One reason the new definition for a planet in the solar system should not be followed is only five percent of the astronomers in the world voted in the 2006 survey. There are many reasons the decision is wrong and many astronomers are upset about the finding.
Because Pluto has been considered to be a planet since it was discovered by the young astronomer Clyde Tombaugh at the Lowell Observatory in Arizona on Feb. 18, 1930, it should be considered a planet today. Three moons have been discovered revolving around Pluto. The largest moon, Charon, was discovered in 1978, Nix in 2005, and Hydra in 2005. Nix and Hydra were discovered using the Hubble telescope. Pluto was thought to be bigger than Mercury for several years.
The dwarf planet Eris was discovered by Mike Brown, Chad Trujillo and David Rabinowitz on Jan. 5, 2005. Eris is expected to be a planet much farther away and a little bigger than Pluto. At the time of the writing of this article, Eris is expected to be close to its aphelion at about 97 astronomical units (AU) from the Sun and Pluto has a predicted current distance of 39.5 AU from the Sun. An AU is the average distance from the Earth to the Sun (about 149,597,870.66 kilometers or about 92,955,807.25 miles according to NASA).
In 800 years, it is predicted that Eris will move in closer than Pluto (Neptune and Pluto did the same thing from Feb. 7, 1979 to Feb. 11, 1999). The fact that Eris and Pluto might have diameters equal to about 2330 kilometers is one reason Pluto is being considered for reclassification. Eris was first thought to be bigger, but Eris and Pluto have appeared to be about the same size in recent calculations. Ganymede, a moon of Jupiter, is bigger than Mercury, Pluto and Eris. According to NASA, its radius is about 2,631.2 kilometers, making its diameter about 5,262.4 kilometers. In miles Ganymede's diameter is approximately 3267.95 miles.
The radius of Io, also a moon of Jupiter, is about 1821.6 kilometers, or diameter of about 3643.2 kilometers. Io's diameter in miles is about 2262.42 miles. Titan, the largest moon of Saturn, has a diameter of about 5,150 kilometers, or approximately 3,200 miles. The radius of the moon of Jupiter named Europa is approximately 1560.8 kilometers, or about a 3121.6 kilometers diameter. In miles Europa's diameter is about 1938.52 miles. Another moon of Jupiter named Callisto has a radius of approximately 2410.3 kilometers, making its diameter approximately 4820.6 kilometers. In miles, the diameter of Callisto is approximately 2993.59 miles.
The diameter of Pluto is about 2,360 kilometers, or in miles it is 1465.56 miles. The radius of Mercury is 2,439.7 kilometers, or a diameter of 4879.4 kilometers. The diameter in miles is approximately 3030.11 miles.
Going by NASA's figures above, Jupiter’s moon Ganymede and Saturn’s moon Titan are both probably bigger than Mercury, Pluto and Eris. This seems to make all three the correct size to be "dwarf" planets; one reason Pluto should not be classified as a dwarf planet.
Eris has an aphelion of 9,068,609,883 miles (97.56 AU) and a perihelion of 3,582,660,264 miles (38.54 AU). It was 96.7 AU from the sun in 2009, very close to its aphelion. It will be close to its perihelion again in about 2257. The perihelion is the closest a planet's orbit comes to the sun and the aphelion is the farthest a planet's orbit gets from the sun. Eris is probably the tenth planet of the solar system.
The perihelion of Pluto is 2,756,872,958 miles (29.667 AU) and the aphelion is 4,583,311,152 miles (49.31 AU). The fact that Pluto’s probable aphelion (49.5 AU) is greater than Eris’ probable perihelion (37.9 AU) is why Pluto and Eris are expected to change places with respect to their distance to the sun.
The Hubble space telescope can only take pictures of the largest objects on Pluto. Maybe the spacecraft named New Horizons launched in January 2006 and scheduled to arrive at Pluto in 2015 will find out more about the planet.
In 2006, the first new criteria for planets would have made it 12 planets in the solar system. The planets included the usual nine planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus and Pluto. It also included the asteroid Ceres that lies in the asteroid belt between Mars and Jupiter, the moon of Pluto Charon, and a newly discovered object, 2003 UB313. The newly discovered object 2003 UB313 is the aforementioned Eris.
The criteria required for a body in the solar system to be a planet was questioned in detail in 2006. Much discussion and disagreement took place. The first attempt increased the total number of planets to 12, but an alternate set of criteria that caused Pluto to be reclassified as a "dwarf" planet was accepted. However, there appear to be several reasons Pluto is still a planet of the solar system, including the fact that the moons Titan and Ganymede are also bigger than Mercury, Pluto has three moons, Eris is three times as far as Pluto is from the Sun and therefore not in its area, and only five percent of the astronomers were present in the meeting.