Pluto: Planet or not? Before we can answer this question we need
to know what the word planet is for, and that takes us back to the ancient greeks who called
Mercury, Venus, Mars, Jupiter, Saturn, the Moon and sun planets. Basically if it moved across the sky and was
bright, it was a planet. This is a terrible start for the word because,
1) it excludes Earth from the list and 2) it groups wildly different things together. But the greeks couldn't know how different
the Moon was from Saturn, because the best technology they had to observe the Universe
was sadly limited. It would take several thousand years until
the industrious Dutch made the first telescopes and astronomy became much more interesting. Astronomers could now confidently rearrange
the solar system -- an elegant scientific advance that no one could possibly object
to -- and reclassify its parts, dropping the Sun and moon from the list of planets and
adding Earth. Now, if it orbited the Sun, it was a planet. As time went on and telescopes got better
and better each new century brought with it the discovery of a new planet. Which brings us to this familiar solar system:
nine planets orbiting one star. And looking at this model makes people wonder,
why do astronomers want to ditch Pluto? The problem is pictures like this in textbooks
are lies. Well, not lies exactly, but unhelpful. They give the impression that the planets
are similar-ash in size and evenly-ish spaced, but the reality couldn't be more different. Here, dear Terrans, is our home planet Earth,
and this is Jupiter next to it at the correct scale -- rather bigger than you probably thought. If we take this diagram and adjust for the
correct sizes of the planets it looks like this. Unless you're watching the video in fullscreen
HD mode, you might not even be able to see Pluto. So size differences are vast, and Pluto is
the smallest by far. But it's not just small for a planet, it's
also smaller than seven moons: Triton, Europa, our own Moon, Io, Callisto, Titan, and Ganymede. Even if you show the correct relative sizes
the distances are still a problem. Think about it, if Jupiter was this close
to Earth it wouldn't look like a dot in the night's sky but would be rather overwhelming
-- so it must be really far away, which makes drawing it to scale rather a challenge. If you want the length of a piece of paper
to represent the distance from Mercury to Pluto, then giant Jupiter would be the size
of a dust mite on that page, and Pluto a bacterium. But excluding Pluto from the plant club just
for being tiny and far away isn't reason enough and quickly brings out the Pluto defenders. In order to understand what Pluto really is,
we need to first discuss a planet you've never heard of: Ceres. Back in the 1801, astronomers found a new
planet in the huge gap between Mars and Jupiter -- it was a small planet, but they loved it
anyway and named it Ceres. The next year astronomers found another small
planet in the same area and named it Pallas. A few years later they found a third one,
Juno, and then, funnily enough, a fourth one, Vesta. And for a several decades children learned
the 11 planets of the solar system. But, astronomers kept finding more and more
of these objects and became increasingly uncomfortable calling them planets because they were much
more like each other than planets the on either side, so a new category was born: asteroids
in the asteroid belt -- and the tiny planets were relabeled which is why you've never heard
of them. And it was a good decision too, as astronomers
have now found hundreds of thousands of asteroids, which would be a lot for a kid to memorize
if they were all still planets. Back to Pluto. It was discovered in 1930 making it the 9th
planet. First estimates put Pluto about the size of
Neptune, but with more observations that was revised down, and down and down. While Pluto shrank astronomers started to
find other, similar objects orbiting in the same zone. Sound familiar? While school kids kept memorizing the nine
planets, some astronomers grew uneasy about including Pluto because the size estimates
continued to shrink, they learned that Pluto is made mostly ice, and they continued to
find lots and lots of icy objects at the edge of the solar system just like Pluto. This problem could be ignored as long as no
one found an ice ball bigger than Pluto, which is exactly what happened in 2006 with the
discovery of Eris. Once again, astronomers recategorized the
solar system and grouped these distant objects, including Pluto, into a new area called Kuiper
belt. And that's the story of Pluto -- a miscategorized
planted that finally found its home -- just like Ceres. But this story is really less about Pluto
than it is about realizing the word 'planet' isn't very helpful. The first four planets are nothing at all
like the next four, so it's even a little weird to group these eight together which
is why they often aren't and are separated into terrestrial planets and gas giants. And now that we have telescopes that can see
planets around stars not our own, and we've found rogue planets drifting in empty space
and brown dwarfs -- objects that blur the very line between planet and star -- the word
planet becomes even less clear. So as we increase our knowledge of the Universe
the category of 'planet' will probably continue to evolve, or possibly, fall out of favor
entirely. But, for the time being the best way to categorize
the stuff in our solar system is into one star, eight planets, four terrestrial, four
gas giants, the asteroid belt, and the distant Kuiper belt, home to PlutoοΏ½
I've watched it 3 times. Still trying to find the creeper.
Needs more Makemake and Haumea. Why leave out the dwarf planets with the best names?
More proof that Holst got it right
How much money can I give him so he does this for a living?
I loved the 2010 space odyssey reference with Europa
Creeper appears somewhere between 1:00 and 1:59, I think. Definitely needed fullscreen HD to see that.
Unless you switch to full HD mode.. switch
Crossposted to r/SpaceVideos.
Also worth noting is that Pluto is off axis, and rotates the wrong direction, leading us to believe it wasn't formed in the original compacting disk that the rest of the planets were formed from.