Why is pluto not a planet?

Answer 1

When the IAU (International Astronomical Union) redefined what classifies something as a planet, Pluto no longer met the requirements.

"IAU decision to reclassify Pluto

Main article: 2006 redefinition of planet

The debate came to a head in 2006 with an IAU resolution that created an official definition for the term "planet". According to this resolution, there are three main conditions for an object to be considered a 'planet':

1. The object must be in orbit around the Sun.
2. The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
3. It must have cleared the neighbourhood around its orbit.[97]

Pluto fails to meet the third condition, since its mass was only 0.07 times that of the mass of the other objects in its orbit (Earth's mass, by contrast, is 1.7 million times the remaining mass in its own orbit).[98][99] The IAU further resolved that Pluto be classified in the simultaneously created dwarf planet category, and that it act as prototype for a yet-to-be-named category of trans-Neptunian objects, in which it would be separately, but concurrently, classified.

There has been some resistance amongst the astronomical community towards the reclassification.[100][101][102] Alan Stern, principal investigator with NASA's "New Horizons" mission to Pluto, has publicly derided the IAU resolution, stating that "the definition stinks, for technical reasons."[103] Stern's current contention is that by the terms of the new definition Earth, Mars, Jupiter, and Neptune, all of which share their orbits with asteroids, would be excluded.[104] His other claim is that, since less than 5 percent of astronomers voted for it, the decision was not representative of the entire astronomical community.[104] Marc W. Buie of the Lowell observatory has voiced his opinion on the new definition on his website and is one of the petitioners against the definition.[105] Others have supported the IAU. Mike Brown, the astronomer who discovered Eris, said "through this whole crazy circus-like procedure, somehow the right answer was stumbled on. It’s been a long time coming. Science is self-correcting eventually, even when strong emotions are involved."[106]

Among the general public, reception is mixed amidst widespread media coverage. Some have accepted the reclassification, while some are seeking to overturn the decision, with online petitions urging the IAU to consider reinstatement. A resolution introduced by some members of the California state assembly light-heartedly denounces the IAU for "scientific heresy," among other crimes.[107] The U.S. state of New Mexico's House of Representatives passed a resolution declaring that, in honour of Tombaugh, a longtime resident of that state, Pluto will always be considered a planet while in New Mexican skies, with March 13 being known as "Pluto Planet Day".[108] Others reject the change for sentimental reasons, citing that they have always known Pluto as a planet and will continue to do so regardless of the IAU decision.[109] Some observers view this rejection as an attempt to bend the rules in order to keep the only planet discovered by an American classified as such. [110]"

Does that help?

Answer 2

Main reason: it does not fit the definition of a [main] planet as set out by the International Astronomical Union.

It does meet the definition of a planetoid (anything other than a main planet in orbit around the Sun), of a minor planet and of a dwarf planet.

Although there is no official definition yet, Pluto (and Charon) would be in a "binary dwarf planet" system because their common centre of mass lies outside Pluto (and Charon).

By comparison, the Earth-Moon centre of mass lies well inside Earth.

In essence, if we had known then what we know now about Pluto and other Trans-Neptunian Objects, Pluto probably would never have been listed as a full-fledged planet.

It was thought to be more massive than Earth (we now know that it is a lot less than the Moon) and it was thought to be responsible for perturbations in Neptune's orbit (it is not).

Answer 3

According to the International Astronomy Union, there are 3 requirements that a body must meet to be a planet:

1. To orbit around a star. Pluto is OK with this.

2. A planet must have an hydrostatic balance so it has an approximately spherical shape. We are not certain how is Pluto´s shape but wait this is not the most important thing.

3. A planet must be the largest and most massive object in its orbit. Since the orbits of Pluto and Neptune intersect each other, Pluto doesn´t comply this requirement. In a certain moment, Neptune is the most massive object in Pluto´s orbit and that disqualifies Pluto completely.

Sorry Pluto, you must go with the dwarf planets.

Answer 4

I have pluto in the "first house' conjunct my ascendant in my chart,and i feel it's strength very strongly in my personality,because i am the type who can be obsessive about things,and i have a hard time letting things or people go,and when i want something i go after it with full force,and put like everything into what i want,and sometimes that scares me a little because i can go to extremes so much that i make myself almost sick which isn't good at all,but i do it.I have a tendency to push myself really hard with anything that i do,and i won't stop until i get what i want all done or the way i want it done.It's almost like an all or nothing attitude with me even though i have libra as my rising sign.

Answer 5

He got demoted to 'minor planet' status because he failed his last round of tests at obedience school.

He's lucky he didn't get put down...

Joking!

Pluto was named after the 'god of the underworld' by the ancients.
When Clyde Tombaugh discovered it in 1930, his first exclamation to his boss, Mr. Slypher, was, "Mr. Slypher, I've found your 'Planet X'.
Since that time, Pluto has been relegated to the status of 'minor planet' because it doesn't fit the criteria for the definition of 'planet'.
It is still one of the largest Kuiper Belt objects known to date, but if the astronomical community allowed Pluto to remain a planet (with its own credentials intact), there would also need to be many other solar system bodies admitted to 'planet status', as well.
It was simply easier to cut Pluto, than to admit at least 3 other objects to the list of official 'planets'.
Personally, I grew up being taught that there were 9...

Drag...

Clear Skies!
Bobby

Answer 6

It got kicked out of The Planetary Society for being "cold" to other members.

Pluto's orbit does not intersect or "interfere with" Neptune's orbit. The minimum distance between their orbits is 2.4775 AU, when Neptune and Pluto are at 278.19 and 278.29 degrees heliocentric ecliptic longitude, respectively. However, due to an orbital resonance, Pluto and Neptune almost never come within 10 AU of each other.

Answer 7

Because of its composition (rocky snowball) and because beyond Pluto, there are numerous bodies with the similar characteristics.

If we include Pluto, then we would have to come up with perhaps hundreds of new planet names for these objects.

But for the romance of science, I would keep this one little 'mistake'! I know that theories come and go, and errors in concepts are corrected all the time, and this might well be the beauty of Science: its search for the truth and ability to disabuse myth.

However, keeping lil ol' Pluto, would serve as an example of our errors in thought. Erring is a beautiful thing, for it invokes humility in us, and challenges our ephemeral ideas.

Answer 8

As Pluto is a member of objects in the Kupier Belt, it is not defined as a planet since it has not cleared it's orbit of other objects.

Answer 9

because it fits more into the category of an asteroid.. If pluto is a planet then a dozen or more heavenly bodies would also fit the category of a planet

Answer 10

I miss Pluto, too, but it isn't classified as a planet because
1) It is too small
and
2) Its orbit interferes with Neptune's orbit.