CfA to Host Debate on "What Is a Planet?"

[bystander]

In 2006, when the International Astronomical Union (IAU) voted on the definition of a “planet” and booted Pluto out of the club, confusion resulted. Was a “dwarf planet” a small planet or something else? Was a “dwarf fruit tree” a small tree or something else? Almost eight years later, most astronomers and the public are still as uncertain about what a planet is as they were back then.

On September 18th, three different experts in planetary science will present each of their cases as to what a planet is or isn’t. Science historian Dr. Owen Gingerich, who chaired the IAU planet definition committee, will present the historical viewpoint. Dr. Gareth Williams, associate director of the Minor Planet Center, will present the IAU’s viewpoint. And Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, will present the exoplanet scientist’s viewpoint.

After these experts have made their best case, the audience will get to vote as to what a planet is or isn’t and whether Pluto is in or out. And just like the IAU, you have to be present to cast your ballot! The results will be announced on Friday, September 19th.

Watch It Live

Date: Thursday, Sept. 18, 2014
Time: 7:30 p.m. EDT
URL: http://www.youtube.com/user/ObsNights

The talk will also be archived on the Observatory Nights YouTube channel immediately following the event.

Got this in an e-mail.

[Ann]

The Pluto debate.

Sorry, but Pluto is what it is. Wasting so much energy on how we should label it suggests to me that we are missing a point here.

So let everyone call Pluto what they like. Are there eight planets in our solar system, or are there nine? The answer is that there is a bewildering number of mostly small bodies out there. We probably need some sort of cutoff point so we can label them in categories of large and small ones. But how important is that cutoff point? What does it matter if we say that there are eight planets in our solar system, or if we say that there are nine?

Suppose we find a Pluto-sized body somewhere in the Alpha Centauri system. Does it make a difference if we call it a planet or a minor planet?

A Pluto-sized body is what it is.

Ann

[bystander]

If you think this just about Pluto, I think you are being extremely short sighted.

[Ann]

I found this on somewhere on the net and couldn't resist, sorry...

Behold, for I am Pluto, almostest of worlds!

But, bystander, I realize that there is more than the "fate" of Pluto at stake here. For example, when is a cold lonely body less massive than 13 Jupiters a rogue planet, and when is it a brown dwarf?

Ann

[geckzilla]

No exoplanet even falls within the IAU's definition of "planet" which is another part of the debate. Pluto is just the charismatic and much-loved figurehead. Couldn't the demarcation between planet and star be whether or not fusion is occurring within?

[bystander]

What about Ceres, Eris, Haumea, and Makemake; or, for that matter, Sedna, Salacia, Quaoar, and Orcus; not to mention 2002 MS₄ and 2007 OR₁₀. And let's not disregard Charon. In my opinion Charon and Pluto should be considered a binary planet.

[geckzilla]

I didn't learn about any of those in elementary school. They all may or may not be more fantastic than Pluto but Pluto is the only one who belonged at the end of My Very Educated Mother Just Served Us Nine Pizzas. Pluto is ... Pizza! They all do matter, though.

[Nitpicker]

I didn't learn about any of those in elementary school. They all may or may not be more fantastic than Pluto but Pluto is the only one who belonged at the end of My Very Educated Mother Just Served Us Nine Pizzas. Pluto is ... Pizza! They all do matter, though.

The classification for "fantastic" is a whole other debate, geck. That the criteria for planets are seemingly to be put to a vote by whoever turns up, hints that the new criteria will be just as troublesome as the current.

[geckzilla]

It will probably always be troublesome but I think the idea is to refine our definitions to a point of least trouble. I was mulling over the idea that perhaps instead of a black and white system of planet or no planet, a gradation could be used. You can answer a series of questions relating to stars, comets, asteroids, Kuiper belt objects, planets, etc. Pluto could be some percent KBO-like and another percent planet-like while other KBOs would share much less planet-like attributes. I have no problem considering Pluto both a KBO and a planet. This isn't something I have put a lot of thought into the specifics of but conceptually it seems like it would offer some flexibility and relieve the tension that goes along with forcing a rounded cube into a circular or square hole.

[Ann]

Geck wrote:
I was mulling over the idea that perhaps instead of a black and white system of planet or no planet, a gradation could be used.

Hmmm. Pluto is perhaps 80% a planet.

Ann

[MargaritaMc]

Click to play embedded YouTube video.

Silicon Valley Astronomy Lectures 2011

How I Killed Pluto and Why It Had It Coming

Dr. Brown, who has found many of the worlds at the edge of our solar system, shares the inside story of how he discovered "other Plutos" out there beyond Neptune. Among these was Eris, which is now known to be about the same size as Pluto. He named that new world for the goddess of discord, because, as he describes with his characteristic humor, its discovery resulted in a private and public controversy that led to a redefinition of what a planet is.

The lecture is over an hour long but he is a good speaker.

Margarita

PS. Dr Brown is discoverer or co-discoverer of the list of dwarf plants and ¿cubewanos? given by bystander http://asterisk.apod.com/viewtopic.php? ... 50#p232028

[rstevenson]

... ¿cubewanos? ...

Nice one! To save others from peering into the depths of Google...

Wikipedia English - The Free Encyclopedia
A classical Kuiper belt object, also called a cubewano ( "QB1-o") is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axes in the 40–50 AU range and, unlike Pluto, do not cross Neptune’s orbit. That is, they have low-eccentricity and sometimes low-inclination orbits like the classical planets. The name "cubewano" derives from the first trans-Neptunian object (TNO) found after Pluto and Charon, . Similar objects found later were often called "QB1-o's", or "cubewanos", after this object, though the term "classical" is much more frequently used in the scientific literature.

Rob

[MargaritaMc]

... ¿cubewanos? ...

Nice one! To save others from peering into the depths of Google...

Wikipedia English - The Free Encyclopedia
A classical Kuiper belt object, also called a cubewano ( "QB1-o") is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axes in the 40–50 AU range and, unlike Pluto, do not cross Neptune’s orbit. That is, they have low-eccentricity and sometimes low-inclination orbits like the classical planets. The name "cubewano" derives from the first trans-Neptunian object (TNO) found after Pluto and Charon, . Similar objects found later were often called "QB1-o's", or "cubewanos", after this object, though the term "classical" is much more frequently used in the scientific literature.

Rob

I did a nine week course with Mike Brown (a freebie MOOC via Coursera) and learnt SOOOOO much! Including about cubewanos (and plutinos and comets and asteroids and, and, and... And more about Mars and Jupiter, with a light dusting of Moon, Mercury, Earth and Saturn, Uranus and Neptune, than I thought possible for my poor head to absorb!)

http://en.m.wikipedia.org/wiki/Classica ... elt_object
The orbits of various cubewanos compared to the orbit of Neptune (blue) and Pluto (pink).

Click to view full size image

http://en.m.wikipedia.org/wiki/(15760)_1992_QB1 for people who want to know about 1992 QB1. And its discoverers
Jane X. Luu and David C. Jewitt

By the way, Mike Brown has a lively, informative and interesting - if only sporadically written - blog: http://www.mikebrownsplanets.com/

There is a particularly nice piece here ( the first of three) about the discovery of Sedna, my favourite solar system object.
http://www.mikebrownsplanets.com/2010/1 ... .html#more The others can be found here.

Sedna takes 12,000 years to go around the sun on its elongated orbit, and it never comes close to any of the planets.

Click to view full size image

As might be discernable, I'm just a leetle bit enthusiastic about this stuff!

M

[bystander]

CfA: Is Pluto a Planet? The Votes Are In
Center for Astrophysics | 2014 Sep 22

Click to play embedded YouTube video.

What is a planet? For generations of kids the answer was easy. A big ball of rock or gas that orbited our Sun, and there were nine of them in our solar system. But then astronomers started finding more Pluto-sized objects orbiting beyond Neptune. Then they found Jupiter-sized objects circling distant stars, first by the handful and then by the hundreds. Suddenly the answer wasn't so easy. Were all these newfound things planets?

Since the International Astronomical Union (IAU) is in charge of naming these newly discovered worlds, they tackled the question at their 2006 meeting. They tried to come up with a definition of a planet that everyone could agree on. But the astronomers couldn't agree. In the end, they voted and picked a definition that they thought would work.

The current, official definition says that a planet is a celestial body that:

1. is in orbit around the Sun,
2. is round or nearly round, and
3. has "cleared the neighborhood" around its orbit.

But this definition baffled the public and classrooms around the country. For one thing, it only applied to planets in our solar system. What about all those exoplanets orbiting other stars? Are they planets? And Pluto was booted from the planet club and called a dwarf planet. Is a dwarf planet a small planet? Not according to the IAU. Even though a dwarf fruit tree is still a small fruit tree, and a dwarf hamster is still a small hamster. ...