00:00:01
Pluto: Planet or not?
00:00:04
Before we can answer this question we need
to know what the word planet is for, and that
00:00:07
takes us back to the ancient greeks who called
Mercury, Venus, Mars, Jupiter, Saturn, the
00:00:10
Moon and sun planets. Basically if it moved
across the sky and was bright, it was a planet.
00:00:16
This is a terrible start for the world because,
1) it excludes Earth from the list and 2)
00:00:21
it groups wildly different things together.
00:00:23
But the greeks couldn't know how different
the Moon was from Saturn, because the best
00:00:26
technology they had to observe the Universe
was sadly limited.
00:00:29
It would take several thousand years until
the industrious Dutch made the first telescopes
00:00:33
and astronomy became much more interesting.
00:00:36
Astronomers could now confidently rearrange
the solar system -- an elegant scientific
00:00:39
advance that no one could possibly object
to -- and reclassify its parts, dropping the
00:00:43
Sun and moon from the list of planets and
adding Earth.
00:00:45
Now, if it orbited the Sun, it was a planet.
00:00:48
As time went on and telescopes got better
and better each new century brought with it
00:00:52
the discovery of a new planet.
00:00:53
Which brings us to this familiar solar system:
nine planets orbiting one star.
00:00:57
And looking at this model makes people wonder,
why do astronomers want to ditch Pluto?
00:01:01
The problem is pictures like this in textbooks
are lies. Well, not lies exactly, but unhelpful.
00:01:06
They give the impression that the planets
are similar-ash in size and evenly-ish spaced,
00:01:09
but the reality couldn't be more different.
00:01:11
Here, dear Terrans, is our home planet Earth,
and this is Jupiter next to it at the correct
00:01:16
scale -- rather bigger than you probably thought.
If we take this diagram and adjust for the
00:01:20
correct sizes of the planets it looks like
this. Unless you're watching the video in
00:01:24
fullscreen HD mode, you might not even be
able to see Pluto.
00:01:27
So size differences are vast, and Pluto is
the smallest by far. But it's not just small
00:01:31
for a planet, it's also smaller than nine
moons: Triton, Europa, our own Moon, Io, Callisto,
00:01:37
Titan, and Ganymede.
00:01:38
Even if you show the correct relative sizes
the distances are still a problem. Think about
00:01:41
it, if Jupiter was this close to Earth it
wouldn't look like a dot in the night's sky
00:01:44
but would be rather overwhelming -- so it
must be really far away, which makes drawing
00:01:49
it to scale rather a challenge. If you want
the length of a piece of paper to represent
00:01:53
the distance from Mercury to Pluto, then giant
Jupiter would be the size of a dust mite on
00:01:57
that page, and Pluto a bacterium.
00:01:59
But excluding Pluto from the plant club just
for being tiny and far away isn't reason enough
00:02:03
and quickly brings out the Pluto defenders.
00:02:05
In order to understand what Pluto really is,
we need to first discuss a planet you've never
00:02:09
heard of: Ceres.
00:02:11
Back in the 1801, astronomers found a new
planet in the huge gap between Mars and Jupiter
00:02:15
-- it was a small planet, but they loved it
anyway and named it Ceres.
00:02:18
The next year astronomers found another small
planet in the same area and named it Pallas.
00:02:22
A few years later they found a third one,
Juno, and then, funnily enough, a fourth one,
00:02:27
Vesta. And for a several decades children
learned the 11 planets of the solar system.
00:02:31
But, astronomers kept finding more and more
of these objects and became increasingly uncomfortable
00:02:35
calling them planets because they were much
more like each other than planets the on either
00:02:39
side, so a new category was born: asteroids
in the asteroid belt -- and the tiny planets
00:02:43
were relabeled which is why you've never heard
of them. And it was a good decision too, as
00:02:47
astronomers have now found hundreds of thousands
of asteroids, which would be a lot for a kid
00:02:52
to memorize if they were all still planets.
00:02:54
Back to Pluto. It was discovered in 1930 making
it the 9th planet. First estimates put Pluto
показать еще
русский▼
English
