Ever since ancient times, celestial bodies have been a massive source of interest and mystery for humanity. Today, in astronomy, the dwarf planets are some of the most mysterious celestial bodies. This category of planets was created not so long ago. Its creation became the result of lengthy arguments between the scientists in reference to the planets of our solar system and their classification and the features that define them. Currently, apart from the eight planets in our solar system, the astronomers recognize five dwarf planets.
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Pluto is the most well known of the dwarf planets. The story of its discovery is very peculiar. Predicted to be out there in 1915 by Percival Lowell, Pluto was finally discovered by a self-taught astronomer called Clyde Tombaugh in Lowell Observatory by a lucky chance.
In 1930 Tombaugh spend quite a very long time studying photographs of the fragments of space by means of using “blink comparator”, the device designed to compare paired photographs and detect the differences between them to find objects that moved (Beyond the Planets – the discovery of Pluto, n. d., para. 5).
Such photographs show a lot of various bodies and also false objects that can be very confusing, but Tombaugh’s eyes, apparently, were very sharp, so he managed to locate Pluto. (Original photos compared by Tombaugh, n. d.).
The fact that the scientist chose that particular area of the sky to examine was just a lucky accident. Initially, Pluto was recognized as the ninth planet of our solar system. Its mass and size were also considered much larger than they turned out to be later. Pluto’s temperature is one of the oldest known to science; it is minus 375 degrees F. The surface of this body is covered in gigantic craters, some of which were named after the characters of “Star Trek,” the well-known TV show about space adventures.
Pluto is 2274 km in diameter, its density is 2.3 g/cm3, it has retrograde rotation, and its axis is tilted by 17 degrees. Pluto has always been the focus of rigorous arguments among the scientists, first of all, for a long time, it was impossible to study its features well since it is so far away.
Secondly, Pluto’s orbit is very different from the orbits of the eight planets of the solar system, it has an elliptical shape, so normally Pluto is further away from the Sun than all of the planets, but there are times when its unusually shaped orbit brings it closer to the Sun than Neptune is. Finally, Pluto’s orbit is tilted in relation to the orbits of the eight planets, which all move parallel to each other.
As a result of the arguments caused by this list of significant differences between Pluto and the eight planets of our solar system, the science came up with a solution to introduce a new category to distinguish between the planet-mass objects that cannot be called planets or natural satellites. The astronomers agreed to call them dwarf planets.
In total, the contemporary science knows about five dwarf planets. Apart from Pluto, there are also Eris, Haumea, Makemake, and Ceres. According to their scientific definition, dwarf planets are to be of round shape and orbit the Sun directly. The difference between planet-mass objects known as planets and dwarf planets is that the latter is much smaller and cannot clear their orbits of the presence of other bodies. Dwarf planets are also known to have a smaller size than planets and their natural satellites.
All of the five known dwarf planets are smaller than the moon the Earth has, but dwarf planets cannot be considered as moons as they orbit the Sun. In fact, dwarf planets may have their own moon, for example, Pluto has a natural satellite that is rather large, and its name is Charon. The introduction of the new category of dwarf planets was caused by the discovery of several objects of significant size located in the disk of space debris that stretches outside of Pluto’s orbit; this disk is known as Kuiper belt.
The objects found there mainly consist of ice because they are very far away from the Sun. Interestingly enough, together with other significantly sized bodies found in the asteroid belt that is situated between Jupiter and Mars, the scientists currently count up to one hundred and twenty-five planet-like objects that directly orbit the Sun. This number does not include a huge variety of smaller objects that were also cataloged by the astronomers.
Pluto was not the first dwarf planet that was initially classified as a planet. Ceres, with its orbit located in the asteroid belt between Mars and Jupiter, was first observed in 1801 and recognized as a planet of the astronomers of that time (Redd, 2013, p. 1). Its discoverer’s name was Giuseppe Piazzi. When the multiple smaller objects overcrowding the asteroid belt were discovered, the scientists decided to downgrade this body to the status of an asteroid, just like the objects around.
Ceres was promoted again and became a dwarf planet in 2006 after the same decision was made about Pluto. The peculiarity of Ceres is that it is considered rather suitable for hosting life the way we know it. Besides, among the other icy bodies, Ceres is located the closest to the Sun, which makes is much warmer so that its ice can melt (Redd, 2013, p. 2).
Ceres is carefully examined as it may become the breaking point in relevance to the existence of water in the middle solar system, just like the moon of Jupiter called Europa and Saturn’s satellite Enceladus. Ceres is much smaller than other dwarf planets. Its diameter is around 952 km, and its density is 2.07 g/cm3.
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Eris is the dwarf planet that came very close to being pronounced a planet based on data provided by Hubble, the world’s most powerful telescope that works from space. Hubble helped the scientists calculate the size of Eris, which made it larger than Pluto. This caused a debate among the astronomers who needed to decide whether Eris had to become the tenth planet, or Pluto had to be downgraded to the status of the dwarf planet (Dwarf Bodies in the Solar System, 2008, p. 68).
The final decision is well known, Pluto ended up to be denoted, and this is how the solar system lost one of its planets. This, actually, is not the first time something like this happens to the solar system. For example, during the 1820s, when Pluto has not been discovered yet, the notes of solar system included data about eleven planets, some of which later turned out to be asteroids (Dwarf Bodies in the Solar System, 2008, p. 67).
Just like Pluto, Eris is located in the Kuiper belt; it also has an elliptical orbit that is even more eccentric than that of Pluto. Eris is the largest among the five dwarf planets with a diameter of 2397 km and a density of 2.52 g/cm3. Another similarity between Eris and Pluto are their atmospheres that seem only to occur when the objects come closer to the Sun and freeze when they move away.
Makemake is the third-largest dwarf planet. It is also suspected to have an atmosphere. The special feature of Makemake is the complete absence of natural satellites around it; all the other dwarf planets have at least one moon. Makemake is also one of the most recently discovered large celestial bodies. The scientists noticed Makemake in 2005. Makemake is estimated to be 1502 x 1430 km in diameter, and it has a red spectrum due to the heavy presence of methane in its atmosphere.
Finally, Haumea is, probably, the most interesting looking dwarf planet. First of all, it has a rather unusual shape. Haumea is elongated and can be compared to an egg or an American football. Its size includes three parameters, 2000 x 1500 x 1000 km as the planet is an ellipsoid. (Dymock, 2010).
Haumea is covered in ice. The scientists have a theory that Haumea appeared after two rather large objects bumped into each other. This theory is confirmed by the pieces with the same spectrum found around Haumea. Another peculiarity of Haumea is its very fast axis rotation, which may be another reason why Haumea is so elongated (Dymock, 2010, p. 45). Haumea makes a complete turn on its axis within only four hours. This dwarf planet was discovered in 2004 by an astronomer Mike Brown and his crew.
Summary and Conclusion
All of the currently known dwarf planets were discovered in different periods of time since the 1800s till 2005, whereas the planets such as Venus, Mercury, or Mars have been discussed ever since ancient times. The reasons why dwarf planets were not discovered earlier are their small size and their rather distant location. Even today, when the astronomers have such powerful devices as Hubble, dwarf planets such as Eris and Haumea can only be theorized about because not much data is available about them due to their far away placement.
Dymock, R. (2010). Asteroids and Dwarf Planets and How to Observe Them. Berlin, Germany: Springer Science & Business Media.
Dwarf Bodies in the Solar System. (2008). Hubble 2008: Science Year in Review, 1-77.
Original photos compared by Tombaugh. Web.
Redd, N. T. (2013). Dwarf planet Ceres: ‘A game changer in the solar system’. Web.