 pixels. The exposure per pixel is hence about 1/10 of the comet. Assuming the same albedo results in an apparent diameter of about 1/3 pixel or about 7 arc seconds.

For an assumed distance of 10 m this would mean an estimated diameter of the grain of about 10m * 2 * tan 9.7e-4° = 0.34 mm.

This is still the big assumption, and could conceivably be orders of magnitude off.

The velocity will have two components - the orbital velocity of Rosetta and the ejected velocity of the particles. The former is easy to estimate given the orbital radius and period. The latter I know nothing about. I don't even know which (if either) might dominate. Indeed I'd expect some distribution of ejected velocities. But even an order of magnitude would tell us something about the size and distance of the particles we're seeing.

Correct! There are still a few degrees of freedom in the system. Albedo/scattering and gamma-correction (for grain size estimates) are the other two, besides some minor uncertainties in image analysis.
For Rosetta's velocity relative to the center of mass of the nucleus, the escape velocity of an object at a distance of 10 km from a mass of 1e13 kg is
sqrt(2 GM/r) = sqrt(2 * 6.672e-11 Nm²/kg² * 1e13 kg / 10,000 m) = 36.5 cm/s.
The velocity for a circular orbit is slower by a factor of sqrt(2), hence 25.8 cm/s.
At 9 km distance from the center of mass it's 27.2 cm/s for the circular orbit.

If we take the 27.2 cm/s as an estimate for the relative velocity to the dust, the distance would be (using the proportionality of velocity and distance) about 10 m * 27.2 cm/s / 1.6 cm/s = 170 m.
No idea, whether this assumption is realistic. From the geometry of the jets, it may be possible to infere the velocity of the grains causing the scattering there. But it's not clear, whether a velocity obtained that way can be used for the individual observed grains. There may be a different observational bias.

There are some faint, short streaks indicating, that there are grains further away; hence the distance for the brighter streaks should be far less than the distance to the comet. This still leaves much uncertainty.
Blur (by the optics) of the dust streaks might be another approach to find some constraints for the distance.

http://blogs.esa.int/rosetta/2014/10/27/co...tch-24-october/

New mosaic alert! Yowsers, that's jagged.

Phil

I can't find anywhere the total amount of kilometers traveled by Rosetta till now, any help?

"rendezvousing with the comet required travelling a cumulative distance of over 6 billion kilometers"

http://www.esa.int/Our_Activities/Space_Sc...asked_questions

Factsheet:

Launch date: 2 March 2004

Journey milestones:
1st Earth gravity assist: 4 March 2005
Mars gravity assist: 25 February 2007
2nd Earth gravity assist: 13 November 2007
Asteroid Steins flyby: 5 September 2008
3rd Earth gravity assist: 13 November 2009
Asteroid Lutetia flyby: 10 July 2010
Enter deep space hibernation: 8 June 2011
Exit deep space hibernation: 20 January 2014
Comet rendezvous manoeuvres: May - August 2014
Arrival at comet: 6 August 2014
Philae lander delivery: November 2014
Closest approach to Sun: 13 August 2015

Mission end: 31 December 2015

http://www.esa.int/Our_Activities/Space_Sc...setta_factsheet