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Kepler
Kepler discovered that the planets orbit in a ellipse (a flattened circle). He found this information by calculating mars's orbit. -
Gravity
Gravity was discovered by Isaac Newton in 1655. Gravity is one of the factors that keeps the planets in orbit. -
Inertia
Inertia was discovered by Galileo but was named by Isaac Newton. Inertia is the tendency of all objects and matter in the universe to remain still. Inertia is the second factor that keeps the planets in orbit. -
Asteroid
The first asteroid was discovered in 1801 by Giuseppe Piazza. An asteroid is like a miniature planet. They orbit around the sun and have their own rotation. -
Discovery of the first comet
The discovery of the first comet was in 1846. A comet is a small body made of dust and ice. -
Neptune
Neptune was discovered in 1846 by James Challis and Johann Galle. Neptune is an outer planet. Jupiter, Saturn, and Uranus are also outer planets. The characteristics of the outer planets are very big, made mostly of hydrogen and helium, and teh center is rocky. -
Willamette Meteorite
Willamette Meteorite was discovered by Ellis Hughes in 1902. A meteorite is what people call a shooting star. It is a rock from space. They begin their lives as meteors, but when they land on Earth they are called meteorites. -
Pluto
Pluto was discovered in 1930 by Clyde W. Tombaugh. Pluto differs from the outer planets because it doesn't have any rings and it is very small and it is not gaseous like the others. -
Mercury was visited
Mercury was visited by Mariner 10. Mercury is one of the planets in the group of inner planets. That group also includes Venus, Earth, and Mars. The inner planets are small and have rocky surfaces. They are often called the terrestrial planets because they are very similar to Earth.
