A Walk Through the Solar System

by Wm. Robert Johnston and Carol Lutsinger
last updated 6 October 2003

Welcome to UTB's Walk-Through Solar System Model! As you complete this tour, every meter you walk equals 13 million kilometers! (Or every foot you walk is 2.5 million miles!)

In the model, the Sun is the size of a softball near the library. The Earth and the other planets are represented by small dots or spheres going down the Paseo walkway. Notice that in our model, the planets are nearly lined up. But in reality, the planets are all going around the Sun, so they are usually in many different directions from the Sun. As you journey from planet to planet, think about the fact that no person has ever been to another planet. Robot space probes have visited most of the planets, sending back pictures and teaching us much about them.

The Sun is a star, 100 times as far across as the Earth. It is made of superheated hydrogen and other gases. It shines because of nuclear reactions taking place in its center, releasing the energy of 10 billion large hydrogen bombs every second!

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.
Are you tired yet? But this only takes you to the furthest planet. The nearest star--other than our Sun--is Alpha Centauri. If we included it in our model, it would be a softball in Boston, Massachusetts! Do you want to count how many steps to there? Alpha Centauri is just the first star you could reach out of several hundred billion that make up our galaxy, the Milky Way Galaxy! There are thousands of stars you can see in the clear, dark night sky, all in our galaxy. Astronomers have found planets around some of these other stars, just like our Sun's family, the solar system. Beyond our galaxy are other galaxies, each with millions or billions of stars. It's a big universe!

Would you like to learn more about the solar system and astronomy? Your school library or the city library has good books and magazines. There are also some good web sites on the Internet. You might check for sites about the NASA space probes that have taught us the things you've learned today--plus much more!

Brownsville has astronomy clubs for children and adults both--check the newspaper for meetings. The University also has resources. Astronomy is exciting and fun, so there are people here that would love to teach you more!

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.

Last modified 6 October 2003.

UTB/TSC Physics and Astronomy Department -- http://www.phys.utb.edu
Center for Gravitational Wave Astronomy -- http://cgwa.phys.utb.edu
Brownsville Alliance for Science Education -- http://www.phys.utb.edu/base/

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