What does Pluto most resemble? A comet.

Since Pluto and Neptune cross orbits, is it possible that the two planets will collide? No, they actually can’t collide because Pluto’s orbit takes it much higher above the Sun’s orbital plane. When Pluto is at the same point as Neptune’s orbit, it actually much higher up than Neptune.

Will Pluto eventually collide with Neptune? No, because the two planets have an orbital resonance that prevents them colliding.

What causes the “gaps” observed in the asteroid belt between Mars and Jupiter? Jupiter’s gravity causes orbital resonances that nudge asteroids out of these areas. The force of gravity in small asteroids is less than the resistance of the rock to deform.

Other notable meteor showers include the Leonids, associated with comet Tempel-Tuttle; the Aquarids and Orionids, linked to comet Halley, and the Taurids, associated with comet Encke. Most of this comet debris is between the size of a grain of sand and a pea and burns up in the atmosphere before reaching the ground.

stony-iron meteorites

Meteor showers associated with particular comet orbits occur at about the same time each year, because it is at those points in the earth’s orbit that the collisions occur.

These are much larger than comets. An asteroid only 5 km across would be classi- fied as small; Ceres, the largest, is 100 times bigger than this. They show no coma activity and the reflectance spectrum is similar to that of asteroids. They are bigger than standard comets but smaller than a typical asteroid.

Einstein’s theory of special relativity says that time slows down or speeds up depending on how fast you move relative to something else. Approaching the speed of light, a person inside a spaceship would age much slower than his twin at home. Picture a four-dimensional fabric called space-time.