How many planets are there?
Most people would probably say 8, unless you’re one of the holdouts hanging onto the dream
of Pluto one day being reinstated.
Sorry to burst your bubble, but this video isn’t about Pluto.
In ancient times a planet was anything that moved across the sky in relation to the stars.
With the advent of the scientific revolution, the use of the term ‘planet’ was changed
to be a body that orbited the Sun.
With this definition there were 6 planets; Mercury, Venus, Earth, Mars, Jupiter, and
Saturn.
From 1801-1807 four new bodies, Ceres, Pallas, Juno, and Vesta, were discovered that orbited
the sun and so were added to the official list of planets.
For nearly half a decade these 11 planets stood.
Then, by the 1950’s, having learned more about the new planets, and with the discovery
of Neptune in 1946, it became clear that the four additions were drastically different
than the rest of the celestial bodies, and so they were removed from the official list
of planets.
While no official definition was made at the time, it was generally understood that a planet
was any ‘large’ body that orbited the sun.
You see how that word ‘large’ isn’t very specific.
Well low and behold that caused a lot of confusion decades later with the discovery of Pluto
in 1930.
Initial observations led to the belief that Pluto was much larger than Earth, and so it
was easily adopted as the ninth planet.
Then, over time, as more measurements came in, Pluto got smaller and smaller and now
we understand that it’s less than 1% the size of Earth.
But that wasn’t an insurmountable problem, it was still larger than all other known asteroids
and seemingly did not exist with any near neighbors.
But then….. in 2005, Eris, a dwarf planet past Netpute was discovered which was 27%
more massive than Pluto.
And by this time it became clear that there were far more Pluto sized objects at the edge
of our solar system than previously thought.
So there were two options.
Either Pluto is a planet, which would make Eris and the likely many more Pluto sized
bodies that would come to be discovered planets, or kick Pluto from the exclusive list.
So, in 2006, the IUPAC, the International Union of Pure and Applied Chemistry, agreed
on a definition of a planet that set it as a body orbiting the sun with enough mass to
make a nearly round shape and has cleared all neighbors out of its orbit.
Because of the existence of Pluto’s three close neighbors, Quaoar, Sedna, and Eris,
Pluto was demoted to a dwarf planet.
So now, what’s all this about a ninth planet.
Both Pluto and Neptune were mathematically predicted before they were first discovered
based on their invisible pull on their neighbors.
For example, Pluto was discovered because Percival Lowell, among others, was convinced
that Neptune was continually in the wrong place.
Why?
Some massive object, more distant than Neptune, was tugging on it, competing with the Sun
gravitationally for control over Neptune.
(If you want to learn more about Percival Lowell check out this video here about the
mystery of the canali on mars).
Interestingly, Neptune was almost not discovered by mathematical predictions and instead almost
discovered by the first person who could have possibly discovered a new plant, the first
to turn a telescope to the heavens, Galileo.
Galileo turned his telescope on the planets and was immediately fascinated by the system
of Jupiter and its moons.
While he was observing Jupiter on January 27th, 1613, he recorded two stars in his field
of view.
One was a genuine star, but the other was actually Neptune.
Remarkably, Galileo observed the pair again the following night and even noted a strange
occurrence that the two stars appeared to be further apart.
So close to discovering that one of the stars was the planet Neptune.
And now Caltech researchers have found mathematical evidence suggesting there may be a "Planet
X" deep in the solar system.
This hypothetical planet orbits our Sun in a highly elongated orbit far beyond Pluto.
The object, which researchers have nicknamed "Planet Nine," could have a mass about 10
times that of Earth making it similar in size to Uranus or Neptune and orbit about 20 times
farther from the Sun than Neptune.
It would take this new planet between 10 and 20,000 years to make just one full orbit around
the Sun (where Neptune completes an orbit roughly every 165 years).
This announcement does not mean there is a new planet in our solar system.
The existence of this distant world is only theoretical at this point and no direct observation
of the object nicknamed "Planet 9" have been made.
This mathematical prediction of a planet could explain the unique orbits of some smaller
objects in the Kuiper Belt, a distant region of icy debris that extends far beyond the
orbit of Neptune.
Since the announcement, astronomers are now searching for the predicted planet (even if
only to snag dibs on the naming rights).
The researchers calculated that there’s only a one in 500 chance that what they are
seeing is just observational bias, indicating that there predictions are probably quite
accurate (or I guess that their models really aren’t).
So who knows, maybe we’ll be back to nine planets before you know it.
Well that’s it for today on Everything Science.
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