Instrument commissioning phase, Beginning final approach to the comet Options

[machi]

We know distance (~5500 km) so resolution is slightly over one hundred meters per pixel (102-103 m/pix).
Images on the ESA's site are 8× magnified.

[dilo]

If you pay attention to last frame, there is a "welding" flat region between the two portions, made of darker material compared to the bright ring all around the contact; my impression about the "white collar" is that it could be made of fresh material exposed during last passages, when volatile substances (previously filling the gap between the two portions) sublimated; obviously, this idea is highly hypothetic! Only spectral analysis, joined to high-resolution morphology, could help to confirm or not this model...

[nprev]

Given the processing & enhancement done to these images & their size in pixels, is the resolution sufficient yet to determine if the albedo differences Dilo noted are real? For example, the bright 'ring' at the lobe contact point in particular sure looks like it might be specular; maybe the rest of the surface appears just as bright from the right illumination angles.

[Phil Stooke]

Very nice new images - here's a differently processed version.

Phil

[Explorer1]

Looks like new NAVCAM's will be given out daily from now to arrival. Better than OSIRIS weekly I suppose?

[Phil Stooke]

The shape model is interesting as well. It may be obvious to people but I should point out that the small peaks are artifacts - they are produced by the spatial interpolation process which converts a sparse set of points to a full DEM.

Phil

[JohnVV]

-- edit-
this is the OLD light curve shape file
are you referring to the nasa/jpl/naif shape file


-- the NEW one ( early look)
the animation on the esa page

http://www.esa.int/spaceinimages/Images/20..._model_of_comet

[Phil Stooke]

The one just released by ESA, which contains several little spiky hills. I don't want people thinking they are real - for one thing the model is based on the earlier set of images with very low resolution. For another, most of the 'hills' are on the outer edge of the 'big end', which was hardly visible in the images because of the viewing angle.


Phil

[Phil Stooke]

This is more like the real resolution of the data. Not to deny the fantastic job the science team has done with such early data. I am only saying the high resolution rendering can't be relied on in every detail.

Phil

[Gerald]

Given the processing & enhancement done to these images & their size in pixels, is the resolution sufficient yet to determine if the albedo differences Dilo noted are real? For example, the bright 'ring' at the lobe contact point in particular sure looks like it might be specular; maybe the rest of the surface appears just as bright from the right illumination angles.

There isn't a final assessment yet, but dilo's hypothesis is well on the same line as the science team considers as likely.
Rosetta-Komet: Ein Blick auf die Oberfläche (Rosetta Comet: A Look onto the Surface) :

Momentan können wir mit Sicherheit lediglich sagen, dass der Halsbereich heller aussieht als der Kopf und der Körper des Kometenkerns“, sagt Holger Sierks vom Max-Planck-Institut für Sonnensystemforschung (MPS), der Leiter des OSIRIS-Teams. Materialunterschiede, unterschiedliche Korngröße oder topographische Einflüsse könnten dafür verantwortlich sein.

Auch wenn die aktuellen Bilder, die aus einer Entfernung von 5500 Kilometern entstanden, noch nicht hochaufgelöst sind, erinnern sie die Wissenschaftler an den Kometen 103P/Hartley. Die NASA-Mission EPOXI hatte diesen Körper 2010 im Vorbeiflug besucht. Während die Enden des länglichen Kometenkerns eine raue Oberfläche aufweisen, erscheint die Mitte glatter. Forscher glauben, dass sich in dieser Taille Material ablagert, das zunächst emittiert wurde, dann aber den Einfluss des Schwerefeldes des Kometen nicht verlassen konnte. Im Bereich der Taille befindet sich der Masseschwerpunkt von 103P/Hartley.

Ob diese Überlegungen auch auf den Halsbereich von 67P zutreffen, ist noch unklar. Eine andere Erklärung für eine hohe Reflektivität in diesem Bereich könnte eine andere Oberflächenzusammensetzung sein. Das OSIRIS-Team hofft, in den nächsten Wochen spektrale Daten des Kamerasystems zu erhalten. Mit Hilfe verschiedener Filter kann OSIRIS mehrere Wellenlängenbereiche aus dem reflektierten Licht herausfiltern. Auf diese Weise lassen sich charakteristische Fingerabdrücke bestimmter Materialien oder Zusammensetzungen identifizieren.

"At the moment we can just tell with certainty, that the collar zone looks brighter than the head and the body of the cometary nucleus", says Holger Sierks of the Max-Planck-Institut für Sonnensystemforschung (MPS), OSIRIS Principal Investigator. Differences of material, different grain size, or topographical influence could be responsible.

Although the current images, which have been taken from a distace of 5500 kilometers, aren't yet highly resolved, they remind the scientists at comet 103P/Hartley. The NASA mission EPOXY visited this body in a 2010 flyby. While the ends of the lengthy cometary nucleus show a rough surface, the mid appears smoother. Researchers think, that material precipitates at this waist, which first has been emitted, but then couldn't escape the influence of the field of gravity of the comet. In the region of the waist the barycenter of 103P/Hartley is located.

Whether these thoughts hold true for the collar zone of 67P, isn't yet clear. Another explication for a high reflexivity in this region could be a different composition of the surface. The OSIRIS team hopes to get spectral data of the camera system within the next weeks. By using different filters OSIRIS can filter out several ranges of wavelengths of the reflected light. That way characteristic fingerprints of certain materials or compositions can be identified.

[dilo]

---the bright 'ring' at the lobe contact point in particular sure looks like it might be specular; maybe the rest of the surface appears just as bright from the right illumination angles.

It was my suspect too... however OSIRIS Principal Investigator Holger Sierk said "The only thing we know for sure at this point is that this neck region appears brighter compared to the head and body of the nucleus,"
(source http://www.jpl.nasa.gov/news/news.php?release=2014-24)

[Gerald]

The big media event will be on 6 August.

[nprev]

Good enough for me, and thanks for the translated information, Gerald. Nice catch, Dilo! This mission is growing more exciting by the day.

EDIT: If the impact precipitate origin of the bright area is correct, does that in turn imply that the barycenter of the two lobes is there? If so, this may be evidence that the smaller lobe is a bit denser than the larger one.

[Hungry4info]

One can probably use the rotation video posted last week to determine the centre of mass of the system, and with that, a rough idea of the relative densities of the two bodies.

[Explorer1]

They can also use the spacecraft's own acceleration from C-G's gravity, measuring the radio signals once in 'orbit', (if one can call it that?).