Is pluto a planet?

Answer 1

Pluto is NOT the first celestial body to be removed from planetary status. It has happened before. The fact that people don't know about it doesn't mean it hasn't happened.

But before I chronicle that history, let's just do a quick census of what we now know we have in the solar system: the context in which decisions about planetary status take place.

In antiquity before telescopes were developed, there were only 8 known objects in the Solar System: Mercury, Venus, Mars, Jupiter, Saturn, the Sun, the Moon and the Earth,

So it remained for two thousand or more years then numbers started to mushroom from 1610 (when Galileo discovered 4 moons of Jupiter)
and the present position is.

Stars: 1

Planets: 8
Moons of those planets: 162
(Mercury; 0, Venus: 0, Earth: 1, Mars: 2, Jupiter: 63, Saturn: 56, Uranus: 27, Neptune: 13)

Dwarf Planets: 3
Moons of those dwarf planets: 4 (Ceres: 0, Pluto; 3, Eris; 1)

Small Solar System Bodies: over 343,500
Including:
Kuiper Belt Objects: over 800
Other Trans-Neptunian Objects: Over 200
Asteroids between Mars and Jupiter: over 342,536
Moons of these Small Solar System Bodies: over 80

PROMOTION TO AND DEMOTION FROM THE PREMIER LEAGUE OF PLANETS

3 objects have gained planetary status and kept it; Earth, Uranus, Neptune

27 other objects had it for a while and then lost it again. Pluto is simply the latest in a long line of former planets who were removed from that status in the light of other discoveries and reclassification because of them,

First to get the chop were the Sun and the Moon,

From antiquity up till 1543 and Сopernicus proposing a heliocentric Solar System, There were 7 planets and they all supposedly revolved around the earth (a geocentric system), They were the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn,

Once the Copernican model gained favour, the Sun and the Moon were dropped from the list of planets (and the Earth, no longer believed to be the centre of the universe, was added). Then there were 6.

Then in the 17th Century, the 4 Galilean moons of Jupiter and Titan, Iapeter and Rhea, the first 3 moons of Saturn to be discovered. were defined by their discoverers as planets but came to generally be regarded as moons, as that new concept became accepted.

Since the acceptance of the heliocentric model over the geocentric model, the solar system has been seen as having various numbers of accepted planets over the years:

1543 - six (Mercury, Venus, Earth, Mars, Jupiter and Saturn) (among those who accepted the new view)
1781 - seven (with Uranus)
1807 - eleven (with 1 Ceres, 2 Pallas, 3 Juno and 4 Vesta)
1845 - twelve (with 5 Astraea)
1846 - thirteen (with Neptune)
1851 - twenty-three (with 6 Hebe, 7 Iris, 8 Flora, 9 Metis, 10 Hygiea, 11 Parthenope, 12 Victoria, 13 Egeria, 14 Irene and 15 Eunomia)
1852 - eight (without Ceres and the asteroids)
1930 - nine (with Pluto)
2006 - eight (without Pluto)

When the objects 1 Ceres, 2 Pallas, 3 Juno and 4 Vesta were found orbiting between Mars and Jupiter in the early 1800s, they were declared and accepted as planets (though Herschel, who had discovered Uranus 20 years beforehand, felt they were disappointingly small and did not really rank alongside his discovery; he therefore coined the term "asteroid" for them),

They remained classed as planets for many years. However, as more and more objects began to be found in the same region of the solar system, they became classified as asteroids, along with their orbital kin. Just as well as we now know of 342,536 asteroids. To have 342,544 planets would be getting silly.

A similar scenario has occurred with Pluto. It was first discovered beyond Neptune in 1930 and was accepted by the IAU as a planet after it was initially believed to be larger than the Earth. However, after further observation it was found that Pluto was actually much smaller, being less massive than the Moon.

After more than 1,000 similar new bodies were found beyond Neptune during the 1990s and the early 2000s, the IAU decided to reclassify Pluto as a dwarf planet in 2006. If Pluto remained a planet. there were a dozen more approaching its size (and one exceeding it) for which equal claims to planetary status could be advanced. As with the category "asteroid" 150 years ago it was deemed wiser to create a new categiory "dwarf planet" for the legion of new discoveries to be placed in.

Finally, when Sedna and Xena (now renamed Eris) were discovered in 2003 they were both widely hailed as The Tenth Planet in the media. And the recent IAU decisions in Prague are in part intended to disabuse the public of that notion, that the media can award planetary status.

SUMMARY:
The 27 rejects were reclassified as
stars: 1
moons: 8
asteroids: 15
dwarf planets: 2
extended scattered disk objects: 1

The basic point is that as science advances, it sometimes needs to rethink its categories and classifications along more logical lines. That is what has just happened to Pluto.

Answer 2

Pluto
Pluto, the last planet to join the heavenly pantheon, became the first to leave it. The status of Pluto had been under discussion for some time, but with the discovery of 2003 UB313, nicknamed Xena, the question became acute, for it seemingly had as much right as Pluto to be called a planet.

Answer 3

Not any more.

Based on the new definitions of how to define a planet Pluto is no longer classified as a planet.

But to make Pluto feel better about being demoted they are now calling it a dwarf planet. :)

Answer 4

Well, the astronomers, in all their wisdom, now say no. Patrick Moore has always said that he never regarded Pluto as a planet although it's going to take more than them saying so to erase the little blighter from most people's minds. You'll still get people saying there's nine planets (Pluto being the ninth) for decades to come. Besides, it spoils my nice Mnemonic 'My Very Easy Method Just Sums Up Nine Planets' so I'm not letting go of Pluto that easily.

Answer 5

According to the latest definition from last month Pluto is considered a dwarf planet.

Answer 6

Pluto is now a big space rock. Due to the size of the rock, it is too small to be a planet.

Answer 7

Definitely, recent declaration got us all thinking.
Astronomically the scientists have done their part n who knows better than them on that front. But everything has so many aspects.....like the planets have astrology besides astronomy....
Now chronologically, astrology dates much much ago than astronomy....and astrology, which is actually a science, has always taken the planets to be nine...this provides the last planet with some solid ground....and us the reason to believe that it IS a planet.

Answer 8

Where have you been? They just declassified Pluto as a planet, and made it to a Dwarf Planet.

Answer 9

Bruce is correct. Scientists reclassify things from one class to another all the time, usually plants or bacteria, sometimes animals. This never makes the news even though it is more likely to affect people than some distant object.

Why reclassification of some rocky iceball (or is it a icy rockball) from one class to another should upset people is beyond me. It does not affect anyone. Most of our great-great-grandparents did not know it existed.

The reclassification does not degrade it's discovery, the fact that it turns out to be so small makes the discovery even greater.

Answer 10

Pluto is no longer considered a major Disney character and has been demoted to a canine sidekick.