Inner Planets Outer Planets Inner vs. Outer Pluto

1. Inner Planets Outer Planets Inner vs. Outer Pluto Planets PowerPoint

2. Inner Planets • The inner planets are called terrestrial planets because they have a solid surface and are similar to Earth. • These planets are composed of heavy metal, such as iron and nickel and have few or no moons and no rings. • The inner planets are of similar size and have high densities compared to the larger gas giants among the outer planets.

3. Outer Planets • The outer planets, also called Jovian planets or gas giants, are gaseous with no solid surfaces and only liquid . • The outer planets are so much larger than the inner planets that they comprise 99% of the mass of the celestial objects orbiting our Sun. • The outermost part of these planets may be slushy. Below the surface, hydrogen and helium are in a liquid form. At the center is a rocky core. • Each of these huge planets has its own system of moons. • Rings around Saturn have been seen for many years. They are probably made mostly of water, ice, and other icy particles. Recently, rings have been discovered around two more giant planets — Jupiter and Uranus. Scientists expect to find rings around Neptune, too.

4. Inner vs. Outer • The inner planets (those planets that orbit close to the sun) are quite different from the outer planets (those planets that orbit far from the sun). • The inner planets are: Mercury, Venus, Earth, and Mars. They are relatively small, composed mostly of rock, and have few or no moons. • The outer planets include: Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet). They are mostly huge, mostly gaseous, ringed, and have many moons (again, the exception is Pluto, the dwarf planet, which is small, rocky, and has one large moon plus two tiny ones). • Generally, the farther from the Sun, the cooler the planet. Differences occur when the greenhouse effect warms a planet (like Venus) surrounded by a thick atmosphere. • As the planets orbit the Sun, they travel at different speeds. Each planet speeds up when it is nearer the Sun and travels more slowly when it is far from the Sun (this is Kepler's Second Law of Planetary Motion). .

5. Pluto • Pluto's orbit is different from those of the planets. The planets all orbit the Sun close to a flat reference plane called the ecliptic and have nearly circular orbits. In contrast, Pluto's orbit is highly inclined relative to the ecliptic (over 17°) and highly eccentric (elliptical). This high eccentricity leads to a small region of Pluto's orbit lying closer to the Sun than Neptune's. • Pluto's rotation period, its day, is equal to 6.39 Earth days. Like Uranus, Pluto rotates on its "side" on its orbital plane, with an axial tilt of 120°, and so its seasonal variation is extreme; at its solstice, its northern hemisphere is in permanent daylight, while its southern hemisphere is in permanent darkness. • Pluto fails to meet the third condition, since its mass was only 0.07 times that of the mass of the other objects in its orbit (Earth's mass, by contrast, is 1.7 million times the remaining mass in its own orbit). • The IAU further resolved that Pluto be classified in the simultaneously created dwarf planet category, and that it act as the prototype for the plutoid-category of trans-Neptunian objects, in which it would be separately, but concurrently, classified

6. By Kyra Dankers 2 -11-2010 Astronomy