Uranus System Imaging Options

[JRehling]

Thanks, Phil. I found a diagram showing how the uranian system was oriented at the time of the V2 flyby, but it's hard to read a 4-dimensional reality as rendered in 2 dimensions.

For each moon, at the time of V2, there was effectively a division of the moon into quadrants. Two were in sunlight. One was in uranusshine. One was in neither. Uranusshine imagery would depend upon whether or not V2 ever could see that uranusshine quadrant and furthermore took an image at that time.

Saturn and Neptune in certain ways are each more favorable for this – you can get the night sides of the moons receiving a full planetary shine rather than ~1/4 brightness. Also, Saturn is even more huge in the skies of its moons than Uranus is for its moons.

[Explorer1]

Saturn and Neptune in certain ways are each more favorable for this – you can get the night sides of the moons receiving a full planetary shine rather than ~1/4 brightness.

Unless you catch the system during one of the two equinoxes per Uranian year, though in that case an orbiter doesn't need to bother with night illumination at all since the full globe gets sunlight through one orbit and you can just target a flyby for the appropriate portion of the local day. An orbiter around 2050, the next equinox, would be ideal!

[JRehling]

Yes, all systems are equal if visited at their respective equinoxes. Temporarily, there is no difference in observation opportunities.

As noted earlier, the capabilities of ground-based telescopes will improve dramatically in the next decade, and then there's no concern about timing. The coming telescopes should be able to provide resolution for Triton (and Neptune's other moons) about as good as we see of Ganymede in this image:

https://sites.astro.caltech.edu/palomar/cur...09_wallace.html

And for the uranian moons, the resolution will be about 50% sharper.

[TrappistPlanets]

Yes, all systems are equal if visited at their respective equinoxes. Temporarily, there is no difference in observation opportunities.

As noted earlier, the capabilities of ground-based telescopes will improve dramatically in the next decade, and then there's no concern about timing. The coming telescopes should be able to provide resolution for Triton (and Neptune's other moons) about as good as we see of Ganymede in this image:

https://sites.astro.caltech.edu/palomar/cur...09_wallace.html

And for the uranian moons, the resolution will be about 50% sharper.

yay, i want to see Triton's north during equinox, hopefully the telescopes are already a thing before the neptunian equinox
by using these telescopes we can see the unseen territory of voyager, wonder will there be a another ice cap of nitrogen like on the south or would it all be cantaloupe terrain (in voyager false colors if the whole north is cantaloupe, it would all be green and the north would be white with black spots due (plumes )

so would the uranian moons be about the same resolution as Pluto from Hubble?

[HSchirmer]

Unless you catch the system during one of the two equinoxes per Uranian year, though in that case an orbiter doesn't need to bother with night illumination at all since the full globe gets sunlight through one orbit and you can just target a flyby for the appropriate portion of the local day. An orbiter around 2050, the next equinox, would be ideal!

Interesting timing, but with Uranus, as with Pluto, don't we run into the problem of ephemeral ices?
What I mean is, when Uranus and its moons are in 'rotisserie mode" and essentially 100% of the surface receives sunlight, then you're going to have a sublimation driven 'fluffed up" atmosphere.

When you've got polar only illumination, you're got an interesting possibility that a fair-fraction of the atmosphere is going to freeze out into a lump on the dark side of the moon.

So, yes at the equinoxes we'd be seeing "the entire surface" but each solstice, you'd get a new surface as the atmosphere freezes out and snows down over half the moon.

[JRehling]

so would the uranian moons be about the same resolution as Pluto from Hubble?

More than an order of magnitude better than that. The ground-based telescopes will have much better resolution than Hubble (for any given target) – an improvement of 16x is cited – and Uranus is considerably closer than Pluto.

[JRehling]

Interesting timing, but with Uranus, as with Pluto, don't we run into the problem of ephemeral ices?
[...]
So, yes at the equinoxes we'd be seeing "the entire surface" but each solstice, you'd get a new surface as the atmosphere freezes out and snows down over half the moon.

There is no known atmosphere on four of Uranus's five biggest moons. CO2 has been detected at Titania. There's no indication that it would freeze out or snow down.

Even without the ability to resolve these bodies, we can observe their light curves even with modest equipment. Unless there's a published finding that Titania shows this, I wouldn't presume that it occurs.

Even if so, we'd be seeing the sunlit portion in all cases. If something happens in the long winter night, no, we will never see that, because we're observing from the same direction as the Sun. We also didn't see that Saturn's winter polar regions are relatively blue for the same reason.

[HSchirmer]

Even if so, we'd be seeing the sunlit portion in all cases. If something happens in the long winter night, no, we will never see that,

Agreed, and accurate as always! On rethinking, I should have said two things differently.
- First, what about those 'short winter nights" when the subsolar point is almost tracing a great-circle along the Uranian moon's equator, in contrast to when the sub solar point is locked on a pole?
- Second, I should have been more precise, it's also about sublimation and deposition under exospheric conditions, not just atmospheric conditions: similar to Mercurian and Lunar craters trapping ices, even though there's no atmosphere.
Perhaps there is a sublimation / deposition driven latitude dependent 'hoarfrost line' during solstice, where ices accumulate and freeze out.
During equinox, that's a more interesting question, would there be a longitude dependent 'hoarfrost line" from sublimating ices condensing back behind the dawn?

[Antdoghalo]

I wonder how well the JWST will be able to resolve these moons.

[JRehling]

I doubt that there will be anything like this observable from Earth. We don't see it at Callisto or Iapetus. We see Mars's winter cap emerge from springtime and thaw. Titania has a trace atmosphere at best.

[JRehling]

The JWST will have about the same resolution as HST. Despite the larger aperture, longer wavelengths limit resolutions. Ground based telescopes are going to blow away the HST, and therefore JWST as well, in terms of resolution. Of course, they will be more limited in terms of observation opportunities, but with Uranus's moons, a total of about a dozen observations for each spread out over a couple of decades will completely begin and end the mapping observations that a given instrument is capable of.

The JWST's aperture will be 6.5 m.

EELT's aperture will be 39.3 m.

[TrappistPlanets]

WE NEED A URANUS ORBITER TO go to URANUS'S MOONS
ASAP (when its in equinox)

[nprev]

UMSF's own Ian R making new discoveries in old Voyager 2 data, and also making space news headlines!

Outstanding work. Your title will be upgraded shortly.

[Ian R]

Why, thank you, kind sir!! Since the article neglected to show the image itself, here it is along with an explanatory schematic:

[stevesliva]

Not the first "new images show" article that doesn't show the new images, unfortunately. Thanks for sharing!