NOTE: I think either possibility suggested below is possible, I'm not looking for arguments why one of them would be your favorite like this answer. Instead, I'm looking for a fairly conclusive answer; either by ruling one out beyond reasonable doubt, or better yet by supporting your answer with authoritative sources discussing these particular artifacts in these specific images.

For discussion of the GIF below, see:

  1. this answer

  2. New Horizons Mission page February 8, 2019 New Horizons' Evocative Farewell Glance at Ultima Thule; Images Confirm the Kuiper Belt Object's Highly Unusual, Flatter Shape

  3. New Horizons’ Evocative Farewell Glance at Ultima Thule

I see a lot of white dots that repeat in each frame, moving steadily left to right. But I also see a lot of similar white dots that do not.

Going frame by frame, the ones without the collective left-to-right motion often appear in one frame only, but in some cases I can convince myself (but not others) that a dot may appear in two adjacent frames, just moving in a different direction.

Which makes me wonder if it could be debris around the asteroid, or between it and New Horizons, basically anything close enough that it doesn't appear fixed on the celestial sphere.

One of the reasons for all of the occultation observations in 2017 and 2018 (see also Timing shadows from the Kuiper belt! Any news? Did it work? and Will the upcoming observations of occultation by “Ultima Thule” (2014 MU69) be of a single object, or two?) of MU69 (Ultima Thule) was to check for the possibility of a debris field around MU69 that might make a very close flyby dangerous. None were discovered but the unusual shape was suggested by the strange occultation results.

Question: What are these white dots? Real objects, noise or cosmic rays in the silicon sensor, or something else?

Borrowed from this answer to the question Will there be back-side photos of Ultima Thule? and originally from New Horizons’ Evocative Farewell Glance at Ultima Thule

enter image description here

Mission scientists created this "departure movie" from 14 different images taken by the New Horizons Long Range Reconnaissance Imager (LORRI) shortly after the spacecraft flew past the Kuiper Belt object nicknamed Ultima Thule (officially named 2014 MU69) on Jan. 1, 2019. The central frame of this sequence was taken on Jan. 1 at 05:42:42 UT (12:42 a.m. EST), when New Horizons was 5,494 miles (8,862 kilometers) beyond Ultima Thule, some 4.1 billion miles (6.6 billion kilometers) from Earth. The object’s illuminated crescent is blurred in the individual frames because a relatively long exposure time was used during this rapid scan to boost the camera’s signal level – but the science team combined and processed the images to remove the blurring and sharpen the thin crescent. This is the farthest movie of any object in our Solar System ever made by any spacecraft. The images reveal an outline of the “hidden” portion of the Ultima Thule that was not illuminated by the Sun as the spacecraft zipped by, but can be “traced out” because it blocked the view to background stars also in the image.

Credits: NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory

Also in YouTube:

  • $\begingroup$ I'm still debating if this is better asked here or in Astronomy SE. It's on-topic in both places, arguments can be made both ways. Any thoughts? $\endgroup$ – uhoh Feb 9 at 3:06
  • $\begingroup$ I think noise can be eliminated as, noise effects randomly to many pixels randomly distributed. And Cosmic rays, well until and unless one crosses Oort Cloud, I doubt cosmic rays can effect so many pixel in just one second in the image sensor. New horizon rotates at about 30 degrees per second, and looking at total rotation of celestial sphere it appears to be 1 second video to me. As to what those white dots are, could it be that the ultima Thule reflection from sun just over exposes the surrounding pixels shadowing the stars for some duration? $\endgroup$ – Prakhar Feb 9 at 5:48
  • $\begingroup$ Better not rule anything in or out without hard numbers. There is more than one kind of noise, and we don't know how the images were post-processed yet. I think you are way off on your estimate of time, let's see if we can find some data. I've re-edited the question and have now included the source I used for the GIF image above, as well as a quote. Also, in this answer you can see how the distance and angle changes over time. $\endgroup$ – uhoh Feb 9 at 7:16
  • $\begingroup$ What makes you think its a way off estimate? If the camera rotates at about 30°/s, if it is say 6 second video, ultima thule image would turn by 180°.. Is it not? $\endgroup$ – Prakhar Feb 9 at 7:27
  • 1
    $\begingroup$ @Prakhar the individual images have just become available now including individual timestamps and exposure times! pluto.jhuapl.edu/soc/UltimaThule-Encounter $\endgroup$ – uhoh Feb 10 at 4:43

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