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BruceMoomaw
(Thanks to Emily Lakdawalla):

http://sciencenow.sciencemag.org/cgi/content/full/2006/127/1
elakdawalla
QUOTE (BruceMoomaw @ Jan 31 2006, 01:20 PM)

Actually SigurRosFan deserves the credit! I must get half of my blog entry material from the sharp-eyed people on this site...
http://www.unmannedspaceflight.com/index.p...indpost&p=39115

Since I posted that, I've gotten an email from someone saying that there will be a publication in Nature tomorrow that flip-flops again on the size of UB313 -- hopefully another sharp-eyed watcher will post that link here as soon as it appears!

--Emily
SFJCody
QUOTE (elakdawalla @ Jan 31 2006, 09:36 PM)
Actually SigurRosFan deserves the credit!  I must get half of my blog entry material from the sharp-eyed people on this site...
http://www.unmannedspaceflight.com/index.p...indpost&p=39115

Since I posted that, I've gotten an email from someone saying that there will be a publication in Nature tomorrow that flip-flops again on the size of UB313 -- hopefully another sharp-eyed watcher will post that link here as soon as it appears!

--Emily
*


There's a post on the badastronomy forums saying that the orbital period of the satellite has been found to be 15.42 days. Not sure what the source was.
Rob Pinnegar
QUOTE (SFJCody @ Jan 31 2006, 06:19 PM)
There's a post on the badastronomy forums saying that the orbital period of the satellite has been found to be 15.42 days.

Four significant figures already, and with those fuzzed out images? Guess it could be true -- but it sure sounds like bad astronomy, alright.
MichaelT
I just read that the Max-Planck-Institute for Radio Astronomy in Bonn has confirmed a size of 3000 km. That was announced yesterday and can be read here (German). On the institute's website I could not find a press release, though. So I don't know any more details...

Michael
SigurRosFan
Here's the detailed press release:

- http://www.unmannedspaceflight.com/index.p...indpost&p=39431

--- Note on reports of an HST size measurement (31.1.)

Mike Brown gave a public talk recently where he presented some preliminary results [Albedo 0.92 news] on an attempt to measure the size of UB313 with the Hubble Space Telescope. A journalist picked this up and reported it, against Mike Brown's explicit request. In response to this report Mike Brown stated on Jan 31:

"Contrary to rumors otherwise, we're just in the preliminary stages of analyzing the HST data. When we are done we should have a very precise measurement. The study that is coming out in Nature is the best info that we have for now about how big and reflective it is. The uncertainties are large, but it seems a solid result to me. I hope that we will have the HST analysis done within perhaps a month, and I'll be able to say more then." ---
David
QUOTE (SigurRosFan @ Feb 1 2006, 01:19 PM)


Then:
"The so-called "tenth planet," announced last July to much fanfare, is a "smidge" bigger than Pluto rather than earlier estimates of 25% to 50% larger, a planetary scientist reported here on 25 January."

Now:
"Here we report observations of the thermal emission of 2003 UB313 at a wavelength of 1.2 mm, which in combination with the measured optical brightness leads to a diameter of 3,000±300±100 km; here the first error reflects measurement uncertainties, while the second derives from the unknown object orientation."

If 2003 UB313 is 3000 km in diameter, then it is 30% larger than Pluto, which is a bit above the going rate for smidges these days. If it is at the lowest end of the given range (2600 km) it is still 14% larger than Pluto.
Rob Pinnegar
QUOTE (SigurRosFan @ Feb 1 2006, 07:19 AM)
A journalist picked this up and reported it, against Mike Brown's explicit request.

Yeah, you can always trust the discretion of the media. Hey, they wouldn't deliberately misinform the public just to sell newspapers!
AlexBlackwell
QUOTE (elakdawalla @ Jan 31 2006, 09:36 PM)
Since I posted that, I've gotten an email from someone saying that there will be a publication in Nature tomorrow that flip-flops again on the size of UB313 -- hopefully another sharp-eyed watcher will post that link here as soon as it appears!

From the February 2, 2006, issue of Nature: One over the nine.
JRehling
Incidentally, don't forget that Pluto "shrank" throughout its lifetime, too, in at least two steps. I can remember when it was bigger than Mercury, and maybe bigger than Mars. wink.gif

It would be interesting if size estimates consistently shrank for newly-discovered objects, as though there were a regression to the mean effect, or a pro-big bias on the part of the early researchers... Who wants to think that they discovered something tiny?

PS: Titan has shrunk a bit, too... wink.gif
TritonAntares
QUOTE (JRehling @ Feb 1 2006, 09:17 PM)
Incidentally, don't forget that Pluto "shrank" throughout its lifetime, too, in at least two steps. I can remember when it was bigger than Mercury, and maybe bigger than Mars.  wink.gif

It would be interesting if size estimates consistently shrank for newly-discovered objects, as though there were a regression to the mean effect, or a pro-big bias on the part of the early researchers... Who wants to think that they discovered something tiny?

PS: Titan has shrunk a bit, too...   wink.gif

...as Triton did.

As child I read in an old astronomy library book from the '50s - I think it was from Otto Struve - Triton's diameter should be ~6000 km:
'Wow, a moon nearly as large as Mars...' ohmy.gif
I'm not quite sure what it was before Voyager II - maybe about 3500 km,
but at the the end it came down to poorly 2720 km, probably the same size as UB313 now.

If we get more cases like Pluto, Triton, UB313, we'll find a 'shrinking law' from 'detection-diameter' to real diameter at the end... tongue.gif

Bye.
Big_Gazza
I have heard a rumour that one of the Mormons secret beliefs is that Heaven is not on another plane of existance but is on a hidden planet past the orbit of Pluto. Yeah, I know sounds kinda wierd, but who am I to judge rolleyes.gif

Anyway, with 2003 UB313 being discovered, what is the opinion of the good folks from Salt Lake City? At least they can have the certainty of knowing they have somewhere to go, though I don't think they need to pack sunglasses and tanning lotion. A nice warm jacket might be well advised.
Bob Shaw
QUOTE (Big_Gazza @ Feb 3 2006, 12:01 PM)
I have heard a rumour that one of the Mormons secret beliefs is that Heaven is not on another plane of existance but is on a hidden planet past the orbit of Pluto. Yeah, I know sounds kinda wierd, but who am I to judge  rolleyes.gif

Anyway, with 2003 UB313 being discovered, what is the opinion of the good folks from Salt Lake City?  At least they can have the certainty of knowing they have somewhere to go, though I don't think they need to pack sunglasses and tanning lotion. A nice warm jacket might be well advised.
*


Do you think they'd like to sponsor some KBO missions, or would that take the fun out of things for them?

Bob Shaw
AndyG
QUOTE (Bob Shaw @ Feb 3 2006, 01:24 PM)
Do you think they'd like to sponsor some KBO missions, or would that take the fun out of things for them?
*

Not at all. Though with their endless interest in genealogy, it's likely the instrument package would be ditched for thousands of names-on-DVDs... wink.gif

Andy G
Rob Pinnegar
QUOTE (TritonAntares @ Feb 2 2006, 06:27 AM)
As child I read in an old astronomy library book from the '50s - I think it was from Otto Struve - Triton's diameter should be ~6000 km.

If I recall right, that was because of Triton's unexpectedly high reflectivity.

The 6000-km figure was still around in the 1970s; I'm pretty sure it was included as an upper limit in Ludek Pesek's book "Solar System" which was from about 1979.
ljk4-1
For what this is worth, Sky & Telescope is now including 2003 UB313
in its online section "This Week's Planet Roundup" right after Pluto:

2003 UB313 (magnitude 19, in Cetus) is getting low in the southwest after dark. This is the "tenth planet" discovered last year; see our articles on its discovery and on the finding of its moon. Advanced amateurs with good CCD setups have been imaging 2003 UB313 and tracking its motion. The discovery team is informally calling the object and its moon Xena and Gabrielle, for the TV warrior princess and her longtime companion. The official names they will get are still tied up in committees of the International Astronomical Union. According to the February 1st Nature, "Xena" is unquestionably larger than Pluto: 3,000 kilometers in diameter compared to Pluto's 2,300.

http://skyandtelescope.com/observing/atagl...ticle_110_1.asp
JRehling
QUOTE (Big_Gazza @ Feb 3 2006, 03:01 AM)
I have heard a rumour that one of the Mormons secret beliefs is that Heaven is not on another plane of existance but is on a hidden planet past the orbit of Pluto. Yeah, I know sounds kinda wierd, but who am I to judge  rolleyes.gif
*


http://en.wikipedia.org/wiki/Kolob

More sensational and also more fun:

http://nowscape.com/mormon/mormons5.htm
punkboi
QUOTE (JRehling @ Feb 10 2006, 10:50 AM)


I thought heaven was on Venus. According to Scientologists.

Oh wait, the leader supposedly came on a spaceship from Venus. Now, I'm confused. huh.gif

biggrin.gif
Katie
QUOTE (JRehling @ Feb 10 2006, 10:50 AM)


I've been Mormon my whole life and I must say I never heard any of that. ohmy.gif

I always sorta figured Kolob was more a figurative place than a literal one. Well that's what I always figured anyway.

They apparently keep the crazy space travel beliefs of the early Mormons out of church these days but still I laughed when reading that second link.

I hate to disappoint people but most of that stuff is no longer taught in the church and whether it was truly official Mormon doctrine at one time I really don't know.

Only a few things on there are legitamately true and official Mormon doctrine to the best of my knowledge. However Mormons truly do believe there are other earth-like planets inhabited by humans. As for the other stuff about space aliens impregnanting women well I never heard that. laugh.gif

I personally don't believe that Kolob is a real physical place that a space craft could go to and I have never heard it preached that way. But I think that site was meant to be funny and not true. tongue.gif
BruceMoomaw
QUOTE (Big_Gazza @ Feb 3 2006, 11:01 AM)
I have heard a rumour that one of the Mormons secret beliefs is that Heaven is not on another plane of existance but is on a hidden planet past the orbit of Pluto. Yeah, I know sounds kinda wierd, but who am I to judge  rolleyes.gif


*


I hope that isn't the same one Lovecraft was talking about...
ljk4-1
I like the idea that when you die you get to evolve into higher and higher levels of beings until you can become the God of your very own Universe! Kinda like moderating a forum, I bet, only with a few extra perks.

But the whole not drinking coffee and listening to the Osmonds thing - I'm still traumatized by the Donny and Marie Show from the 1970s.

http://www.timewarptv.com/Default.aspx?tabid=143
ljk4-1
Looks a lot like Europa! cool.gif


UB 313: Larger than Pluto

Illustration Credit & Copyright: Thierry Lombry

Explanation: What do you call an outer Solar System object that is larger than Pluto? Nobody is yet sure. The question arose recently when 2003 UB313, an object currently twice as far out as Pluto and not in the plane with the rest of the planets, was verified recently to be 30 percent wider than Pluto. UB313's size was measured by a noting its distance from the Sun and how much infrared light it emits. Previous size estimates were based only on visible light and greatly affected by how reflective the object is.

Whether 2003 UB313 is officially declared a planet will be answered shortly by the International Astronomical Union. In the above picture, a scientific artist has imagined UB313 in its distant orbit around the Sun coupled with a hypothetical moon.

http://antwrp.gsfc.nasa.gov/apod/ap060207.html
BruceMoomaw
If they declare Pluto a planet but 2003 UB313 a non-planet -- a proposal I have heard seriously made by one member -- I am officially going to give up on Western civilization.
David
QUOTE (ljk4-1 @ Feb 11 2006, 09:53 PM) *
In the above picture, a scientific artist has imagined UB313 in its distant orbit around the Sun coupled with a hypothetical moon.

http://antwrp.gsfc.nasa.gov/apod/ap060207.html


That would have to be an incredibly long-distance zoom shot to get the sun that size -- at the distance 2003 UB313 is, the sun ought to be tiny. And where does the back-illumination that's brightening the back side of "Xena" (but not, curiously, "Gabrielle") come from?
tty
QUOTE (ljk4-1 @ Feb 11 2006, 08:12 PM) *
I like the idea that when you die you get to evolve into higher and higher levels of beings until you can become the God of your very own Universe! Kinda like moderating a forum, I bet, only with a few extra perks.
http://www.timewarptv.com/Default.aspx?tabid=143


Reminds me of an episode in the old "B C" comic strip. Curls, the local philosopher is preaching reincarnation, and explains that everything will be reborn in a higher form.

"Then what are humans reborn as?"

[brief silence]

"Money, I suppose"

tty
Katie
QUOTE (Big_Gazza @ Feb 3 2006, 03:01 AM) *
I have heard a rumour that one of the Mormons secret beliefs is that Heaven is not on another plane of existance but is on a hidden planet past the orbit of Pluto. Yeah, I know sounds kinda wierd, but who am I to judge rolleyes.gif

Anyway, with 2003 UB313 being discovered, what is the opinion of the good folks from Salt Lake City? At least they can have the certainty of knowing they have somewhere to go, though I don't think they need to pack sunglasses and tanning lotion. A nice warm jacket might be well advised.



It's not true. wink.gif

I'm a life long Mormon but until you posted it here I'd never heard anything about Heaven being a space planet. I know it sounds entertaining but the truth is Mormons believe the same creation story as most Christians found in genesis and that Heaven is a spiritual plane of existance rather than a planet. Sorry if I crushed anyone's beliefs of us as crazy space people. tongue.gif

QUOTE (ljk4-1 @ Feb 11 2006, 11:12 AM) *
I like the idea that when you die you get to evolve into higher and higher levels of beings until you can become the God of your very own Universe! Kinda like moderating a forum, I bet, only with a few extra perks.

But the whole not drinking coffee and listening to the Osmonds thing - I'm still traumatized by the Donny and Marie Show from the 1970s.

http://www.timewarptv.com/Default.aspx?tabid=143


Being a single woman I don't get a planet. sad.gif Probably my biggest issue with the mormon church is how they treat single people.

I was born in 1980 so I guess I got lucky and missed the Donny and Marie show. My dad always called it the Donny and Mafreak show. Not sure why.
ljk4-1
QUOTE (Katie @ Feb 12 2006, 11:06 PM) *
Being a single woman I don't get a planet. sad.gif Probably my biggest issue with the mormon church is how they treat single people.

I was born in 1980 so I guess I got lucky and missed the Donny and Marie show. My dad always called it the Donny and Mafreak show. Not sure why.


That is deeply unfair. You have every right to be a goddess as much as the next Mormon female - or non-Mormon female, for that matter.

If you can, track down a few episodes of Donny and Marie. You will fully understand the reactions of your father and myself after watching them, trust me.
Bob Shaw
QUOTE (ljk4-1 @ Feb 13 2006, 04:55 AM) *
That is deeply unfair. You have every right to be a goddess as much as the next Mormon female - or non-Mormon female, for that matter.

If you can, track down a few episodes of Donny and Marie. You will fully understand the reactions of your father and myself after watching them, trust me.


No! No! Not the white, shiny teeth! And Jimmy, the poisoned dwarf Osmond...

...when I read about 'heaven' being a *real* planet I could go to, I nearly joined up on the spot, but if it's just that spiritual malarkey then I'll stick with the Old Deep Ones, thanks. You know where you stand with unspeakable evil from the depths of space and time, which is basically in the queue to be eaten.

Aiiii!

Bob Shaw
BruceMoomaw
Actually, it's kind of flattering that the Great Old Ones (did Lovecraft ever realize that the acronym was "GOO"?) consider us tasty enough to be eaten. Great Cthulhu seems to have considered us a positive delicacy -- you know how hard it is to stop after just one human...
Bob Shaw
QUOTE (BruceMoomaw @ Feb 13 2006, 11:37 PM) *
Actually, it's kind of flattering that the Great Old Ones (did Lovecraft ever realize that the acronym was "GOO"?) consider us tasty enough to be eaten. Great Cthulhu seems to have considered us a positive delicacy -- you know how hard it is to stop after just one human...


Bruce:

Er, not personally, never been able to finish a whole one. Is there something you're trying to tell us?

Hmm...

Bob Shaw
edstrick
"I can't believe I ate the ***WHOLE*** THING!
dvandorn
Personally, I'd be more worried about your stuffed animals!

Tales of the Plush Cthulhu

-the other Doug
BruceMoomaw
QUOTE (Bob Shaw @ Feb 14 2006, 08:57 AM) *
Bruce:

Er, not personally, never been able to finish a whole one. Is there something you're trying to tell us?

Hmm...

Bob Shaw


Nope. Most of my enemies are, unfortunately, not fit for human consumption.
SFJCody
Brown to discuss 'Xena' discovery

http://www.pasadenastarnews.com/news/ci_3525265
SFJCody
Amateurs spot 10th planet
http://www.spaceflightnow.com/news/n0602/20xena/
SFJCody
The IAU will publish beginning of September 2006 the definition of a "Planet".
http://www.iau.org/TRANS-NEPTUNIAN_OBJECT_2003_UB.324.0.html
BruceMoomaw
Dear God, I hope they don't decide that Pluto is a planet but this new thing isn't. I could tolerate anything but that...

In any case, now we can look forward to comparable decade-long squabbles about the precise definition of "moons" as opposed to "ring particles", and whether we should call newly discovered objects "asteroids" or "comets" when we don't know how much ice is in them. The joys will be endless!
Bob Shaw
QUOTE (BruceMoomaw @ Mar 4 2006, 10:48 PM) *
Dear God, I hope they don't decide that Pluto is a planet but this new thing isn't. I could tolerate anything but that...

In any case, now we can look forward to comparable decade-long squabbles about the precise definition of "moons" as opposed to "ring particles", and whether we should call newly discovered objects "asteroids" or "comets" when we don't know how much ice is in them. The joys will be endless!


Bruce:

Comets are getting drier and drier, and some asteroids might be quite wet...

...sounds like tearing hair out time!

Bob Shaw
SFJCody
No news for a while, which is kind of a shame. I heard a rumour that the satellite might have been an imaging artifact, but it's probably not true.
Rob Pinnegar
Well, it's only been a month or so since the last news update. It would be great if there was something new every day, but, "that ain't so".
SFJCody
UPDATE!

http://www.gps.caltech.edu/~mbrown/planetlila/
ljk4-1
FOR RELEASE: 1:00 pm (EDT) April 11, 2006

Erica Hupp/Dwayne Brown
Headquarters, Washington
(Phone: 202/358-1237/1726)

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
(Phone: 410/338-4514; E-mail: villard@stsci.edu)

PRESS RELEASE NO.: STScI-PR06-16

HUBBLE FINDS THAT THE 'TENTH PLANET' IS SLIGHTLY LARGER THAN PLUTO

NASA's Hubble Space Telescope has resolved the "tenth planet," nicknamed
"Xena," for the first time and has found that it is only just a little
larger than Pluto. Though previous ground-based observations suggested
that Xena was about 30 percent greater in diameter than Pluto, Hubble
observations taken on Dec. 9 and 10, 2005, yield a diameter of 1,490
miles (with an uncertainty of 60 miles) for Xena. Pluto's diameter, as
measured by Hubble, is 1,422 miles.

Xena is officially catalogued as 2003 UB313. It is the large object at
the bottom of this artist's concept. A portion of its surface is lit by
the Sun, located in the upper left corner of the image. Xena's
companion, Gabrielle, is located just above and to the left of Xena.

For electronic images and additional information about the research on
the Web, visit:

http://hubblesite.org/news/2006/16

http://www.nasa.gov/hubble

For more information, contact Robert Tindol, California Institute of
Technology, Pasadena, CA, (phone) 626-395-3631, (e-mail)
tindol@caltech.edu, or Mike Brown, California Institute of Technology,
Pasadena, CA, (phone) 626-395-8423, (e-mail) mbrown@gps.caltech.edu .

The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. The Space Telescope Science
Institute in Baltimore conducts Hubble science operations. The Institute
is operated for NASA by the Association of Universities for Research in
Astronomy, Inc., Washington.
BruceMoomaw
Robert Roy Britt, in his blog on this subject ( http://www.livescience.com/blogs/author/robbritt ), positively DEMANDS that both Pluto and 2003 UB 313 not be called "planets" yet, unless the IAU gives us permission to do so. Who died and made YOU King of the Solar System, Robert?
Bob Shaw
QUOTE (BruceMoomaw @ Apr 12 2006, 01:09 AM) *
Robert Roy Britt, in his blog on this subject ( http://www.livescience.com/blogs/author/robbritt ), positively DEMANDS that both Pluto and 2003 UB 313 not be called "planets" yet, unless the IAU gives us permission to do so. Who died and made YOU King of the Solar System, Robert?


Bruce:

Perhaps the Touch of A Noodly Appendage has elevated him?

Let me rephrase that...

Bob Shaw
David
QUOTE (BruceMoomaw @ Apr 12 2006, 12:09 AM) *
Robert Roy Britt, in his blog on this subject ( http://www.livescience.com/blogs/author/robbritt ), positively DEMANDS that both Pluto and 2003 UB 313 not be called "planets" yet, unless the IAU gives us permission to do so. Who died and made YOU King of the Solar System, Robert?


Well, actually he indicates that if the IAU does give us permission to do so, it will be the sign of the Apocalypse.
Stephen
QUOTE (BruceMoomaw @ Apr 12 2006, 12:09 AM) *
Robert Roy Britt, in his blog on this subject ( http://www.livescience.com/blogs/author/robbritt ), positively DEMANDS that both Pluto and 2003 UB 313 not be called "planets" yet, unless the IAU gives us permission to do so. Who died and made YOU King of the Solar System, Robert?

Well, to be fair he is trying to make a legitimate point:
"Objects like Pluto and 2003 UB313 should be called minor planets or dwarf planets or something else that denotes their relative insignificance compared to the four inner terrestrial planets and the four outer giants. And therein lies the precedent: We already have terrestrials and giants. Just add dwarfs."

That sounds like the very solution astronomers used to resolve the pesky problem of Ceres and the asteroids (aka "minor planets") back in the 1800s.

Unfortunately, given we already do have a class of astronomical bodies dubbed "minor planets" you have wonder whether it would be wise to either extend that name to Kuiper Belt objects or invent a special term ("dwarf planets") for KB objects that could well end up be confused for the other one.

In particular, I notice astronomers themselves seem to be at pains to avoid using the word "asteroid" for KB objects. Yet if they did start using "minor planet" as a label for such objects, or a name which could well be confused with it (eg "dwarf planets"), then the existing association in many people's minds between "minor planets" and "asteroids" may well eventually lead to the "asteroid" label being applied to KB objects also, even if only by lay folk.

***

One further point on the more general issue of "is it/is it not a planet?"

The whole debate seems to depend not on the nature of the object but on its size. Yet in a sense it is not just size that seems to matter either. It is arguably as much about numbers. So long as there was only one body in the asteroid belt or out in the Kuiper Belt nobody--including astronomers--seemed to much mind calling both "planets". It was only when asteroids and Kuiper Belt objects started to proliferate like rabbits that astronomers started getting cold feet about the term.

Yet curiously this need to distinguish Pluto and Ceres from planets does not apply to two other general terms: stars and moons.

There are red supergiants out there and there are red dwarfs, but at the end of the day they are all termed "stars". (Only with "brown dwarf" does there seems to be a reluctance to use the word; and then it's arguably because of their nature: brown dwarfs are seen as failed stars.)

So too with "moon". While we sometimes hear the term "moonlet" bandied about, nobody seems to be (yet) suggesting we reserve that prestigious term "moon" for the larger objects circling planets and use some other label ("minor moons"? "dwarf moons"? "lunar objects"? "orbital rubble"?) for the riff-raff. (Although maybe astronomers are holding fire on that debate until Cassini or some successor probe actually images a few of the house-size "moons" in Saturn's rings.)

That raises the question of whether this present "is it/is it not a planet" debate--as well as the one back in the 1800s--doesn't involve more than modicum of--er--snobbery. Or to phrase the issue another way, I cannot help feeling the only reason this debate has arisen at all with "planet" is because Earth just so happens to bear the label "planet"; and despite all that has come and gone there is still a subconscious wish, even amongst some astronomers, for Earth to be part of a group with a certain degree of--shall we say--exclusivity.

Meaning that if Earth had been a moon rather than a planet would we now be arguing over whether to admit Janus to the hallowed ranks whilst not giving two hoots about using "planet" for Pluto and Ceres?

Thus, it is all right for Jupiter to be called a "planet". That then puts Earth among the giants. smile.gif We are even prepared to tolerate midgets like Ceres and Pluto being one--so long as there was only just one of each. Once there start to be too many of such small fry the feeling seems to be that the term "planet" is losing its currency. Hence, while nobody seems to mind labelling Janus or Miranda "moons" were they orbiting the Sun rather than Saturn & Uranus nobody would be calling them "planets". Similarly with Pluto or (say) Ida. Were Pluto or Ida in orbit around a planet astronomers would be quite happy to label both of them "moons". Only when they start circling the Sun does size suddenly become an issue.

======
Stephen
nprev
The IAU & everyone else has to face up to one fundamental fact: the objects in the Solar System exist along a continuum of sizes, from individual hydrogen atoms to Jupiter. Defining what is and is not a planet will always be a purely arbitrary convention by any objective standard, except for the apparent distinction that a planet has to independently orbit the Sun. Maybe it's time to throw out the concept entirely...?

Well, short of that heresy, maybe we just need to distinguish between "major" and "minor" planets. If that definition were adopted, I'd say that Mercury becomes the standard minimum body, and we have eight major planets. (Let's face it: it's embarrassing that Pluto is only half the size of the Moon!)
Stephen
QUOTE (nprev @ Apr 12 2006, 03:41 AM) *
Well, short of that heresy, maybe we just need to distinguish between "major" and "minor" planets. If that definition were adopted, I'd say that Mercury becomes the standard minimum body, and we have eight major planets. (Let's face it: it's embarrassing that Pluto is only half the size of the Moon!)

The problem is that it's easy to say that now with just one solar system and nine (or eight or ten, depending on who's counting) planets. What happens when we start finding solar systems where the equivalent of Mercury is the size of Europa or Triton? Is the response of astronomers to be: Sorry, you have to be "this big" to qualify as a planet. smile.gif

======
Stephen
BruceMoomaw
I remain convinced of what I said in 1999: if you are going to call some things "planets" at all, it must be on the basis of their being above some size -- and since that size is ultimately entirely arbitrary, let's set it at some figure that (just barely) lets Pluto retain its historical status that everyone's used to, while not letting a lot of smaller riffraff join the club. 2000 km seems the perfect figure for this purpose. Then -- for the sake of everyone's sanity -- let's DROP THE SUBJECT.
Betelgeuze
QUOTE
The problem is that it's easy to say that now with just one solar system and nine (or eight or ten, depending on who's counting) planets. What happens when we start finding solar systems where the equivalent of Mercury is the size of Europa or Triton? Is the response of astronomers to be: Sorry, you have to be "this big" to qualify as a planet.

For some reason the exoplanets in the PSR 1257+12 system never get a lot of attention, yet they are as small or even smaller as Pluto. Did we discover small planets or are they the first asteroids/minor planets we found around another star?
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