Hello, As you can see in the picture, there is a dark ring on an asteroid, is it noise in the picture? or something else? totally it is like a ring not a burned pixel.
looks flat on the image plane, not as if it was on asteroid surface. Also, it is more sharp than other details in the picture. I guess it is an artifact from the lenses (dust?).
Maybe a deeper look with an imaging software could help, the surface intensity should give some clues.
In absence of an idea of the scale factor for the image, it is impossible to tell if it is due to dust on the lens, an artifact of image processing, or (very unlikely) an actual topological feature. Can you please let us know which mission/instrument this image was taken from? Dust on the lens should show an identical feature at the same image position in other frames as well. Asteroids do show some craters, but the illumination on this ring is too flat , as compared with that on the ridges, and other surface features, for it to be real.
What about the bright feature on the asteroid limb, just to the right of the dark ring?
The bright feature reminds me of Io's volcanos.
Compare: http://news.nationalgeographic.com/news/2007/05/images/070502-volcano-io.jpg
But volcanism is unlikely on an asteroid. Could be an ejecta plume (like those made of water seen on Ceres)
http://static.ddmcdn.com/gif/herschel-cool-shots-02-670x440-130501.jpg
We know dark rings from lunar craters (see e.g. http://www.lpi.usra.edu/meetings/LPSC99/pdf/1350.pdf ). Dark rock ejecta (melted, then cooled) from an impact now residing on a bright ice layer over the rock.
But first one has to rule out artefacts from image processing and dust on the lens (does this dark ring appear on all pictures ?).
The fissures (lower left) remind me of the features seen on Europa, another moon of Jupiter. Compare:
http://rack.0.mshcdn.com/media/ZgkyMDE1LzA1LzI2LzU1L2V1cm9wYS4wOTJhNS5qcGcKcAl0aHVtYgkxMjAweDk2MDA-/08f01c65/2e5/europa.jpg
Compare two images taken of lunar surface, 425 km orbit. One original, one blurred 5%. Imaging info included.
Dust somewhere in the optical system looks very unlikly. How such a shape could result?
If we would know the kind of mission (see the question of F. Sutaria !!!) we could reason on whether it is a shadow of the spacecraft. Notice that near the asteroid belt the sun appears as a rather small light source which throws sharp shodows over long distances.
The shape of that feature, if we suppose something like a dust grain, is common, it comes from an out-of-focus light-blocking point.
Also, it could not be present on previous or following images, because external events (wind, telescope movements) can move it.
Roberto, my dust grains never behave that way. Can you provide any evidence?
Sure, Ulrich, here is a simple example:
http://www.eso.org/~ohainaut/ccd/CCD_artifacts.html
scroll down to Fig.8b.
Maybe you didn't notice the effect because of a short focal length (1m or less), when using longer FL (10m) it comes evident.
In absence of other pictures of the asteroid, I also agree with Roberto: the ring may be produced by a speck in the optical path of the camera. But there are some intriguing features:
-the ring appears to me elongated in the limb direction. But the shadows cast by specks are typically round due to the simmetry of the optical system.
-on the other hand, the picture appears to be taken from a space mission. To produce such a ring-like feature, the speck must be near the focal plane: in the CCD window, in the filter, etc... so I think it would be inside the optics. And I can not imagine how such a speck could end in the optical path given that the optics are assembled in clean rooms. Dust from space must be outside the optics.
It would be great if there were other pictures taken from other angles to confirm or discard the "dust speck" hypothesis.
Regards
Is it possible that the "speck" maybe a micrometeorite hit on the glass of the window or of the lens that took the picture?
Can be a regio with a different albedo.
Or, as the others said, a flat issue.
salaam
I agree with the general consensus of my respected colleges. the next thing to do is rule out any photo defect and move on to other possible explanations such as why a surface feature would have such high contrast. if the surface material is light in color and subsurface material is dark a recent impact could explain this result, however one would expect to see more of these features.
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