The New Horizons team released the following photo of Charon today

enter image description here

This choice of image seems rather odd to me for a number of reasons. First of all, according to Emily's schedule, there were 3 images slated to come down from Charon. These 3 images were chosen months ago, with some slight tweaks based off of the timing. LORRI is a square imaging camera. The fact that the image was rectangular seems odd to me. I've confirmed with the provided data that the height of this image is 1024 pixels, as expected from LORRI. However, the width appears to be about half that. What this tells me is that the right hand part of the image must have been deep space. Considering that every image released now is a contingency, it seems odd that the very edge of the moon is the area of focus, and even more that the moon was missed.

I've come up with a number of theories as to why this image is cut off, along with some thought behind them.

  1. The images could have been looking for dust or at the shadowed region. This seems unlikely because the exposure for such an image would have been different, and I doubt this would be a high priority image.
  2. The image was deliberately set for the edge of the moon, and it missed the mark slightly (About 1 field of view). This seems likely, but I'm not sure why the edge of the moon would be such a high priority image.
  3. The image was intended to be near the center of the moon, but missed the mark by quite a bit, barely capturing the edge of the moon. This is the one that has me the most fearful, hinting there is a chance that many of the best images could be missed because of some kind of a positioning error, which could be very bad.
  4. The 3 images were chosen of different parts of the moon (Center, middle, somewhere between?), and this was the one of the 3 deemed most interesting, again with a likely slight targeting miss.
  5. The predicted uncertainty was high. As a result, the 3 images were spaced well apart, to ensure the Moon was there. 3 images were downlinked, spaced in the uncertainty range such that there was a good chance Charon would be in the field of view. This one just happened to be on the edge, by coincidence.
  6. Part of the image was removed because the science team didn't want to include it, for some interesting science it holds. This seems to me to be very unlikely.
  7. Part of the image was cropped due to some significant artifacts that resulted from image compression/ dropped data. This one has some merit, as least as high as any other suggestion on here.
  8. Only part of the image was downloaded. This seems really unlikely, as all LORRI images we have seen so far are squares.

It's entirely possible none of these is correct as well. Bottom line, why was this image selected as one of the top 3 high resolution Charon images (As determined without knowing at all what Charon looked like), and why did so little of it come through in the image?

  • 3
    $\begingroup$ Some additional possible explanations: - Image was received partially corrupt, and we're seeing the part that was saved. We will get all of it on full data replay. - Image was intentionally cropped to focus on specific feature and/or complete image is a subject to embargo period on science data (or some other conflict of interests). - Image is from "Fail Safe" dataset, is highly compressed, and the part missing suffered too many compression artifacts and was cropped out of it to avoid speculation on features that aren't there. Raw image in later replays won't suffer from this. $\endgroup$
    – TildalWave
    Commented Jul 17, 2015 at 2:36
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    $\begingroup$ Another possibility. They wanted to photograph the edge between light and dark in order to get the shadows that indicate the height of objects. They did not want too much of Charon beyond this region because the 'brightness' of the areas that are in full light would have blown out the photo (making the fine detail in the horizon harder to see). $\endgroup$ Commented Jul 17, 2015 at 3:06
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    $\begingroup$ I think they chose an image near the terminator because they want long shadows to estimate altitudes of mountains. And they would do an occultation of the Sun behind Charon, right? Maybe this photo is of the edge where the occultation will take place? $\endgroup$
    – LocalFluff
    Commented Jul 17, 2015 at 3:08
  • $\begingroup$ I partly agree with @TildalWave - maybe a whole square image was made, but only part of the data has been transmitted so far as the probe is still very busy on other work. So instead of transmit all three images planned in the Charon mosaic, maybe they asked for just the terminator section which would have a more photogenic look. The rest will follow. $\endgroup$
    – Andy
    Commented Jul 17, 2015 at 7:43
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    $\begingroup$ Another explanation (maybe this is the most obvious): they're giving a presentation later with more of what they've found, and are saving the full image for that anyway. Maybe they just wanted to get this one particular detail out to the press as soon as they could? $\endgroup$
    – Andy
    Commented Jul 17, 2015 at 8:28

2 Answers 2


In fact, the New Horizons team is now admitting that they missed the Pluto image, and likely Charon as well. Here's a few quotes from the Washington Post.

If you look at the first big close-up photo of Pluto, you’ll notice the shadow line, the terminator. The spacecraft wasn’t supposed to aim right there

And later on:

The New Horizons team was aiming for a rectangular box in space 90 kilometers by 60 kilometers. They hit their box, but came in a little bit high, which translated to arriving about 72 seconds early and 40 miles closer to Pluto’s surface.

It seems like they were aiming for the first pictures to be in shadowed regions, but not at the edge. In Pluto's case, they missed a bit and had the terminator, in Charon's case it missed a bit more. But this was actually planned, it just resulted in less pleasing pictures to begin with. In fact, this can be seen from the recently released raw image of Charon.

enter image description here

Bottom line, the first picture wasn't in the exact optimal place, but it was in fact within the expected error box. I'm confident that when we see the raw images Friday, there will only be the small sliver we saw of Charon, with a whole lot of blank space, but that's okay. By the time all of the images come across, the entire visible portion of Pluto will have been photographed in high resolution.


LORRI images may be cropped to save bandwidth.

This figure is an example of a LORRI 1x1 image that is missing some data. In this case, the data are missing by design to reduce downlink data volume using a process called "windowing". The region of interest, also called the "window", is captured from the LORRI detector (the location of Pluto is marked), and the rest of the image is not even downlinked.

I'm not sure whether the "slice" is necessarily down the middle, or if they saved the parts that weren't downlinked. It does seem pretty certain that the terminator was the most interesting part, so that's all they scheduled for immediate downlink.

enter image description here

  • $\begingroup$ That seems unlikely for this use case, but it's possible. Hmmm... $\endgroup$
    – PearsonArtPhoto
    Commented Jul 19, 2015 at 21:48
  • $\begingroup$ Further evidence indicates this was not the answer. Still, it is interesting... $\endgroup$
    – PearsonArtPhoto
    Commented Jul 22, 2015 at 12:47

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