Comments on: What 50 AU looks like

By: Jonathan Wald

Jonathan Wald — Mon, 26 Sep 2005 17:56:11 +0000

I love this debate! When they started discovering larger and larger KBOs, I knew it would bring the discussion of what is really a planet â€“ especially Plutoâ€™s status â€“ to a head. Weâ€™ve dodged the question for too long. Now everyone is talking. It is lively and entertaining, and will probably be one of the better remembered parts of early 21st century astronomy. Personally, I have always gone with the conclusion that any object orbiting the sun with enough gravity to pull itself into a sphere should be considered. Since a number of asteroids fit that definition, it would probably not fly with the general public. â€œGuess what Mrs. Teacher, this year you can teach the 3rd grade that we have 23 planets!â€? That leaves us with historical planets and picking arbitrary sizes. Pluto is a “historical” planet, and would be next to impossible to dethrone after 75 years. My suggestion: go with the class mentioned above called “Kuiper Planets” to go along with the Terrestrial Planets and Gas Giants. Pluto, and anyhing bigger, would be a member of this class. It is very arbitrary, but draws the line based on 75 years of tradition. If too many are discovered, we can revisit the definition later. After all, Ceres was first called a planet.

By: Doug McElroy

Doug McElroy — Mon, 15 Aug 2005 15:37:01 +0000

Yes, it looks like UB313 and Pluto are unusually large for TNOs and unusually
small for “regular” planets. Pluto at least has been “grandfathered” in as
a planet for nigh on 70 years now. So that probably qualifies UB313, too.

By: Wolfgang

Wolfgang — Sat, 06 Aug 2005 12:48:29 +0000

If there is indeed a 10th planet, does this mean my horoscopes were incorrect ?

By: Jyri Leskinen

Jyri Leskinen — Tue, 02 Aug 2005 20:39:56 +0000

We really need more complex classification system than the current simple major planet/minor planet system.

Although it doesn’t really matter what they are called — every classification is more or less arbitrary, and every object is unique in its own way — it is good to have astronomical objects classified anyway; for example, if someone says you that an object is a plutino, and you know what ‘plutino’ means, you immediately understand that it is like Pluto a Kuiper Belt object in 2:3 orbital resonance with Neptune.

By: Zamboni Schwartz

Zamboni Schwartz — Tue, 02 Aug 2005 18:50:40 +0000

Hmmmm…..that Nature article was interesting, but I have a different idea.

The new objects seem to be slightly blurring the line between planets and KBOs. Not only is one larger than pluto, but one also has its own moon very much along the lines of Charon.

When is the IAU going to realize that existing definitions of “Planet” are totally arbitrary, beurocratic designations?

There are already three different classes of planet in our solar system. There are the inner “terrestrial” planets, the big gas giants Jupiter and Saturn, and the two smaller “icy” gas giants, Uranus and Neptune.

When pluto was discovered, the Kuiper Belt as a whole hadn’t been. So, without truly understanding it, they classified it as a “planet”. Now, after the discoveries of objects like Quaoar and Sedna, the KBOs like Pluto are getting a new designation because of their distance and orbital eccentricities/inclines.

But with these truly large worlds, some with moons, are we simply going to have to create a whole new class of planet? What if we were to discover something slightly larger than 2003 UB313 a little bit futher out? What if the orbit was also inclined, which would explain why it hadn’t been discovered yet, but also less eccentric? What if it had an orbit around the same, or slightly less, eccentricity than Pluto? How would we classify it?

Is it maybe time to designate a new classification of “Kuiper Planets”?

By: Robert

Robert — Tue, 02 Aug 2005 17:27:19 +0000

Spoken like a true skeptic. I see why you like reality the way it is.

By: Mendel

Mendel — Tue, 02 Aug 2005 17:23:57 +0000

This has surely been an exciting few days. Thanks for the pictures!

I think UB313 should be called a planet if it indeed is bigger than Pluto and also travels closer to the sun occasionally.

By: The Bad Astronomer

The Bad Astronomer — Tue, 02 Aug 2005 16:49:00 +0000

Actually, Michelle, it is. It’s about 1/2 as bright as EL61, so we’re going to go for it eventually. UB313 isn’t up until early in the morning, and our ‘scope isn’t fully automated yet– no one (including me!) wants to stay up that late just to get some pictures. Plus the ‘scope primary use is for other objects, so while I’ve been able to get an hour on it to do this, the main stuff takes precedence.

By: Michelle Rochon

Michelle Rochon — Tue, 02 Aug 2005 12:33:13 +0000

I wonder, is it possible to image the far away one, UB313 I believe, with your telescope??

It’s just fun to be able to image big chunks far away…

By: Jyri Leskinen

Jyri Leskinen — Tue, 02 Aug 2005 09:27:49 +0000

Wow, it really moves! If only such a short timespan could provide a good orbit estimation.

Richard Board,
Nature website has an article about the future definition of planethood.
http://www.nature.com/news/2005/050801/full/050801-2.html

The discovery of 2003 UB313 have forced the IAU committee to hurry, and “[...] a definition should be ready by the end of the week.”

Phil Brady,

* Minor Planet Center lists all the unusual (i.e. non-Main Belt asteroids) here: http://cfa-www.harvard.edu/iau/lists/MPLists.html

* David Jewitt (one of the discoverers of the first Kuiper Belt object) has a good Kuiper Belt website: http://www.ifa.hawaii.edu/~jewitt/kb.html

* And of course, you can always try Wikipedia: http://en.wikipedia.org/wiki/Kuiper_belt (that page includes links to all the largest trans-Neptunian objects)

By: Phil Brady

Phil Brady — Tue, 02 Aug 2005 06:58:33 +0000

“we know things in a matter of hours or days” — sort of. Thanks to the Web of a Million Lies, we can get information within hours or days after it’s officially released, but the time between discovery, confirmation, and publication is still on the order of months to years, especially in astronomy. Who wants to be remembered as the follow-up act to Pons and Fleischmann? (Thus sayeth the layman.)

Even with the historically unprecedented access to scientific data and information, I still can’t seem to find a concise listing of the TNOs, Plutinos, cubewanos, whateveros that are popping up like summertime weeds. I’ve heard of Quaoar, and Sedna, and Orcus, and DW 200?, and, and…. Anyone with a good page that has all these beasties?

By: Richard Board

Richard Board — Tue, 02 Aug 2005 04:43:32 +0000

So what’s your opinion, Phil? Is it a planet or not? What will the International Astronomers group decide? This is so cool. What a great time to be alive. It must have been just as exciting for guys like Galileo and Keppler, et al, when they made their astonishing discoveries. Just think how long it took for them to notify the scientific community in those days, not to mention convince the general public of new concepts those discoveries inferred. Now we know things in a matter of hours or days. Too much!