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NASA / JPL-Caltech
It turns out that Eris, shown in this artist's conception, may be Pluto's denser twin.
It's been almost a year since astronomers suggested that Eris, the icy world whose discovery prompted Pluto's controversial reclassification in 2006, wasn't as big as they originally thought. Now the official word has leaked out unofficially: Pluto just might be the largest dwarf planet after all — although Eris is still seen as more massive.
The latest measurements were reported last week in Nantes, France, at a joint meeting of the American Astronomical Society's Division of Planetary Sciences and the European Planetary Science Congress. But as the Planetary Society's Emily Lakdawalla explains, it took a while for the report to become public, due to worries about the journal Nature's rules on embargoes and confidentiality.
Here are the statistics: Based on measurements made last November during the dwarf planet's occultation of a faraway star, Eris' diameter is estimated at 2,326 kilometers (1,445 miles). A similar set of measurements, published in 2009. estimated that Pluto was at least 2,338 kilometers (1,453 miles). When you include the margin of error, Pluto is essentially Eris' equal in size.
"It could be smaller, it could be larger; basically, it is a twin," Lakdawalla quoted Paris Observatory astronomer Bruno Sicardy, the lead researcher for the Eris measurements, as saying at the conference.
Lakdawalla held back from reporting what Sicardy said because she was asked to. The research paper about the measurements is under consideration for publication in Nature, and Sicardy said the journal's editors told him he could discuss the results only if he instructed his audience not to report them publicly. The implication was that Sicardy's paper would be tossed out if his team's findings appeared in the press.
The audience was all abuzz about the findings, of course, but Lakdawalla said she wouldn't "break anything until somebody else breaks it."
She did, however, refer to the zipped-lip situation in a Twitter message to Embargo Watch's Ivan Oransky. Long story short, Oransky checked with Nature and was told that "researchers with papers in submission at a Nature journal can certainly present at a scientific meeting but shouldn't court the press." Oransky blogs about the back-and-forth today on Embargo Watch, but the bottom line is that Sicardy needn't have feared having his paper rejected, as long as he confined his public remarks to the presentation.
If Nature sticks to the reported publication plan, the paper will be published on Oct. 26. Today, a lot of the details came out not only on Lakdawalla's blog, but also on Scientific American's Observations blog — which is interesting, because Scientific American is part of the Nature Publishing Group. (SciAm's John Matson helpfully included a link to Sicardy's conference report.)
So what else do Sicardy and his colleagues say? Although Pluto and Eris are roughly the same size, Eris is more massive, which implies it's "mainly composed of rocky material, with a relatively thin ice mantle," the astronomers say. They suggest that Eris once had a thicker layer of ice, most of which was "blasted away" as the result of a catastrophic cosmic collision.
Sicardy and his colleagues also note that when you factor in Eris' distance, its observed brightness and its relatively small size, the dwarf planet stands out as one of the brightest bodies in the solar system, after the Saturnian moons Tethys and Enceladus. They suggest that the dwarf planet is so bright because it has a surface layer of nitrogen or methane frost, due to the freezing-out of its atmosphere.
A similar freeze-out might well happen on Pluto as it heads out to the farthest point of its orbit around the sun. Eris, meanwhile, is coming closer to the sun — and at some point the nitrogen or methane might thaw back into the atmosphere.
The two worlds seem destined to stand in the planetary pantheon as separated twins — in possession of moons, seasons, their own distinctive geologies and potentially some kind of cryovolcanic activity. Should they really be regarded as non-planets, or is it better to see them as a different class of planets? I argue for the latter in my book, "The Case for Pluto," but I'd love to hear what you think. Please feel free to add your comments below.
More about dwarfs and other planets:
- Pluto debate is about more than one little world
- Interactive: The new solar system
- Eris looks a lot like Pluto
- Eight decades of Pluto
- The Pluto files on msnbc.com
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With the success of the Voyager missions photography of the eight planets in our solar system, we then wondered if we would ever get to see our ninth planet, Pluto, up close. Unfortunately Pluto was not in the proper alignment for the Voyager missions. New Horizons was launched in 2006, precisely to accomplish this unfinished business. Suddenly, Pluto gets downgraded to minor planet status while New Horizons is en route. I'm sure the New Horizons team is walking on egg shells since that day. Nonetheless, this revelation exemplifies the difficulty that even scientists experience when dealing with new discoveries that challenge convention. The need for improved accuracy in classifying planetary bodies is particularly acute as extra-solar planets are now being discovered by the dozens. In retrospect, New Horizons' role in providing close-up photos of dwarf planet Pluto will be uniquely positioned to add useful data to our knowledge of our solar system. Pluto, proud traveller, here we come!
Dave
I believe when Horizon gets to the 9th Planet Pluto, again I say the 9th Planet, Horizon is going to blow the hats off a lot of scientist when they find that there is a lot more going at Pluto then they would have ever expected. One of them being that the moon Charon being in such a close orbit around Pluto, that there will be a lot of title forces and friction going on causing a lot of heat being generated, with that said, this theory I have would explain why some scientist are just now thinking and/or finding that Pluto mite have a thin atmosphere. We will see, maybe, just maybe with Horizon opening our eyes for the first time, the scientist that demoted Pluto will scratch there heads and rethink Pluto as once again being the 9th planet. LOL Anyway to me Pluto will always be the 9th planet.
Have a good day, Tom And Lyn
Sorry about my bad spelling, my eyes are just not what they use to be. Tom And Lyn
When I was 5 years old I was taught and told that Pluto was the 9th Planet, I am 45 years old today an I still believe Pluto is the 9th planet. That will never change LOL
Have a Good day. Tom And Lyn
You bring up the point that our generation (I am roughly the same age) will be the last to keep Pluto in our thoughts as a planet. From this point on younger generations will never hear it being called a Planet. They will call it that extra rock at the edge of our solar system.
How times change
I believed in Santa Claus at that age, too.
Until 1995, I believed gas giants couldn't exist close to stars, then came 51Pegasi, and a host of others.
We always spoke in terms of dwarf and giant stars.
We now call brontosaurus, apatasaurus.
The Universe shows us stuff that didn't fit our old pigeonholes, it would be irrational not to adjust to accommodate them.
Things change.
And Pluto itself doesn't care. It's still the same interesting object it always was...
Frank, me thinks you are missing the spirit of the Plutonian memory..
just an observation.
When I was a kid (I'm around 46 now), they thought Pluto was half the size of Neptune. I remember reading different books, some saying Pluto was half the size of Neptune and Uranus, some said it was Earth size, some twice Earth size. Now it's a dwarf planet with 3 (or is that 4) satellites.
Can't wait for New Horizons to put some of the lingering question to rest.
Tony In Dallas And Tony - From - NJ
Thanks for your optimism, as for me, I am holding onto hope for the little guy "Pluto", and I cant wait to see New Horizon blow the roof off the house. This always happens when we send a new prob to take a look at a new place for the fist time, it cuts through all the speculation and guess work, that we thought was so right, but turns out to be so wrong. I know there is a lot of questions about Pluto, shortly most all of them will be laid to rest and we will know the facts.
Have a good day Tom And Lyn
another problem I see ( when we find out the true facts about Pluto) is there will be a lot of bruised egos out there that will continue to discredit Pluto as a planet to try to keep their reputations intact.
What true facts might those be? Thanks to its moon, we already have the mass of both pretty well settled. We'll certainly learn new things for sure, but it's not like it's going to turn out to be a gas giant (or anything else that might change its dwarf planet status) after all...
Funny thing is I grewup with the teaching that Pluto was the 9th planet in our solar system. I get the feeling that the classification has been changed as to justify making change just for the sake of change. If its not that big of an issue then why change it? I often its more to justify the academics thinking and grant requests as well as their egos. Like I said is change just for the sake of change awlays a good thing? Just one mans humble opinion....
Mark, I disagree with the change in Pluto's status (I'm a planetary astronomer, and along with many in my line of work I still consider Pluto to be a planet), but in no way whatsoever did the change in Pluto's classification to dwarf planet have anything to do with grant requests, or change for the sake of change.
While I disagree with the small group who voted for this change, I do not impugn their motives.
To me, Pluto will always be the "double planet".
I remember seeing an episode of Starhustler -- yes, it was WAY before 1997 -- (RIP Jack Horkheimer!) on PBS where he said that "we're just finding out more and more about the outer planets, and Pluto has a moon that's almost the same size as it! The moon Charon."
The reason I recall it was because as a young kid, it was A Big Deal to stay up (that is, manage to stay up!) that late as he was on after Doctor Who... it was probably 1983 or so come to think of it.
All I see here is that both require a much closer look, in person would be nice, .... cold, but nice none the less. (with all appropriate gear of corse)
Dwarf planets are a third class of planets, small planets large enough to be in hydrostatic equilibrium but not large enough to gravitationally dominate their orbits. That was the intent of Dr. Alan Stern when he coined this term in 1991. What this new information does show is that the four percent of the IAU who voted on the controversial demotion did so prematurely, based on false information--specifically, that Eris was bigger than Pluto. This latest round of the debate was sparked by the controversy that Pluto couldn't be a planet if Eris were bigger and Eris were not considered a planet.
Actually, the New Horizons team are not at all "walking on eggshells." Stern heads that team, and he simply rejects the demotion outright. In his New Horizons updates, he continues to refer to Pluto and all dwarf planets as planets. Members of the NH team are much more focused on what we will learn from the flyby regarding Pluto's complex atmosphere and composition. This data will tell us what Pluto is, not an IAU vote.
This whole embargo notion is highly problematic. It seems very arbitrary as well. Why is it okay to withhold information for nearly a year, then confide in one particular astronomy journalist and ask her not to share the information with anyone else. This reeks of favoritism, and it does not speak well for the science community.
Laurel
I agree 100% Nice post. Tom And Lyn
So, I suppose Warwick Davis and Verne Troyer are third class humans?
Stern has repeatedly brought up a point that astronomers have not addressed: If Earth were in Pluto's orbit, it would not gravitationally clear its orbit, therefore, Earth would be a dwarf planet.
He also brought up the observation that some of his colleagues were uncomfortable with having to classify a large number of objects as planets, possibly hundreds or thousands, and they didn't want to do that. That is an emotional response and has no room in astronomy. If a solar system happens to have 1000 planets, then it has 1000 planets whether you are comfortable with that or not.
I never understood why the star trek classification system for planets was not adapted or a modified version of it. That would solve so many issues when classifying planets. .
A's and B's for the Stars and numbers for the planets?
It was never specified in the Star Trek universe what their planet classification meant. All you really had to know, was that 'Class-M' was essentially Earth-like and habitable. (Just saying 'Class-M' was simpler, and not Earth-centric. There are others in the Federation from similar worlds, such as Vulcan. The 'stardate' system is likely for that same reason. ETs don't care about Earth dates.) I recall another letter reference to a gas giant, but that's all. It was just a plot device that didn't need to be fleshed out.
And we learned in ST-Enterprise the the 'M' was not from an alphabetical sequence, but short for 'Minchara.'
(I'm trying to write a story myself, that has a scene where I wanted to say that the star of a particular planet was an F-7, but none of the characters in the scene were from Earth, and would likely not use a classification system the reader would recognize. There are one or two similar passages with no humans present, where I had to go ahead and refer to a distance in light-years for the reader's benefit, even though light-years and parsecs are both units derived from the particular characteristics of the orbit of Earth, and would be different for another world...)
That's what universal translators are for. Heck, even Hitchhikers had the Babelfish.
Minor planet, major planet, dwarf planet, rocky dwarf planet, gas giant planet, planet, etc., it is all about definitions. The worlds themselves do not change. As with everyone else in the US, I was taught that there were 9 planets. My 1945 World Book Encyclopedia states: "...it is thought to have four or five times the earth's mass." Once its true size was found in the 70s, I quit regarding it as a "planet" in the sense of the 4 inner planets and the 4 gas giants. I taught my two daughters to answer 9 if asked how many planets, but then also told them that there are really only 8.
Pluto and Eris are very similar to each other. In contrast, Pluto and Eris are very different from Neptune. They are also very different from Mars or Earth. Similarly the rocky inner 4, except for size, have more in common with the dwarf planet Ceres, than the gas giants. If the definition of a planet, without adjectives or modifiers, were to include Pluto, then the term "planet" would have almost no meaning. It wouldn't be useful. This is because just about any round object orbiting our sun or any other star would by definition be a "planet".
From the time of its discovery, until the late 1970s, the best available measurements of Pluto kept finding it smaller than the previous measurements. In effect, Pluto seemed to be disappearing. The IAU vote didn't do anything other than to try to make the term "planet" meaningful.
If we find out that Eris truly is "more massive" because of it's rocky core, does that mean it becomes the "ninth" planet, with Pluto still demoted? To me, anything out that far should not be termed a "planet", especially if its composition is mostly ice. --S--
And for gas giants, a significant part of the planet's mass is its atmosphere. Total mass is what matters. That's all gravity (and so, it ability to clear an area) cares about, not what the mass is, nor how far from the Sun.
Remember, some people still suspect (though the data is pretty soft) that there's one or more seriously big objects somewhere way out there...
Long Live Pluto, Ninth Planet of the Sol system!!!!!
Call me what you want, just don't call me late for dinner. It really doesn't matter if you call it a planet or a dwarf planet or whatever. The arguments about the gas giants and the rocky planets being so different they should have different classifications is actually more meaningful, but notice, they do have a different classification. Gas Giants. So Pluto and Eris are quite similar, rocky planets that are so far away that the atmosphere is frozen out.
So call them what you will, just keep studying them and understanad them. It's what makes us human.
As for New Horizon. I doubt that any scientist would opt not to send the mission becasue Pluto was "demoted" from planetary status.
Just keep up the good work.
BTW - one of the neater aspects of New Horizons is that the mission is carrying a bit of Clyde Tombaugh's ashes; a more than fitting tribute to the man who discovered (the PLANET!) Pluto.
New Horizon is a great mission. Pluto (& Eris etc.) is so different from the other worlds that NASA has sent spacecraft to. The story of Clyde Tombaugh is a great one. He did not discover just one new world, but rather a whole new class of 'planets'. Instead of calling them "Plutoids", perhaps they should be called "Tombaughs" to honor him and his discovery.
Hmm, doesn't matter. What is it called, the Ort cloud ? If exploring a planet or that cloud object the whole thing is important. If, and I do mean if, we ever go to the stars, understanding that cloud will be important to getting out of the solar system. I'm thinking of warping trajectory than hitting anything. There may be other problems. Both voyagers are in that cloud and I understand we are learning a little about it.
I'm ready to Occupy Nasa to insist Pluto be put back to planet status! lol
Tony, NASA is already on board with this, so the Occupation needs to be at the headquarters of the IAU (International Astronomical Union) in Paris.
Gotcha, re-writing signs and crossing out Nasa. Adding IAU.
Save Pluto!!
Michael
It Seems only fitting to honor Clyde Tombaugh in this manor. But I would bet he would have never known he or his ashes would have flown so close to a planet he found. This is very nice indeed. Thanks for the post. Tom And Lyn
Tony, will the assault begin at dawn?
5 AM, Pluto time.
OK, sign? check. synchronize watch? check. Oh, wait, relativity will cause our watches to read different times. We will never be able to coordinate this.
Hahaha, yes you are right. Hmm, it's really difficult to Occupy Pluto
If you synchronize it to Hawaiian time, it doesn't matter when you show up, couple hours early, few hours late, all the same.
We need a true "Universal" time zone. That way, we are always on time.
Tony - We do. It's "UTC" or "Greenwich Mean Time" if you prefer.
Yeah, but I think NJTony was talking about something more in line with "stardates".
TonyInDallas: Which would need to be standardized on some fixed point. May as well be GMT. Can't tell the day without the hour... thus you'd have "Earth Time" or maybe "Earth Relative Time" based on whatever the time/date is in Greenwich.
Why not use a pulsar? Or maybe coordinated time measurements from two pulsars? That would be quite Galactic if not Universal.
The easiest reason: we already have GMT, and it's reasonably accurate. We have billions of records across centuries of time based on it. And it's useful from a planetary POV (Hi, it's 12.23 EST right now!). So... why change? Why make for more calculations for something like date/time, which is something the whole planet basically agrees with anyway?
I mean, we could just as well use Paris time, but that doesn't help.
Sorry, I thought we were talking about tracking time while away from Earth. I suppose orbital synchonization with Jupiter might make more sense if we were colonizing within the Solar System, or just use Earth time, but which time zone?
Yes, I meant a stardate. Why are we still limiting ourselves in thinking our earth time is it? lol
Obviously if we picture our earthly border being stretched far into space, then Universal time isn't that earthly.
I was getting a little deeper than just asking what UTC was Mark.
Tonys- Yes, of course. My point was that even if we do leave Earth, it's going to be a very small percent of the populace that does so for centuries if not millenia. It makes more sense (IMO) to go by Earth time vs some nebulous (pun!) stardate. Kind of like AD -- we're still dating time on Earth by the birth of Jesus Christ even though believers are a minority.
Yes, we should be counting the years from the date of JFK's death. That would make more sense.
I use a Nostradamus calendar, but I have to figure out what it means.
A Nostradomus calendar? That would be a calendar that is put together in date order, then the days and months and years are scrambled, and then written in a cryptic poetic form?
In the second month of Ceasar, in the year two enemies die; the fourth day of Saturn;
That means I am about to get more coffee to wake up from a long weekend.
Or an asteroid is about to hit Earth, can't say for sure.
Pluto can be promoted again.Â
Yes, it's original promotion to "Planet" may have been a mistake, but....there IS something to be said for leaving well enough alone. Pluto shoulda been "grandfathered" into remaining a planet.Â
Notice, they waited until AFTER Clyde Tombaugh died to demote Pluto. It would have been TRULY sad to have pulled the hard work from such a devoted scientist in his final years.Â
Â
In the end it doesn't matter if Pluto or Eris is the larger - they are both dwarf planets and does not change their status in the Solar System.
Ha, ha "Star Trek" classification of planets would be amusing - but have no criteria assigned to them nor do they define what a planet is.
Ceti-Alpha six?
Class M?
Alan
If you have time? I made a video about our Solar System, it is on my Youtube Channel "Thomasp671", The name of the video of corse is "The Solar System" The video is not to scale like you say in your Book "The Case For Pluto" But it dose tell a story about how Beautiful and how big the Solar System is and How Small all of us really are. Thanks for your Time.
Tom And Lyn And Thomasp671 On YouTube.
Alan
I just finished Reading Your Book " The Case For Pluto" I have to say it Brought me to tears, and I love the way you are sticking Up For Pluto. My Hope is that history will keep it on the map. It was a very nice read. Thanks Tom And Lyn
As a Planetary Systems scientist (Planetary scientist)I regard both Pluto and Eris as planetary bodies..... planets. And to further dismantle the "Pluto in not a planet" theory...the moon is a planetary body as well...99.9% of all Planetary Systems scientists regard Pluto as well as many other planetary bodies as "Planets"...what most people may not realize is the IAU vote only consisted of a very small % of the IAU community...and of that small % there were only a few of Planetary Systems scientist present. Now I do not know what the vote count was but I do know that there were those who voted against it. I am willing to bet that the Planetary Systems scientists that were present voted against it!...the fact is if a vote were to take place and further... it was indeed the Planetary Systems scientists that were to vote on it. (in my opinion these are the folks that should have been the ones to vote on it) Pluto's status would not have changed. It is just my opinion but I believe if a vote was necessary it certainly should have been the Planetary Systems Scientists and not the Interstellar Matter scientists,Space & High Energy Astrophysicists,Variable Stars scientists... et cetera...that should have been voting on it in the first place!
And for those of you who do not think it is a very big deal as to what is classified as a planet give this a look
Send your complaints to Guess I can not post IAU addy on here
Starhammer
Thanks For clearing that up!!!!! I hole heartedly agree with you and your post. Planetary scientist like you are the ones I believe who is going to come out in the end to give back Pluto’s Name, and the ones who should have debated this long ago to keep Pluto’s standing as a Planet. Thanks For your post my friend and thanks for standing up for Pluto. Tom And Lyn
What is the problem with labeling pluto a planetoid rather then a planet? I grew up with knowing it was a planet but for me I find a planetoid is more fitting especially since we are most likely to find many more "planetoids" out in that far orbit. When does the term planet going to stop?
I look at it like pluto is in a sub category of planet. it prety much fits.
Our astronomers are and have been wrong about so many things that, their penchant for labeling things should be left to them, its their only factual contribution to astronomy. Giving names and classifications to things unseen by anyone but a chosen few. Manned flights and missions may reach Pluto, or pluto, if you choose, but I doubt it because it is thirty eight times as far from us as Mars is. Logistically, we have not solved the problem of keeping a crew alive for the eighteen month duration of this planned mission. Their are no McDonalds between Earth and Mars and certainly not one Wendys between Earth and (P)luto. Our problem is the same as those sixteenth century ships of exploration, food and water, with one additional missing element, air. One day the government will see the folly of manned flights and there expense and limit our explorations to unmanned flights. After all, all of the rocks and soil brought back from the Moon can be found on Earth in a less pristine condition. If and when any are returned from Mars they will be found to be of the same ilk. Its like the reverse of carrying coals to Newcastle. Only in this case we are going to Newcastle getting coal and bringing it back to Virginia and comparing it with coal mined in that State. It might have a slight different composition but it would still be coal.
Thanks Starhammer For your post
To me, the argument about whether or not pluto is a 'planet' is completely pointless. It seems like the only real drivers in the argument are emotional.
There is an increasing number of bodies being discovered orbiting around stars, and common sense can infer that other solar systems have a great many things orbiting it's star, that range in size from specks of dust to not quite stars.
IMO The lines drawn in the sand about which body is which are completely arbitrary, and only really matter to people who really care about labels.
It's almost like listening to two people argue about at which precise milligram a rock is no longer a rock and is instead a boulder.
I feel bad for people that cant handle the change, with space exploration and its future if you cannot accept change then you have a problem because once we get out butts out there and really start to explore just our solar system we are going to have to relabel and classify things that we were taught. If you cannot accept that they the problem is with you and you will be left behind with history.
Things are going to have to be renamed, reclasified otherwise its going to be impossible to organize all the new discoveries.
The only constant is change. This will never change.
isn't a dwarf planet still a planet?
<sarcasm on>
Pffft, no. That's like saying a dwarf human is still a human.
<sarcasm off>
Ok, here's the deal on whether Pluto is a planet, dwarf planet, planetoid ,whatever. since it's basically an ice ball, and has a pronounced elliptical orbit (its furthest orbit point is in the kuiper belt) It's a kuiper belt object. REGARDLESS of any other name you want to give it. Hell, if its orbit was skewed any more we'd probably call it a comet. I propose we table this argument until we get a probe out to it and really look this object over good.--S--
What does this do to the accretion theory. The ultra wide variance in the masses, sizes, compositions and distances make this theory highly improbable. A more probable theory, that of an exploding core of the Sun is much more believable. The core of the Sun is layered in shells of all of the elements in a radioactive state. When it exploded it tossed some portion of all of these elements into a surrounding mass of space gas which is primarily the Hydrogen proton. What do you get when you combine Hydrogen and Oxygen, water. What are the major Planets composed of in the main Hydrogen, Oxygen and Carbon with traces of many of the other elements. All solid bodies have as their principal compound Oxides and Carbides with traces of all the other elements. The total anount of mass outside the Sun is just about one percent of the Sun's mass, and that one percent is composed of approximately ninety five percent of three elements in compound form, Hydrogen, Oxygen and Carbon. Except on Earth all water on every other solid body is in the form of ice. On bodies having a mass less than fifty percent Earth's mass water vapor cannot be held to the surface gravitationally. Mars possibly once had water ice on its surface, but due to the low atmospheric pressure on its surface and with its distance being just outside the comfort zone, during periods of heat this ice was gradually evaporated as water vapor and escaped into space. What water it still may contain is found at its poles as ice or may be trapped beneath its surface at some depth. The Earth originally was layered in possibly ten miles of ice as it performed an orbit with an aphelion distance of nearly a billion miles from the Sun with a perihelion distance greater than two hundred million miles. On one of its orbits it managed to pick up a satellite which greatly altered its mass relationship with the Sun and put it into a new orbital configuration closely approximating our present distances. The ice shell melted and eventually volcanoes brought land up through the water to form our present land mass. About one third of all the water on Earth is contained in that structure known as the Earth's crust.
The theory that our Moon was a creation of a collision between some mass and the Earth's mass is not sustained by the nearly globular structure of the Moon. If it had been torn from the Earth's mass, we should have a lobsided Earth structure where the collision took place. It is obvious that if the heat had been generated to render the Earth and the Moon into two molten masses, and thus caused them to reform as globular shapes, such heat would have evaporated all of the water on Earth. A more likely explanation is the Moon was captured as a satellite while Earth was in or at aphelion distance from the Sun from one of the major Planets. The additional mass to this now dual body system reconfigured our orbit into a close approximation of our present distance. We know or we surmise that we know that several bodies in orbit around the major Planets have been captured either from other Planets or from bodies reaching a status where the two orbits were at near aphelion positions to each other. The ultimate velocity of any body at aphelion is zero. If a nearby larger mass is available the smaller body can be captured. Its aphelion position may be in relation to the Sun or any other body it is orbiting.
Tony from NJ, ours is NOT the last generation that will think of Pluto as a planet. The IAU decision, made by four percent of the group, most of whom are not planetary scientists, continues to be opposed by an equal number of professional astronomers, many of whom signed a formal petition rejecting the definition. I encourage anyone with kids to read the section at the end of Alan Boyle's book on how to talk to kids about planets. Pluto can and will continue to be regarded as a planet by future generations if we actively make sure that this happens. Also, Pluto is both a Kuiper Belt Object and a planet. The first tells us where it is; the second tells us what it is. It is not a comet, and it is not primarily an icy body, as it is estimated to be 70 percent rock. Pluto is also geologically differentiated into core, mantle, and crust, just like Earth is, and it has an atmosphere and weather. These are what make it a small planet. As for accepting change, this should not be done blindly or simply for the sake of change. Any time someone proposes a change, we have to question whether that change is an improvement. Sometimes it is, but in the case of the IAU definition, it was not.
Thank you Laurel. I am among the astronomers who insist that Pluto is still a planet, dammit!
(And with the above post this vine has been officially "Laurelled" - we are honoured! FR request sent....)
While I completely agree with you, I have to ask whether Pluto is still included in school books as a planet, or if it has been removed or listed as a non planet. That is why I mention ours being the last generation to hear Pluto being officially called a planet. (As a dad of two teens I should have asked them what's in the school books but I keep forgetting. :) )
Most of us grew up hearing Pluto IS a planet, and it means more to us to keep it that way. Newer generations may not feel as strongly because of what they heard growing up. That is what my concern is. I hear more and more young people say that Pluto is NOT a planet. This is what they are hearing, so it seems that it has become an official way of looking at it.
I think some people are saying Pluto is NOT a planet because they don't consider DWARF Planet to be a Planet. This may have more to do with educators overemphasizing the NOT planet rather than teaching about the new category. Gas Giant is a category, why not dwarf?
And again, shouldn't Neptune and Uranus be classified as Dwarf Gas Giants? Maybe after New Horizons, Pluto will be changed to Miniature Dwarf Gas Giant?
What I don't get is this, and maybe you can shed some light on it Michael. If it's the condition that hasn't cleared out it's obit that keeps the IAU from saying it's a planet, then why are any of the "planets" in this system considered planets? As far as I know, all of them have a bunch of debris located in L4 and L5 with Jupiter having a huge bunch of crap at those two points. Or does the IAU make an exception to those areas?
Mitchell
Hiya Mitchell!
I am not the best person to attempt to defend the IAU's definition, given that I think that it is flawed, but their central point is this - rather than thinking of the situation as "something that has cleared its orbit" (because, as you point out, NOTHING in our Solar System has cleared its orbit), it's more a case of "a planet is the absolute master of its domain" - it is the undisputed champ of its orbital zone.
Jupiter, Earth, and the rest of the Gang of Eight are clearly the champs of their orbits; there is nothing else of similar size in their orbital zone.
Pluto, however, is too small to clear its region of all the other similarly-sized objects, hence (according to the IAU) not worthy of the full-fledged planet designation.
My first problem is this - the IAU's definition is completely dependent on where in the Solar System we are talking about. If we moved switched Pluto and Mercury, we'd find that Pluto would likely be of sufficient mass to have cleared the zone from the Sun to about 1/3rd of an astronomical unit. Mercury, however, even tho EVERYONE is happy to agree that Mercury is indeed a full-fledged planet, lacks sufficient mass to clear Pluto's region (~50 AU's out). Move Mercury, and it's no longer a planet?
It gets worse.
Move Earth a bit further than Pluto - let's say to the orbit of Eris - and we would find that even the Earth lacks sufficient mass to clear the "Eris zone".
Move far enough out - about 150 AU's (or somewhat farther than is Voyager 1) and even JUPITER would lack sufficient mass to clear that zone.
I do not believe that where a body happens to be in the Solar System should determine whether or not it is a planet. A planet should be a planet, no matter where it happens to orbit.
Another way to look at the definition; both Ganymede (moon of Jupiter) and Titan (moon of Saturn) are larger than the planet Mercury. Geologically they are both planet-like worlds. How come they are not planets? Just because of where they happen to orbit?
In the remainder of astronomy, a star is a star, no matter where it may be, if it is of a certain mass, composition, and hot enough to support fusion at its core.
Similarly, a galaxy is still a galaxy, ranging from tiny "dwarf" galaxies to behemoth monsters that are dozens of times larger than our own Milky Way.
Why isn't a planet a planet, no matter where it may be, if it is of sufficient mass and composition?
Why this lack of consistency in astronomical classification?
Well, if that's the case, then how can we consider Neptune a planet since Pluto/Charon are significant bodies that intersect Neptune's orbit? Despite it's irregular orbit, there's nothing at this point in time to suggest that Pluto hasn't been in this orbit for the past billion+ years, giving Neptune plenty of time to get rid of it. Even if Neptune was the initial cause of Pluto's orbit, it's still there and hasn't been taken care of.
Even still, I've always argued "what happens if we find a small gas giant at the edge of the Kuiper Belt?" There definitely wouldn't have been enough time for it to clear out it's orbit (if it ever could at that distance), and certainly wouldn't be a master of it's domain. Not to mention all your arguments also.
It's such a poorly defined definition, passed in such a distasteful and even disgraceful manner, that it just begs the questions "Is this mostly(or all) about ego? Getting your name in as a player, mover/shaker of astronomy and all that? That it's our opinion and that's the only thing that matters?" and whatnot.
Seriously, why haven't the rest of you left flaming bags of dog poo on their steps? *grins* Yeah, I know, that's going too far, especially since I assume you know at least some of them, but metaphorically speaking lets say.
*sigh* I sorry, I sometimes have an extremely hard time with blatant stupidity, especially when dealing with people who should absolutely no better, and this just reeks of it no matter how you slice it.
Mitchell