Hubble catches Pluto red-faced

By Phil Plait | February 4, 2010 1:07 pm

Pity poor Pluto. The debate over its planethood has caused much consternation over the years. Part of the problem is that it’s so dinky and so far away! If it were closer, or bigger, we almost certainly wouldn’t be having this debate.

But whether or not you think Pluto should be part of the gang or not, one thing is certain: it’s a world unto itself. And to bring this point literally home, the Hubble Space Telescope has revealed the changing face of this tiny iceball:


These images, just released today (but taken in 2002), represent the most detailed surface map of Pluto ever taken. Even in Hubble’s Advanced Camera for Surveys Pluto is only a few pixels across, but it’s possible using sophisticated image processing techniques to tease out the detail seen.

Here’s a nifty animation of Pluto rotating using these maps:

Very cool. But these maps are more than just eye candy. They show significant changes on Pluto’s surface since the last maps were made using Hubble 16 years ago. Pluto’s north pole is brighter and the south pole darker, implying that material has migrated from one pole to the other, or at least that the poles are changing in different ways. Pluto orbits the Sun "on its side", dramatically more tilted than Earth’s mere 23.5°. Right now, the north pole of the world is facing the Sun, meaning it’s summer on Pluto’s northern hemisphere (as it’ll remain for a long time, given Pluto’s 248 Earth-year long year).

Not only that, these images show that Pluto has reddened quite a bit in the past few years. This is one reason it took so long to release the images; Marc Buie, the astronomer who took them, saw some things in the data that were difficult to understand, and wanted to make sure they were correct. These images are composites of pictures taken using a blue and a green filter. During the time these observations were made, in 2000 – 2002, Pluto got much darker in blue, which was unexpected. Pluto’s moon, Charon, did not get any bluer, indicating that the cause was something intrinsic to Pluto and not that something weird happened with Hubble.

So why is Pluto redder now? That’s not clear. In general, ultraviolet light from the Sun interacts with the chemicals on Pluto, creating reddish organic molecules; this is seen on lots of distant, icy objects in the Kuiper Belt (the region past Neptune where Pluto orbits). Incredibly, even at the numbing distance of over 4 billion kilometers (3 billion miles) from the Sun, Pluto is still strongly affected by it. But this is happening while overall the northern hemisphere got brighter and the southern darker. You’d expect Pluto to get darker if it gets redder, so clearly there’s more going on here than meets the eye.

hst_pluto_map_feb2010These maps will prove crucial in planning the imaging run of the New Horizons probe, which will scream past Pluto in 2015. Having even a crude map in advance of the encounter will help scientists plan their limited time more carefully.

Plus, these Hubble images may very well be the best view we’ll get until New Horizons gets to Pluto, for that matter. And whether you think Pluto is the littlest planet or one of the biggest of the Kuiper Belt Objects, it’s a fascinating place worthy of a lot more study. And in just a little more than five years we’ll see fantastic images of it, too. I can’t wait!

Video courtesy Emily Lakdawalla (and my thanks to her for a helpful conversation). Image and video credit: NASA, ESA, and M. Buie (SwRI)

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (57)

  1. PLANET! Darned right!

    I hafta wonder though, if the newly-serviced Hubble could get better pix of the PLANET Pluto than they could get in 2002? Might make an interesting comparison.

  2. I am exited too Phil! Excited in the same way I was when Cassini was years away from Saturn. I tried to imagine the views and science we would get from the ringed planet and my expectations were eclipsed by what reality gave us. Here’s to a perfect Pluto fly-by.

  3. Bob Allee

    I agree with Mark. It would seem best to re-image Pluto with Hubble, maybe in early 2014.

    I hope there are mountains.

  4. Oh my, whatever Pluto is, it’s a pretty sight!

  5. Michael Verrenkamp

    That’s really cool but also Pluto continues its frustration in terms of really showing us anything.

    Can’t wait until 2015 when (the craft of which I have briefly forgotten it’s name of) NASA finally get to study it up close. That’s an event Im pumped for. :)

  6. The key sentence from today’s telecon was Mike Brown’s statement that no other body in the solar system is changing so much in such a short time (not counting comet nuclei and colliding asteroids, of course), which is due to the cold conditions in the Kuiper Belt: They allow frosts to move and change quickly, esp. when orbits are quite eccentric. And this, my friends, is another good reason that Pluto and kin are classified as mere dwarf planets today: Real planets just should not do such crazy things. Even after the rare global dust storm, for example, Mars looks basically like before.

    @Mark: At the telecon we learned that new ACS images were planned in 2008, but the camera broke just before they were to be taken. It’s back now – but the necessary high-resolution channel is dead for good. Lower-resolution images with the WFPC2 were taken since and more will be taken with the WFC3 starting this April – but they will have far lower resolution than the pictures unveiled today.

    Interestingly even the ild ACS raw images are far worse than the FOC raw images from 1994, as this comparision drastically shows – this is why it took years of number-crunching to get the high-resolution imagery we have now. Which makes me wonder why they never installed a camera in the HST again that matched the super-high resolution of the good old FOC.

  7. Whether we call it a planet or a dwarf planet is irrelevant, it is what it is. I don’t understand why people make such a big deal about its classification. The only difference is school kids will have one less name to memorize in science class (and presumably someone will have to think up a new mnemonic device).

    That being said, I am equally excited to see high-res images of Pluto!

  8. Nexus6

    I can’t believe people are still not getting over the whole ‘planet’ debate with pluto.

    Nevertheless interesting times ahead, I am curious to see if any long time pictures show any remnants of ring systems or debris in the same orbital plane as the three satellites :)

  9. Not the littlest of the planets, no. There are smaller planets, plenty of them. One of the biggest KBOs, certainly. Which means it’s also one of the biggest of the dwarf planets, and these are the smallest of the planets.

    Round = planet. It’s so easy… 😉

    2014-2015 will be wonderful years. Pluto AND Ceres, oh my! Can’t wait. I just can’t wait.

    And then, Juno and the Jupiter system. W00t! And until then, Mercury and Vesta! And Mars. And maybe the Moon. And Venus.

    I’m just missing a whole fleet of Mars rovers. And a mission to Uranus. And another one heading to Neptune.

  10. Just curious, but the data was mapped to a perfect sphere. It looked to me, as the image rotated, that some dark areas could be valleys, assuming that it Pluto is not even close to a perfect sphere. I’m curious as to what the relative brightness data might say about the actual shape of Pluto?

  11. @Dan: when you say real planets should not do such crazy things, you’re saying that about half of the extrasolar Jupiters discovered so far are not real planets. Because about half of them are going round their stars in highly eccentric orbits, much more eccentric, in fact, than that of Pluto.

    I’m speaking about Jupiter-sized planets here. Real planets. Not puny little things like… the Earth.

    Makes sense? It doesn’t does it? Exactly.

  12. XMark

    It’s okay Pluto… I’m not a planet either.

    Oh man, I can’t wait for 2015. It’s like, I’ve known about Pluto since I was a kid, and still we haven’t got more than a few pixels of detail on it.

  13. These images of Pluto look just a little bit less detailed than the best images we had of Mars in the pre-spacecraft, pre-Hubble days. Back when everything was fuzzy, all the moons were dots at best, and we thought Saturn was the only planet with rings.

    It’s been a magnificent half-century to be alive. Here’s hoping for an equally-magnificent next 50 years!

  14. Steve Paluch

    Thanks for this update on Pluto. I can’t wait until NH gets there. My only regret for that mission is that it is a deep space mission, instead of an orbiting Pluto object. Oh well.

  15. ARS

    Great. Pluto: You will be always a planet in my heart… :-))
    By the way, jumping to a different subject, Phil, I don’t remember having read anything about those great happenings like the 10.23 event and homeopathy suicide organized by skeptics’ associations. I find it both funny and illustrating. And some names like “Mercurius Solubilis” are worth enjoying.

  16. Dan

    “Pluto’s north pole is brighter and the south pole darker, implying that material has migrated from one pole to the other”

    Clearly there is a huge population of reflective ice people on Pluto, and they migrate to the North pole in Summer.

  17. vince charles

    @John M Knight: “It looked to me, as the image rotated, that some dark areas could be valleys”

    The valley/mountain relief that this implies would be truly staggering. Pluto would have to be shaped like some kind of skull or rose or something. Just consider the horizontal distances implied by the albedo features… and then do some Lunar observing.

  18. vince charles

    @Jorge: “Round = planet. It’s so easy… ”

    So, Ganymede, Titan, Callisto, Triton et al. are planets?

    Triton *would* have been a planet… then it suddenly wouldn’t. And eventually it will be a ring.

  19. Johno

    @Dan Fischer #6
    Here’s 2 pictures of a planetary feature taken a few months apart:

    They look completely different to me.

    So by your new definition of a planet, I guess our puny dirtball isn’t a real planet either. But Ceres is a real planet now, because there’s no record of its surface features changing during the last 200 years.


  20. Cairnos

    It’s obvious what’s happening. The reptillian aliens are warming up the massive engines that will be used to alter Plutos orbit so that it intersects with earths at which point the hybrid shapechangers who have infiltrated our society will activate (by means of chemtrails laid down by jets disguised as passenger jets) the dormant virus that is contained in all the ‘vaccines’ we have been forced to take as children (it was grafted into the vaccines by the human quislings running Big Pharma) so that apart from thier human allies and a breeding population of human slaves the world will be depopulated when Pluto (or Nibiru as it’s inhabitants call it) is close enough for the aliens to invade sometime in late 2012.

    Did I miss any?

  21. What a cute little fuzzy whatsit.

  22. @vince: Yup. Secondary planets. Because they share most geological characteristics with the primary planets (especially the terrestrial and the icy ones, of course) and, as you ponted out with your Triton example, because primary planets may be captured and become secondary planets and secondary planets may free themselves and become primary.

    (If/when Triton becomes a ring, it obviously changes significantly. The same is not true with captures and releases: bodies remain basically unchanged when those happen.)

    Then we’d have single planets, like Mercury, Venus, Mars or Ceres, double planets, like the Earth and Pluto systems — and Neptune too —, and multiple planets. Jupiter would be a quintuple, f.i., composed of a gas giant and four terrestrial planets. The same kind of organization stars show (the Centauri multiple star is an example, composed by a close G2/K1 binary and a distant M5 dwarf companion). Or the asteroids. Sylvia, f.i., is called a triple asteroid.

    I love me some coherence. And simplicity and universality in definitions. :)

  23. Plutonium Being from Pluto


    Great pictures! :-)

    Looks like a lovely summer decade or five in the north and a brisk deade or five winter in the South. Makes me feel homesick. Sigh.

    Of course we Plutonium based Plutonian lifeforms and all our artefacts are *inside* the surface in a nice little liquid layer just outside the core! 😉

    [Yoda voice on] Not a planet? Too small, surrounded by other worlds! Pah! My home this is! [/Yoda voice off] 😉

  24. StevoR

    Of course Pluto is a planet – a dwarf star is still counted as a star (in fact 90% of all stars incl. our Sun are dwarfs and not giants or others) and therefore a dwarf planet equally must still be a planet.

    A good – simple, clear, logical and easy to determine – definition for planet is that a planet is an object which:

    a) Has enough gravity to be in hydrostatic equilibrium (i.e. is round or if rapidly spinning a rotationally flattened spheroid. Thus not an asteroid or comet.)

    b) Is incapable of ever being self-luminous through shining by nuclear fusion. (I.e. is not a star or brown dwarf.)
    c) Is not directly orbiting another planet. (I.e. is not a moon.)

    Once an object has been classified such we can then assign it toa particlar class of planet given its nature in terms of composition, internal structure, size, orbit, etc ..

    Eg. rocky and Earth-sized = terrrestrial planet,
    Gaseous Hydrogen & Helium & orbiting at Jupiter’s distance = gas giant
    Gaseous H & Helium & orbiting at Mercury’s distance = Hot Jupiter
    Icy & Pluto-sized orbiting in at Pluto’s distance = Ice dwarf
    Has a composition of hot high-pressure ices = Hot Ice (eg.Gliese 436*)
    Has a mass between 10 & 2 Earths = Super Earth
    Orbits a pulsar = Pulsar planet
    Et cetera..

    What’s wrong with having lots of planets in our solar system – many ice dwarfs as well as four gas gainst and four terrestrial rocky worlds? I think a division of our solarsystem into the three basic classes – the rocky, the gassy & the icy makes a lot of sense.

    I think our solar system contains many planets incl, Pluto & its fellow ice dwarfs. Here’s my list of what I’d consider planets basedon a sound and logical definition rather than the IAU rubbish one :

    Planets larger than Pluto – Jupiter, Saturn, Neptune**, Ouranos**, Earth, Venus, Mars, Mercury, Eris


    Planets smaller than Pluto : Makemake, Haumea, Quaoar, Sedna, Orcus, Varuna, Ixion, “Buffy” (2004 XR190), Ceres, Pallas & Vesta – so far with more to be added if necessary as they’re found.

    Which is 9 planets that are larger than Pluto and 11 that are smaller than Pluto making Pluto actually an *average* sized planet and bigger than many other worlds! 😉

    As I’ve pointed out on numerous occassions here, the IAU definition esp. the abusrd & itself poorly defined “orbital clearing” criteria is illogical, inconsistent and frankly downright unscientific and should be scrapped immediately and replaced with a reasonable alternative such as the definition I’ve suggested. That incidentally is based on the *initial* & more representative Prague 2006 IAU version decided on before a minority clique with an anti-Pluto agenda undemocratically hijacked the meeting in amove that has caused astronomy considerable greif and harm ever since.

    Awesome photos & great write up – Thanks Bad Astronomer. :-)


    * or potentially “gas dwarf”

    ** NB. Neptune and Ouranos are close in size but while Ouranos has a smidin larger radius, Neptune has more mass 17 – 14 x earth respectively hence it is listed ahead. For the name see :

    The “Ouranos not Uranus” facebook group.

  25. Dan @#6: Sorry man, we tried to fix the HRC too, we really tried. We only had two and a half hours of EVA time. Not even the mighty mighty John Grunsfeld could pull two electronics boxes in that much time! Sorry!

  26. Astroquoter

    This is one reason it took so long to release the images; Marc Buie, the astronomer who took them, saw some things in the data that were difficult to understand, and wanted to make sure they were correct.

    That would have to be the Marc Buie mentioned here in Govert Schilling’s excellent book, ‘The Hunt For Planet X’, which BTW I would very highly recommend :

    “…Marc Buie can very easily imagine what it must be like to walk around on Pluto: with less than 1% of your weight on Earth because of the low gravity, at temperatures of 230 degrees below zero, in the twilight because the Sun is nothing more than a dazzling star in the black sky, across snowfields of methane ice and transparent crystals of frozen nitrogen and with a gigantic moon hanging overhead – at least if you are on the right side of the planet.”
    – Page 61, ‘The Hunt For Planet X’, Govert Schilling, Copernicus Books, 2009.

    & it sounds like we’re having photographic confirmation of seasons & weather, erosian via sublimation and deposition via snowfall precipitation on Pluto as noted here :

    “During its summer, the frozen nitrogen on Pluto evapourates to create a temporary atmosphere. With the onset of winter the nitrogen turns to frost and falls back to the surface. On Pluto the winter weather doesn’t merely deteriorate – it completely disappears.”
    (& you thought it was cold lately – ed!)
    – Page 19, ‘The Planets’, McNab & Younger, BBC Worldwide Ltd., 1999.

    How can a place with such fascinating weather and geology, a place which may boast a dark dusty ring system as well as three moons of its own, one extremely large (Charon, Hydra & Nix), a world that is clearly round and larger than most others as was noted be anything *other* than a planet?

    Its worth noting & quoting that Isaac Asimov also considered the much smaller world of Ceres to rightfully be a planet here :

    “… he had left out a planet. It was not his fault; everyone leaves it out. I leave it out myself when I list the nine planets, because it is the four-and-a-halfth planet. I’m referring to Ceres; a small but respectable world that doesn’t deserve the neglect it receives.”
    – Page 63, chapter 5 “The World Ceres” in ‘The Tragedy of the Moon’ by
    Isaac Asimov, Mercury Press, 1973.

    If Ceres is a planet which doesn’t deserve the neglect it recieves then surely this is even more true and applies even more so to Pluto! 😉

    It will be interesting to see how NewHorizons encounter with Pluto affects this debate if things haven’t already changed (back) by then and whether reporters, astronomers, etc .. still stick to the seemingly untenable & clumsy IAU line when they see Pluto up close as clearly being far more planet-like than asteroid-or-comet-nucleus-like in nature.

  27. Plutonium Being from Pluto

    If you haven’t already seen these three articles on Pluto and its status by respected astronomer & science writer Ken Croswell they are also well worth a look and very thought & imagination provoking :

    1)Pluto-Neptune analogue exoplanetary system :

    The sun-like, albiet slightly smaller & dimmer, star HD 45364 hosts two planets in a 3:2 resonance just the same as Neptune & Pluto are in! The inner planet has at least 3.5 times the mass of Neptune but on average is about as far from its star as Venus is from the Sun. The outer planet is more massive – it has at least 2.2 times the mass of Saturn [Saturn = 95 x earth so around 200 earth mass – ed.] and is slightly closer to its star than the Earth is to the Sun. Clearly these are planets and equally clearly they are in the same orbital relationship that excluded Pluto in some peoples eyes thus providing an instant counter-example to the “orbital clearance” nonsense!

    Aptly for a planetary system supporting Pluto’s case, this system is located in Canis Major – the Big Dog constellation! (Hmm.. I wonder if Pluto-haters are also dog-haters generally? ;-))

    2) Pluto question 1 – If Pluto was orbiting where Mars is then?

    NB. Ken Crowell offers an alternative definition of planet of his own here too – his being that :

    A planet of the Sun is herein defined as an object orbiting the Sun with a diameter equal to or exceeding Pluto’s. By this definition, the Sun has ten known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, and Eris.”

    3) Pluto question 2 – If any other planet was where Pluto is now then?

    How bright would the other larger planets appear if they were orbiting where Pluto does? Would they be visible to the unaided eye?

    – StevoR (a.k.a. Plutonium being from Pluto)

  28. @Dan: You say, “And this, my friends, is another good reason that Pluto and kin are classified as mere dwarf planets today: Real planets just should not do such crazy things.”

    Says who? What do you mean by “real planets?” Those you deem real? Earth has more in common with Pluto than it has with gas giant Jupiter. Jorge, is right; your definition of “real planets” (gee, what are “fake planets?”) would exclude a large number of the 429 known exoplanets, one of which has a comet-like orbit, another a system of two giant planets orbiting in a 3:2 resonance like Neptune and Pluto.

    As a dynamic world with geology and weather, Pluto shows it has more in common with the other, bigger planets than it does with most Kuiper Belt Objects except the few large ones, which should be considered planets too. Most KBOs in Pluto’s orbital path are tiny and do not have these features. These images show that before making definitive classifications, we should first get the data and analyze it; otherwise, we are defining objects without knowing significant factors about them.

    Children should NOT be taught one less planet. That is a tremendous disservice to them. They should be taught that our solar system has abundant planets, and that dwarf planets, which should be designated a subclass of planets, are the most numerous kind. Alan Boyle puts it best in his book “The Case for Pluto” by saying the number of planets in our solar system is four terrestrials plus four gas giants plus many more.

  29. gar

    Clearly Pluto must have gotten word of its demotion from planet to dwarf planet, and now it’s turning red with anger!

  30. Definition debates are tiresome and useless, but I might as well throw in my two cents as it seems that this thread has been dominated by nostalgiomaniacs.

    While some see beauty in a simplicity of definitions relating to roundness and solar orbit only, I also find a certain aesthetic, and admittedly a somewhat parochial one in the fact that our solar system’s smallest planet is more massive than its largest moon.

    While some argue that excluding Pluto from the realm of planets ignores its special status as a round body directly orbiting the sun, it should be pointed out that any system of classification imposed upon reality by intelligent beings hoping to understand it will have trade-offs in how and whether certain characteristics are emphasized or not. Reality was not created for the sake of human classification schemes–rather, human classification systems were created for the sake of simplifying what is really a much more complex than presented reality for the sake of processing by our particular intelligences.

    Finally, I find the ire over what is essentially a minor privileging of system of sets to present publicly over another. And if in fact advocates of Pluto’s planethood were to look closely at all the merits of each system, they would see that the current approach has the most long term utility in educating the public of the nature of our solar system, whose dynamics are in fact dominated mainly by nine objects–the sun and the eight planets. Pluto itself is not in 3:2 orbital resonance with Neptune without reason.

    While the smaller bodies of the solar system may be of interest to those who seek a deeper understanding the totality of our solar system, those looking for an accurate big picture are actually disserviced by the listing of Pluto as an object on par with the eight whose orbits have set the shape of today’s solar system.

    Pluto is a fascinating object–it’s tidally locked with its largest companion, the fact that it at times comes closer to Uranus than it ever does to the planet whose orbit it crosses is an interesting reflection of the nature of orbital resonances and its location beyond the realm of typical human experience probably endows it with many yet undiscovered properties–none of which is cheapened by the fact that it has now been classed with a set of other round objects that has a lesser effect on the shape of today’s solar system.

    Pluto’s classification as planet came at a time when such assignments were made ad hoc and it wasn’t understood that Pluto’s mass was less than a fifth of that of our moon. Surely at the very least, advocates of a broader definition of the term planet must accept that a definition based upon principles is preferable to one determined by the local zeitgeist without any sense of international standardization.

    Finally, I will reemphasize the most important aspect of this discussion: regardless of what the predominant framework for classifying heavenly objects is, the objects’ underlying reality does not change. Pluto did not change that day that the IAU made it’s decision. The only thing that changed was a human classification system.

    In the end, 100 years from now, school children who read about the history of astronomy will marvel at the past obstinance of those defending a quaint, outdated view against what will presently be taken as a universal given. History has taught us that an idea that is solely held by those to set in their ways to change the way they view the world is doomed to die with them. Pluto’s planethood is one such idea, but it is far from the most significant or meaningful idea to suffer such a fate.

  31. Gr'Rshak

    What would the Death Star from Star Wars look like, were it the same size as Pluto and given Hubble’s resolution.

    Also, I’d like to extend best wishes to India and China, whom I am sure are very grateful to President Obama for giving them the Moon. Note to future taikonauts or bollynauts, whatever:

    Since you’ll be the next ones to visit Tranquility Base, pay no attention to the “Finders Keepers” note that impish scamp Buzz Aldrin attached to the American flag. It’s all yours.

  32. Todd

    2015….thats too long errrrrr
    Ive always been fascinated by Pluto, glad to see we are just 5 years away.

  33. MaDeR

    Heeeree we gooo agaaainn…

    Award for “most idiotic argument in favor for Pluto in this thread” goes to Laurel Kornfeld for “think of children!!!oneone” mentality.

    Explanation: taughing children about Pluto as planet or as dwarf planet is “disservice”. Explanation for children WHY Pluto was considered as planet and why now is not considered as planet is much more useful. Of course, this is exactly what you don’t want to be done for obvious reasons.

    Secondary award goes to Dan Fisher for non sequitors presented as things that… somehow… have revelance to planethood (or lacking of). Changing too much, indeed. Ironically, this one was from antiplutonist.

  34. Someone needs to hand the image data over to the guys at CSI. They’ll get their image enhancing software on to it and before you know it’s we’ll have a street level map. :)

  35. Kevin Heider

    I suspect Io (the spherical one, not the asteroid) might argue that it changes faster…

  36. Can I point out that 4 billion km is NOT equal to 3 billion miles? It’s 2.5 billion miles. 3 billion miles would be 4.8 billion km.
    Also, those are American Hemisphere (short scale) billions (x10^9), not European (long scale) billions (x10^12).
    ‘swhy we has scientific notation.
    Of course, calling it 4 Tm would eschew all obfuscation.

  37. I reckon the Plutonians were smartening the place up in preparation for the IAU debate.

    If only Buie had done his processing quicker, how different everything would have been. Now Plutonian civilisation is in a death spiral of low self-esteem, because of the heartless way American children are being indoctrinated by the IAU mafia, egged on by Mike Brown.

  38. My comment about children is not about thinking of their feelings; it is about taking into consideration that they learn the entirety of the solar system and not an abbreviated form that leaves out a significant class of planets. Also, it is based on the fact that in many cases, children have already been taught incorrect information, namely, that Pluto is an asteroid. This is a problem.

    @MengBomin: Pluto’s planethood is not a “quaint, outdated idea” held by people who refuse to accept change. It is based not on “local zeitgeist” but on the scientifically sound definition that an object in hydrostatic equilibrium orbiting a star is a planet. It is those who insist that dwarf planets are not planets at all, who maintain there can be only two types of planets (terrestrial and jovian) in the solar system and that they must be limited to a small number who are actually resistant to change. The paradigm shift we are facing is one from 8, 9, or 13 planets in the solar system to potentially one of hundreds. This is an extension of the Copernican principle that Earth is not the center of anything, is not even special. Similarly, planets are not rare, unique, or “special,” they are everywhere. Orbital dynamics are acknowledged in sticking to the orginal definition of dwarf planet created by Dr. Alan Stern, specifically, that a dwarf planet is a planet by virtue of what it is–an object large enough to be shaped by its own gravity–but of the dwarf subcategory because it is not large enough to gravitationally dominate its orbit. Dwarf planets may not have a significant a role in the architecture of the solar system as the other classes of planets, but this does not mean they are not planets at all!

    No one can presume to know what children will be reading in 100 years because most of that will be based on information yet to be learned. By that point, there may be 10 subclasses of planets. The only thing we can know is that this debate will be part of a larger context of controversy that has surrounded many discoveries within our solar system and others.

  39. Kevin Heider

    >children have already been taught incorrect information, namely, that Pluto is an asteroid.

    I don’t know anyone teaching that Pluto is an asteroid. But yes, Pluto can be compared to an asteroid. Like an asteroid, Pluto is pushed around by the dominant (important) planets.

    >orbiting a star

    As long as people continue to *suggest* an object is important only if it directly orbits a star, I see no real problem with the IAU definition excluding Titan, Triton, Europa, or Pluto.

  40. I’ve been trying to figure this out – since they’re mutually tidally locked, what face of Pluto faces Charon? Is it the 0° view not shown in these images?

  41. Michelle R

    Planet or not, Pluto’s my friend.

    can’t wait for New Horizons to get there!

  42. Pi-needles

    It seems a bit unfair and odd that Mercury which has no moons or atmosphere or complex weather is still counted as a planet when Pluto which has all these is not.

    Not that I want to remove Mercury from planethod – to me it seems a good “default” planet ie. a planet when all you have is the ball of rock and nothing else. 😉

    But however you define Pluto and whatever you think of its categorisation, these are awesome images and it is immensely impressive that we’ve been able to get them. :-)

  43. Plutonium being from Pluto

    @ 43. Kevin Heider Says:

    I don’t know anyone teaching that Pluto is an asteroid. But yes, Pluto can be compared to an asteroid. Like an asteroid, Pluto is pushed around by the dominant (important) planets.

    Its a very different thing *comparing* Pluto to an asteroid and wrongly saying it *is* one.

    You could compare Pluto to a giant chocolate chip icecream & it wouldn’t make it one.

    Here’s how I’d compare Pluto to an asteroid :

    “Pluto is very different from an asteroid because it is so much larger than them that it has attained “hydrostatic equilibrium” or is round through its own gravity while asteroids are not! Pluto also has a large moon, Charon, which itself is gravitationally round as well as two smaller moons an atmosphere with weather and possibly also rings which no asteroid can boast therefore Pluto is clearly NOT an asteroid but a planet.” 😉

    Incidentally, if I recall right, didn’t the IAU give Pluto a “minor planet number” which technically sorta says they, absurdly, think that it *is* an asteroid?

    It sure doesn’t look like an asteroid to me – take a look at the images above & compare them with images of real asteroids such as Gaspra, Ida, Mathilde, Eros etc .. & you’ll see what I mean.

    As long as people continue to *suggest* an object is important only if it directly orbits a star, I see no real problem with the IAU definition excluding Titan, Triton, Europa, or Pluto.

    Huh? You do know Pluto orbits our Sun directly whereas those others are all moons don’t you? Titan orbits Saturn, Triton orbits Neptune and Europa orbits Jupiter. Excluding moons make sense – excluding a planet like Pluto does not.

  44. Plutonium being from Pluto

    It sure doesn’t look like an asteroid to me – take a look at the images above & compare them with images of real asteroids such as Gaspra, Ida, Mathilde, Eros etc .. & you’ll see what I mean.

    Seriously click on & & to view real asteroids & then scroll up to the top of the screen to view those Pluto images again and then try telling me you think the IAU is right to include Pluto as an asteriod! (Wish I knew how to embed pics here & also wish we were given more editing time like, say, an hour rather than 15 min.)

  45. Jya Jar Binks Killer

    So the IAU and some here think Pluto isn’t a proper planet? Once you start with this planet-killing madness where does it stop?

    Mercury is small, airless and moon-less so it clearly isn’t a planet either. 😉

    Neptune has Pluto crossing its orbit and if that rules Pluto out we gotta be fair and rule that it’s orbit *also* isn’t clear and so Neptune’s NOT a planet but only a “dwarf planet” too! 😉

    Jupiter? Its got all those trojan asteroids along its path so it cannot be a proper world – it must be too small for full planet-hood! 😉

    Saturn, look at those messy rings cluttering up its vicinity – we can’t have a planet like that, now can we! 😉

    Mars is obviously so near the asteroid belt that it might as well be redesignated as just another large outlying member and an asteroid itself just like Pluto was. 😉

    Uranus? What a silly name – consider yourself struck from the list! 😉

    Venus? Come on, that place is really hell and hell isn’t a planet, its gone from the list too! 😉

    Now we’re just left with just our Earth. But, wait on a minute, what’s that awfully large moon there? Does that mean Earths orbit isn’t clear and that we’re actually part of a double planet? Double planets? Huh! Can’t have them – strike Earth from the solar system list too! 😉

    That’s where we’re hading folks! This reclassifying of planets into not-planets has got to be stopped & reversed before it gets even madder & leaves our solar system entirely empty and planet-less. Bring back Pluto and send out those crazy IAU clowns! 😉

  46. @Cairnos – Yes, you did miss something! The Kennedy assassination magic bullet couldn’t have possibly followed the trajectory it supposedly did, unless acted upon by an outside force. What outside force? A giant magnet! This was a test of the Nibiru magnet system, designed to keep it on alignment as it approaches Earth, and then to function as a magnetic lift conveyor to transport all the human slaves to Nibiru. (This is the real purpose of the LHC.) They were supposed to build it in Texas (then called the SCSC.) Why didn’t they? Problems with field containment in the 1963 test, so they were afraid all the hunters in Texas would notice their bullets behaving oddly when they activated it, so they built it in Switzerland instead, because they don’t have a 2nd amendment there.

  47. Plutonium Being From Pluto has very accurately described the significant differences between Pluto and asteroids. Also, Kevin Heider argues that “like an asteroid, Pluto is pushed around by the dominant planets.” The problem with this statement is that it takes no account of the geophysical composition of Pluto itself–what Pluto is. If Earth were in Pluto’s orbit, it would also be “pushed around” and unable to “clear that orbit” of tiny Kuiper Belt Objects. We cannot define an object solely by the where it is and the way other objects interact with it while completely dismissing the characteristics of the object itself.

    As for the spherical moons of planets, I have no problem with creating a new category, secondary planets, for moons large enough to be in hydrostatic equilibrium. This term has been used to describe them before, indicating that their primary orbit is around another planet, and their secondary orbit is around the Sun. Colloquially, we could continue to refer to them as moons. However, when we study them up close; for example, if we land a probe on Europa, it is important to recognize that some of them are geologically differentiated, have weather, have volcanoes, and as such are actually planets.

  48. Kevin Heider

    >We cannot define an object solely by the where it is
    >and the way other objects interact with it

    Why not? This is pretty much how everything in the solar system has been defined. Traditional asteroids are mainly located in the main-belt and most have fairly stable orbits. Comets come close enough to the Sun to outgas. Centaurs are in unstable orbits between the gas giants (real planets). The Kuiper belt is a region beyond Neptune. Moons orbit an object that orbits the Sun.

    to Plutonium:
    1. Moons? Many asteroids have multiple moons.
    2. Atmosphere? Pluto’s atmosphere is likely only seasonal when Pluto is near perihelion. Comets and some centaurs have temporary atmospheres when near perihelion.
    3. Rings? We know that moons can also have rings.

    Pluto is a (round) protoplanet that never finished accreting enough mass to dominate the region around it.

    You do know that Pluto has more in common with the large spherical icy moons than it does with the dominant eight planets, right?

    “asteroid < Pluto < IAU planet" Why the issues?

  49. Messier Tidy Upper

    ^ The “dominant” eight planets vary more amongst themselves than Pluto & the other planets do.

    Mercury has less in common with our Earth than the Earth does with Pluto.

    Jupiter and Mercury are vastly different types of bodies.

    Earth & Mars & Pluto are more similar to each other & have more in common than Saturn or Neptune do vs Mercury.

    Lets say planets are as different and wide ranging as stars are which range from solar dwarfs to red supergiants & blue hypergiants immensely larger & millions of times brighter than our Sun to tiny, cold as sunspots red and brown dwarfs that are much more common, much longer lived, yet are tens or even hundreds of times fainter and the only size of Jupiter. Or city-sized neutron stars & black holes that used to fuse yet no longer do.

    If it fuses (or used to), its a star.

    If it doesn’t & is still big enough to be round, its a planet.

    If its too small to make itself round, its an asteroid or comet.

    That basic division (with a large number of sub-classes) make sense to me. 😉

  50. Kevin Heider

    >If it doesn’t & is still big enough to be round, its a planet.

    This is the only alternative to the IAU definition that makes sense. This definition should require Triton, Titan, Europa, etc. to be treated on the same footing as Pluto.

    Even Alan Stern (July 2008) has suggested that most scientists do not see it that way.

    And as I have said many times before, I doubt the general public wants to accept the Earths moon as a planet just to keep Pluto as a planet.

  51. In terms of planet classification, there are two main schools of thought, which (as a biologist), can be compared to biology.
    In any ecosystem, we can classify the organisms within that ecosystem in two ways – taxonomically, and ecologically. The difference is that taxonomic identification will specifically identify the origins and relationship of each organism, but not their role in the community. Each ecosystem may have a completely different set of organisms. Classifying living things ecologically, on the other hand, ignores the origins and relationships, and looks at the role in the community. Each community will have primary producers, primary consumers, secondary consumers, etc., regardless of the taxonomy of those organisms.
    At the last IAU meeting, the dynamicists argued for, essentially, an ecological definition of “planet” – one that classifies a planet based on its “role” in the solar system, rather than its shape and composition, which would be a taxonomic definition.
    I don’t really have a problem with this, except for the fact that in biology the two systems of classification are *not mutually exclusive*. I would have liked to see a set of definitions that allow classification by type (rocky, gaseous, icy) *and* by dynamic role (Giant, major, minor, satellite, etc), but then I am Canadian, so I like compromise :-)

  52. That’s not Pluto, that’s Rorschach. Wrong cartoon.


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