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NASA recently published this photo taken by Juno, at a distance of about 700,000kms from Jupiter:

enter image description here

The overall quality (very grainy around the darker regions, a bit washed-out in the brighter areas, and not the greatest dynamic range even in areas that are properly exposed) and resolution of this photo seems to compare poorly against images taken from ground-based telescopes:

enter image description here

...and also from the images that we can get using Hubble:

enter image description here

...both of which would have been shot at distances of closer to 600 million kms from Jupiter.

I understand Juno will get even closer to Jupiter than it currently is, but at the moment it's nearly 1000x closer to Jupiter than Hubble/Earth-based observatories and returning images that, at best, appear to be on par with what we can accomplish using terrestrial telescopes.

Is there a reason for this (like maybe the images released were shot in a low-resolution/low-bandwidth mode that doesn't actually use the camera's full capabilities), and what sort of improvements in the image quality can be expected as Juno reaches its closest orbital altitude? If the image quality can't be expected to drastically improve, was there a reason for not equipping the mission with better imaging technology that can at least clearly eclipse what we can attain by using Earth-local resources?

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    $\begingroup$ What is the blue thing on the north pole in the third image? $\endgroup$ – user985366 Aug 29 '16 at 19:02
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    $\begingroup$ Auroras in UV light nasa.gov/feature/goddard/2016/… $\endgroup$ – user985366 Aug 29 '16 at 19:08
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    $\begingroup$ To add to the Aurora comment/question: the image in question is a composite image combining a far-UV photo from June 2016 with a visible light image take in a previous year hubblesite.org/newscenter/archive/releases/2016/24 [Incidentally, I really wish composite images like this would be prominently labelled as such when released by Hubble/Nasa/Esa etc] $\endgroup$ – user2705196 Aug 31 '16 at 18:21
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Short answer: JunoCam is not a scientific instrument; It was put onboard solely to get some neat pictures. It is not necessary for the scientific mission, and is mostly there just for public interest. You can interact with JunoCam by voting on what it takes pictures of.

Long answer: There are several reasons which combine to result in Juno only being able to take lower-quality pictures.

  1. Juno itself is spin-stabilized. It is constantly rotating, at about 2 rpm, so it cannot focus on any spot for long.
  2. According to Wikipedia, Junocam is "capable of color imaging at 1600 x 1200 pixels." This results in a resolution of 15 km/pixel. Compared to the Mars Reconnaisance Orbiter's HiRISE camera, which is able to take pictures at 0.3 m/pixel, this is not a very high resolution.
  3. The environment around Jupiter is filled with radiation. JunoCam is not inside the radiation vault, because it would be unable to take pictures. This means that JunoCam is only expected to survive about 8 orbits. The longer it orbits, the more its pictures will likely deteriorate. I recall reading an article somewhere about what this deterioration will look like, but I cannot find it anymore.
  4. At Jupiter's orbit, data rates are limited. JunoCam will only be able to return about 40 megabytes of data per orbit. This means that some quality may have to be sacrificed in order to get more pictures back.
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    $\begingroup$ @JacobKrall I suppose what I meant by that is that it is not part of the primary scientific mission. Juno would have flown with or without the camera, and it was added almost as an afterthought. $\endgroup$ – Phiteros Aug 29 '16 at 15:21
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    $\begingroup$ Because the data rate for a 20MP camera simply isn't available and that camera is radiation hardened. $\endgroup$ – Joshua Aug 29 '16 at 17:36
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    $\begingroup$ Just adding more megapixels would only make the signal to noise ratio worse. Using a physically larger sensor would require significantly larger and more massive optics. And that is completely ignoring that the amount of download bandwidth is very limited; more megapixels would directly correspond to fewer images taken. $\endgroup$ – Dan is Fiddling by Firelight Aug 29 '16 at 17:36
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    $\begingroup$ @TylerH - You have to understand "space cameras" (radiation and temperature hardened) are 1000x more expensive than what's in your phone. They are made by companies you've never heard of, and they are ridiculously expensive. Yes, the technology advances and prices come down, but cameras for spacecraft don't resemble consumer cameras at all. Most of them are hand-built from multiple off-the-shelf parts, all of which are wicked expensive. $\endgroup$ – Jasmine Aug 29 '16 at 18:29
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    $\begingroup$ @JacobKrall - That's just a sensor though. To configure that sensor into an actual camera, at the lowest cost I could find is \$4000, and that does not include support equipment like power supplies, gimbals, heaters, and software and hardware to capture the images. So, $10K easily, for one of those only suitable for use on Earth. $\endgroup$ – Jasmine Aug 29 '16 at 19:30

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