In 2006, Pluto was officially declared not to be a planet anymore. It was, instead, announced a dwarf planet. What caused this decision?

Pluto is tiny - scientists think it's about 2,300 kilometers in diameter. There are several moons in our solar system larger than the planet. Another feature that caused it to be demoted is its orbit. The planet's orbit cuts through that of Neptune's.

Scientists began to find objects beyond Pluto. They were mostly smaller than Pluto, and have been named Kuiper Belt Objects (KBOS). There is estimated to be at least 70,000 that are over 100 kilometers across. In 2000, astronomers started to find objects closer to Pluto's size. Then they found Eris. Eris was larger than Pluto. It cuts inside Pluto's orbit when closest to the sun and, when furthest, is twice as far as Pluto's orbit. It takes more than 550 years to circle the sun.

All these discoveries meant that, if Pluto was to be called a planet, then Eris should be called one too, as well as many KBOS. Scientists, in 2006, voted on the definition of a planet. A planet had to be a sphere. A planet had to be in orbit around a star. And a planet couldn't be with a group of other objects, orbiting peacefully. That was the final blow for Pluto. It is now classified as a dwarf planet.

Space Junk

Space is full of junk.

When the astronauts went to the moon, they left trash there. Very expensive trash. The amount of trash in space is becoming a problem. And with more satellites going up every year, the amount is growing quickly. It is estimated that there is nearly 2 million kilograms of space junk in low Earth orbit. Much of this is being tracked as it orbits the earth. There are about 10,000 objects that are about the size of a grapefruit or larger.

If a piece that large were to hit a satellite or space station, it could do some serious damage. If an object a centimeter or larger, moving at 40,000 kilometers an hour, were to hit something, it would be the equivalent of throwing a bowling ball at speeds of 500 kilometers an hour at a human being. The Space Shuttle has returned with large chips in its windshield (I don't think there are winds in space, but you know what I mean) that came from colliding with a speck. Impacts from space junk have been thought to disable two satellites.

So what can we do? Most of this junk will eventually fall to Earth. However, this can take a while, and it's a hazard to astronauts. There is a 1 in 91 chance that an astronaut could be hit with a piece big enough to penetrate their suit. The astronaut would be very lucky to survive. As if their jobs weren't already full of dangers.

Black Holes

Black holes are regions of space that have such massive gravitational pull that not even light can escape. No one has ever directly seen a black hole. There is thought to be one in the center of our galaxy, 40,000 times larger than the sun.

How is a black hole formed? There are many theories. The most common is that when a big star, about three times the size of the sun, reaches the end of its life, its stability cracks under its own gravity. The radius of the star shrinks and it starts to devour everything that's close enough. We cannot actually see a black hole. However, we can see the area of space affected by it. It is the event horizon, where there is no light. It is called a horizon because, like a horizon on our own planet, we cannot see beyond it.

If you enter an event horizon of a black hole, you will start to accelerate under the influence of gravity. You may start to orbit around the black hole, bumping into other pieces of matter. The jostling might throw you away from the black hole, or it might knock you into it. It won't go black as you go over the event horizon. You'll be able to see what's outside of the event horizon. The light everywhere will appear strange and distorted by the gravity.

If you look down, you'll see the singularity, which is a point where all physical laws have, basically, become indistinguishable from each other. At this point, you will begin to stretch and very quickly loose interest in what is going on around you. Fortunately, this should be fairly quick. Predictions about the inside of a black hole can be made, but it eventually gets too weird for science to describe. And a visit to a black hole is highly inadvisable.