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Uranus from Saturn?
Guest_Enceladus75_*
post Oct 23 2008, 01:26 AM
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Does anyone know if Cassini has taken any images of Uranus or Neptune from Saturn? I know that they would have little scientific use but perhaps they have been taken for calibration purposes?

And if such images exist, do they resolve the disk and colour of each ice giant? Thanks!
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stevesliva
post Oct 23 2008, 02:54 AM
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It would seem that if you filter the PDS by target, no.
http://starbrite.jpl.nasa.gov/
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ugordan
post Oct 23 2008, 08:00 AM
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As far as I know, Cassini imaged neither Uranus or Neptune, unless the target was labeled as "SKY". It did image Jupiter from Saturn's distance on a couple of occasions and that's about it.

Judging by the Jupiter images there wouldn't be much to see anyway.


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dmuller
post Oct 23 2008, 10:42 AM
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I think I saw that Cassini shot an image of Alpha Centauri rising over the rings (if memory serves me right). I dont recall anything on Uranus or Neptune


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ugordan
post Oct 23 2008, 10:56 AM
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Yes, stellar occultations were performed numerous times with some well known stars over the past years. Typically I think UVIS is prime with ISS/VIMS riding along. Here's one such RGB snapshot, pre-ingress and somewhat motion smeared.

For comparison, a natural color shot of Jupiter taken from Saturn, a rough indication of the NAC resolving power (magnified 2x). Note Jupiter is still vastly closer than Uranus.


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Ken90000
post Oct 23 2008, 02:05 PM
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Another thing to consider is the location of the planets. They are basically on the otherside of The Sun throughout the Saturn mission. Cassini was probably closer to Uranus and Neptune while it was on Earth than it is now.

Galileo did image Uranus, Neptune, Saturn and Titan while orbiting Jupiter
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tasp
post Oct 23 2008, 02:05 PM
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I'm just speculating, but possible use of Uranus and/or Neptune pics might be to refine positional data on solar system objects. With the recent 15 mile Enceladus pass, it looks like Cassini's location in space is known to extreme precision, and a series of nav shots of other solar system objects would give the optical navigation team some real 'meat and potatoes' data for plying their craft.


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tedstryk
post Oct 23 2008, 02:24 PM
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QUOTE (tasp @ Oct 23 2008, 02:05 PM) *
I'm just speculating, but possible use of Uranus and/or Neptune pics might be to refine positional data on solar system objects.

No.


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ugordan
post Oct 23 2008, 02:47 PM
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QUOTE (tasp @ Oct 23 2008, 04:05 PM) *
it looks like Cassini's location in space is known to extreme precision

We know Earth's position with even greater accuracy. How does Cassini position w/respect Saturn help with other solar system objects?


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IM4
post Oct 23 2008, 03:29 PM
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QUOTE
Does anyone know if Cassini has taken any images of Uranus or Neptune from Saturn? I know that they would have little scientific use but perhaps they have been taken for calibration purposes?


Neither Uranus or Neptune. Pluto was imaged recently:

http://adsabs.harvard.edu/abs/2008DPS....40.3601H
QUOTE
Sequence planning for the New Horizons flyby of Pluto on 2015 July 14 requires an accurate estimation of the surface scattering properties at high solar phase angles ( 90 deg). As seen from the Earth, however, the solar phase angle of Pluto never exceeds 1.9 deg. We are fortunate to have been afforded the opportunity to begin to regularly integrate Cassini-ISS imaging of Pluto into Cassini Optical Navigation (Op-Nav) sequencing. We report on space-based photometric observations of Pluto on the following dates, with the solar phase angles listed in parenthesis: 2007 March 31 (11.94 deg), 2008 March 01 (13.63 deg), 2008 July 09 (14.21 deg). Additional Cassini Op-Nav imaging of Pluto was scheduled for 2007 September 12 and 2007 October 05 but were lost due to spacecraft safing and a data overrun event, respectively. Reduction of the Op-Nav imaging of Pluto is made complex by the extremely dense stellar background: near-simultaneous observations of the Pluto fields at the JPL Table Mountain Observatory (TMO) 0.6-meter telescope allows for proper subtraction of faint background sources. Combined data from Cassini-ISS and TMO data gives a preliminary phase coefficient in the R band of Beta = 0.06 +/- 0.02 mag per deg. We shall present results that incorporate a more detailed analysis. In order to constrain potential volatile transport on the surface of Pluto due to changing solar illumination geometry and heliocentric distance, we have recently measured (2007 October-2008 March) a Bessel R-band rotational lightcurve of the planet at TMO which exhibits a lightcurve amplitude of 0.15 +/- 0.02 mag. We shall compare our new lightcurve to historical Pluto lightcurve measurements and to the expected secular lightcurve changes based on the HST albedo map.

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dmuller
post Oct 23 2008, 03:39 PM
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QUOTE (Ken90000 @ Oct 24 2008, 01:05 AM) *
Another thing to consider is the location of the planets. They are basically on the otherside of The Sun throughout the Saturn mission. Cassini was probably closer to Uranus and Neptune while it was on Earth than it is now

Indeed: http://www.heavens-above.com/solar-escape.asp


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tasp
post Oct 23 2008, 05:51 PM
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QUOTE (ugordan @ Oct 23 2008, 09:47 AM) *
We know Earth's position with even greater accuracy. How does Cassini position w/respect Saturn help with other solar system objects?




Triangulation from such a baseline would seem to be a surveyors dream. Perhaps I am overlooking something ??


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ugordan
post Oct 23 2008, 06:11 PM
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For all intents and purposes the position of the planets is known to a good enough degree of accuracy. Even if you really nailed their location now, the orbit perturbations would soon swamp your future predictions I'd say.
For planetary flybys, there's always an optical navigation campaign you can rely on on approach which gives you accuracy when you really need it, rather than extrapolating from a past, accurate snapshot.


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