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Posted by: elakdawalla Oct 12 2007, 03:38 PM

http://www.ifa.hawaii.edu/info/press-releases/PlutoPictures/Pluto-Tholen-10-07.html

"Almost 30 years after the discovery of Pluto's large moon, Charon, a University of Hawaii astronomer [David Tholen] has used a ground-based telescope to take an image of the Pluto system that exceeds the sharpness possible with the Hubble Space Telescope..."

And still at least 6 years until spaceborne telescopes will do better than groundbased adaptive optics systems...wonder if JWST (due to launch in 2013) or New Horizons (approaching Pluto in 2015) will get there first?

--Emily

Posted by: nprev Oct 12 2007, 04:13 PM

Oh, man...that is just distilled & purified cool...thanks, Emily! Gotta love Pluto's 122 deg axial tilt...

Posted by: stevesliva Oct 12 2007, 05:01 PM

Sharper... but better? I recall some albedo mapping done by Hubble...

Posted by: PDP8E Oct 12 2007, 05:39 PM

Here is the Hubble/Pluto pix
I wonder if we will be able to match this up when Pluto-Express returns ground truth?

Cheers

Posted by: ugordan Oct 12 2007, 05:45 PM

Pluto-Express?

Posted by: elakdawalla Oct 12 2007, 05:53 PM

Those Hubble albedo maps are models, based upon many observed mutual occultations of Charon and Pluto. Charon crosses a bit of Pluto -- takes out a bit of Pluto's light -- then next time it crosses on a slightly different chord -- takes out a different bit of Pluto's light -- watch enough of those and you can get a very low-resolution sense of where there may be big bright spots and big dark spots on Pluto and also Charon. I don't think any of these images actually resolve surface features on Pluto. Just remember how few pixels Hubble gets on Ceres -- then extrapolate that to Pluto's distance.

--Emily

Posted by: PDP8E Oct 12 2007, 05:54 PM

Oh Yeah...New Horizons...

Posted by: Alan Stern Oct 12 2007, 06:10 PM

Emily- The HST images definitely resolved Pluto. See the original AJ paper or the press releases. In the image above the inset is the *actual* image: see the polar caps and other spots?

Alan

Posted by: elakdawalla Oct 12 2007, 07:02 PM

Oops -- sorry! I must have been thinking of something else...

--Emily

Posted by: tedstryk Oct 12 2007, 07:07 PM

Here is one of the actual views from the FOC set that has been posted a lot (and no, I didn't do anything to it).



Additionally, here is the more recent map, in color, from Hubble's ACS HRC (images taken in 2002-2003)



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

This view, also in color, is one produced in from the 1980s mutual event data (the data that Emily was thinking about) by the team of Young, Crane, and Binzel.



This set, by Marc Buie and others (I believe Alan Stern was also involved), is also based on the mutual events. Note that because of the fact that Charon stays over the same hemisphere, only one side of Pluto and one side of Charon could be mapped. The other sides were approximated using light-curve data. The mutual-event derived data on Pluto can be seen on the left, the mutual event derived data on Charon can seen on the right.

Posted by: PhilCo126 Oct 12 2007, 07:28 PM

The never-ending discussion, (very or overwhelmingly) large ground based telescopes or space based telescopes?
Hubble has about factor 40 less light gathering power than Keck and might be a factor 10 more expensive, but Hubble has a higher annual amount of observing time.
Keck’s light gathering power allows to obtain a more precise spectrum of faint stars…
However, space-based and ground telescopes are complementary… and to conduct IR astronomy, we better take our (unmanned) telescopes into space, preferably to L2

Posted by: scalbers Oct 12 2007, 09:12 PM

Here is William Johnston's Pluto map (scroll to bottom) that does some merging of the light curve data with Hubble imagery. This is one way to get the "best of both worlds".

http://www.johnstonsarchive.net/spaceart/cylmaps.html

Posted by: Louise Sharples Oct 12 2007, 09:31 PM

Nicely separated, but no surface details, unlike the Hubble images. Colour me unimpressed.

Posted by: tedstryk Oct 12 2007, 10:12 PM

Granted, it isn't better than Hubble, but for a ground-based image of something so faint, it is quite incredible. Glib comments like this are certainly not called for.


Scalbers: That map seems to just use the general color from the mutual events data, which at any rate only cover one hemisphere.

Posted by: nprev Oct 13 2007, 12:35 AM

This is probably a dumb question (yeah, putting on my dunce hat, here), but why are the albedo maps depicted as equatorial projections? Pluto's axial tilt as I mentioned before is around 122 deg with respect to its orbit, and the Keck & Hubble images appear to give us a nearly polar view.

I know I'm missing something obvious here since its rotation period has been well-known for decades, but would appreciate enlightenment.

Posted by: tedstryk Oct 13 2007, 02:17 AM

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.

Posted by: jgoldader Oct 14 2007, 04:01 AM

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

Posted by: ustrax Oct 15 2007, 09:43 AM

You are right Jeff, the objective was, as Tholen http://spaceurope.blogspot.com/2007/10/plutos-family-portrait-with-david.html, 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.

Posted by: stevesliva Oct 15 2007, 08:16 PM

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.

Posted by: JRehling Oct 16 2007, 12:14 AM

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.