Most planets have comparably simple incidents of discovery. Venus, Mars, Jupiter, and Saturn were visible since forever. When Galileo observed Jupiter and Saturn for the first time he uncovered their true nature. Same is true for Venus and Mars. Uranus was discovered by William Herschel while he was observing the Sky. And Earth, well we were evolved into it. A bit interesting is the story of the discovery of Neptune, which was discovered based on mathematical calculations after observations in the changes in the orbit of Uranus caused by the planet Neptune. But none of them match the weird story of the discovery of Pluto.
Pluto: Identity Crisis Survivor
Pluto was discovered based on mathematical calculations that predicted the presence of a ‘Planet X’ beyond the orbit of Neptune to account for the changes caused in the orbits of the planets Neptune and Uranus. When it was discovered it did not match the size requirement of Planet X, plus later it was found that the calculations used to discover it was also off. In a way, the discovery of Pluto was possible because of a mathematical error.
Discovery and Naming
The ex-planet was discovered on this day in 1930 by Clyde Tombaugh for Lowell Observatory. Clyde Tombaugh was under high praise by the then director of Lowell Observatory, Vesto Slipher (who also found independently that Universe is expanding). Vesto Slipher trusted Clyde Tombaugh with the task of analyzing photo plates and look for the elusive planet X. Which he did so by examining two photo plates in rapid succession and spotted Pluto in the Kuiper Belt moving against the background of constant stars. This put to an end the lifetime struggle of Percival Lowell’s hunt for the Planet X. Though Pluto was not, in fact, Planet X, its discovery was welcomed. Since then the picture quality and our knowledge of the planet only increased.
Pluto was named after the Roman God of the underworld, Pluto, by the then 11-year-old girl, Venetia Katharine Douglas Burney from Britain. She has a crater, an asteroid and an instrument on New Horizons named after her. Even the Greek God of Hell, Hades is also called Plutons, from which Pluto is derived. Maybe the idea came from the dark regions of the Solar System. Later observations showed that Pluto also had a moon, called Charon. Later observations by Hubble Space Telescope showed that it had four other moons too, named Nix, Styx, Hydra, and Kerberos. All the moons of Pluto have been named after the mythological characters related to the underworld God. Styx is the river that separates the world of the living and the dead. Charon is the boatman responsible for carrying souls of the damned across the river, Styx. Nix is the mother of Charon and the Goddess of darkness. Hydra is the seven-headed serpent guarding the underworld while Kerberos is the three-headed dog (which also inspired the dog guarding the Sorcerer’s stone in Harry Potter). While most of us think that Pluto was named after the Disney character, it’s actually the other way around.
Pluto was originally thought to be a planet, and it remained so until the discovery of another trans-Neptunian body (Beyond the orbit of Neptune), called Eris. Pluto, the tenth planet, was 27% smaller than Eris. This caused confusion as to whether Eris should be classified as 11th Planet. Slowly many such bodies started to be discovered, and the number of possible planets in the solar system sky-rocketed. Here came the need for the International Astronomical Union (IAU) to lay down rules for any celestial object to be classified as a planet. The rules are as follows:
- The candidate is sufficiently massive so that its own gravity forces it into a spherical shape.
- The candidate has cleared its orbit of any debris. There should not be a lot of massive space rocks in the same orbit as the candidate and on a collision path with it.
- The candidate’s orbit should not cross the orbit of another planet.
- The candidate’s moon should revolve around it.
Pluto and these other new candidates violated one or more of these rules. Pluto particularly violates these as follows:
- Pluto is a very small body, measuring two-thirds of Earth’s moon, Luna. Its diameter is 2302 km only or the size of an average American state.
- Pluto is a part of the Kuiper belt, which is a belt of icy objects beyond the orbit of Neptune, similar in nature to the asteroid belt. Hence the orbit of Pluto is not cleared.
- For a short time during its journey around the Sun, Pluto is actually closer to it than the planet Neptune. The orbit of Pluto crosses that of Neptune at two places. The orbit is also tilted to the plane of orbits of another planet by almost 50 degrees. For 1979-1999 Pluto was at its perihelion to the Sun and was closer to us than Neptune.
- When Charon was discovered, it was found that the two bodies: Charon and Pluto were almost similar in mass, hence they orbited each other around a common barycenter. The barycenter is the common point around which two bodies revolve. Usually, the Barycenter of a planet and its moon lies within the planet and so the moon basically goes around the planet. But because of their unusual motion, Pluto-Charon is also called double planets.
Under the above points Pluto, along with all the other related bodies discovered, was designated as a dwarf planet. Some other dwarf planets include Eris, Ceres, Makemake, Vesta etc. Just to clarify, Pluto is still a part of the solar system, but just classified as a dwarf planet, not a planet. When it was demoted, the news “Pluto is no more a planet” was understood as “Pluto is no more” by many giving rises to theories that perhaps it was engulfed by a black hole. These are just nice and entertaining stories, not facts.
What Do We Know?
Since its discovery, Pluto has been a center of curiosity, and we have tried to know as much as we can about this distant and elusive neighbor. From Hubble to Voyager to New Horizons, with every mission, our understanding of Pluto has increased. The flyby of Pluto by New Horizons in 2015 was the first mission to the dwarf planet. Till then all the observations were distant ones. This was the first time humanity got the front seat view of the tiny Pluto.
Pluto takes almost 6 Earth-days to complete one rotation. The duration of one Plutonian year is 248 Earth years. The axial tilt of the planet makes it rotate sideways as if doing a barrel roll. The distance of Pluto from sun on an average if 5.8 billion km or 39 AU. From that far, Sun shines very dimly. Every day on Earth, there is a time before sunset when the brightness of the sky is just as much as the brightness on Pluto when its noon over there. This time is called Pluto time. If you are reading this on the day of the publication of this post, the Pluto time is around 06:03 PM.
Study of data from New Horizons tells us that the surface of Pluto is rich in frozen Nitrogen, Methane and Carbon monoxide. The atmosphere too is rich in the Nitrogen, Methane and Carbon dioxide. The chemical composition of the atmosphere causes the rain there to be red in color. This is not water rain, but the rain of the chemicals present in the atmosphere. While the surface if Pluto is frozen, it is thought that near the core, the temperature would be warmer and that the mantle and core of Pluto might have water. Another interesting finding is that the revolution time of Charon is equal to the rotation period of Pluto. This causes Charon to stay at the same point in the sky of Pluto. Constant like the pole star, but not as much useful.
Ice dwarfs like Pluto are also classified as Plutoids, as they are thought to have the same chemical makeup as Pluto. The moon of Neptune, Triton, is thought to be a Plutoid that has been captured by the gas giant.
Tip of The Iceberg
When New Horizons flew by Pluto, the high definition images revealed that Pluto, the beloved dwarf planet, had a surface feature that looks like the doodle of heart. This was actually an internet sensation. Later studies found that this was a wasteland on the Planet. The area is named Sputnik Plantia. The planet’s surface has both hills and plains. Since then many new pictures of the dwarf planet have been released, loved by the people, and studied by the experts.
Pluto holds the key to understanding the Kuiper belt, and the evolution of the solar system much better. Data from the New Horizons mission is still being analyzed and studied. They are opening doors to future missions targeting Pluto in particular. Now New Horizons is continuing its journey of reaching new limits of exploration. On this new year’s eve the spacecraft did a flyby of Ultima Thule, which is the farthest object to having been studied by any mission. Meanwhile, the curiosity with Pluto has just arisen, and more is yet to be discovered. We have just uncovered the tip of the iceberg. Happy birthday, Pluto!
Before you leave here are some eye-candy photos of the dwarf planet.