Page 86 - The Creation Of The Universe

84 THE CREATION OF THE UNIVERSE

n imaginary space-traveler approaching the solar system from
interstellar space would encounter a very interesting scene. Let
Aus imagine that we are such travelers and that we're arriving
at the plane of the ecliptic–the great circle of the celestial sphere in
which all the major planets of our solar system move. The first planet
we will meet is Pluto. This planet is quite a cold place. The temperature
is around -238°C. The planet has a thin of atmosphere that is in a
gaseous state only when it draws slightly nearer to the sun in its rather
elliptical orbit. At other times, the atmosphere becomes a mass of ice.
Pluto, briefly, is a lifeless sphere enveloped in ice.
Advancing towards the Sun, you next encounter Neptune. It is cold too:
approximately -218°C. The atmosphere, consisting of hydrogen, helium and
methane, is poisonous for life. Winds blowing nearly 2,000 kilometers an
hour blast across the surface of the planet.
Next is Uranus: a gaseous planet with rocks and ice on its surface. The
temperature is -214°C and the atmosphere again consists of hydrogen, he-
lium and methane–unsuitable for human beings to live in.
You reach Saturn after Uranus. This is the second biggest planet in the
solar system and is particularly notable for the system of rings encircling it.
These rings are made up of gases, rock and ice. One of the many interest-
ing things about Saturn is that it is composed entirely of gas: 75% hydro-
gen and 25% helium and its density is less than that of water. If you want
to "land" on Saturn, you'd better produce your spaceship to be like an in-
flatable boat! The average temperature is again very low: -178°C.
Coming up next is Jupiter: the biggest planet in the solar system, it is
318 times the size of Earth. Like Saturn, Jupiter is also a gaseous planet.
Since it is difficult to distinguish between "atmosphere" and "surface" on
such planets, it is hard to say what the "surface temperature" is but in the
upper reaches of the atmosphere, the temperature is -143°C. A notable fea-
ture of Jupiter's atmosphere is something called the Great Red Spot. It was
first noticed 300 hundred years ago. Astronomers now know that it is an
enormous storm system that has been raging in the Jovian atmosphere for