Pluto is probably a big chunk of rock and ice that is covered by a layer of frozen nitrogen and carbon monoxide. None of our flying robot explorers have gone by Pluto... So, there's a lot about Pluto that we just aren't sure of. Pluto has a reddish color due to fit's frozen methane being hit with radiation for billions of years. (Our drawing is of a black and white picture.)

No way! Brrrrrr... It's WAY too cold! It's the furthest away from the Sun and coldest planet in the solar system (except, possibly, for the frozen ice on our moon). We think the thin atmosphere is made of nitrogen and carbon dioxide. You definitely don't want to try to breathe this stuff! There is frozen water on Pluto, but it's under a bunch of frozen poison stuff.

To escape Pluto's gravity and get out into space, a rocket has to travel at a speed of 2,727 mph or 1.2 km/sec. That's about 42 times faster than your parents are allowed to drive on a U.S. highway!

Pluto's only known moon, Charon, was discovered in 1978. The really cool thing is the way Pluto and Charon rotate... As Charon moves around Pluto, they each keep the same face towards each other all the time. No, they really aren't striped, we just did that so you can see it more clearly.

 

Pluto was discovered by accident. Scientists thought they had predicted the existence of a ninth planet because they found a wobble in Neptune's orbit. This would mean that there was something big pulling on it - like a ninth planet. They pointed their telescopes to where they figured this ninth planet would be. They looked and looked and found nothing. It turned out that the wobble they found was only a mistake in their data! A long time later, the ninth planet, Pluto was found... But it had nothing to do with this other search.

One of the coolest things about Pluto is that it rotates in the opposite direction of most of the other planets! If we look down on the planets from above we see that Pluto rotates clockwise (the way a clock's hand move around the clock) and all the other planets (except Uranus and Venus) and all the moons spin counterclockwise (like if the clock's hands were moving backwards). Check out this picture:

Scientists think there may be thousands of little icy planets like Pluto on the outer edge of our solar system.

It would take 500 Pluto's to equal the Earth's mass.

NASA is has plans to make a new flying robot explorer that will fly by Pluto in 2013. The project is called the Pluto-Kuiper Express and it will give us a really close up look!

Sun | Mercury | Venus | Earth | Our Moon | Mars | Jupiter | Saturn | Uranus | Neptune | Pluto

Sources:
In Quest of the Universe, 2nd ed. by Karl F. Kuhn
Voyages Through the Universe, 2nd ed. by Fraknoi, Morrison and Wolff
Universe by Kaufmann
The Complete Idiot's Guide to Astronomy by Christopher De Pree and Alan Axelrod
The Astronomy Cafe by Sten Odenwald