Everything Everywhere Daily: History, Science, Geography & More - How Many Planets Are There?

Episode Date: July 28, 2020

Poor Pluto. It was totally unknown, then it was a planet, and now it’s not a planet anymore. This change in the status of planets isn’t the first time such a thing has happened. Since the dawn of history, the number of things we call a planet has gone up and down. Find out why Pluto got demoted from a planet, and learn about our human history with planets on this episode of Everything Everywhere Daily. Learn more about your ad choices. Visit megaphone.fm/adchoices

Poor Pluto. It was totally unknown, and then it was a planet, and now it's not a planet anymore. This change in the status of planets isn't the first time such a thing has happened. Since the dawn of history, the number of things we call a planet has gone up and down. Find out why Pluto got demoted from a planet and learn about our human history with planets on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time. to uncover the parts of the story that may have gone unnoticed.

It effectively turned day into night. And how it shaped the world now. Time travel with us every week on the Thuline podcast from NPR. This episode of Everything Everywhere Daily is sponsored by listeners like you. Creating a daily show like this isn't easy. Researching, writing, and recording a daily show takes quite a bit of time. And you have to do it every single day. Over on patreon.com, there is a small but growing community of listeners who support the show with their donations.

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or click on the link in the show notes. Since humans first looked up at the night sky and saw twinkling lights, they noticed that some of the lights were different. They moved. They moved in regular patterns, and they could track their movement. across the sky over time. These moving lights were eventually known as planets. The word planet comes from Greece,

and in the Greco-Roman astronomy system, there were seven planets. Mercury, Venus, Mars, Jupiter, Saturn, the sun, and the moon. Clearly, the sun and the moon are different from the other planets, and the ancients recognize this. The other planets were moving stars, but the sun and the moon were dis.

They were alternatively referred to as the seven planets or as the five planets plus the sun and the moon. Plato spoke of the sun, the moon, and the five other stars which are called the planets. And Ptolemy noted, the sun, the moon, and the five planets. The underlying assumption behind all of this is that the Earth was the center of the universe. This five or seven planet view of the cosmos stood until the Copernican Revolution, which established the sun as the center of the solar system.

This change of perception of the solar system realized that the sun and the moon weren't planets, but that the Earth was. This changed the number of planets from five or seven, depending on how you defined it, to a solid six. The six planets stood for about 280 years until telescopes became powerful enough where we could see further out in the solar system. In 1781, the astronomer William Herschel thought he had found a comet while doing observations in the constellation Taurus. It never dawned on him that he found another planet, because the planets have been known since time immemorial. He and several other astronomers eventually concluded that it had to be a planet given its movement

and the fact that it didn't show a tail like a comet. They called the new planet Uranus, who was the father of Saturn. This now up the planet count to seven. Neptune was discovered in 1848 when deviations in Uranus's orbit indicated that there might be another planet further out. Unlike Uranus, the discovery of Neptune involved several people hunting it down. The discovery is credited to several people who determined its location from the orbital data of Uranus. Urbane-Laver of France, John Couch Adams of England, and Johann Gottfried Gale of Germany are all credited with the discovery. You're probably thinking that the discovery of Neptune now made eight planets, but that is not the case.

That was because in 1801, Guseppe Piazzi discovered a new planet between the orbit of Mars and Jupiter that he called series. That was planet number eight. Then in 1802, another planet was found in the same orbit of series by Heinrich Olbers that was called Palace. That made nine planets. In 1804, another planet in the same orbit was found by Carl Harding called Juno, and that up the number to 10. And then in 1807, there was another planet found in the same orbit, again by Heinrich Olbers called Vesta, which made for 11 planets. By 1851, there were now over 20 planets and they were discovering more all of the time in the same orbit as series. They eventually reclassified all of the planets that were in the orbit of series as asteroids.

All of these planets weren't like the other planets. They were much smaller and all in the same orbit. None of them were big enough to clear out their orbits, so they got demoted. The list of planets was back down to eight. In 1930, an astronomer named Clyde Tombaugh used the new technique of astrophotography to discover a moving dot in the sky, which was later named Pluto by 11-year-old Vanita Burnley from Oxford, England. Almost immediately after a discovery of Pluto, there was controversy as to if it should be called a planet. Pluto, you see, was different. Like the 19th century controversy surrounding series, there was controversy around Pluto almost immediately. Pluto was much smaller than any other planet. After the sun, the next eight largest

things in the solar system are the other planets. Pluto is smaller than seven other moons which orbit other planets. Pluto has a really weird orbit. It's highly elliptical, whereas most of the other planets have near circular orbits. It also crosses the orbit of Neptune, which no other planet does. Unlike the asteroids, however, there was no other object like Pluto that they knew of at the time, so Pluto got added to the list of planets. Sure, it was a bit different, but it was allowed to be a member of the club. There were officially nine planets. But then something happened. It had been theorized that there were other objects beyond Pluto in an area that was known as the Kuiper Belt. In fact, it was estimated that there

might be thousands of objects beyond Pluto. Just like the rush of asteroid belt discoveries in the 19th century, in the early 2000s we saw a rush of discoveries beyond Pluto. The list started to grow quickly. They were Quoar, Sedna, Orcus, Gongong, Hamea, and Makeemake. There was one discovery in particular which really threw a wrench into things. Eris. Eris, you see, had a mass greater than Pluto. If Pluto was a planet, then Eras had to be a planet too. It was hard to justify Pluto as a planet and not Eris.

That would make ten planets. Moreover, all of the other objects found beyond the orbit of Pluto were far more like Pluto than Pluto was like the other planets. This was just like Ceres and the other asteroids all over. again, and this is what caused the most recent controversy about Pluto being a planet. The International Astronomy Union voted to define a planet in 2005 by three criteria. 1. It is an orbit about the sun. 2. It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes

a hydrostatic equilibrium shape. In other words, it's round. And three, it has cleared the neighborhood around its orbit. That third part is what separates Pluto. from the eight other planets. If an object has the first two criteria, but not the third, it's considered to be a dwarf planet, which is what Pluto is now considered. As of today, there are now nine known dwarf planets. The discussion on planets has sort of obscured the fact for most people about how much stuff is really orbiting around the sun. If we take a step below dwarf planet, we enter the realm of minor planets, which includes pretty much any hunk of rock that orbits the sun. And there are 794,832 cataloged objects in the solar system

as of 2019. So it's impossible to have nine planets anymore. Even if Pluto were to be considered a planet, then ERIS would have to be considered one too. And if we let those two in, then we'd have to open the door to a whole bunch of other objects, which would almost certainly grow over time, most probably to a very large number. So rather than lamenting the loss of Pluto as a planet, celebrate its new position as king of the dwarf planets. Executive producer of Everything Everywhere Daily is James Mackala. Special thanks to everyone who supports the show over on Patreon. Please remember to leave a review over on Apple Podcasts.

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