E-mail updates
Follow on Twitter
Subscribe to RSS
M. Showalter / SETI Institute / NASA / ESA
This photo from the Hubble Space Telescope shows Pluto and its five known moons, including a newly discovered satellite indicated as P5. Its provisional name is S/2012 (134340) 1.
Astronomers using the Hubble Space Telescope have discovered Pluto's fifth moon, a little more than three years before a NASA space probe is due to sail past the dwarf planet and its tribe of satellites.
The irregular moon, estimated to be 6 to 15 miles (10 to 25 kilometers) across, was found in the course of checking out the potential collision hazards facing NASA's New Horizons spacecraft for the Bastille Day flyby on July 14, 2015. "The inventory of the Pluto system we're taking now with Hubble will help the New Horizons team design a safer trajectory for the spacecraft," the mission's principal investigator, Alan Stern of the Southwest Research Institute, said in a Hubble news release.
Stern and his colleagues suspect this fifth moon won't be the stuff they find in Pluto's neighborhood. "The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system," said Harold Weaver of the Johns Hopkins University Applied Physics Laboratory.
Call it P5 ... for now
The fifth moon is currently known only by its provisional names: S/2012 (134340) 1, or P5 for short. It'll be up to the discoverers to propose a more lyrical name to the International Astronomical Union, which classified Pluto as a dwarf planet in 2006.
P5 was detected in 14 separate sets of images taken by Hubble's Wide Field Camera 3 on June 26, 27 and 29 plus July 7 and 9. The Hubble team says it's in a 58,000-mile-diameter circular orbit around Pluto that steers clear of the dwarf planet's four other satellites — including the biggest moon, Charon. Two other moons, Nix and Hydra, were discovered in 2006, and the fourth moon (P4) was found in Hubble data last year.
"The moons form a series of neatly nested orbits, a bit like Russian dolls," team leader Mark Showalter of the SETI Institute said in today's news release. He told me that small moons have now been found in the Pluto-Charon system at close to a 1-to-3 orbital resonance with Charon (P5), a 1-to-4 resonance (Nix), 1-to-5 (P4) and 1-to-6 (Hydra). This suggests that the moons were formed from debris blasted away by the collision that led to the coalescence of Pluto and Charon as we know them today.
"This is a very tidy system, and what that means is, it's an orbitally evolved system," Showalter said. "Literally there are shells where the orbits are stable."
Pluto's moons are traditionally named after Greek mythological characters associated with the underworld. Nix, for example, is an alternate spelling for Nyx, the name of the Greek goddess of the night and the mother of the Fates. (The more typical spelling, Nyx, was used previously in the name of an asteroid.) Hydra is the serpentine monster that guarded the gates of the underworld. "It's a very colorful cast of characters," Showalter told me.
For P4 and P5, the team members are holding off on proposing names for now, just in case a P6 comes along. "It's still a moving target, because we don't know what might come along," Showalter said. "I expect that in a month or two, we'll have finished everything we're going to find until New Horizons gets close." Only then will the team seriously consider what the two (or more) moons will be named. If things stay as they are, P4 and P5 will probably be named after a pair of characters with Greek underworld connections, such as Orpheus and Eurydice. (The name Orpheus is already taken, but they could go with a variant, such as Orfeo.)
As of today, Showalter says there are no other Plutonian moon candidates in sight. "Of all the things that we have looked at, that we thought might be moons, none of them has ever been convincing until this came along," he said of P5. "There is no P6 in our back pocket at this time."
The detection ... and the debate
Finding P5 was hard enough. Showalter told me that he first spotted the moon in the data on Saturday, the 7th. He and his colleagues then went back and found signs of the moon in the data gathered earlier, as well as the follow-up imagery captured on Monday. The object is just 0.001 percent as bright as Pluto, and 4 percent as bright as Nix, Showalter said. "We're really at the edge of what we can accomplish with Hubble," he said. "I don't know of any instrument that's going to be better than that."
In an IAU circular issued today, the team reports that P5's brightness is about magnitude 27, which makes it half as bright as P4. The brightness was used to estimate P5's size.
Today's announcement revived the debate over whether Pluto should be counted as a planet, period, rather than a dwarf planet. The difference, as outlined by the IAU almost six years ago, has to do with how much a celestial body has "cleared out the neighborhood of its orbit." In my book, "The Case for Pluto," I set out the argument for counting Pluto and other worlds that have a basically roundish shape as types of planets, even if they're put in the dwarf category.
"The name 'dwarf planet' really doesn't bother me," Showalter said. "When you think of a bonsai tree, it's still a tree, and what's interesting about it is that it's really, really small. I think of Pluto the same way. ... It only gets more interesting with each one of these discoveries that comes along. If you don't like the term 'dwarf planet,' call it a 'bonsai planet.'"
I like that approach. But what about you? Feel free to weigh in below with your comments on Pluto, P5, or your suggestions for the names of the bonsai planet's newest moons.
More about Pluto:
- Final push for Pluto's postage stamp
- Scientists spot Pluto's fourth moon
- Carbon monoxide found in Pluto's air
- Pluto debate is about more than one little world
- Cosmic Log archive on Pluto
Last updated 4:30 p.m. ET.
In addition to Showalter, Weaver and Stern, members of the discovery team include A.J. Steffl and M.W. Buie.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.
Leave a Comment:
actually it waas my error, the hydra guards the entrance on earth to the underworld, you are correct. lol my bad cerberus does do the things ii mentioned tho it lies as i said, the entrance to hell itself beyond the river styx
Tartarus i believe was the name for hell then lol
The main factor criteria involved with determining that status of a planet is not really how many Moons orbit it but can simply be summed up as how many humans are able to be placed the object.
Which is what a planet is really about, placing humans on it in order to inhabit the planet to make it our own.
The more humans that are able to be placed on a planet means that the planet will enjoy a higher status among a planetary scale.
Hmm, haven't heard that definition before. :-)
not that surprising. what the hell else is there out there to be gravitated to?
The IAU definition is not based in a "ontological" scientific method, in no other
branch of "subsisting" science that am I familiar with, continues something that anachronistic. "We're going to call it a cow, except when it's in a herd, then it is a dwarf cow? It is a river, except when there are other rivers near by, then it is a dwarf river, or would it now be a creek, or a stream". Fact is real geologists call a river a river independent of whether there are other rivers nearby. In science, we call things what they are based on their attributes, not what they are next to. So to most planetary scientist this is absurd.
And the IAU definition is even worse, because it produces different
categorizations for identical objects, depending on where they are. Reread what
I just wrote and let it sink in.
In science, we take large numbers of disparate facts and reduce them to
see patterns. We use the patterns to reduce the amount of information. It is the
reason we name species and genera and families and families into an orders, orders into a classes, classes into a phylums, and phyla into a Kingdoms as far a biological sub-groupings. It's also the reason we have names for certain types of geological features, and so on in other fields.
If you wish Pluto to be called something different, if you do not believe your
son or daughter will be able to comprehend more then eight objects in our solar system as planets, then do what most logical planetary scientist do, call them... "kiuper belt planets", hell think about it, are we now going to change the definition of Pluto's moons? Because if Pluto has not cleared its orbit then nor has any of it's moons, are they now dwarf moons?
Here are the facts, planetary scientists study planetary bodies, and guess what,
it will be "planetary scientist" that will be studying Pluto. Not a "dwarf planetary
scientist", although some of the scientists may be less then average in height,
but until the IAU changes their title as well, they are "planetary scientists".
The fact is the moon is a planetary body as well, it just happens to be a satellite
of earth, and planetary bodies that orbit other planetary bodies are called moons (satellites), unless they are part of a ring system then they are called
"shepherd" moons, oh no I should not have brought that up, now the "mighty"
IAU may demote Pluto even further and "vote" it to be a "dwarf shepherd moon
kiuper belt ice object"(..l..) (Are you kidding me?)
Just a few more things to think about, if mercury was replaced with a moon
sized body, it would still be a planet even if it were the size of the smallest moon in the solar system simply because it is a celestial body that is in orbit around the Sun, and has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and has cleared the neighborhood around its orbit.
What many people may not realize is the farther away a planetary body is from
the solar systems center the more likely it is, that planet will not have "cleared"
its orbit to a lesser degree. This is because, the farther away from the solar center you are the more accretion disk matter there is, and the longer the planetary accretion process takes.
The clearing of an orbit is a planet evolutionary process that is on-going,
from the birth of a solar system until there is no longer any matter to be accreted. And as far as we know that continues even after the solar death of that system. Earth continues to grow every second, it is hit by dust and debris. It is a process that "real" planetary scientists call accretion. And no planetary body that we are aware of has truly cleared there orbit.
A few years ago I was privileged to be able to witness jupiter continueing to clear its orbit, you may have rememered the event as well, shoemaker levy?
There are different periods of this accretion process from gravitational collapse of the molecular cloud, to stellar ignition, to Late Heavy Bombardment era. among others and will continue the accretion process, until there is no matter left to accrete. Were there any planets in the LHB era? according to the IAU definition no. Jupiter was nearly the size it is today, but in its LHB era. It would have not cleared its orbit to the degree it is today.
I could write another thesis on the subject, but have done that.
And as long winded as this is, I am trying to make a point.
Our solar system is not static, it is alive and growing. And the fact remains that Pluto and the like are still in a stage of accretion. In fact Pluto may still be in what is called planetary migration. But until we have a better understanding of the total solar system evolutionary process. To use the "cleared the neighborhood around its orbit" as part of the definition, is unscientific, this is something any reputable planetary scientist should know.
I work at the Lunar and Planetary Institute, my field is called planetary
sciences, I am a planetary scientist, It seems to me absurd to be in the
position, the day after the IAU vote, not to understand the basic attributes of
those objects after which the field is named, and of which I have dedicated
24 years of my life to researching, and nine year previous to that
earning the degrees in which to enter this particular field.
So, speaking strictly as someone that knows a little bit about this subject, this
is my feeling.
The IAU treated this Pluto "vote" debacle in a very unscientific way, saying, "We
just won't count those things as planets." And you even had, believe it or not,
some very accomplished astronomers, in some cases saying, "We can't have
50 planets. My daughter will never remember the names of all of them."
That's not a very scientific way of going about it, since we have countless
numbers of stars, galaxies, asteroids and everything else.
What the IAU did is essentially unforgivable, because it teaches disrespect for
science. This new definition, which creates a circumstance where an
Earth, Venus, Neptune, Jupiter..etc aren't planets in every circumstance, it just doesn't breed respect for science.
People can look at pictures of objects that obviously look like planets, and they
get ruled out because they happen to be near something else, not what they
are, but what they're near, again, it breeds disrespect.
And when you show pictures of scientists voting, it's just awful. Because there
are a lot of people in our society who then think science is arbitrary and
political, that global warming and climate change aren't real, that evolution is
just some idea to be voted on. And when it appears that science is decided by
votes, it makes all of science look arbitrary. And that is not at all what science
is.
Most planetary scientists aren't even in the IAU. The IAU's made up primarily of
people who study galaxies and stars mostly. So the members are not experts
on planets to a greater degree. I am a planetary scientist and have many sub
categories that I specialize in, I know many other planetary scientist, and If
it should have been voted on in the first place,(not) it should have been the
planetary scientist that did the voting, but science is not voting on what
something is or is not. Can you imagine voting whether the world is round or not?
There are far more determining factors that go into planetary science then,
it's orbit, is it round and what it is next to, much more.
There are many people that would be shocked to learn how many
planetary bodies there actually are in our little solar system, And the fact that
there are, can not be changed by a vote. Again, how is voting, a process of
scientific study?
Much more than a simple blog post - it's a guest editorial; A+1!
The only point I'd suggest to add is the fact that there are moons in our Solar System that are larger than the "planet" Mercury. The bodies that comprise our Solar System can be placed on a continuum. From a structural point of view there is no clear line between those that are just larger, and those just smaller, from one another.
For those damned orbital dynamicists (the group opposing Pluto's planethood) it's all about how bossy your proposed planet is - you "gotta be big enough to clear your neighbourhood" and all that. The problem is that a planet would need to be bigger and bigger as one moves further and further out in the Solar System to clear its orbital zone. Move Earth to Pluto's orbit, and you would find that our own "planet" is too small to clear the zone with the volume of Pluto's region of space. Go far enough out, and even a Jupiter-mass world would be insufficient to clear its orbital zone.
Pluto is a planet, dammit.
Dammit, you're right!
I agree on pretty much all of your points. This is why the whole planet/non-planet thing bores me to tears. It struck me at the time that the whole IAU vote was about was panic over how many planets school children would have to remember in the future. You're right, that's not science. It's culture.
These self important, self promoted intellects with their insect authority complexes might want to rename the sun, bulb, or orb someday. It is simply an indication that they have failed to to shed the most embarrassing of human traits. If you want to see how stupid a cop, scientist or many other people can get just give them a moment of publicity or put them in front of a camera. The people who call Pluto a dwarf planet have dwarfed themselves in the eyes of normal people.
We know that the sun is a star, we can tell based on it's properties, just like we could tell by Pluto's properties that it isn't a planet because it hasn't cleared it's orbit of debris due to insufficient mass
Why not just call Pluto a sun-orbiting entity, or sun-orbiting doo-dad?
There is already a KBO called Ixion.
The discovery of the new moon around Pluto, I wonder if that qualifies Pluto to be reclassified as a planet. It seems like if they demoted it to a dwarf planet instead, they usually don't have moons orbiting them and they don't orbit around other planets but Pluto does. Of course, Pluto knows nothing about all this.
There are planets that do not have moons (Venus, Mercury), and there are asteroids that DO have moons (Ida, Kleopatra, Debussy, and hundreds more).
There is even discussion if Saturn's moon Iapetus once had its OWN moon once upon a time.
Having a moon, or not, in no way impacts whether an object is classified as a planet.
Michael, a complete aside. Who suspects Iapetus once had a moon and how would they know? Can you direct me to a paper or an article about this?
I once asked an astronomer why moons didn't have moons. He was under the impression that the orbital resonances make such systems unstable and that a situation like that couldn't persist for long. Presumably there is math to express this, but I've never seen it. Then again he could have just been speculating. I do not believe there is a single example in our solar system of a satellite with a natural satellite of its own.
A couple of the recent papers:
http://www.agu.org/pubs/crossref/2012/2011JE004010.shtml
http://www.agu.org/pubs/crossref/2012/2012EO140028.shtml
An excellent lay description from Emily Lakdawalla:
http://www.planetary.org/blogs/emily-lakdawalla/2012/3389.html
A red, or redish, haired lady? Hmmmmm....
Darn, she appears to be married.
You are about 9 years too late Tony....
That's ok, my lady of almost 5 years is a college professor, sociology. She's pretty neat, too.
That is a heckuva interesting hypothesis. I actually find most of it convincing. The explanation as to why we don't see more moons with equatorial ridges seems a bit strained though.
Can I just say that the people who still want to argue about the planetary status of Pluto are now boring me to death? Seriously, has it altered Pluto in any way, made it a more or a less interesting object? Are you really that hung up by the fact you were told it was a planet in grade school and you just can't wrap your mind around the idea that viewpoints have changed? What is this about? Why is this so freakin' important?
I honestly feel like I'm the only person in the world who is at all interested in astronomy that this doesn't make a scrap of difference to. The IAU could have gone either way and said that all those tiny bodies were planets or they could have decided that not only are they not, but that those big planets like Jupiter were so different from little planets like Earth that they are an entirely distinct type of celestial body and it wouldn't have made any difference to me. It is strictly an issue of taxonomy and doesn't actually effect the natural world in any way.
I'm a planetary astronomer. Yes, I am (as you put it) "hung up on" Pluto's classification.
If you don't care feel free to move on; it's a big Universe and please do enjoy what's out there that grabs your interest. For me, it's planets that fascinate me; it is my life's work.
Classification is a large part of what science does; we describe and try to understand the natural world around us.
I get that classification has some importance to how we file away our facts, it's damn near *everything* in biology, I get that. What I *don't* get is how serious scientists are willing to allow members of the public to consider the reclassification of Pluto a "demotion" or to treat it as anything more than an issue of culture. It tends to make me take them less seriously as scientists.
If I were you, I would be treating that as an issue.
Michael, if we are to have different classifications of planets, shouldn't we have different classifications of their satellites? There are vast differences between Luna, Titan and Ganymede and what orbits Mars.
Even if you exclude the satellites of Mars, there are still HUGE differences between Luna, Ganymede and Titan! There is no way you could consider those the same type of body. If they all orbited the sun on their own, they would be called terrestrial planets, but ones as different as Mercury, Venus and Earth.
The point being that their size and gravity allow them to be spherical, while the satellites of Mars are glorified irregular shaped asteroids.
Red Wolf-2228177, Several dwarf planets have natural sattelites as do several asteroids. Haumea, Eris and Pluto all have sattelites.
Dear Eoanthropus:
Thanks for that information. Also, referring to your prior blog, I don't find science boring even if the scientists change their minds a lot. They are learning and well on their way to progress.
I'm sorry, did I say I found science boring?
Personally, I am rejecting the demotion of Pluto. Pluto will always be my 9th planet. Five moons, come on! Pluto is a planet.
I thank you!
Alan,
I am just a reader who likes the Cosmic Log blog a lot. Love the article above. I have a question though (arises from my lack of knowledge about space science), in th article you mention that the brightness of this new moon was used to measure the size of it. I remember reading a previous article () here and how scientists under-estimated the size of this asteroid as it was only reflecting back around 2-4% of light. Could it be possible that the size of the P5 is also under-estimated? Again like I said may be this question is completely irrelevant as the size detection based on brightness approaches might be different in both cases and this is where my layman status about space science might be showing. But I was just curious.
Thanks for all the wonderful articles.
Dear aggp11:
I'm not the one that can answer that particular question. It is a very intelligent question that you asked. Hopefully, you will get an answer. I will be interested in knowing the answer too. I had always wondered how do they really know that Jupiter, Uranus and Neptune are really gas planets, that they are just a ball of gas instead of being the real thing, a planet that is dirt and rock or at least rock. A satellite has never gotten close enough to analyze them to determine it.
They can also over-estimate size on brightness, just as they can underestimate it.
We will know in about 3 years, though, when New Horizons gets there.
I think that is at the heart of my central question. The cumulative mass of the entire Plutonian system is not very large.
I wonder if in the inner solar system such a grouping could maintain itself.
Yes, it's possible that it's over or underestimated, for sure, if it's unusually shiny or unusually dark. As Tony says, we should know in 2015.
This is enough to get Pluto reinstated in the solar system! Pluto is a planet, I tell you!
Alright. Explain to me and everyone else why this is a meaningful debate.
Need I explain?
It's up to you to decide if you need to explain. Someone has asked you to.
Couldn't we just have some fun with this???? If Pluto is a dwarf planet, couldn't we just name the moons after Snow White's little friends. Personally, I think it would be fun to ask if anyone has seen Grumpy lately. I do understand the need for some sense of decorum...just trying to lighten up the blogosphere.
I don't comment on articles frequently but the whole dwarf planet thing is my pet peeve. I'm still stumped how many people miss this simple, devastating response to the IAU's definition that Pluto is not a planet because it hasn't "cleared out it's neighborhood."
By the IAU's definition, if Jupiter were located sufficiently far out in the solar system (like the Kuiper Belt) or if it were a rogue planet (which recent estimates put at 100M throughout the MWG), it would no longer be classified as a planet. In fact, it would be a dwarf planet. But we would all still agree that it would strain credulity to call Jupiter a dwarf planet, would we not? Defining a planet by its location and not its characteristics is ludicrous.
I'm with you, Alan. If they really want to distinguish them from other planets, I suggest they call them Plutonians, similar to Jovians being distinguished from Terrestrials. They clearly are a distinct but realated type of body to other planetary bodies. Additionally they are clearly distinct from irregularly shaped asteroids, comets and other undersized KBO's.
Dear The Big Lebowski Legacy:
Wow, where did you get that nickname? That's a good idea in your article. We should consult with the Plutonians in case they think we're really up to dominating and colonizing their planet, Pluto.
There is something to be said for that notion. it is clear that Ceres is a completely different type of body from the others that are currently called dwarf planets.
Like Pluto, Ceres was once considered a planet. How come no one is burning up the Internet whining about that? For that matter, so were Pallas, Vesta and Juno. Why isn't some true believer beating a drum and declaring "Juno will always be a planet to me!"? An imponderable mystery that!
Ceres, Pallas, Vesta, Juno backers unite!
Ceres, yes. Pallas, Vesta, and Juno - not so much.
If it's spherical it's a planet. If it looks like a potato then it's a plan-not.
How do you feel about Haumea?
Haumea is way cool. And yes, in my book, spherical enough to be dubbed a planet.
It would be fun to explore the idea of density, as well as "sphericalness" (hydrostatic equilibrium) as part of the description of planethood. Is it still a planet if it's mostly ice? Hmmm....
I guess you have to decide how useful it is to have minutely described classifications rather than a single category of non-radiating bodies that orbit a star that may contain several classifications within it, not unlike....well, not unlike the system we use now.
@RedWolf -- The name stems from the fact that I am a huge Jeff Bridges fan, Tron Legacy was awesome and TBL is quite possibly the most quotable movie ever. I've never committed to watching it all the way through, mainly because I can't tolerate a shiftless, middle-aged loser as a central character, but have learned over the years that many of the phrases, words, etc., that I use in casual conversation actually made their way from TBL to me through the lexicon built by my age group.
Queue the Uranus jokes from the morons.
one so far.
When I was younger, Pluto was a PLANET and had only ONE moon, Charon. Oh how times change!
When I was younger the Earth was the center of the universe......
:-)
Earth? Universe? When I was young, I was too busy hiding from dinosaurs to worry about such things.
However, I do remember when Pluto was considered about half the size of Neptune.
All I remember from my younger days was a really big bang!
It's too bad that gravity fields cannot be imaged. Then, any and all bodies that orbit our sun could be measured and photographed based upon the gavitational fields alone. However, this would not give you a detailed photograph of it's atmosphere or surface features, but, it would give you an indication of the size and mass of said object from the sun. These fields could only be measured from the most massive object acting on the object trying to be photographed though, because the sun is what holds all of these planets in place... a real, tangible, field, that we need to learn more about.
Starhammer, you hit the nail on the head and covered all the bases. Pluto is a planet because it orbits a star and is large enough to be rounded by its own gravity. What is really troublesome is hearing people blindly accept something as truth because a group that calls itself an "authority" issued a decree. That is dogma, not science. Just saying "the experts have decided" doesn't make something fact. Plus, the majority of IAU members who voted on this are not even planetary scientists but other types of astronomers. It seems like there are also some astronomers who have decided in advance that no matter what new discoveries are made, Pluto can never be considered a planet. Are their egos bruised because the 2006 decision has remained controversial this long or because members of the public and amateur astronomers, who they think should have no say in this matter, are rejecting their decision? If a position is weak and makes little sense, such as the notion that dwarf planets are not planets, or is absurd in potentially designating the same object as a planet in one location but not in another, why shouldn't the public question it and yes, reject it? Are some astronomers threatened by people thinking for themselves? Just the fact that time has passed doesn't mean we should accept a flawed definition and "move on."
Most of us who support Pluto's planet status also support planet status for Ceres, Haumea, Makemake, and Eris and potentially other spherical Kuiper Belt Objects. Vesta and Pallas are borderline because they are not quite spherical; however, they are much more complex compositionally and structurally than the majority of tiny asteroids in the asteroid belt. They probably deserve an intermediate category such as "sub-dwarf planet" or "protoplanet."
Alan, why do you say the IAU is not likely to take up the planet definition issue again? Do you mean in 2012 or any time in the forseeable future? This is very troubling because it indicates an inability to consider they might have made a mistake and an insistence on shutting off any further debate. If this is the way they plan on handling the issue, the best thing would be to have planetary scientists form an new group of their own and come up with their own planet definition.
"Pluto's moons are traditionally named after Greek mythological characters associated with the underworld."
Seems like an opportune time to honor President Obama by naming something for him.