Like continents planets are defined more by how we think of
them than by some ones after the fact pronouncement.
Michael Brown
Maybe this world is another planets hell.
Aldous Huxley
How many planets are there in the
solar system? A few years ago the answer
was universally accepted to be nine now, however, the issue is more
contentious. The word planet itself derives from the Greek word for wanderer, a
word that describes there migration across the seemingly static background of
the stars.
We have documentary evidence of the
major planets going back many thousands of years. Mercury, for example, was first recorded by Asian astronomers as
early as 1480bc. In the 17th century we invented the telescope and
literally opened the cosmos up. Now we were able to see the majesty of the
solar system in its entirety: from the
raging red storm on Jupiter, the splendid rings around Saturn and the coterie
of moons that orbit around Jupiter not to mention the canal like channels on
mars.Uranus was discovered in 1781 by William Herschel originally believing it to be a rouge star however thanks to his diligent tracking of the object he was able to prove that it orbited the sun thereby securing its position as a planet. Herschel originally wanted to call his discovery Georgium Sidrum literally translated as George’s star in honour of his patron king George III who had appointed him astronomer royal. The name was not popular outside of Britain however and ultimately the name Uranus was put forward by Johann Kale
There are slight imperfections in Uranus orbit that led to predictions that it was disturbed by another celestial body that lay beyond it. Astronomers scoured the expected location looking for the wandering interloper and in 1840 Neptune was discovered by Frenchman Urbain Jean Joseph Le Verrier narrowly beating British astronomer John Coach Adams to establish the find. Finally in 1930 Pluto was confirmed. The American astronomer Clyde Tombaugh discovered it however he did not name it. A contest was ran and British schoolgirl Venetia Burney won with her classics inspired suggestion of Pluto after the god of the underworld.
Pluto
Dethroned
The solar system stood at nine
planets for 75 years until Michael Brown and his team
discovered that Pluto was not alone in the chill depths of the solar system
having found a handful of sizeable objects not far from Pluto’s orbit at the
cold edge of the solar system. They even found one larger than Pluto itself,
they called it Eris after the goddess of strife in Greek mythology.
The astronomical community had a conundrum. Should Eris be recognised as the
tenth planet? The outer reaches of the solar system are littered with ice
smothered objects of which Pluto and Eris are simply the largest, moreover, rocky
asteroids of similar size were known elsewhere such as Ceres (named
for the roman goddess of agriculture) a 950km
diameter asteroid that was found in 1801 by Giuseppe Piazzi
between mars and Jupiter while searching for Neptune
In 2005 a committee of the
international astronomical union (the IAU), the professional body of
astronomer, met to decide Pluto’s fate. Brown
wanted to protect the status of Pluto as culturally defined also that Eris
should be considered a planet as well.
Others considered that all the bodies beyond Neptune are not ‘real’
planets. In 2006 a vote was held and a new definition of a planet was
formulated until this point there was no ‘hard and fast’ scientific
definition. A planet is defined as a
celestial body that orbits the sun, is massive enough that its own gravity
makes it round and has cleared the region around its orbit. According to these
rules Pluto is not a planet as it hasn’t
cleared other bodies from its orbit, so Pluto Eris and Ceres were named dwarf
planets smaller bodies apart from moons remained unspecified.
A planet is defined as a celestial body that orbits
the sun, is massive enough that its own gravity makes it round and has cleared
the region around its orbit
The definition was made for our own solar system but works just as well for systems beyond it. There are serval hundred planets known to orbit alien suns, identified by their subtle pull they impart on their host stars. Mostly the planets discovered are massive gas giants like Jupiter. Smaller earth like planets are being detected by spacecraft such as Kepler launched in 2009. Similarly the definition of a star has been called into question lately, stars are balls of gas that are big enough to have ignited nuclear fusion in cores thus making them shine. It’s not obvious however where the division between Jupiter like planets and the smallest dimmest stars like brown dwarves.
350BC
|
Aristotle determines that the earth is round
|
1543
|
Copernicus publishes
his heliocentric theory
|
1610
|
Galileo discovers Jupiter’s moons through a telescope
|
1781
|
Uranus discovered by
Herschel
|
1843-6
|
Neptune predicted and found by Le Verrier
|
1930
|
Clyde Tombaugh
discovers Pluto
|
1962
|
First mariner 2 images of Venus
|
1992
|
First extrasolar
planet discovered
|
2005
|
Brown discovers Eris
|
