The Recurring Odd Shape Of Comets

a reply to: GaryN

It was imaged by the Osiris camera and we have details on that.

a reply to: wmd_2008

It was imaged by the Osiris camera and we have details on that.

Good! So what wavelength/s were used for that image?

originally posted by: GaryN
a reply to: wildespace

By the way, looking at this excellent photo, it's even clearer to me that I'm not looking at a solid rocky body.

And it can't be anything conventional if the 'experts' are correct about it's density. From Wikipedia:

Comet 67P/C-G
102±9 kg/m³

Silica
2648 kg/m3

Water
999.9720 kg/m3

Ice is about 90% the density of water. So what the heck is it made of? Or is it hollow?

Such low density (somewhere between the density of cork and styrofoam) points to lots of voids in the comet. It's basically a rubble pile of ices, dust, and empty space.

Here are the details on Rosetta's OSIRIS camera : www.planetary.org...
It includes filters in the visible part of spectrum: red, orange, green, and blue. I'm very much looking forward to RGB images of the comet.

P.S. correction - the image in my previous post was taken with the NAVCAM, which is a different camera: starbrite.jpl.nasa.gov...
If I understand correctly, it doesn't use filters, and registers all incoming visible light.

a reply to: AnarchoCapitalist

I don't know everything, but I do know the dirty snowball model of comets is a joke.

Then you will find this hilarious:

www.spacedaily.com...

a reply to: wildespace

I'm very much looking forward to RGB images of the comet.

Any RGB images will not be the same thing as taking an RGB image on Earth, they will be spectral reflectance lines of specific elements.

A NAC image available today:
blogs.esa.int...

Taken on 7 August 2014, from a distance of 104 kilometres through the orange filter of the OSIRIS narrow-angle camera. They are separated by 17 minutes and the exposure time is 138 milliseconds.

With the orange filter they may be looking for pyroxene reflectance spectra.
SYSTEMATICS OF VESTOID REFLECTANCE SPECTRA BY 600-AND 650-nm BANDS.
www.lpi.usra.edu...

By using different filters, and examining the spectra, they can further pin down the most likely materials by comparing the expected spectral lines in each band with those observed, for each element.
Good to see they are giving the exposure time too. 0.138 sec may seem like a short exposure time, but given the sensitivity of the instruments, they are likely still looking at some very weak, and 'thin' emissions, not naked eye visible IMO.

originally posted by: GaryN
a reply to: wildespace
Any RGB images will not be the same thing as taking an RGB image on Earth

It will be. Combining RGB filters produces a true (or very near true) colour image. As pointed out at www.planetary.org... "For true-color NAC images, look for RGB combinations"

OSIRIS already has a filter for Orthopyroxene, as well as some other chemical compounds.

originally posted by: AnarchoCapitalist
The comet is composed of rock - solid rock - there are no volatiles beneath the surface.

Except the comet has now been PROVEN to have 1/10th the density of an asteroid (.3g/cm3), and is 100% not solid rock. It would float in water, it's 1/3 the density of water. This is EXACTLY what was predicted. It is exactly NOT what EU predicted.

Enjoy your crow.

www.bbc.com...
www.abovetopsecret.com...