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Voyager 2 imaging of Triton
Doug M.
post Feb 4 2014, 07:31 PM
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Gorgeous. Makes you wonder if Pluto will have similar "cantelope" terrain? Some other sort of geologically active surface? Or just ancient craters on ice?

Whatever is there, we should (eventually, weeks and months after flyby) get good pictures of it -- NASA says that New Horizons will give us "images with resolution as high as 25 m/pixel, 4-color global dayside maps at 0.7 km/pixel, hyper-spectral near infrared maps at 7 km/pixel globally and 0.6 km/pixel for selected areas". The late Argo proposal for a mission to Neptune -- a flyby with a subsequent visit to a Kuiper Belt Object -- would have been basically New Horizon with a somewhat different instrument suite and 2010s technology. It would have flown as close as 200 km (!) to Triton, which would have allowed resolutions down in the tens-of-meters range.

Argo depended on a Jupiter-Saturn flyby, though -- a planetary alignment that will go away for a long time in 2020. So, probably not.


Doug M.
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john_s
post Feb 4 2014, 09:55 PM
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Couple comments:

1) I thought the crisp horizon shot of the canteloupe terrain was taken after that blurrier overlapping image, but maybe I'm mis-remembering. I guess I'm biased in favor of the horizon shot, because it's sharper, but also because I wrote the original press release caption for it, back in 1989 smile.gif .

2) I'm not sure where the 25 m/pixel number came from for the best New Horizons resolution on Pluto- the best resolution will actually be about 90 meters/pixel (much better than that best Voyager Triton image).

John
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Doug M.
post Feb 5 2014, 08:58 AM
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QUOTE (john_s @ Feb 4 2014, 11:55 PM) *
2) I'm not sure where the 25 m/pixel number came from for the best New Horizons resolution on Pluto- the best resolution will actually be about 90 meters/pixel (much better than that best Voyager Triton image).


John, that figure comes from this NASA page. The quote is from the 'Mission Profile' section:

"Flyby of Pluto will occur nominally on 14 July 2015. The encounter period begins 6 months prior to closest approach. Long range imaging will include 40 km mapping of Pluto and Charon 3.2 days out. This is half the rotation period of Pluto-Charon and will allow imaging of the side of both bodies which will be facing away from the spacecraft at closest approach. New Horizons will fly within 10000 km of Pluto at a relative velocity of 11 km/s at closest approach and will come as close as 27,000 km to Charon. During the flyby the instruments should be able to obtain images with resolution as high as 25 m/pixel, 4-color global dayside maps at 0.7 km/pixel, hyper-spectral near infrared maps at 7 km/pixel globally and 0.6 km/pixel for selected areas, characterization of the atmosphere, and radio science results. Because of the limited power available, the instruments will be duty cycled during encounter."


Doug M.


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Stefan
post Feb 5 2014, 10:59 AM
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QUOTE (john_s @ Feb 4 2014, 10:55 PM) *
1) I thought the crisp horizon shot of the canteloupe terrain was taken after that blurrier overlapping image, but maybe I'm mis-remembering. I guess I'm biased in favor of the horizon shot, because it's sharper, but also because I wrote the original press release caption for it, back in 1989 smile.gif .

That's fascinating, John, you must have been so excited at the time! Do you remember what you wrote?
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tedstryk
post Feb 5 2014, 11:43 AM
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John, is this the original caption? I'm assuming it is referring to true resolution, as the resolution in km/pixel is better than that.


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john_s
post Feb 5 2014, 08:51 PM
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Yes, and yes. I was a post-doc at the time, working with imaging team member Dave Morrison. I felt very lucky to be there- and even luckier to have also been at the Saturn and Uranus flybys, as a grad student.

That NSSDC quote is just plain wrong- the math doesn't work, given the resolution of the LORRI camera (5 microradians) and the stated encounter distance (10,000 km). Probably not worth fixing at this point, though…

John
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machi
post Feb 6 2014, 12:15 AM
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QUOTE (dtolman @ Feb 4 2014, 02:48 AM) *
Sorry - wasn't clear. I wasn't asking if we could get Voyager level resolution, I already understood that was impossible - I was wondering what telescopes now or in planning for the next 10 years had _Hubble_ comparable resolution for outer-system objects.


As Phil already said, some telescopes are already better than HST in infrared. For now best images are from Keck II and Gemini.
Keck II is even comparable in absolute terms to HST, if atmospheric conditions are good. Best resolution is then around 0.03 arcsec.
This is equivalent to 4 resolution elements across Triton disc or ~650 km at Neptune distance.
HST has same resolution in wavelength near UV/visible border. New instrument - GPI on Gemini has similar resolution.
In near future (this year?) SPHERE will be available on VLT (ESO) with peak resolution around 0.02 arcsec (6 elements across Triton's disc).


QUOTE (Doug M. @ Feb 4 2014, 10:00 AM) *
Daaah, the Webb not the Watt. Excuse me.

A new generation of ground-based Extremely Large Telescopes will come online in the next decade. Both the Thirty Meter Telescope (Hawaii) and the European Extremely Large Telescope (Chile) are currently scheduled for first light in 2022. ...
How well they'd image a moon of Neptune is beyond my limited physics, though. Anyone?

Doug M.


TMT has planned resolution better than 0.01 arcsec with IRIS camera (0.008?). This is better than 200 km at Neptune and ~10-15 resolution elements for Triton disc at best.
E-ELT will be even better. It's exoplanetary imager EPICS has planned resolution up to 5 miliarcsec. With this resolution numbers are 110 km and 25 resolution elements for Triton.

But those are results for optimal conditions. Ground telescopes are dependent on good atmospheric conditions and powerful systems of adaptive optics. And adaptive optics needs for optimal operation bright point sources of light. Bright stars are best for this but such stars are available only for small areas of sky. Modern telescopes with adaptive optics are equipped with lasers which can produce artificial stars in atmosphere. With this lasers, telescopes are not so limited in their choice of targets on the sky, but results are always worse than in case with bright natural star.

This is example how Triton might look from E-ELT EPICS under optimal conditions and how it looks now from HST (FOC camera) (both images are magnified):
Attached thumbnail(s)
Attached Image
Attached Image
 


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MarcF
post Feb 6 2014, 09:20 PM
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Even if there will be no mission to Neptune and Triton for a while, I think there might be still some discoveries to be made by using new image processing techniques of old Voyager pictures. I'm convinced that these images still hide some secrets. And we have some very talented people here. So keep going on processing them !
Best regards.
Marc.
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