Uncovering the Truth: The Demotion of Pluto and the Search for New Dwarf Planets

[Algr]

The discovery of Eris prompted the creation of the category "Dwarf Planet" for Pluto and some other objects. They said that there would be hundreds of others, but 5 years later, no one has found any more. Is this right?

Is the demotion of Pluto based on a mistake? Or did everyone just stop looking for dwarf planets?

 

[mathman]

From Wikipedia:

The IAU currently recognizes five dwarf planets—Ceres, Pluto, Haumea, Makemake, and Eris.[7] However, only two of these bodies, Ceres and Pluto, have been observed in enough detail to demonstrate that they fit the definition. Eris has been accepted as a dwarf planet because it is more massive than Pluto. The IAU subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 (and hence a mathematically delimited minimum diameter of 838 km[8]) are to be named under the assumption that they are dwarf planets. The only two such objects known at the time, Makemake and Haumea, went through this naming procedure and were declared to be dwarf planets.

It is suspected that at least another 40 known objects in the Solar System are dwarf planets,[9] and estimates are that up to 200 dwarf planets may be found when the entire region known as the Kuiper belt is explored, and that the number might be as high as 2,000 when objects scattered outside the Kuiper belt are considered.[9]

 

[Algr]

Yes, but they haven't discovered any in five years. There were all these discoveries in 200-2005, and then nothing.

 

[tiny-tim]

i think there should be at least seven dwarf planets …

and they should all be named after characters from disney ​

 

[Algr]

They were promising us dwarf planets bigger then Mars. We've been ripped off!

 

[mathman]

They were promising us dwarf planets bigger then Mars. We've been ripped off!

What's your hurry? It is a question of allocation of resources. Astronomers have plenty of projects. I doubt if this one has a high priority.

 

[Algr]

Well, if these objects don't exist, then it is like Pluto has been demoted under false presences. I recall an argument against pluto being "we don't want a hundred planets". I never liked this because the number of natural elements went from four to over a hundred and no one ever started inventing ideas about clearing the orbit of electrons... But now even the "hundred planet" thread doesn't exist.

"Clearing the neighborhood" seems as arbitrary (And less honest) as just setting a minimum size in miles for how big an object has to be to be a planet. How big is a neighborhood? Is Venus in Mercury's neighborhood?

 

[Janus]

Well, if these objects don't exist, then it is like Pluto has been demoted under false presences. I recall an argument against pluto being "we don't want a hundred planets". I never liked this because the number of natural elements went from four to over a hundred and no one ever started inventing ideas about clearing the orbit of electrons... But now even the "hundred planet" thread doesn't exist.

"Clearing the neighborhood" seems as arbitrary (And less honest) as just setting a minimum size in miles for how big an object has to be to be a planet. How big is a neighborhood? Is Venus in Mercury's neighborhood?

This is not the first time that a heavenly body has lost planet status. The asteroids Ceres, Pallas, Vesta and Juno were all classified as planets and remained so for about half a century before losing their status. This re-classification occurred even though no other asteroid larger than Ceres was found.

It also must be remembered that Pluto's size has been down-graded since its discovery and designation as a planet. At that time Pluto and its major moon Charon could not be separately resolved, so we thought that we were looking at a larger single body rather than two smaller ones.
First estimates in 1931 put it at 1 Earth mass.
This was lowered to 0.1 Earth masses in 1948 (the mass of Mars) and then to 0.01 Earth masses (about the mass of the Moon) in 1976

Upon Charon's discovery in 1978, and confirmation in the late 80's, its mass was lowered again to 0.002 Earth masses. Pluto had become the incredible shrinking planet. From then on Pluto's status as a planet was on shaky ground.

 

[Algr]

Pluto is 5 times smaller then Earth. Jupiter is 12 times larger. Are Jovians planets? They have more in common with stars. You can't even land on Jovians.

 

[Vagn]

Pluto is 5 times smaller then Earth. Jupiter is 12 times larger. Are Jovians planets? They have more in common with stars. You can't even land on Jovians.

The definition of a planet is dependant on how it forms, they form differently to stars, which is one of the main differences between a large gas giant and a small brown dwarf.
A brown dwarf usually forms in the same way as any other binary star, by the gravitational collapse of a large gas cloud, which spins too fast and splits into two separate stars, one larger star and a brown dwarf. In contrast a gas giant forms by accretion of dust and gas in the protoplanetary disk surrounding a star.

Brown Dwarfs are usually defined as having a mass between 13 Jupiter masses and 80 Jupiter masses. At ~13 JM a brown dwarf can begin to fuse Deuterium and so can't be called a planet.

 

[Radrook]

I always thought that Pluto referred to the god of the underworld and not to the Disney dog.

 

[Algr]

The definition of a planet is dependant on how it forms, they form differently to stars,

Oh? Then how did Tau Boötis b form? How could you tell if a given planet in an odd orbit actually formed around it's current star? If you include formation in the definition of a planet, then you'll have objects that can never be defined one way or the other. This makes the word useless.