Assignment 4: The Changing Pluto

Pluto and its three moons.

Pluto is the furthest from planet Earth and therefore very little is known about this planet's physical characteristics. It is known to have less than 20% of Earth's diameter, consisting of a rocky core that is surrounded by a mantle of water ice. Pluto was previously thought of as the ninth planet of the solar system, as well as being the smallest. Today it is known as a dwarf planet which orbits the Sun just like any other planet, but is much smaller - so small that it cannot clear objects out of it's path. Pluto is nearly 40 times as far from the Sun as the Earth. It orbits the Sun in an oval and therefore sometimes seen as closer to the Sun and other times further - even during its closest point to the Sun, it is billions of miles away. It was also discovered that Pluto is located in a region called the Kuiper Belt. Here there are thousands of small icy objects like Pluto. Pluto also has 3 moons - Charon, Nix, and Hydra; Charon being the largest of the three. The reason that triggered the thinking of Pluto not being an actual planet of the solar system is the discovery of Eris. In 2003, an astronomer thought he had discovered a new planet just beyond Pluto, that was larger than Pluto itself. Therefore, Pluto became a dwarf planet due to its size and location in the solar system.

Discovery of Pluto

Solar system with 9 planets - Pluto included

It wasn't only until 1930 that Pluto was discovered by an astronomer by the name of Clyde Tombaugh. This was because Pluto was so small that a very powerful telescope would be needed to see it. Clyde Tombaugh was born in 1906 in the United States on a farm. He grew up with a passion in stargazing due to the encouragement of his uncle and father. Tombaugh had been dissatisfied by his telescopes he had purchased and so decided to build one himself. Over his lifetime, he had built more than 30 telescopes. In 1928, he had built a very accurate 23 centimeter reflector which was the telescope that had allowed him to make detailed drawings of both Mars and Jupiter. After creating these drawings, he had submitted them to Lowell Observatory where they subsequently offered him a position as a junior astronomer. Once he accepted the job, he had joined the search for Lowell's Planet X - a planet beyond Neptune which was a big project they were working on. His task consisted of him taking a picture of a small portion of the night sky each day which was then later compared to each other in order to identify a moving point of light that may be a planet.He displayed one image and then blinked the second image to see if any objects had moved from night to night. On February 18th 1930 Tombaugh saw an object moving at a certain speed which was then named Pluto by a young school girl. After viewing 65% of the sky along with monthly observations, he discovered an object which was then later named as Pluto. Even after the discovery, Tombaugh went back to school at University of Kansas and obtained his masters in astronomy. However, while doing so he would go back to the observatory every summer to continue on his work. Tombaugh also had immense insight in Mars for he described the surface of Mars - full or craters. He had also taught at two universities.

Pluto - Dwarf Planet

Pluto's orbital inteference with Neptune, along with Eris'
orbit.

In August 2006, Pluto was demoted to a dwarf planet due to its relevant size to the other planets. It was then realized that Pluto was neither a Terrestrial planet or a Jovian planet and so people wondered how to classify objects such as Pluto - it was just a large icy body orbiting the Sun. The first essential change to how we view Pluto started with the findings of the first Trans-Neptunian object. These Trans-Neptunian objects have an orbit that is beyond that of Neptune. In 2003, scientists at Palomar Observatory used a telescope to observe the night sky, where they had discovered what is now known as a dwarf planet called Eris. Even though it was larger than Pluto, it had a moon orbiting around it just like Pluto itself. It was also considered a planet - the tenth planet. However, the Astronomical Union changed their definition of a planet and Eris had become a dwarf planet. This caused massive speculation about Pluto's status as a planet. Therefore, in 2006 a vote was held to decide whether Pluto was a planet or a dwarf planet. Regardless of the small voting percentage (3% for planet and 4% for dwarf planet), it was decided that Pluto was too a dwarf planet. This led the organization to set parameters to allow astronomers to identify planets from other celestial objects. According to the union, a planet requires and orbit around the sun, enough gravity to allow the object itself to become of a spherical shape, and finally the object must clear of all debris in its path.

Plutinos

Orcus and Ixion - Plutinos in the Kuiper Belt.

In 2008 it was decided that such objects that are similar to Pluto should be called Plutoids. Plutinos on the other hand are small icy bodies similar to Plutoids but differentiated from them because of the way they orbited around the Sun. Plutino was derived from the planet Pluto and it means little Plutos. It is in this Plutino region that is home to dwarf planets including Pluto. As Neptune moved further away from the Sun, it started to interfere with orbital motions of many objects, one of them being Pluto. The interference resulted in the objects' (including Pluto's) orbit becoming locked to the orbit of Neptune. However, the two planets do not collide for their periods of revolution are at different ratios. Every two times a Plutino orbits the Sun, Neptune orbits the Sun three times. Orbits and orbital periods of Plutinos are similar to those of Plutos. Examples of Plutinos are Orcus and Ixion. Orcus is referred to as anti-Pluto because it appears on the opposite phase of Pluto - when Pluto is closest to the Sun, Orcus is at its furthest point to the Sun. Orcus is also found in the Kuiper Belt, having a radius of 800km and an orbital period of 245 years. It is colder than Pluto by 10 degrees Celsius (-240 degrees Celsius). Due to its extensive ice coverage on the planet, Ocrus has the highest albedo (reflection of sunlight) compared to any other object in the Kuiper Belt - including Pluto. On the other hand, Ixion is the 5th largest Plutino and is composed of ice and tholin. It also has a longer orbital period than Pluto itself for Pluto's orbital period is 247 years whereas Ixion's orbital period is 249 years. All plutinos are Plutoids but only those Plutoids with orbital periods with Neptune are Plutinos. The three known plutoids are Pluto, Eris, and Makemake.

Theoretical Prediction or Not

However, Pluto wasn't a true theoretical prediction based on celestial mechanics since it was discovered on the basis of the irregular orbits of Neptune and Uranus. There was a hypothesis stating that there must be another gaseous body beyond Neptune that causes deviations within the elliptical orbit. However, once it was found that Pluto was too small to make changes in these large planets (Uranus and Neptune), they realized the deviations in their orbits were due to an overestimation of Neptune's mass. The Titius-Bode's Law was used to predict a planet around 38.8 AU, beyond Uranus. Beyond Uranus they had found Neptune so their prediction of another planet beyond Uranus was accurate, however the Titius Bode's Law was not because Neptune was found at 30.1 AU and not at 38.8 AU. Unlike this discovery of planet Neptune, the discovery of Pluto was not based on theoretical predictions. The inaccurate Titius Bode's Law predicted that Pluto was 30 AU further than its actual distance. Lowell's predictions using mathematics that was created through the observation of both Neptune and Uranus was not able to predict the true orbit of Pluto. Tombaugh had found Pluto by chance and not due to Lowell's predictions which did not help find the planet's location.