Iâve come up with fewer reasons for giving a child a cell phone earlier, but at least two of them are enough to offset a multitude of others. Keeping tabs on them. As each year passes in a childâs life they venture farther from home and for longer periods of time.
Like the inner planets, the outer planets have similar characteristics to one another. The outer planets are so much larger than the inner planets that they make up 99 percent of the mass of the celestial bodies that orbit the Sun. Although mainly composed of gas, the outer planets also have other ingredients.
Why are the inner planets are made of rock and free of gas and the outer planets have trapped gas as part of their structure? The planets Venus, Earth, and Mars actually do have thin (as compared to the size of the entire planet) atmospheres. Mercury has a very low-pressure atmosphere. Most of the reason for this is that small planets do not have a gravitational pull strong enough to hold lighter gases in, and they escape to space.