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Neptunian System Imaging
post Jul 19 2018, 07:26 AM
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Amazing image, although I hope the EELTs will do better (and faster than the next ice giant mission).

Although orbiters are badly needed to both, I wonder if cheaper New Horizons-like flybys might not be more likely
as long as there is suitable geometry for a subsequent large (spherical) TNO flyby after? So many are binaries you'd
get quite a lot of bang for the buck.

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post Jul 19 2018, 06:15 PM
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Here's a state of the art image of Ganymede using the 5m Hale Telescope.


The ELT (named changed from the previous E-ELT) will have 8 times the aperture, and Neptune is roughly 8 times more distant than Jupiter, so that indicates the resolution that will be possible for the Neptunian system and similarly distant objects such as Pluto. Of course, the ELT will not be dedicated to Neptune observations. I think we can safely say, however, that global Neptunian weather patterns can be tracked by other multi-meter telescopes from the ground and so the return-on-investment of Neptune missions decreases accordingly.

For fine detail of the planet and satellites, of course, there's no substitute for being there.

I think one of the best value propositions for Uranus/Neptune missions would be a flyby that targeted one of the larger TNOs and used the ice giants for a gravity assist on the way there. Four such missions could capture >75% coverage of selected satellites (obviously, Triton being one) and then provide an encounter of, potentially, New Horizons type value at Makemake, Haumea, etc. with great synergy in designing and manufacturing four identical craft with New Horizons legacy tech.

I don't see how a Uranus or Neptune orbiter could possibly jump the queue over many potential ambitions to closer targets of very high interest, Enceladus and Titan to name just two.
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post Aug 26 2018, 06:29 PM
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A recreated view of the Neptune system as seen by Voyager 2 at approximately 1615 UT. I picked this time because Voyager made back-to-back observations of Neptune and Triton, so the appearance of these bodies closely approximates what a simultaneous view would have looked like.

Neptune and Triton - Voyager 2

I used a wide-angle OGV shot of Neptune and a narrow-angle GV observation of Triton. I recreated the view using a Neptune Viewer plot taken at the center of the Neptune observation, and then placed the reduced-size image of Triton in the appropriate positions. The slight difference in the direction that the crescent horns point is real - their position relative to the Sun was close enough that the phase angle was different from Voyager's point of view.

There is one improvement that I can think of. Neptune's remaining "major" moons should have been present in this scene as well, but I am not sure about their visibility to an observer at Voyager 2's location. Their small size and the position of the spacecraft suggest that they would only be a pixel or two across in the wide-angle camera and most of that surface would be in darkness. I am planning to look through some Neptune images taken a couple hours later where Galatea and Thalassa are present in the frame, which should help me determine if including them in this image would be appropriate.
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