From the finest details to a crescent seen in 'Farewell', Cassini's parting shots of Dione
NASA's Cassini spacecraft captured this parting view showing the rough and icy crescent of Saturn's moon Dione following the spacecraft's last close flyby of the moon on Aug. 17, 2015.
Cassini obtained a similar crescent view in 2005 (see http://www.ciclops.org/view.php?id=1584 ). The earlier view has an image scale about four times higher, but does not show the moon's full crescent as this view does.
Five visible light (clear spectral filter), narrow-angle camera images were combined to create this mosaic view. The scene is an orthographic projection centered on terrain at 0.4 degrees north latitude, 30.6 degrees west longitude on Dione. An orthographic view is most like the view seen by a distant observer looking through a telescope.
The view was acquired at distances ranging from approximately 37,000 miles (59,000 kilometers) to 47,000 miles (75,000 kilometers) from Dione and at a sun-Dione-spacecraft, or phase, angle of 145 degrees. Image scale is about 1,300 feet (400 meters) per pixel.
North on Dione is up and rotated 34 degrees to the right.
" "I am moved, as I know everyone else is, looking at these exquisite images of Dione's surface and crescent, and knowing that they are the last we will see of this far-off world for a very long time to come," said Carolyn Porco, Cassini imaging team lead at the Space Science Institute, Boulder, Colorado. "Right down to the last, Cassini has faithfully delivered another extraordinary set of riches. How lucky we have been." "
“The end of a melody is not its goal: but nonetheless, had the melody not reached its end it would not have reached its goal either. A parable.” ― Friedrich Nietzsche
Still...just a few more targets to tickle our fancy and awe our intellect. Let's do this right, Cassini.
NASA's Cassini spacecraft will zip past Saturn's moon Dione on Monday, Aug. 17, 2015—the final close flyby of this icy satellite during the spacecraft's long mission. Cassini's closest approach, within 295 miles (474 kilometers) of Dione's surface, will occur at 11:33 a.m. PDT (2:33 p.m. EDT). Mission controllers expect fresh images to begin arriving on Earth within a couple of days following the encounter.
Release Date: August 14, 2015
#NASA #Space #Astronomy #Science #Saturn #Dione #Flyby
#Cassini #Planet #Moon #Orbiter #Spacecraft #Robotic #JPL #ESA
- Yay. I got my Charon craters. Now where are my ice-flow plains?
- A month ago I suggested Charon would look like Uranus's moon Ariel. Similarities pretty good so far.
- Truth is, I'm more excited to see Charon. I suspect it will look something like this.
Ariel (left) Charon (right)
My book: ,https://yadi.sk/i/AkJV6f3BfHxh2
About the Pluto https://youtu.be/mkH7CwUqWrY
Mike Brown @plutokiller
“This is the first clear evidence of faulting and surface disruption on Charon,” says McKinnon, who is based at the Washington University in St. Louis. “New Horizons has transformed our view of this distant moon from a nearly featureless ball of ice to a world displaying all kinds of geologic activity.” "
- Just back from vacation. What's all of this Pluto stuff everyone is talking about?
- The latest Pluto images remind me of early adaptive optics images of Titan: totally cool and thoroughly uninterpretable. Soon, though. Soon.
- I'd do another round of Pluto image speculation but soon we reach the intersection of speculation and information. I'll wait. Just a little.
- OK, friends, the Pluto and Charon images are good enough for a new round of speculation. Let's start here:
- The dominant feature on Pluto is the dark (but not quite continuous) equatorial band. This was nicely explained in 1996 in a paper by Hansen and Paige who showed how nitrogen evaporates from the warm equatorial regions and reaccumulates at the poles, leaving dark substrate behind. Dark substrate is probably tholins. Tholins = organic muck (sorry @PlanetDr).
- Q1: Why is the dark equatorial band not continuous? A: No clue. The "heart" looks like the brightest spot on the surface, and its equatorial
- The heart could just be random feedback. It's bright, so reflects sunlight, so cold, so gets icy, gets brighter, gets colder, etc.
- Still, weird that it is at equator. Maybe something interesting going on there. Keep your eye out.
- North of the dark equator are the patchy tropics. Summer has started here recently, so I suspect this is where ice is currently evaporating and going poleward. Come back in 20 years and it might look just like the equator. Again, nicely modeled in Hansen & Paige.
- Q2: What are the polygonal features? A: Not polygons. Seems unlikely any physical process could form large scale linear features of that sort. Your eye is good at playing tricks on you. I suspect that on the nicely imaged side you'll see no giant polygons.
- Conclusions: even at this range it is really really hard to learn details of what is going on here. Recommendation? Go closer.
- OK, what about Charon? Still too low detail. I want craters, damnit. And I want them now. But I will have to wait.
- On Charon the brightest spots are likely to be ammonia rich water ice flows. Dark spots not dark, just lack of water flows.
- Even now, that's about all I can say. Amazing how fast this is all going to come and go and how much we will wish we saw but didn't.
I mentioned this on Twitter and wanted to mention it here ...
It's possible that the strange distribution of very dark and very light on Pluto is a result of the kind of thermal runaway effect that has made Saturn's moon Iapetus, shown here, look the way it does. Regions that began life as slightly darker, and/or receive more direct sunlight, will grow even more so over time with the vaporization, and hence removal, of ice ... a process we know is happening on Pluto.
This effect can work really well if the ice is not pure ice but has dark impurities in it, as older Pluto ice most certainly does, and there are differences in slopes that result in differential solar heating, and the body is a slow rotater. All conditions are likely present at Pluto.
If some vaporized material remains bound to Pluto, it will eventually condense on the coldest place on the body, making that region brighter. If this happens over billions of years, it could result in a large ice deposit. Those colder locations may be, at this moment, the 'heart', which is on the anti-Charon facing hemisphere and is not receiving what little heat there may be to receive from Charon, as well as the un-solar-illuminated hemisphere of Pluto, which we haven't seen yet, and regions that are not so directly facing the sun.
Science on the fly ... as it happens and maybe totally wrong! We shall see.
Links to Iapetus picture captions:
Hi Res mostly-black view: http://www.ciclops.org/view.php?id=3764
Hi Res mostly-white view: http://www.ciclops.org/view.php?id=3786
Full body view: http://www.ciclops.org/view.php?id=3787
- Here's a figure from that 1996 Hansen & Paige paper showing how Pluto's surface ices move around with time.
- In the fig, the solid line shows the latitude of the sun w/time, the dark regions show where the ice has evaporated, white is ice.
- We're approaching the 2029 summer solstice after which most of the northern ices might have headed south. Process already starting now.
Squiggly, discontinuous white 'line' from mid-left to lower-right reminds me of lower boundary of Triton's polar cap.
Carolyn C. Porco (born March 6, 1953) is an American planetary scientist known for her work in the exploration of the outer solar system, beginning with her imaging work on the Voyager missions to Jupiter,Saturn, Uranus and Neptune in the 1980s. She leads the imaging science team on the Cassinimission currently in orbit around Saturn. She is also an imaging scientist on the New Horizons mission launched to Plutoon January 19, 2006. She is an expert on planetary rings and the Saturnian moon, Enceladus.
She has co-authored over 120 scientific papers on subjects ranging from the spectroscopy of Uranus and Neptune, the interstellar medium, thephotometry of planetary rings, satellite/ring interactions, computer simulations of planetary rings, the thermal balance of Triton’s polar caps, heat flow in the interior ofJupiter, and a suite of results on the atmosphere, satellites, and rings of Saturn from the Cassini imaging experiment.
Porco was responsible for the epitaph and proposal to honor the late renowned planetary geologistEugene Shoemaker by sending hiscremains to the Moon aboard theLunar Prospector spacecraft in 1998.
A frequent public speaker, Porco has given two popular lectures at TED as well as the opening speech for Pangea Day, a May 2008 global broadcast coordinated from six cities around the world, in which she described the cosmic context for human existence. Porco has also won a number of awards and honors for her contributions to science and the public sphere; for instance, in 2008 she was named by Wired magazine as one of '15 People the Next President Should Listen To.' In 2009, New Statesman named her as one of 'The 50 People Who Matter Today.' In 2010 she was awarded the Carl Sagan Medal, presented by the American Astronomical Society for Excellence in the Communication of Science to the Public. And in 2012, she was named one the 25 most influential people in space by TIME magazine.
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