Starship Asterisk*

http://www.planetary.org/blog/article/00002734/ wrote:
Pluto and Charon opposition surges
The Planetary Society Blog
By Emily Lakdawalla Oct. 25, 2010

<<An awful lot of the talks in the Pluto session on Tuesday morning, October 5, at the Division of Planetary Sciences meeting spent more time focusing on how bad weather conditions were during the astronomers' attempts to view Pluto as it occulted background stars than they did on any measurements or science that came out from the data. I finally got some bloggable notes from Marc Buie's presentation on his work observing the Pluto system with Hubble. His talk was an update on what was announced earlier this year, namely that "something has fundamentally changed on the surface of Pluto" between 2000 and 2002. "Every light curve from 1954 to 2000 showed a flat light curve and dark color," he said; but "now there is significant reddening and longitudinally variable" color.

Something I hadn't appreciated before is that, because of Pluto's inclined orbit, we haven't yet seen it at zero phase. Slowly, as the years pass and Pluto's orbital motion brings it closer to the ecliptic, we on Earth can see it at lower and lower phase. Buie reported that as we are seeing Pluto at lower and lower phase, there is no visible opposition surge, and no difference in this behavior with color. However, Charon is different, and a "real surprise." Its light curve shows a strong opposition surge, with strikingly nonlinear behavior. The surge is color-dependent, "which tells me it is related to coherent backscatter, not self-shadowing," Buie said.

Just for explanation's sake, here's what a striking opposition surge looks like in an older observation of Saturn's rings:

Opposition surge of Saturn's rings

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Three views of Saturn captured on different dates with the 2.2-meter telescope at the Calar Alto Observatory in Spain. Phase angles are measured in degrees. On January 13, 2005, Earth crossed the disk of the Sun as seen from Saturn, so Earth-based telescopes saw Saturn and its rings and moons with a "phase angle" (Sun-target-observer angle) of zero degrees. The globe of Saturn does not change much in the three views, but the rings flash into brilliance as the phase angle goes to zero. This effect is called "opposition surge" and was also seen on some of Saturn's moons, especially Enceladus. Credit: Anne Verbiscer >>

http://en.wikipedia.org/wiki/Charon_%28mythology%29 wrote:
<<The name Charon is most often explained as a proper noun from χάρων (charon), a poetic form of χαρωπός (charopós), “of keen gaze”, referring either to fierce, flashing, or feverish eyes, or to eyes of a bluish-gray color. The word may be a euphemism for death. Flashing eyes may indicate the anger or irascibility of Charon as he is often characterized in literature, but the etymology is not certain.

Ann wrote:
Could the reason be that Charon is covered with much purer ice than Pluto? Pluto is really a very red planet (or minor planet), comparable in color to Mars, I think. The color of Charon is different. I've seen a color image of Pluto and Charon where Pluto looked orange and Charon was almost blue. I can think of no reason for Charon to be blue, but apparently its color is at least very different from Pluto's.

Ann wrote:
Is Charon another Enceladus, spewing plumes of ice particles into space
due to tidal interaction with Pluto?

Body    Diameter (km)    Albedo

Enceladus      504    0.99
Triton        2707    0.76
..............................
Pluto         2294    0.61
Charon        1212    0.34
Hydra           81    0.14
Nix            106    0.06

http://en.wikipedia.org/wiki/Triton_%28moon%29 wrote:
<<Triton is the largest moon of the planet Neptune, discovered on October 10, 1846 by William Lassell. It is the only large moon in the Solar System with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation. At 2700 km in diameter, it is the seventh-largest moon in the Solar System. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been captured from the Kuiper belt. Triton consists of a crust of frozen nitrogen over an icy mantle believed to cover a substantial core of rock and metal. Triton is one of the few moons in the Solar System known to be geologically active. As a consequence, its surface is relatively young, with a complex geological history revealed in intricate and mysterious cryovolcanic and tectonic terrains. Part of its crust is dotted with geysers believed to erupt nitrogen.>>

Ann wrote:
Thanks, Art. I wasn't aware of Triton's high albedo, even though it makes excellent sense
given the presence of cryovolcanoes on this moon. (That's what they are called, right?)

Ann wrote:
So Charon's albedo is only 0.34? Well, that makes it a lot brighter than our own Moon, and not that much less reflective than the Earth (whose albedo is 0.42, I believe), but it is no match for Pluto. Interesting. What makes Pluto so red and bright? And what color is Charon really? And why does it react to this "opposition surge" thing, when Pluto doesn't?

And why is Nix so dark(; i.e., albedo only 0.06)?

Is Nix another Phoebe(; i.e., albedo only 0.06)?

Ann wrote:
Love that Moon picture from a very old (French?) motion picture! Was it called "From the Earth to the Moon"? Maybe not... who directed it? Was it that guy called Lumiere or something? (I don't have the energy to google it.)

http://en.wikipedia.org/wiki/Georges_M%C3%A9li%C3%A8s wrote:
<<Georges Méliès (December 8, 1861 – January 21, 1938) was a French filmmaker famous for leading many technical and narrative developments in the earliest cinema. Before making films, he was a stage magician at the Theatre Robert-Houdin. In 1895, he became interested in film after seeing a demonstration of the Lumière brothers' camera. In 1932 Georges Méliès was awarded the Légion d'honneur (Legion of honor), which was presented him by Louis Lumière.>>

http://en.wikipedia.org/wiki/A_Trip_to_the_Moon wrote:
<<A Trip to the Moon (French: Le Voyage dans la lune) is a 1902 French black and white silent science fiction film. It is based loosely on two popular novels of the time: From the Earth to the Moon by Jules Verne and The First Men in the Moon by H. G. Wells.

The film was written and directed by Georges Méliès, assisted by his brother Gaston. The film runs 14 minutes if projected at 16 frames per second, which was the standard frame rate at the time the film was produced. It was extremely popular at the time of its release and is the best-known of the hundreds of fantasy films made by Méliès. A Trip to the Moon is the first science fiction film, and uses innovative animation and special effects, including the well-known image of the spaceship landing in the moon's eye.

Click to play embedded YouTube video.

At a meeting of astronomers, their president proposes a trip to the Moon. After addressing some dissent, six brave astronomers agree to the plan. They build a space capsule in the shape of a bullet, and a huge cannon to shoot it into space. The astronomers embark and their capsule is fired from the cannon with the help of "marines", most of which are portrayed as a bevy of beautiful women in sailors' outfits, while the rest are men. The Man in the Moon watches the capsule as it approaches, and it hits him in the eye.

Landing safely on the Moon, the astronomers get out of the capsule and watch the Earth rise in the distance. Exhausted by their journey, the astronomers unroll their blankets and sleep. As they sleep, a comet passes, the Big Dipper appears with human faces peering out of each star, old Saturn leans out of a window in his ringed planet, and Phoebe, goddess of the Moon, appears seated in a crescent-moon swing. Phoebe calls down a snowfall that awakens the astronomers. They seek shelter in a cavern and discover giant mushrooms. One astronomer opens his umbrella; it promptly takes root and turns into a giant mushroom itself. At this point, a Selenite (an insectoid alien inhabitant of the Moon, named after Selene) appears, but it is killed easily by an astronomer, as the creatures explode if they are hit with a hard force. More Selenites appear and it becomes increasingly difficult for the astronomers to destroy them as they are surrounded. The Selenites arrest the astronomers and bring them to their commander at the Selenite palace. An astronomer lifts the Chief Selenite off its throne and dashes him to the ground, exploding him. The astronomers run back to their capsule (continuing to hit the pursuing Selenites on the way). Five get inside. The sixth uses a rope to tip the capsule over a ledge on the Moon and into space. A Selenite tries to seize the capsule at the last minute. Astronomer, capsule, and Selenite fall through space and land in an ocean on Earth. The Selenite falls off and the capsule floats back to the surface, where they are rescued by a ship and towed ashore.

When originally screened, the film featured a final scene depicting a celebratory parade in honor of the travelers' return. Until recently, this scene was considered lost, and did not appear on any commercially available editions. However, a complete cut of the film was discovered in a French barn in 2002. Not only is it the most complete cut of the movie, but it is also entirely hand-colored. It was restored and premiered in 2003 at the Pordenone Silent Film Festival.

Although most of the editing in A Trip to the Moon is purely functional, there is one unusual choice: when the astronomers land on the lunar surface, the "same event is shown twice, and very differently". The first time it is shown crashing into the eye of the Man in the Moon; the second time it is shown landing on the Moon's flat terrain. The concept of showing an action twice in different ways was experimented with again by Porter in his film Life of an American Fireman, released roughly a year after A Trip to the Moon.

Some have claimed that the film was one of the earliest examples of patasphysical film, while stating that the film aims to "show the illogicality of logical thinking". Others still have remarked that the director, Georges Méliès, aimed in the film to "invert the hierarchical values of modern French society and hold them up to ridicule in a riot of the carnivalesque". This is seen as an inherent part of the film's plot: the story itself pokes fun at the scientists and at science in general, in that upon traveling to the moon, these astronomers find that the face of the moon is, in fact, the face of a man, and that it is populated by little green men.

Méliès had intended to release the film in the United States to profit from it. Thomas Edison's film technicians, however, secretly made copies of it and distributed it throughout the country. While the film was still hugely successful, Méliès eventually went bankrupt.>>

Ann wrote:

Art wrote:
And why is Nix so dark(; i.e., albedo only 0.06)?

Is Nix another Phoebe(; i.e., albedo only 0.06)?

Good question! Then again, why is the Moon so dark?

As far as I can remember, the albedo of the Moon is about 0.06.

Is Nix another Luna? Is Nix, like our Moon, a collisional product?

Ann wrote:
And maybe those very "American balls" (hmmm, that sounded really quite vulgar) resemble a moon or other, although their hues combined with their relatives sizes and albedos make it slightly difficult to figure out which moons that would be...

neufer wrote:

Ann wrote:
And maybe those very "American balls" (hmmm, that sounded really quite vulgar) resemble a moon or other, although their hues combined with their relatives sizes and albedos make it slightly difficult to figure out which moons that would be...

Well the color would suggest that the orange one is covered with tholins like Sedna:

Click to view full size image

Which would probably make the white one with the "tiger stripes" Nceladus.

But going by the name "NICKS" would suggest a member of the Pluto family.

This cutaway model shows a red “shelf” layer of a KBO peeking through the thin, darkened crust above so that the object appears red in telescopes. [i](Credit: NASA/Conceptual Image Lab/Tyler Chase)[/i]

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The sun isn't kind to objects without atmospheres. Bombarded by solar radiation, the surfaces of some comets, for example, tend to be a charred carbon-black. But the 1,000 objects so far directly imaged in the Kuiper Belt – that swath of icy bodies circling around the sun with Pluto – appear to be a wide range of colors: red, blue, and white.

With scant observations to go on – most of the Kuiper belt objects are just a single pixel of light to the Hubble Space Telescope – few hypotheses have been developed to explain the colors. But a new computer model maps out the right combination of materials and space environment that could produce some of those lovely hues. The model suggests that these objects have many layers, and that the red colors of one particularly interesting group of these objects -- the so-called Cold Classical Kuiper Belt -- could come from organic materials in the layer just under the crust.

"This multi-layer model provides a more flexible approach to understanding the diversity of colors," says John Cooper, a Heliospheric physicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "The model calculates the rate at which energy comes in from radiation and could be causing changes at different depths. So we can define different layers based on that."

The layers may have different colors, and could also be dynamic. For example, a deeper layer of relatively pure water ice could erupt upwards to form a new uppermost layer, perhaps accounting for the bright icy surface of Eris, the largest of the known Kuiper Belt objects.

Just how these bodies are composed has been a mystery ever since the first observed Kuiper Belt member, a red Cold Classical named 1992 QB1, was discovered in1992, says Cooper, who presented his model in October at the Division for Planetary Sciences meeting of the American Astronomical Society in Pasadena, Calif. Subsequent discoveries of many more objects created instant buzz not only because they helped demote Pluto from a planet to just-another-Kuiper-Belt-object, but because of the Kuiper Belt's mysterious diversity. These bodies sport not just coats of many colors, but also have different sizes and different orbits.