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Unusually Rapid Changes on Pluto

Here’s something to consider re the recent Pluto news: The Hubble maps of the tiny world that were released yesterday show a resolution of roughly 300 miles per pixel. When New Horizons flies by Pluto/Charon in 2015, it will send images with a resolution of 300 feet per pixel. And we’ve been reminded once again that every time we look deeper into something hitherto unexplored, we’re likely to be surprised. The surprise in this case was the significant reddening of the dwarf planet and the time frame in which it occurred, a mere two years.

I thought the liveliest part of the teleconference on Pluto yesterday was Marc Buie’s response to what had appeared in his datasets. Buie (Southwest Research Institute) was looking at imagery collected by the Hubble Space Telescope from 2002 to 2003 and comparing it with the results of earlier ground-based observations, as well as with Hubble pictures taken in 1994. The dramatic reddening seems to have occurred between 2000 and 2002, even as the illuminated northern hemisphere continued to get brighter.

Asked about his reactions to the newer Hubble imagery, Buie was candid:

“The color change in such a short period had me scared, because it’s so hard to understand. I’ve been checking absolutely everything I can think of, wondering if I screwed this up somehow and got the wrong answer. If I did, I can’t find the mistake.”

Another key point: In the Hubble imagery, the color of Charon remains the same throughout, whereas the reddening of Pluto is pronounced. Have a look at the images below, which represent the most detailed view of Pluto taken to date:

Image: Hubble’s view isn’t sharp enough to see craters or mountains, if they exist on the surface, but Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto’s surface, leaving behind a dark, molasses-colored, carbon-rich residue. The center disk (180 degrees) has a mysterious bright spot that is unusually rich in carbon monoxide frost. This region will be photographed in the highest possible detail when NASA’s New Horizons probe flies by Pluto in 2015. Credit: NASA, ESA and M. Buie (SwRI).

Buie noted that the images represent his best guess at the true color appearance of the dwarf planet. The reddening seems to be caused by ultraviolet radiation from the Sun, which breaks up the methane found on Pluto’s surface and leaves behind a dark red, carbon-rich residue. The surface we’re looking at is doubtless a consequence of seasonal changes, with ice melting on the sunlit pole and refreezing on the dark, southern pole. Pluto’s elliptical orbit contributes to a relatively quick transition between spring and polar summer in the northern hemisphere. Previous observations have shown the mass of Pluto’s atmosphere doubling in the period between 1988 and 2002, evidently because of the warming and melting of nitrogen ice. Even so, this much surface change in a short period is surprising.

Kuiper belt specialist Mike Brown (Caltech) pointed out at the teleconference that the changes on Pluto are more extreme than anything previously seen in the Solar System:

“We see Pluto in these images about as well as we see the Moon with the naked eye. Now imagine the Moon changing by that much in such a short period of time. If we look around the Solar System at the surfaces we can observe, we see changes to the ice caps of Earth and Mars and that’s about it. But Pluto offers up more dramatic changes than anything else. There’s a good reason for this: The Kuiper belt features objects in extreme orbits. Right now it’s in the spring of its year, but by 2108 it will be at its furthest from the Sun. Pluto in winter will be a colder place on which things will freeze out and re-condense.”

This second image gives an idea of the brightening found in the northern hemisphere:

Image: Two Hubble photo maps of the dwarf planet Pluto, as seen in 1994 and 2002-2003. The white areas are surface frost, and the dark areas are a carbon-rich residue caused by sunlight breaking up methane that is present on Pluto’s surface. A comparison of the maps shows that Pluto’s brightness has changed between 1994 and 2003. The northern pole is brighter and the southern hemisphere is darker. Summer is approaching Pluto’s north pole, and this may cause surface ices to melt and refreeze in the colder shadowed portion of the planet. Credit: NASA, ESA and M. Buie (SwRI).

Twelve orbits of Hubble were dedicated to Pluto between 2002 and 2003, using the ACS high resolution camera to make 16 images in each of two filters, one blue, one green, for a total of 384 images. Using dithering techniques and specially developed algorithms to reconstruct a higher-resolution image, the pictures are the result of intense processing requiring twenty computers operating continuously for four years. But they won’t retain pride of place as our best photos of Pluto for long. Buie intends to use Hubble’s Wide Field Camera 3 to make additional observations before New Horizons arrives. The more the better, for the current maps are already in use for planning the brief encounter.

When New Horizons does arrive, it will only have time to photograph one hemisphere in detail. The bright spot seen in the Hubble images, known to be rich in carbon monoxide frost, is a prime target for investigation. Doubtless further surprises await.

The papers are Buie, et al., “Pluto and Charon with the Hubble Space Telescope: I. Monitoring global change and improved surface propertices from light curves,” and Buie et al., “Pluto and Charon with the Hubble Space Telescope: I. Resolving changes on Pluto’s surface and a map for Charon.” Marc Buie’s page on Pluto at SwRI has links to both. They were released on February 4, the 104th birthday of Pluto discoverer Clyde Tombaugh.


Comments on this entry are closed.

  • Gary Allen February 5, 2010, 13:50

    Is it reasonable to argue that Pluto, Charon and Triton originally came from the same Kuiper belt object? Assuming that they did then is it fair to assume that the surface of Pluto will look very similar to Triton?

  • Administrator February 5, 2010, 14:33

    I think a similarity to Triton would be likely, though how strong a case could be made for a common origin is beyond me. Maybe some of our resident astronomers can weigh in on that.

  • Jeff February 5, 2010, 15:47

    Yeah, as soon as I saw those before/after photos it reminded me of the darkening created by ejecta on the surface of Triton. New Horizons is the fastest object ever created by humans, and yet we still have over 5 years to wait before we finally get to see this stuff!

  • James M. Essig February 5, 2010, 18:51

    Hi Paul other Folks;

    I have a very strong interest in planetary geology and stellar mechanics systems because aside from the considerations of individual nuclear and atomic and molecular interactions, such systems can be significantly modeled using classical mechanical considerations such as CFD, FEA, and other numerical methods.

    Not to dwell on the above obvious situations, but with the observation of entangled systems involving only a couple of photons or atoms, it is nice to have the security of classical determinism at work at least at an effective level as such.

    We know at least one thing, regardless of our current and any future limits of our probing of sub-atomic and sub-nuclear systems, we can take solace in the fact that to the extent that we will have ever greater access of larger portions of space time and mass energy, there is virtually no limit to the number of statistical mechanical states and complexities of the ever larger systems we will have access to.

    I like to contemplate the possibilities of emergent phenomenon, such as of the huge possible varieties of biospheres, geospheres, lithospheres, atmospheres and the like of planets and moons, and the perhaps commensurately great varieties of any ETI lifeforms.

    In short, this thread on Pluto has renewed my interest in planetary geology and other planetary scale and larger phenomenon.

  • Adam February 5, 2010, 19:37

    Some kind of catastrophic interaction between Triton and Pluto/Charon has been postulated for decades, but the current opinion is that they’re representative samples of the Kuiper Belt, many of which show signs of collisional evolution into novel binary/multi-body systems. It’s possible that Triton was captured from a binary that got too close to Neptune – one body was lost, taking away the excess angular momentum so Triton could be captured.

  • Lionel February 5, 2010, 20:50

    Data from 2002/03 was under intense processing by 20 computers for 4 years! I’m surprised it takes such a vast amount of work, and impressed by the accomplishment. I’m curious though, the processing took four years but 7 or 8 have passed since the data was taken. What was happening in the other few years?

  • Adam February 6, 2010, 1:42

    Hi Jeff

    “New Horizons” is fast but it’s not the fastest ever. The drop probe from “Galileo” took that prize when it reached ~60 km/s entering Jupiter’s outer atmosphere, though it was only doing 48 km/s relative to the clouds. And “Voyager” 1 & 2 have higher hyperbolic excesses than “New Horizons”. However “New Horizons” was launched at the highest speed ever, 16.5 km/s, which was I think the closest a probe has gotten to heliocentric parabolic velocity at launch.

  • Mark February 6, 2010, 18:02

    Could it be life on Pluto? Not life as we know it of course, but some sort of cryo-life, spreading across the surface in vibrant but very cold color patterns. I’m reminded of the early pre-mariner earth-based photos of Mars when we postulated that this was due to vegetation and seasons.

    Can’t wait for New Horizons to arrive. Too bad it doesn’t carry a small coffee-can sized orbiter that it could fling off and decelerate at the last minute to get planet-wide high resolution photos.

  • James M. Essig February 6, 2010, 19:59

    Hi Folks;

    Regarding Pluto and phase changes within its atmosphere, I had the following anecdotal musings.

    We in the Mid-Atlantic states within the U.S. had a huge snow storm which ended just this late afternoon in Fairfax VA. I was re-imagining looking out the window where I am typing these comments and seeing the snow flakes fall in all the storms fury, or should I say flurry. I then went on to try to visualize all of the snow flakes accumulated in the 22 inches of new snow in my yard, and then by extention, the number of flakes that had fallen in my home town of Fairfax City VA, and then that of the surrounding Fairfax County, and finally that within the entire Mid Atlantic area which includes, the states of North Carolina, Virginia, Maryland, Delaware, New Jersey and the like and realized what it would be like to have to pick through the snow and count the flakes precisely, one by one untill I have counted all of them, the caveat being that they would some how not melt so that I could spend the next trillions of years counting them all.

    Well the number of stars within the observable universe is several orders of magnitude greater than the number of snow flakes that have fallen in the Mid-Atlantic States where 18 inches to over two feet of snow seems to have been the norm and by corrollary so is the number of planets within the observable universe. If fact, the number of stars and/or planets as such is likely greater than the total number of snow flakes that have fallen within the boundaries of what I referred to the Mid-Alantic states over the previous millenium.

    Put in such a perspective, the wealth and diversity of exo-planetary biospheres, lithospheres, hydrospheres, atmospheres, and perhaps animal, plant, and even ETI persons and civilizations that may grace our visible universe is truly amazing. For those of you who are into planetary geology and atmosphereic science as well as into exobiology, I think right here and now over the next few decades as our exoplanet detection and spectrascopic techniques are improved, you are going to have a field day. The strange behavior of Pluto turning more red and becomming brighter just points to the degree of variation and interesting things we will discover, as well as potential destinations for manned star flight.

  • Adam February 6, 2010, 20:04

    Hi Mark & All

    There was a study on using ballutes to place a lander on to Triton or Pluto during a high-speed fly-by. Too untested to have flown with “New Horizons”, but still possible for the proposed “Argo” (“New Horizons II”) mission to the Outer Planets.

    ERRATUM: I said “Galileo’s” drop-probe was the fastest, but in fact “Helios B” went faster during its perihelion in 1976 – it reached 70.22 km/s…


    …had plum forgotten about Helios, which was an early European success.

  • Gary Allen February 7, 2010, 23:43

    Adam said: “It’s possible that Triton was captured from a binary that got too close to Neptune – one body was lost, taking away the excess angular momentum so Triton could be captured.”

    Triton’s orbit is retrograde while Nereid’s orbit is prograde. Having counter orbiting moons in the same system is very unusual. Nereid probably played a role in the capture of Triton by absorbing excess angular momentum.

    Adam also said: “There was a study on using ballutes to place a lander on to Triton or Pluto during a high-speed fly-by.”

    I was involved in that study. It was a quick and dirty unfunded study that only lasted a couple days. The mass constraint of the entry vehicle, the very high entry velocity and the thinness of Pluto’s atmosphere made it immediately clear that this was a no-starter. It seemed nuts to spend all those years to get to Pluto only to do a fast flyby. Unfortunately given the constraints of the mission, there was no way we could do a survivable lander. Perhaps we should have done something useless but symbolic along the lines of putting Lenin’s portrait on the surface of Venus?

  • andy February 11, 2010, 19:38

    Having counter orbiting moons in the same system is very unusual

    Not really, all four gas giants have systems of outer irregular satellites, some of which are in retrograde orbits. Counter-rotating satellite systems around gas giant planets appears to be the norm.

    The unusual situation with Neptune is that it has a massive moon in an inclined and retrograde orbit, which suggests a capture. Note Neptune does have a system of prograde inner satellites within the orbit of Triton.

    As for Nereid being the main sink for the angular momentum during the Triton capture, the problem is that its mass is roughly 3 orders of magnitude less than that of Triton. In short, it doesn’t seem to be a particularly good candidate for braking Triton into the system.

  • Gary Allen February 12, 2010, 3:36

    andy said:
    “As for Nereid being the main sink for the angular momentum during the Triton capture, the problem is that its mass is roughly 3 orders of magnitude less than that of Triton. In short, it doesn’t seem to be a particularly good candidate for braking Triton into the system.”

    It is correct that Nereid is orders of magnitude smaller than Triton. However I originally suggested that Pluto, Charon and Triton all came from the same parent Kuiper belt object. I’ve never heard it suggested that Nereid was a Kuiper belt object. My reasoning is that Nereid was an original moon of Neptune and played a role in the breakup of the parent Kuiper belt object. There would need to be some sort of third body for capture into Neptune orbit to occur otherwise the parent Kuiper belt object would simply have passed through the Neptune system on a hyperbolic trajectory.

    Also, Andy is correct that there are other counter orbiting moons in the Solar System, e.g. Phoebe orbiting Saturn. Phoebe is also believed to be a Kuiper belt object that was somehow captured by Saturn.

  • andy February 12, 2010, 16:21

    Gary Allen: that then brings up the question of why you’d invoke Pluto-Charon as being part of the same system and not some other binary Plutino, like Orcus-Vanth. It is furthermore not entirely clear in this scenario why Triton would end up around Neptune while Pluto-Charon end up in the 3:2 resonance.

    IIRC the population of the 3:2 resonance (i.e. the Plutinos) is expected if Neptune migrated outwards, it is not particularly plausible or necessary that Pluto, Charon and Triton were once part of the same system.

  • Dan Suggs February 15, 2010, 14:31

    Could the variations in color be influenced in any way by fluctuations in the solar output reacting differently with various compounds on Pluto’s surface?

  • ljk April 21, 2011, 0:35

    Pluto May Have Comet-Like Tail

    The latest measurements of Pluto’s tenuous atmosphere indicate that it may be shaped into a comet-like tail, say astronomers

    kfc 04/20/2011

    Pluto’s has a highly elliptical orbit that takes it inside the orbit of Neptune and then out into the distant icy reaches of the Solar System.

    Astronomers have long believed that this would have important effects on the dwarf planet’s atmosphere. Their models indicate that Pluto’s atmosphere is likely to swell as it moves closer to the Sun and the poles sublimate. Later, the atmosphere should condense as it cools down.

    That should make the surface of Pluto a barren windswept land that constantly changes as it is battered by supersonic winds. Indeed, Hubble images show that Pluto’s surface has a number of interesting features that seem to be changing.

    In recent years, other evidence has emerged to back up suspicions that Pluto is more complex than astronomers initially imagined.

    Today, Jan Greaves at the University of St Andrews in Scotland and a couple of buddies reveal the details of their own study of Pluto’s atmosphere using the 15 meter James Clerk Maxwell Telescope in Hawaii.

    These guys find clear evidence of gaseous carbon dioxide at altitudes of up to four times Pluto’s radius. And they say there is significantly more of the stuff than the last time CO was detected in 2000.

    That’s strange. Pluto is currently moving away from the Sun after its closest approach in 1989 and ought to be cooling down. One explanation is that the south pole has recently come out of shadow for the first time in 120 years and for a short time may be evaporating more quickly than the north pole is condensing.

    But Greaves and co’s most interesting discovery is a small red shift in the CO spectrum indicating that Pluto’s atmosphere must be moving away from Earth in an unexpected way.

    Their tentative explanation is exciting: “The marginal CO line red-shift, if real, could indicate a flow forming into a comet-like tail directed away from the Sun,” they say.

    The thinking is that the expanding atmosphere is interacting with the solar wind and being shaped into a tail.

    That could throw the cat among the pigeons next time Pluto’s status as a planet comes up for discussion. It gives ammunition to the naysayers who can now claim that far from being a planet or even a dwarf planet, Pluto is merely a giant comet.

    Astronomers will find out more in the coming years. The world’s telescopes will be increasingly trained on Pluto as the arrival of the New Horizons mission draws near. Its flyby is scheduled for 2015.

    Ref: http://arxiv.org/abs/1104.3014: Discovery Of Carbon Monoxide In The Upper Atmosphere Of Pluto