Chapter 6 - 4

04 Astronomy

Eris and Pluto

Until recently, there was no accepted list of criteria that definitively described what a planet was.

When scientists finally did define the characteristics of planet, Plato was redefined as a dwarf planet, rather than a proper planet like Earth or Mars.

Dwarf planets are bodies in space that orbit around the sun.

As Pluto was no longer considered a planet, the need for further reclassification and new terminology arose.

Finally, astronomers agreed that Pluto was a dwarf planet.

According to the scientific definition, dwarf planets must also have enough of a mass for it to have formed a spherical shape.

Additionally, dwarf plants are distinguished from other planets because they have not cleared neighborhood around their orbit.

This means that other masses or celestial bodies still exit in the orbit of dwarf planes, whereas they do not for other planets.

The last criterion for a dwarf planet is that it is not a satellite.

A satellite is an object in space that orbits around a larger mass, such as the moon.

Currently, there are three recognized dwarf planets: Ceres, Pluto, and Eris.

The discovery of dwarf planets has been the source of much confusion amongst scientists.

Since all three are relatively far away from the sun and Earth, they have been difficult to study.

However, the more information that is gathered about dwarf planets, the more scientists can tell about the different features that each one exhibits.

After being reclassified, Pluto went from being the last planet in the solar system to being the second-largest dwarf planet.

Pluto’s mass has long been disputed, but information gathered from satellites has led to more accurate formulations.

It is believed that Pluto is less than a quarter of the mass of the Earth.

Furthermore, by studying eclipses, astronomers can make good guesses about the size of Pluto.

Currently, scientists think that Pluto has a diameter of 2,390 kilometers.

The distinction of biggest dwarf planet, however, goes to Eris.

Recently discovered, Eris is still largely a mystery to scientists.

So far, they have been able to determine little about the dwarf planet.

However, as technology advances, it becomes easier to study it.

The mass of Eris is larger than Pluto’s by about twenty-seven percent.

Furthermore, the diameter of Eris is also larger than Pluto’s at about 2,600 kilometers.

Approximations about the size of Eris have been based on satellite information, and scientists warn that until more information is gathered, it is hard to determine the exact mass and size of Eris.

Given their uncertainty, some scientists say that the actual diameter of Eris may be up to 400 kilometers more than what they currently think.

Although they have different masses and sizes, the two dwarf planets are actually similar in their chemical and physical make-up.

Pluto is thought to be composed mostly of ice and rocks.

By using special tools, astronomers have learned that Pluto is mostly made up of frozen nitrogen.

It also contains traces of methane ice and carbon monoxide ice.

Comparisons between Pluto and Eris suggest that they have similar compositions.

Methane ice is also known to exist on Eris.

Given their physical similarities, however, it was initially confusing to scientists why the dwarf planets appeared different.

Eris looks grayish while Pluto is reddish.

Later, the difference in their outward appearance was explained by the presence of tholins on Pluto’s surface.

Tholins are materials commonly found on icy planets.

They are responsible for the darker appearance of Pluto.

In addition to having similar compositions, Pluto and Eris share orbit patterns that are very different from those of the planets.

For example, they both have eccentric orbits.

This means that the orbit is more elliptical, or oval-shaped.

Meanwhile, the planets in the solar system have more circular orbits.

The exaggerated ellipses of the dwarf planets’ orbits cause each one to experience extreme temperature changes as they get closer or farther away from the sun.

Unlike other planets, the orbits of Pluto and Eris are also tilted.

If one imagines the planets in the solar system, it would be accurate to envision the orbit of each one lying on one plane.

But the orbits of the dwarf planets Pluto and Eris are slightly inclined.

Pluto is inclined by seventeen degrees while Eris is inclined by forty-four degrees.

The inclination of their orbits causes them to cross Neptune’s orbit.

However, neither dwarf planet ever approaches Neptune, so the risk of collision is impossible.