Pluto: Terra Cognita (Almost)

 

Pluto_animiert_200pxThe image at your right is currently the best and clearest one we have of the former planet Pluto, now correctly classified as a dwarf planet.* If it looks unimpressive to you, you’re not alone.  Based on a series of observations from the Hubble Space Telescope this fuzzy blur is the best we can do with the technology currently in place.

One of the great things about modern astronomy, however, is that our technology can move at incredible velocity. Literally. In the case of the New Horizons probe, our technology is moving at about 31,500 mph. On July 15, 2015 — one year from yesterday — that will put it within just 17,000 miles of this distant little ice world. For the first time, we’ll see exactly what Pluto looks like, and in HD. You’ll likely never see this picture again outside of a history book.

This will be the first time in my lifetime — all 33 years of it — that we’ve seen something this famous and this unknown up so close. By the time I was born, we had sent probes to Mercury, Venus, Mars, Jupiter, and Saturn, and Voyager II swept by Uranus and Neptune before I was old enough to appreciate them; all of them were — to a fair extent — known quantities. This isn’t to say that our discoveries and explorations within our own solar system since then haven’t been amazing: we’ve explored miles of the martian surface, discovered the lakes and rivers of methane on Titan, geysers on Enceladus, orbited major asteroids, and impacted comets head on.

jupiter11

Jupiter, from Pioneer 11.

Amazing, yes, but none of these captured the public’s imagination for more than a few moments. New Horizons should be different: everyone knows what Pluto is, and — as the International Astronomical Union discovered when they demoted Pluto from its status as a planet — people have strong emotions about it. For at least another generation, Pluto will still have a special status, if only as the only ex-planet.

Think of it this way: almost no one outside of astronomy nerd circles can name any of the other bodies that share Pluto’s designation. Orcus, discovered in 2004, has an orbit that’s almost a perfect inversion of Pluto’s, though it’s significantly smaller. Eris, discovered in 2005, is roughly the same size as Pluto, though also further out. Even maps of the solar system that correctly list Pluto as a dwarf planet still include it, but none of these other bodies. For whatever combination of reasons, Pluto continues to hit the public imagination in a way none of these other worlds has (they certainly don’t make it past spell-check unnoticed).

So what do we currently know about Pluto? A few interesting facts:

  • It’s very small; smaller than at least seven moons in our solar system, including our own.
  • It’s largest moon, Charon, is so relatively large and close to Pluto, that it probably makes sense to count the two of them together as a binary planet.
  • In just the last few years, four additional, very small moons have been discovered around Pluto.
  • It has a twin, Orcus. The two both have unusually large moons and have orbits of (very nearly) the same size and at (very nearly) the same inclination to the rest of the solar system. Orcus, however, is much smaller.
  • Almost every important aspect of its discovery and exploration has been by Americans: Clyde Tombaugh discovered it; James Christy discovered Charon; Mike Brown, Chad Trujillo, and David Rabinowitz started the path that led to its demotion by finding similar objects; and New Horizons is a NASA program.

What are we hoping to find out?

  • Is its atmosphere permanent, or does it only stick around while Pluto is relatively close to the Sun? The former had been suspected, but discoveries in just the last year suggest that the latter may be true.
  • Did Pluto and Charon ever have liquid oceans beneath their surfaces?
  • How heavily has Pluto been impacted by meteors?
  • How similar is it to Neptune’s moon, Triton, which has long been suspected to be a Pluto-like object that wandered into the inner solar system?

There will likely be surprises — there almost always are when we do this sort of thing — and that’s the wonder and the joy of it.  I can’t wait to see what we find.

* What defines a “planet” had been a source of contention for some time, and remains so. The difficulty the IAU found itself in in 2006 was that there was no set of objective criteria that could be found that included all nine of the “traditional” planets without including dozens more besides Pluto, which nobody wanted to do (that darn sentimentality again). Their solution was to adopt a definition that excluded Pluto while creating a new category for dwarf planets — which are not planets! — that would include Pluto and another dozen or so objects.

Under the new definition, a planet is a body that 1) orbits directly around a star, 2) is massive enough to form itself into a ball, and 3) has swept its orbit clear of most other objects. A dwarf planet meets the former two criteria, but not the last.

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  1. Yeah...ok. Inactive
    Yeah...ok.
    @Yeahok

    You look older in your avatar.

    • #1
  2. Tom Meyer Contributor
    Tom Meyer
    @tommeyer

    Yeah…ok.:

    You look older in your avatar.

    I prefer “handsomer.”

    • #2
  3. user_1938 Member
    user_1938
    @AaronMiller

    Tom Meyer: Under the new definition, a planet is a body that 1) orbits directly around a star, 2) is massive enough to form itself into a ball, and 3) has swept its orbit clear of most other objects.  A dwarf planet meets the former two criteria, but not the last.

    Thanks for addressing the obvious question. Does Pluto fail the third criterium because of the “moon” of similar size? Or is there a lot of space junk in its orbit?

    Tom Meyer: The difficulty the IAU found itself in in 2006 was that there was no set of objective criteria that could be found that included all nine of the “traditional” planets without including dozens more besides Pluto, which nobody wanted to do (that darn sentimentality again).

    This sounds similar to the core problem of biological taxonomy. Differences and similarities are prioritized to support preset conclusions. It’s not a dishonest practice, really; but it is disappointingly arbitrary.

    I was always more interested in what’s on Earth than what’s beyond. But this was an interesting read. Thanks.

    • #3
  4. Tom Meyer Contributor
    Tom Meyer
    @tommeyer

    Aaron Miller: Thanks for addressing the obvious question. Does Pluto fail the third criterium because of the “moon” of similar size? Or is there a lot of space junk in its orbit?

    Charon (and other moons) don’t count against Pluto.  So far as I understand this, the culprits are Orcus and the other Plutinos, whose orbits cross Pluto’s, but aren’t gravitationally affected by it.  Plutinos, in turn, are defined as objects whose orbits are in resonance with Neptune.

    • #4
  5. user_6236 Member
    user_6236
    @JimChase

    I too have been following this, as I have most of the deep space missions (I was pretty pumped when Voyager reached the “boundary” of the solar system.

    Scientifically, I get Pluto’s demotion, but nostalgically, Pluto will always be a planet to me.  I do hope the pictures are sufficiently hi-res.

    • #5
  6. Tom Meyer Contributor
    Tom Meyer
    @tommeyer

    Aaron Miller: This sounds similar to the core problem of biological taxonomy. Differences and similarities are prioritized to support preset conclusions. It’s not a dishonest practice, really; but it is disappointingly arbitrary.

    Exactly right.  The natural world doesn’t always like to conform to our ideas of order.

    I originally meant to include this in the OP, but the only definition of “planet” that gave the traditional nine, but no others, was “A planet is defined as an object that is either Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto.”

    • #6
  7. Frank Soto Contributor
    Frank Soto
    @FrankSoto

    I’m going to be disappointed.  There’s no way that bumblebee color scheme is going to hold up in higher res images.

    • #7
  8. user_435274 Thatcher
    user_435274
    @JohnHanson

    “Amazing, yes, but none of these captured the public’s imagination for more than a few moments.  New Horizons should be different: everyone knows what Pluto is, and — as the International Astronomical Union discovered when they demoted Pluto from its status as a planet — people have strong emotions about it.”

    I’m probably wrong, but I think the reason that Pluto captured the public awareness, was Disney developed a popular cartoon dog of the same name.

    • #8
  9. Mike H Coolidge
    Mike H
    @MikeH

    John Hanson:

    “Amazing, yes, but none of these captured the public’s imagination for more than a few moments. New Horizons should be different: everyone knows what Pluto is, and — as the International Astronomical Union discovered when they demoted Pluto from its status as a planet — people have strong emotions about it.”

    I’m probably wrong, but I think the reason that Pluto captured the public awareness, was Disney developed a popular cartoon dog of the same name.

     Nah… everyone likes mysterious novelty. It was the farthest, tiniest planet. Rivaled only by Mars and Saturn in uniqueness. 

    • #9
  10. Yeah...ok. Inactive
    Yeah...ok.
    @Yeahok

    Ooops. I meant to write Your contributions here at Ricochet suggested someone with much more experience and wisdom than I’ve witnessed on other young people.

    Sheese, I didn’t know a pluto post would end up on main feed.

    • #10
  11. user_280840 Inactive
    user_280840
    @FredCole

    Tom, I’m excited too, for that same reason.  

    How is Pluto a thing, in our solar system, and we don’t even have a decent picture of it?

    And the Pluto system keeps getting more interesting.  We keep finding more stuff.  I’m excited.

    • #11
  12. hawk@haakondahl.com Inactive
    hawk@haakondahl.com
    @BallDiamondBall

    Looks like some great endurium deposits.

    • #12
  13. hawk@haakondahl.com Inactive
    hawk@haakondahl.com
    @BallDiamondBall

    One of my favorite cartoons is shows Earth with a telescope peering up at Pluto, and a voice says “Ho, Mira! Una pequeno planeta!”  And Pluto makes an obscene gesture, shouting ‘Tu madre is una pequeno planeta!”

    Or something like that.  I still laugh at it.  I’m laughing now.
     

    • #13
  14. Valiuth Inactive
    Valiuth
    @Valiuth

    Fred Cole:

    How is Pluto a thing, in our solar system, and we don’t even have a decent picture of it?

    Well it is so darn far away. What I always find amazing is just how little we know about the very planet we live on. Every time some one dives to the sea floor they always come up with some new species or discovery.  

    • #14
  15. user_280840 Inactive
    user_280840
    @FredCole

    Valiuth:

    Fred Cole:

    How is Pluto a thing, in our solar system, and we don’t even have a decent picture of it?

    Well it is so darn far away. What I always find amazing is just how little we know about the very planet we live on. Every time some one dives to the sea floor they always come up with some new species or discovery.

     That’s cause science is awesome.

    • #15
  16. Whiskey Sam Inactive
    Whiskey Sam
    @WhiskeySam

    If nothing else, Pluto’s demotion gave us Gus’ favorite pick-up line on Psych: “Girl, you heard about Pluto?  That’s messed up, right?”

    • #16
  17. Tom Meyer Contributor
    Tom Meyer
    @tommeyer

    Whiskey Sam:

    If nothing else, Pluto’s demotion gave us Gus’ favorite pick-up line on Psych: “Girl, you heard about Pluto? That’s messed up, right?”

     Ha!  I forgot that one.

    • #17
  18. skipsul Inactive
    skipsul
    @skipsul

    Fascinating stuff all around.

    • #18
  19. Ross C Member
    Ross C
    @RossC

    Pluto remains a planet at my house.  When I look at these unmanned missions like New Horizons or the Mars Rovers or Voyager, I am always amazed and excited.  When I look at the manned space program I am not all that interested.  

    I wonder if Nasa spends similar amounts on both programs or much more on manned flight?

    • #19
  20. Tim H. Member
    Tim H.
    @TimH

    Good post, Tom.  I’m really looking forward to next summer.

    I’m a working astrophysicist, and while I’m mostly in extragalactic work (things outside the Milky Way), I’m dabbling a bit in some planetary topics.  One friend of mine who does mission planning on the MESSENGER space probe (orbiting Mercury) is getting to take a stint at New Horizons next year when it makes its close approach to Pluto.  One of the big problems they have to work out is how close to come to the planet.  If there is a ring system like the gas giants have, or lots of very tiny moons, then the spacecraft might be damaged.  But they won’t know this until they get close enough to get a better view.

    On the IAU mess, I’ve never accepted their “dwarf planet” designation, and neither have many others of us.  The IAU is merely one of many associations of astronomers (some of which objected to this).  They don’t have authority over the meaning of the word “planet” in the languages of the world.  And trying to make it into an “officially” defined term breaks precedent in this area of astronomy.

    • #20
  21. Tom Meyer Contributor
    Tom Meyer
    @tommeyer

    Tim H.: One friend of mine who does mission planning on the MESSENGER space probe (orbiting Mercury) is getting to take a stint at New Horizons next year when it makes its close approach to Pluto.  One of the big problems they have to work out is how close to come to the planet.  If there is a ring system like the gas giants have, or lots of very tiny moons, then the spacecraft might be damaged.  But they won’t know this until they get close enough to get a better view.

    I heard something about that; do you know if there’s any specific reason to think that Pluto would have a ring?

    Tim H.: On the IAU mess, I’ve never accepted their “dwarf planet” designation, and neither have many others of us.  The IAU is merely one of many associations of astronomers (some of which objected to this).  They don’t have authority over the meaning of the word “planet” in the languages of the world.  And trying to make it into an “officially” defined term breaks precedent in this area of astronomy.

     I didn’t realize that.  Is there a different definition others favor?

    • #21
  22. user_358258 Member
    user_358258
    @RandyWebster

    Is that an accurate depiction of its rotational velocity?

    • #22
  23. user_1938 Member
    user_1938
    @AaronMiller

    The current picture is disappointing. As a kid, I always imagined Pluto as intimidating mountains and dark canyons of ice. That GIF makes it look more like a rotten orange.

    • #23
  24. Julia PA Inactive
    Julia PA
    @JulesPA

    Pluto is a planet in my heart and soul forever. The music on this link proves it, even if she is only an incidental “chime.” :)
    http://www.whitevinyldesign.com/solarbeat/

    • #24
  25. Vald the Misspeller Member
    Vald the Misspeller
    @

    There will likely be surprises — there almost always are when we do this sort of thing — and that’s the wonder and the joy of it. I can’t wait to see what we find.

    How come you weren’t this excited about the World Cup? Do I detect a latent hostility to the most popular game in the known universe?

    • #25
  26. Vald the Misspeller Member
    Vald the Misspeller
    @

    Pluto’s not a planet, the tomato isn’t a vegetable, Brontosaurus is actually Apatosaurus and that Amaryllis you got for Christmas?… it’s probably not. Pffft! Next you’ll be telling me that Obama’s not really a White Sox fan.

    • #26
  27. Tim H. Member
    Tim H.
    @TimH

    On the question of rings for Pluto, I don’t know how likely that’s considered, but in the back of my own mind, I’m noting that Pluto has far more moons (five) than any of the terrestrial planets (the rocky inner planets, Mercury through Mars, which tops the list at two).  The Jovian (gas giant) planets all have both lots and lots of moons and have rings.  So the processes that form lots of moons for a planet also seem to form rings.  Rings are often material that’s leftover from forming moons, perhaps in orbits too close to the planet to allow a full-sized moon to form (tidal forces prevent it).  That’s a rough idea—I’d have to look up the literature to say for sure.

    One thing that might prevent Pluto from having rings is its small size.  Maybe it’s small enough that its tidal forces wouldn’t favor a ring system, but I don’t know the numbers.  Nvertheless, with five known moons, four of them found in the last decade, there is a good chance for hard-to-see, tiny debris around it.

    • #27
  28. Tim H. Member
    Tim H.
    @TimH

    On the IAU decision on defining the word “planet”:  The IAU is just one club of astronomers out of many, and it made this move in a way that seemed to take on a kind of universal authority it doesn’t have.  The American Astronomical Society’s Division of Planetary  Science, for example, sent a letter of protest.  My biggest objection is that there doesn’t need to be this kind of bureaucratically-defined, official-seeming designation for the word.  “Planet” as a word in English predates the IAU, and here they are claiming to change its meaning by a vote of a small number of people.  In general in astronomy, we don’t have “official” definitions of words.  We have common practice on how words are used (like common-law vs. the Napoleonic Code), and there are debates on where to draw the distinction between similar terms, but these are carried out in research papers, and if they are resolved at all, it is by other astronomers deciding to follow one practice or another.  Not by having a vote and pretending to settle the issue for everybody.  
    [Cont’d]

    • #28
  29. Tim H. Member
    Tim H.
    @TimH

    For example, in extragalactic astronomy (my area), we have an awful lot of different classification schemes for galaxies.  The Wikipedia article gives you a little taste of what they’re like:  http://en.wikipedia.org/wiki/Galaxy_morphological_classification  (I’m on my iPad and can’t do a better link.)

    The different systems have not, to my knowledge, been codified in any “official” way by the IAU, but merely defined by their original proposers, with other people often suggesting changes—some used by others, some not.  In a parallel with the planet/dwarf planet issue, we have galaxies and dwarf galaxies.  Dwarf galaxies are smaller.  But where is the dividing point?  The Large Magellanic Cloud, usually considerd one of these, is argued by others to be a regular “galaxy,” and we may come to some general agreement in time.  But we will never have the IAU vote on a definition of the word “dwarf galaxy.”  What would be the point?  

    Mike Brown, who discovered some of the large Kuiper Belt Objects (icy planets past Puto) that prompted this move, originally thought one of them was twice the size of Pluto—about as big as Mercury!
    [cont’d]

    • #29
  30. Tim H. Member
    Tim H.
    @TimH

    Eris, it is called, was originally thought to be so big, that it was largely responsible for the IAU move.  But now it is known to be just about the same size as Pluto.  Brown says if he’d known this then, that he might not have pushed the issue.  Oops.

    This is one of the hazards of a Napoleonic Code type approach to scientific terms.  You lock yourself in with whatever your level of ignorance wass at the time.  

    Anyway, those are my main objections.  1) We don’t need private bodies claiming to make official definitions of existing words.  2) “Official” defintions are an awkward idea in science.  3) Much of what prompted the move wturned out to be incorrect.

    As far as looking at planet categories, though, it does make sense to think of Ceres (the largest asteroid), Eris, and Pluto (the largest Kuiper Belt planets) as the largest representatives of bodies of very numerous, much smaller objects—asteroids and Kuiper Belt Objects.  But for those, the long-established “major planet” and “minor planet” terms (distinguished purely on size) would still serve.

    • #30
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