Keck AO photo of Pluto system, Sharper than Hubble! Options

[tedstryk]

The mutual events in the 1980s were at equinox, and Pluto still is relatively close to that equinox, given its long orbit. So, just like Uranus is now roughly evenly lit in both hemispheres and showing us its equator, so is Pluto.

[jgoldader]

To call the new Keck images, at least from what has been released, "better than Hubble" is a stretch.

Well, don't forget, the claim was that the angular resolution was superior to that of HST, which is true. And that's exactly what Dave was aiming for in his project to measure the motions of Hydra and Nix.

Now, if you're referring to the level of surface brightness variation in the images, then the HST images do appear to show a whole lot more variation than the Keck images. But the Keck images are also at ~1.6 microns, not in the optical or UV like the HST images (I can't recall the wavelengths of the FOC or ACS observations). What would have been surprising is if there had been equal brightness variations in the Keck images.

And even if there had been, I don't think I'd expect the same patterns in any case. Unless my memory has failed completely, it was the fact that there are spectral features from many different ices in the K-band (H2O, CH4, CO2 are possibilities) that let Cruikshank & others demonstrate the presence of different ices on Pluto's surface, so when you get out into the IR, the composition of the surface ices, not just the albedo of the ices, would begin to play a significant role.

Jeff

[ustrax]

Well, don't forget, the claim was that the angular resolution was superior to that of HST, which is true. And that's exactly what Dave was aiming for in his project to measure the motions of Hydra and Nix.

You are right Jeff, the objective was, as Tholen told me, to show Nix and Hydra and the future goal is to determine their masses via the measurement of the gravitational perturbation on each other.
Also, the images haven’t been deconvolved, which means (as he explained...) that the diffraction pattern of the telescope hasn't been removed.

[stevesliva]

Well, don't forget, the claim was that the angular resolution was superior to that of HST, which is true. And that's exactly what Dave was aiming for in his project to measure the motions of Hydra and Nix/

He wasn't forgetting. I started the debate with the, "Sharper... but better?" query. He was answering the "better" question without disputing the sharper part. I just wanted to hear what was truly better than Hubble, but also the parts that aren't... the parts that didn't make the press release, because no one touts their limitations It's actually pretty easy to assume that, heck, Hubble's 17 years old, there must be better telescopes in all regards. But we have to keep reminding the people politicians that write the checks for orbiting observatories that it's still not so easy to replace them on earth.

[JRehling]

I just wanted to hear what was truly better than Hubble, but also the parts that aren't... the parts that didn't make the press release, because no one touts their limitations

It's also a matter of whether or not the analysis of these images is as mature, for the purpose of resolving surface details, as was the HST imagery. I've seen the raws for the HST images of Pluto, and they ended up squeezing a lot more detail out of them than pop out in the raws.

I suspect that the "gain" -- the duration of the exposure for the image -- must be gauged differently for resolving surface features vs. for placing the locations of Nix and Hydra. There probably isn't one all-purpose right answer, so I would expect that these observations were conducted in a manner that suited their purpose, not a different purpose. That is, I would guess that the images of Pluto and Charon are at least somewhat "washed out" and that the detail that might have been had with shorter exposures may be unrecoverable. Which is fine; if AO can match or best the best HST/occultation maps, then that can happen on a different occasion.