APOD: Pluto in Enhanced Color (2021 Aug 01)

[APOD Robot]

Pluto in Enhanced Color

Explanation: Pluto is more colorful than we can see. Color data and high-resolution images of our Solar System's most famous dwarf planet, taken by the robotic New Horizons spacecraft during its flyby in 2015 July, have been digitally combined to give an enhanced-color view of this ancient world sporting an unexpectedly young surface. The featured enhanced color image is not only esthetically pretty but scientifically useful, making surface regions of differing chemical composition visually distinct. For example, the light-colored heart-shaped Tombaugh Regio on the lower right is clearly shown here to be divisible into two regions that are geologically different, with the leftmost lobe Sputnik Planitia also appearing unusually smooth. After Pluto, New Horizons continued on, shooting past asteroid Arrokoth in 2019 and has enough speed to escape our Solar System completely.

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[synapsomatic]

Is there an explanation of how they came up with these particular colours and what each of them indicate about the surface?

[Ann]

I said to myself, when I had first looked at the APOD without even seeing the caption, "Lovely picture of Pluto - that one must be color enhanced!". And yeah, it is - both lovely and color enhanced!

Look at the the left half of the heart, and compare its smoothness with the scraggliness of almost everything else. The APOD makes it abundantly clear that some sort of liquid must have flown over this part of Pluto, and then it froze into almost perfectly smooth ice. Near the bottom limb of the image, we can even see how the liquid overflowed its "borders" before it stopped.

Yeah! Pluto is always a looker, but it has rarely looked so good!

Ann

[bystander]

Is there an explanation of how they came up with these particular colours and what each of them indicate about the surface?

... featured enhanced color image ...

[Ann]

Is there an explanation of how they came up with these particular colours and what each of them indicate about the surface?

I don't think the colors are "false". Just "enhanced".

Some parts of Pluto are very dark. Note that the darkest parts of Pluto look reddish in this image. The color is real, but very subtle. Without color enhancement, the darkest part of Pluto may just have looked very dark grayish brown.

At upper right, some parts look peach-colored and some look almost bluish. I think the colors are real, but extremely faint, and without color enhancement the whole area may just have looked pale beige.

I think that the dominant hue of Pluto is beige, which is to say it is very slightly reddish. The most dramatic differences have to do with the darkness or "lightness" of different parts of Pluto.

The way I understand it, some moons, asteroids and other bodies in the Solar system become darker and redder when they are exposed to ultraviolet light from the Sun. The darkening and reddening effect is - or so I think - cumulative, so that rocky and icy bodies grow darker and redder over time.

If that is true, then Pluto's "heart" is so light-colored because this part of Pluto has recently been resurfaced with fresh ice. The darkest parts may be very old.

These two global images of Iapetus show the extreme brightness dichotomy on the surface of this peculiar Saturnian moon. The left-hand panel shows the moon's leading hemisphere and the right-hand panel shows the moon's trailing side. Credit: NASA/JPL-Caltech/Space Science Institute.

---

Alternatively, just maybe the dark parts of Pluto have been literally hit by dark glop from Charon, its large and quite nearby moon. Dark parts of Iapetus, one of Saturn's moons, have presumably been covered by dark material shed by other moons of Saturn. If - and that's a big if - the dark parts of Pluto are dark because they have acquired material from Charon, then this must have happened long ago, and several episodes of resurfacing of other parts of Pluto must have happened since then.

Ann

[JohnD]

Ann makes a case for the Sputnik Platina having been liquid at some time. Does this ignore the abilty of some 'solid' substances to flow over long periods of time? Such as shown by the U of Queensland's Pitch Drop experiment?

And, I note Crater Elliot, and some parallel surface cracks, the Virgil Fossae, in the bottom left quarter (no idea of north or south!) of the picture. One end of the Fossae pases into, or is overlaid, by Elliot. The Fossa enlarges as it approaches the crater, exactly as liquid draining from the Fossae into the crater would erode the sides, widening the channel.

Similar "water erosion" features have been seem on Mars, but I don't believe that liquid water can ever have existed on Pluto. So it can't be liquid water, and another explanatuon must be found. Should we be looking for alternatives on Mars, too, and not falling into a 'Early Wet Mars' myth?

JOhn

[orin stepanek]

Ah! Beautiful Pluto! Maybe small in stature, but large in geology! I'd
rate Pluto 2'nd in beauty and Saturn 3'rd! Mother Earth 1'st; of
coarse!

Pluto in a minute! Love her narrations!
https://www.youtube.com/channel/UC7yXXC ... 2gNWETiygA

[neufer]

And, I note Crater Elliot, and some parallel surface cracks, the Virgil Fossae, in the bottom left quarter of the picture. One end of the Fossae pases into, or is overlaid, by Elliot. The Fossa enlarges as it approaches the crater, exactly as liquid draining from the Fossae into the crater would erode the sides, widening the channel. Similar "water erosion" features have been seem on Mars, but I don't believe that liquid water can ever have existed on Pluto. So it can't be liquid water, and another explanation must be found.

Click to play embedded YouTube video.

Doom Mons, one of the most reliably identified cryovolcanoes on Saturn's moon Titan

---

<<A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock. Collectively referred to as cryomagma, cryolava or ice-volcanic melt, these substances are usually liquids and can form plumes, but can also be in vapor form. After the eruption, cryomagma is expected to condense to a solid form when exposed to the very low surrounding temperature. Cryovolcanoes may potentially form on icy moons and other objects with abundant water past the Solar System's snow line (such as Pluto).

In 2007, observations by the Gemini Observatory showing patches of ammonia hydrates and water crystals on the surface of Pluto's moon Charon suggested the presence of active cryovolcanoes or cryogeysers. Subsequent observations by New Horizons in 2015 found that Charon has a youthful surface, supporting this idea. Pluto itself has two features that have been identified as possible cryovolcanoes, being mountains with indented peaks. A 2019 study identified a second likely cryovolcanic structure around Virgil Fossae, a series of troughs in northeastern Cthulu Macula, west of Tombaugh Regio. Ammonia-rich cryolavas appear to have erupted from Virgil Fossae and several nearby sites and covered an area of several thousand square kilometers; the fact that the ammonia's spectral signal was detectable when New Horizons flew by Pluto suggests that Virgil Fossae is no older than one billion years and potentially far younger, as galactic cosmic rays would destroy all the ammonia in the upper meter of the crust in that time and solar radiation could destroy the surface ammonia 10 to 10000 times more quickly. The subsurface reservoir from which this cryomagma emerged may have been separate from Pluto's subsurface ocean.

One potential energy source on some solar system bodies for melting ices and producing cryovolcanoes is tidal friction. Translucent deposits of frozen materials create a subsurface greenhouse effect that would accumulate the required heat. Signs of past warming of the Kuiper belt object Quaoar have led scientists to speculate that it exhibited cryovolcanism in the past. Radioactive decay could provide the energy necessary for such activity, as cryovolcanoes can emit water mixed with ammonia, which would melt at 180 K and create an extremely cold liquid that would flow out of the volcano.

Indirect evidence of cryovolcanic activity was later observed on several other icy moons of the Solar System, including Europa, Titan, Ganymede, and Miranda. Cassini has observed several features thought to be cryovolcanoes on Titan, notably Doom Mons with adjacent Sotra Patera, a feature regarded as "the very best evidence, by far, for volcanic topography anywhere documented on an icy satellite." Cryovolcanism is one process hypothesized to be a significant source of the methane found in Titan's atmosphere.

In September 2016, NASA JPL and NASA Goddard scientists released findings that the large Ahuna Dome on Ceres is a "volcanic dome unlike any seen elsewhere in the solar system. [The large] mountain is likely volcanic in nature. Specifically, it would be a cryovolcano -- a volcano that erupts a liquid made of volatiles such as water, instead of silicates. ... the only known example of a cryovolcano that potentially formed from a salty mud mix, and that formed in the geologically recent past." In addition, at least some of Ceres' well-known bright spots (notably including the ones in Occator crater) are likely also cryovolcanic in origin. A study published in March 2017 suggests that Occator's most recent large eruption occurred about 4 million years ago and thus that Ceres may still be active.>>

[Ann]

And, I note Crater Elliot, and some parallel surface cracks, the Virgil Fossae, in the bottom left quarter of the picture. One end of the Fossae pases into, or is overlaid, by Elliot. The Fossa enlarges as it approaches the crater, exactly as liquid draining from the Fossae into the crater would erode the sides, widening the channel. Similar "water erosion" features have been seem on Mars, but I don't believe that liquid water can ever have existed on Pluto. So it can't be liquid water, and another explanation must be found.

Click to play embedded YouTube video.

Doom Mons, one of the most reliably identified cryovolcanoes on Saturn's moon Titan

---

<<A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock. Collectively referred to as cryomagma, cryolava or ice-volcanic melt, these substances are usually liquids and can form plumes, but can also be in vapor form. After the eruption, cryomagma is expected to condense to a solid form when exposed to the very low surrounding temperature. Cryovolcanoes may potentially form on icy moons and other objects with abundant water past the Solar System's snow line (such as Pluto).

In 2007, observations by the Gemini Observatory showing patches of ammonia hydrates and water crystals on the surface of Pluto's moon Charon suggested the presence of active cryovolcanoes or cryogeysers. Subsequent observations by New Horizons in 2015 found that Charon has a youthful surface, supporting this idea. Pluto itself has two features that have been identified as possible cryovolcanoes, being mountains with indented peaks. A 2019 study identified a second likely cryovolcanic structure around Virgil Fossae, a series of troughs in northeastern Cthulu Macula, west of Tombaugh Regio. Ammonia-rich cryolavas appear to have erupted from Virgil Fossae and several nearby sites and covered an area of several thousand square kilometers; the fact that the ammonia's spectral signal was detectable when New Horizons flew by Pluto suggests that Virgil Fossae is no older than one billion years and potentially far younger, as galactic cosmic rays would destroy all the ammonia in the upper meter of the crust in that time and solar radiation could destroy the surface ammonia 10 to 10000 times more quickly. The subsurface reservoir from which this cryomagma emerged may have been separate from Pluto's subsurface ocean.

One potential energy source on some solar system bodies for melting ices and producing cryovolcanoes is tidal friction. Translucent deposits of frozen materials create a subsurface greenhouse effect that would accumulate the required heat. Signs of past warming of the Kuiper belt object Quaoar have led scientists to speculate that it exhibited cryovolcanism in the past. Radioactive decay could provide the energy necessary for such activity, as cryovolcanoes can emit water mixed with ammonia, which would melt at 180 K and create an extremely cold liquid that would flow out of the volcano.

Indirect evidence of cryovolcanic activity was later observed on several other icy moons of the Solar System, including Europa, Titan, Ganymede, and Miranda. Cassini has observed several features thought to be cryovolcanoes on Titan, notably Doom Mons with adjacent Sotra Patera, a feature regarded as "the very best evidence, by far, for volcanic topography anywhere documented on an icy satellite." Cryovolcanism is one process hypothesized to be a significant source of the methane found in Titan's atmosphere.

In September 2016, NASA JPL and NASA Goddard scientists released findings that the large Ahuna Dome on Ceres is a "volcanic dome unlike any seen elsewhere in the solar system. [The large] mountain is likely volcanic in nature. Specifically, it would be a cryovolcano -- a volcano that erupts a liquid made of volatiles such as water, instead of silicates. ... the only known example of a cryovolcano that potentially formed from a salty mud mix, and that formed in the geologically recent past." In addition, at least some of Ceres' well-known bright spots (notably including the ones in Occator crater) are likely also cryovolcanic in origin. A study published in March 2017 suggests that Occator's most recent large eruption occurred about 4 million years ago and thus that Ceres may still be active.>>

Click to view full size image

Criminy... a rose!

Ann

[neufer]

Doom Mons, one of the most reliably identified cryovolcanoes on Saturn's moon Titan

---

Criminy... a rose!

Click to play embedded YouTube video.

Pluto's pre–New Horizons theoretical structure

---

<<Pluto's density is 1.87 g/cm³. Because the decay of radioactive elements would eventually heat the ices enough for the rock to separate from them, scientists think that Pluto's internal structure is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of water ice. Pluto's abundant surface volatiles imply that Pluto is either completely differentiated (and thus has liberated all of the volatiles that had been locked away in its water ice) or formed within less than a million years after the circumstellar disk was cleared (when volatiles were still available to be incorporated into Pluto).

The diameter of the core is hypothesized to be approximately 1700 km, 70% of Pluto's diameter. It is possible that such heating continues today, creating a subsurface ocean layer of liquid water and ammonia some 100 to 180 km thick at the core–mantle boundary. Studies based on New Horizon's images of Pluto reveal no signs of contraction (as would be expected if Pluto's internal water had all frozen and turned into ice II) and imply that Pluto's interior is still expanding, probably due to this internal ocean; this is the first concrete evidence that Pluto's interior is still liquid. Pluto is proposed to have a thick water-ice lithosphere, based on the length of individual faults and lack of localized uplift. Differing trends in the faults suggest previously active tectonics, though its mechanisms remain unknown. The DLR Institute of Planetary Research calculated that Pluto's density-to-radius ratio lies in a transition zone, along with Neptune's moon Triton, between icy satellites like the mid-sized moons of Uranus and Saturn, and rocky satellites such as Jupiter's Io.

Ice II is a rhombohedral crystalline form of ice with a highly ordered structure. It is formed from ice Ih by compressing it at a temperature of 198 K at 300 MPa or by decompressing ice V. When heated it undergoes transformation to ice III. Ordinary water ice is known as ice Ih. Different types of ice, from ice II to ice XIX, have been created in the laboratory at different temperatures and pressures. It is thought that the cores of icy moons like Jupiter's Ganymede may be made of ice II. The properties of ice II were first described and recorded by Gustav Heinrich Johann Apollon Tammann in 1900 during his experiments with ice under high pressure and low temperatures. Having produced ice III, Tammann then tried condensing the ice at a temperature between −70 and −80 °C under 200 MPa (2,000 atm) of pressure. Tammann noted that in this state ice II was denser than he had observed ice III to be. He also found that both types of ice can be kept at normal atmospheric pressure in a stable condition so long as the temperature is kept at that of liquid air, which slows the change in conformation back to ice Ih. In later experiments by Bridgman in 1912, it was shown that the difference in volume between ice II and ice III was in the range of 0.0001 m³/kg. This difference hadn't been discovered by Tammann due to the small change and was why he had been unable to determine an equilibrium curve between the two. The curve showed that the structural change from ice III to ice II was more likely to happen if the medium had previously been in the structural conformation of ice II. However, if a sample of ice III that had never been in the ice II state was obtained, it could be supercooled even below −70 °C without it changing into ice II. Conversely, however, any superheating of ice II was not possible in regards to retaining the same form. Bridgman found that the equilibrium curve between ice II and ice IV was much the same as with ice III, having the same stability properties and small volume change. The curve between ice II and ice V was extremely different, however, with the curve's bubble being essentially a straight line and the volume difference being almost always 0.0000545 m3/kg.>>

[ta152h0]

Next stop, Sagitarius A? pass the ice cold one

[neufer]

Next stop, Sagitarius A? pass the ice cold one

• The Sun orbits Sagitarius A at a velocity of ~220 km/s.
  
  New Horizons is traveling at a mere ~14 km/s relative to the Sun;
  therefore, NH orbits Sagitarius A in much the same fashion as the Sun, itself.

[JohnD]

Thank you, neufer, and Ann for the tutorial on cryovolcanism!
But I repeat - there is no possibilty of liquid water on the surface of Pluto, or of amonia in liquid form, or methane either, when the appearance of the Virgil Fossae as it approaches Elliot resembles an eroded water channel. Ice II or III will change phase to normal Ice 1 if the pressure on it is released, becoming normal ice vapour or a solid.

Not withstanding recent reports of "Flexible Water Ice" https://www.newscientist.com/article/22 ... -breaking/ this is also in a very special and specific situation, of long single crystals of ice, micrometers wide. Sure, like pitch, Ice 'flows', else we would not have glaciers on Earth, but they produce a distinctive erosion pattern which is different from flowing water.

I repeat, when a flowing liquid is impossible, do we need to work out a different geological mechanism for such patterns, and not just assume warm, wet aeons in earlier times? Otherwise, Solar System models that have suggested that our gas giants formed nearer to the Sun must assume that Pluto did so too!
John

[neufer]

But I repeat - there is no possibilty of liquid water on the surface of Pluto, or of amonia in liquid form, or methane either, when the appearance of the Virgil Fossae as it approaches Elliot resembles an eroded water channel. Ice II or III will change phase to normal Ice 1 if the pressure on it is released, becoming normal ice vapour or a solid. Not withstanding recent reports of "Flexible Water Ice" https://www.newscientist.com/article/22 ... -breaking/ this is also in a very special and specific situation, of long single crystals of ice, micrometers wide. Sure, like pitch, Ice 'flows', else we would not have glaciers on Earth, but they produce a distinctive erosion pattern which is different from flowing water. I repeat, when a flowing liquid is impossible, do we need to work out a different geological mechanism for such patterns, and not just assume warm, wet aeons in earlier times? Otherwise, Solar System models that have suggested that our gas giants formed nearer to the Sun must assume that Pluto did so too!

Click to play embedded YouTube video.

There is no possibilty of liquid (800 to 1,200 °C) magma flowing on the surface of our cool (−98 to 57 °C) Earth.

When a flowing liquid is impossible, we need to work out a different geological mechanism for such patterns, and not just assume a hot aeons in earlier times. Solar System models that have suggested that our gas giants formed nearer to the Sun must assume that Earth did so too!

[JohnD]

Good point, neufer! Nicely made!
And lava tubes are a feature of both Earthly and Lunar geology. So, perhaps a coating of ice over a flowing river of water?

BUT! Look at the shape of the Virgil Fossa as it approaches Elliot (click on my pic above for an enlarged version)
The Fossae are jagged rifts, that clearly have opened and could release gas or liquid. As the rift approaches the crater, its walls become widened, rounded and smoothed, as would a channel carrying a liquid. No sign of a roof, or any residue (unless the orange stripe is that) so whatever flowed, flowed all away, or evaporated.

Lava tube maps that I can find online tend to have parallel walls. See: https://www.researchgate.net/figure/Map ... _257557579 for an example.
JOhn

[neufer]

Good point, neufer! Nicely made!
And lava tubes are a feature of both Earthly and Lunar geology. So, perhaps a coating of ice over a flowing river of water?

BUT! Look at the shape of the Virgil Fossa as it approaches Elliot (click on my pic above for an enlarged version)
The Fossae are jagged rifts, that clearly have opened and could release gas or liquid. As the rift approaches the crater, its walls become widened, rounded and smoothed, as would a channel carrying a liquid. No sign of a roof, or any residue (unless the orange stripe is that) so whatever flowed, flowed all away, or evaporated.

Lava tube maps that I can find online tend to have parallel walls. See: https://www.researchgate.net/figure/Map ... _257557579 for an example.

Click to play embedded YouTube video.

Mars Global Surveyor image showing lava flows of different ages at the base of Olympus Mons. The flat plain is the younger flow. The older flow has lava channels with levees along the edges. Levees are quite common to lava flows on Mars.

---

<<Olympus Mons is the result of many thousands of highly fluid, basaltic lava flows that poured from volcanic vents over a long period of time (the Hawaiian Islands exemplify similar shield volcanoes on a smaller scale). Like the basalt volcanoes on Earth, Martian basaltic volcanoes are capable of erupting enormous quantities of ash. Due to the reduced gravity of Mars compared to Earth, there are lesser buoyant forces on the magma rising out of the crust. In addition, the magma chambers are thought to be much larger and deeper than the ones found on Earth.

The flanks of Olympus Mons are made up of innumerable lava flows and channels. Many of the flows have levees along their margins. The cooler, outer margins of the flow solidify, leaving a central trough of molten, flowing lava. Partially collapsed lava tubes are visible as chains of pit craters, and broad lava fans formed by lava emerging from intact, subsurface tubes are also common. In places along the volcano's base, solidified lava flows can be seen spilling out into the surrounding plains, forming broad aprons, and burying the basal escarpment. Crater counts from high-resolution images taken by the Mars Express orbiter in 2004 indicate that lava flows on the northwestern flank of Olympus Mons range in age from 115 million years old (Mya) to only 2 Mya. These ages are very recent in geological terms, suggesting that the mountain may still be volcanically active, though in a very quiescent and episodic fashion.>>