MERCURY - THE HOT PLANET
If you remember anything about
Mercury, remember that it is the closest planet to the Sun and really hot. Temperatures on Mercury get up to 460 degrees Celsius. An average temperature on Earth is about 15 degrees Celsius (although it has a wide range). The Sun beats down on little Mercury all day long.
The amazing thing is that there is a side of Mercury that faces away from the Sun. Temperatures on the dark side of the planet can drop to less than negative 180 degrees Celsius. It's a whopping 640 degree temperature change from the hottest to the coldest part of the planet. The temperature ranges are a direct result of the very long days on Mercury. It takes 58 Earth days for Mercury to complete one of its days. This slow rotation affects the temperatures on the surface. Very long days allow the temperature to build for long periods of time.
VENUS IN THE NUMBER TWO POSITION
The second planet away from the Sun is called
Venus. It's ironic that Venus is named after the Roman goddess of love and beauty. Venus is one of the harshest planets in the Solar System. It's over 460 degrees Celsius. It has clouds of
sulfuric acid in an atmosphere of
carbon dioxide. Lava is found across the surface after being spewed from
volcanoes. While a harsh place for you, scientists think it's an amazing planet.
YOUR BLUE HOME
The third planet from the Sun is your home. The
Earth is the only known planet where life can survive. As far as we know, there is no other planet in the universe like Earth. We have a very narrow temperature range that allows water to remain a
liquid. Life has developed over millions of years because of that liquid. What else makes us special? Most of our atmosphere is made of
nitrogen (N), a relatively inert gas. If we had clouds of sulfuric acid or methane (like other planets), life may have never developed.
MARS IN THE FOURTH POSITION
Mars is the fourth planet from the Sun. It is a very active planet like the Earth. It has evidence of volcanoes, plate tectonics, and liquid water (as opposed to ice) on the planet. It even has polar
ice caps like the Earth, with water in the north and solid
carbon dioxide in the south. With all of these similarities, Mars is still nothing like Earth. It only has 40% of our gravity because the mass of the planet is so much smaller. Also, its atmosphere is made up of carbon dioxide and has less than 1% of the atmospheric pressure of Earth.
MIGHTY JUPITER
Jupiter is the largest planet in our Solar System. Its mass is over 300 times the mass of the Earth. If you look at its atmosphere and over 20 moons, you could say that Jupiter is almost like another Sun. There is only one thing missing -- Heat. There is a magical time in a star's life when nuclear reactions start and the star begins to burn. Jupiter never got to that point.
Jupiter is classified as a
Jovian planet. The Jovian planets are
gas giants that orbit the Sun. Gas giants don't have solid surfaces of rock like other planets. You will find some rock at the core of the planet, but it is very little when compared to the planet as a whole. As you move deeper into the planet, you find very dense gases that have become liquids. All of the Jovian planets are huge compared to the Earth but tiny when compared to the Sun. Jupiter has a diameter of 85,000 miles while Earth is only 7,600 (the Sun is about 870,000 miles). Jupiter is often one of the brightest objects in the sky because of its size.
A FLOATING PLANET?
Saturn is the other big planet in our Solar System. You will find its orbit just outside of Jupiter in the sixth position. It is a gaseous planet like Jupiter and those gases give Saturn a very
low density. The big astronomy joke is that if you could find a lake big enough and put Saturn in the water, it would float. Its density makes it lighter than water. While knowing Saturn's density is a fun fact, we know that the thing you will remember is that Saturn is the planet with the big
rings. While other planets in our Solar System have rings, Saturn's can be seen from Earth. The Cassini spacecraft is studying the moons and rings of Saturn for several years.
LEARNING ABOUT URANUS
The seventh planet from the Sun is
Uranus. William Hershel discovered it in 1781. It is one of the four gas giants in our Solar System, but is much smaller than both Jupiter and Saturn. You will find that Uranus is similar in some ways to Neptune, the eighth planet. Only one Voyager probe has flown by Uranus so very little is known about the planet.
Like other planets we discussed, Uranus is a planet largely composed of gases. It has a light blue color because of the
methane in its atmosphere. The atmosphere of hydrogen, helium, and methane is constantly swirling around the planet. As you move from the core to the surface of the atmosphere, you will discover liquid rock, ice, and molecular hydrogen. There is no layer of metallic hydrogen like Jupiter and Saturn.
NEPTUNE IN THE EIGHTH POSITION
Neptune is the eighth planet form the Sun. It wasn't discovered until 1846. It wasn't even actually seen with a telescope for several years after that. Astronomers noticed some funny movements in the orbit of Uranus. The changes in the expected orbit were so large than they decided another planet must exist. They made the calculations, looked in the right place, and found Neptune.
ANOTHER GIANT
Neptune is huge in size compared to Earth. When you compare it to the other gaseous planets like Jupiter and Saturn, it is the smallest. Like the other Jovian giants, Neptune's atmosphere is made up of hydrogen and helium. It also has large amounts of
methane that give it a deep blue tint. It is very similar to Uranus.
See that big swirl in the atmosphere? Just like Jupiter, Neptune has large
storms swirling in its atmosphere. When Voyager II passed by, it took pictures of a storm that was big enough to hold the Earth. The storm was moving at more than 500 miles per hour. The speeds inside of the storm could have been more than seven times the speed of the fastest winds on Earth.
DISCOVERING PLUTO
We didn't even know that
Pluto existed until the 1930's. Astronomers studied the orbit of other planets in the area and noticed a little wobble. The wobble was big enough for astronomers to start looking for a source. Eventually Clyde Tombaugh found Pluto. In recent years, additional large bodies have been discovered just beyond Pluto's orbit.
For such a small object, there is a lot of debate about Pluto. Its size is one of the big reasons that astronomers stated that it is no longer considered a true planet. The International Astronomical Union (IAU) met in August 2006 and decided that Pluto would be classified as a
dwarf planet. The change comes because of Pluto's size and eccentric (strange) orbit. It passes in an out of the orbit of Neptune and doesn't orbit in the same plane as the other planets. It's a weird little object. Astronomers decided that this weird little object would no longer be a planet. Even though a small object, Pluto has its own satellite (moon) named
Charon.
