|The first planet from the Sun is Mercury. How many steps is it from the Sun to Mercury? ___ Mercury takes 88 days to make one trip around the Sun. There is no air or water on Mercury, only a rocky surface very hot during the day--but also very cold during night: from one sunrise to the next is 176 of our days. The surface of Mercury, like many other planets and moons, is scarred with craters blasted out by the impacts of asteroids and comets.|
Venus is the next planet from the Sun. How many steps is it from Mercury to Venus? ___ Venus takes 224 days to go around the Sun once. Venus is almost the same size as the Earth, but its atmosphere is thick and hot. Underneath the clouds the rocky surface of Venus is hotter than Mercury! Venus is often the brightest planet we can see, brighter than any star in the night sky.
Next is our very own Earth. How many steps from Venus to the Earth?_____ You are standing on the planet Earth right now, even as it moves through space. How many days does it take the Earth to go around the Sun? ____ We call this a year. The Earth is sometimes called the Blue Planet because most of its surface is covered by water. Earth also has a breathable atmosphere--the only planet in the solar system with a useful amount of oxygen. With water and oxygen, the Earth can have--life! Earth has one moon--since it's ours, we call it the Moon. It is about one-fourth the size of the Earth. If the Moon were in our model, it would be a speck about 3 centimeters (1 1/4 inches) away from the Earth. Besides craters, the Moon has vast, dark lava rock plains--you can see these when you look at a full Moon. The Moon's phases change during each month, since the sunlight on it changes as it goes around the Earth every 27 days. The Moon is the only place people have been in our solar system besides the Earth! The Moon has no water and no air. When the Apollo astronauts went to the Moon, they were protected by heavy spacesuits--which weren't heavy there. This is because the Moon's gravity is only 1/6th of the Earth's. How much would you weigh on the Moon?____
The fourth planet is Mars. How many steps from the Earth to Mars? Mars is only half the size of the Earth, and it takes almost 2 years for Mars to go once around the Sun. On the surface of Mars there are volcanoes as big as New Mexico, a canyon as long as the United States, and many more interesting features! Mars has a thin atmosphere of carbon dioxide, and it is so cold that any water is frozen into ice. But there are also ancient channels that look like they were formed by flowing water. Scientists think that Mars might have been warm enough for liquid water in the past. NASA has several probes looking at Mars or on their way, including Mars Global Surveyor, Mars Odyssey, and Mars Express. Between Mars and Jupiter are most of the asteroids. The largest, named Ceres, is the size of Texas, and the smallest ones are the size of houses! There are millions of these chunks of rock and metal, each in its own lonely orbit around the Sun. These are just some of our solar system's tiny members. There are also chunks of dirty, fluffy ice called comets, and also dust that sometimes gives us pretty meteor showers!
The fifth planet is Jupiter, the largest planet in the solar system. How many steps from Mars to Jupiter? _____ All the other planets in the solar system could fit inside Jupiter three times! Jupiter takes 12 years to go once around the Sun. Jupiter is a gas giant planet. The surface of Jupiter we see is the top of clouds in its atmosphere, just like for the other gas giant planets. Suppose you were to drop into Jupiter's atmosphere--and were protected from the heat and pressure! Eventually you would find the pressure so great that the gases of the atmosphere turn to liquid! Most of Jupiter is liquid hydrogen, but there is a core of rock "only" as big as the Earth. Jupiter has many moons, but four of them are as large as small planets: Io, Europa, Ganymede, and Callisto. Scientists are especially interested in Europa, because its icy crust may be hiding an ocean of liquid water! NASA's Galileo space probe just ended its mission after teaching us much about the Jupiter system.
The next planet is Saturn, another gas giant. How many steps from Jupiter to Saturn? ___ Saturn takes 29 years to go around the Sun. Saturn is called the Ringed Planet because of its beautiful rings. The rings are actually billions of small pieces of ice and rock, from 1 millimeter to a few meters in size, all orbiting Saturn like individual moons. Saturn has many real moons, one which is larger than Mercury. This moon, Titan, has a thick hazy atmosphere and might even have lakes of natural gas. The Cassini space probe will reach Saturn in 2004, so look for exciting pictures then!
Uranus is the next planet. How many steps from Saturn to Uranus? ___ Since Uranus was too dim to be known in ancient times, it was the first planet discovered by astronomers using telescopes. Uranus, a gas giant, takes 84 years to complete one orbit about the Sun. It has icy moons and several dark, narrow rings. It has a very unusual tilt, so that now we see the north pole of Uranus almost face on.
Neptune is the next planet--most of the time! How many steps from Uranus to Neptune? ___ Neptune takes 165 years to complete one orbit around the Sun. Neptune is a gas giant and has an unusual family of icy moons--one called Triton has geyser-like ice volcanoes!
The last planet, right now, is Pluto. (It is missing from our model right now, but it would go next to the SETB building.) Pluto has a less circular orbit than the other planets. It takes 248 years to complete one orbit around the Sun, but for a short part of each orbit Pluto is closer to the Sun than Neptune. The last time this happened was from 1979 to 1999. Pluto and Neptune never get close to each other, however. Pluto is made of rock and frozen ices. Pluto has a moon half as large as Pluto itself, but both of them together are still smaller than the Earth's Moon. Astronomers now think that Pluto is related to a collection of icy asteroid-like objects that orbit beyond Neptune--some almost as big as Pluto. Pluto is the only planet that has not yet been seen up close by a robot space probe.
|Image credits: NASA (Earth, Mercury); NASA, JPL (Venus, Saturn, Uranus, Neptune); Viking Project, USGS, NASA (Mars), NASA, JPL, Univ. of Arizona (Jupiter); Alan Stern/ Southwest Research Institute, Marc Buie/Lowell Observatory, NASA, ESA (Pluto). Supported by BASE (Brownsville Alliance for Science Education)/ENLACE, BISD (Brownsville Independent School District), and UTB/TSC Physics and Astronomy Dept./CGWA (Center for Gravitational Wave Astronomy). May be reproduced for non-profit use.|