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New Hubble Images Show Pluto is Changing

New images of Pluto from the Hubble Space Telescope. Credit: NASA, ESA, and M. Buie (Southwest Research Institute).

Pluto-philes (and astronomers, too) have always bemoaned the fact that the best image of the principal dwarf planet wase just a fuzzy, pixelized haze. Bemoan no more. The most detailed look to date of the entire surface of Pluto has been constructed from hundreds of images taken by the Hubble Space Telescope. The images were taken during 2002 to 2003, and it took four years of computer crunching and software tweaking to create the global images. Surprisingly, the images show Pluto changed noticeably during the two-year photo shoot; the dwarf planet’s color became “redder,” and astronomers could see Pluto’s ice sheets were shifting.

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“These Hubble pictures represent a true-color appearance of what you would see if you were near Pluto, comparable to looking at our own Moon with the naked eye,” said principal investigator Marc Buie of the Southwest Research Institute. “We now know we’re looking at something that has the biggest surface changes of any object in our solar system.”

The pictures show nitrogen ice growing and shrinking, getting brighter in the north and darker in the south.

Buie and planet hunter Mike Brown from Caltech introduced the Hubble images during a teleconference with reporters today, and emphasized how surprised they were with the changes seen on Pluto in just a relatively short period of time. Even accounting for seasonal changes, seasons can last 120 years in some regions of Pluto.

The top picture was taken in 1994 by the European Space Agency's Faint Object Camera. The bottom image was taken in 2002-2003 by the Advanced Camera for Surveys. The dark band at the bottom of each map is the region that was hidden from view at the time the data were taken. Credit: NASA, ESA, and M. Buie (Southwest Research Institute)

They said the images underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes. While they believe the changes are driven by the seasons, it may mostly come from how quickly things can change on Pluto. The seasons are propelled as much by the planet’s 248-year elliptical orbit as its axial tilt — unlike Earth where the tilt alone drives seasons. On Pluto spring transitions to polar summer quickly in the northern hemisphere because Pluto is moving faster along its orbit when it is closer to the Sun.

“If Earth had such an extreme orbit, and we were experiencing a nice springtime day with 60-70 degree F temperatures, as the orbit changed it could suddenly drop to -90 degrees F,” said Brown.

There is also a mysterious bright spot on the center of Pluto, which has been observed in earlier images. But the spot is unusually rich in carbon monoxide frost.

Click here to see a video of Pluto rotating.

The astronomers said Pluto is so small and distant that the task of resolving the surface is as challenging as trying to see the markings on a soccer ball 40 miles away. Buie said we won’t have a better look at Pluto until the New Horizon’s spacecraft is six months away from the dwarf planet in 2015.

The images were taken with the Advanced Camera for Surveys on HST, and the 348 images taken in 2002 and 2003 were the last ones taken of Pluto with high enough resolution to be useful. “I had time allocated two years ago to look at Pluto, which came just three or four weeks after the high resolution camera failed,” Buie. “That was very disappointing.”

But the images do show Pluto is significantly redder than it had been for the past several decades. Astronomers use the word “red” to mean it reflects more red light than blue or green light. To the human eye, Pluto has a yellowish-orange color, and is about 20% redder than it used to be. “It’s not as red as the surface of Mars, but more red than Io,” Buie said.

Red is usually associated with carbon. The astronomers said there is also methane, which is not usually stable in an environment like Pluto’s.

“This business about the color change had me scared for awhile,” Buie confessed. “I got the result years ago, but it was so hard to understand and believe. I’m still nervous about it. It could be that I completely screwed this up, but I can tell you Charon is on the same images, and Charon has the same color throughout but Pluto changed. I don’t’ know how the camera system on HST could have given me the wrong colors on Pluto.”

This was previously the best image of Pluto, taken in 2000 by HST. Credit: Eliot Young (SwRI) et al., NASA

Someone suggested that Pluto is reddening because of its recent demotion from full planethood. “Yes, people have said that Pluto is mad at me,” said Brown, who has the nickname of the “Pluto killer” because he discovered other Kuiper Belt objects which led to the new class of dwarf planets.

“For a long time Pluto was this lonely oddball that we didn’t have anything else to compare it with,” said Brown. “Understanding this all as a new class of objects is a much more interesting way of looking at the solar system and it is quite a bit of fun, too.”

More information from Buie’s webpage on the Pluto images.

The paper about the images isn’t posted online yet, but it will be up on this webpage soon.

Source: Conference call.
Additional images and info from NASA


Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • DrFlimmer February 6, 2010, 2:55 AM

    Maybe that’s why we call them exo-planet. Another category of planet, just like dwarf planet, and means that the planet orbits another star 😉

  • laurele February 8, 2010, 10:40 AM

    @Torbjorn Larsson I strongly disagree with your statement that spherical Kuiper Belts are “glorified comets.” Spherical KBOs have less in common with comets than with the planets. They are much larger–no comet is anywhere near Pluto’s size; they are about 75 percent rock, and their orbits are far less elliptical than those of comets–they never come into the inner solar system near the Sun the way comets do. Comets lose mass every time they approach the Sun. Geological differentiation is a crucial difference as well. No comet is geologically differentiated or has active geology and weather.

    Planet formation is still poorly understood. Some of the large planets are believed to have migrated from the place they initially formed early in the solar system’s history. In one exoplanet system, a giant planet has a very comet like orbit. We cannot be certain that all types of planets formed in the same manner.

    There is no reason an object must gravitationally dominate its orbit to be considered a planet. For small planets like Pluto and Eris, the designation of dwarf planet, if made a subclass of planet, would tell us both that these objects are spherical and that they are too small to dominate their orbits. But again, that doesn’t make them not planets.

    Also, any object brought close enough to its parent star will develop a tail due to sublimation. Put Earth 30 times closer to the Sun than it is now (the equivalent of putting Pluto in Earth’s orbit), and it will develop a tail as well.

    You admit that “Of course having undergone the same differentiation process these objects share more traits with planets than their undifferentiated kins do.” Doesn’t this mean that classifying these objects with comets is problematic? Just because an object has one or two characteristics of another object doesn’t make it that object (i.e. the large exoplanet in a comet like orbit around its star is not a comet). Blurring such important distinctions is a disservice in any definition.

  • Paul Eaton-Jones February 10, 2010, 2:00 AM

    Surely seasons are dependant on axial tilt not proximity to the sun. So whether or not Pluto is moving towards perihelion or aphelion that doesn’t determine its “spring” or “autumn”, does it? Or does it depend on where the observer is on the surface of the object? Earth is at perihelion in early January and we in th enorth call it winter while my relatives in Aus and NZ call it summer.