An Earthling's Guide to Outer Space

by Bob McDonald

  A better option is to gently push the asteroid just a little off its course so it will miss the Earth. One way of doing that is to send a spacecraft out to meet it. The spacecraft would use its rocket engine to push on the asteroid and alter its course.

  Another idea is to simply hit the asteroid with something heavy. We would have to be careful not to hit it too hard, of course; otherwise we might break it into pieces. We’ve sent out spacecraft to see what asteroids look like close-up, and we found that many of them are made of very loose material, almost like gravel, so they break apart very easily. We could hit the asteroid gently again and again until we nudge it off course. A mission called DART, which stands for Double Asteroid Redirection Test, will try out this idea on a small asteroid.

  We could also use explosives to change the asteroid’s course. Again, we wouldn’t want to blow up one big problem into a bunch of smaller ones. But if a large bomb were detonated beside the asteroid instead of right on it, the force of the blast could nudge it off course.

  In science fiction, such as Star Trek, a tractor beam is sometimes used to tow a smaller spacecraft into a bigger one. No such beams actually exist, but believe it or not, the same thing can be accomplished using gravity alone. All objects possess gravity, so if a massive spacecraft was parked beside an asteroid, there would be a small gravitational attraction between the two of them. This would normally cause the spacecraft to crash into the asteroid. But if the spacecraft ran its engines and pulled against the asteroid’s gravity and toward itself, the asteroid would be pulled toward the ship. This gravitational tug, while not very strong, would be enough to steer the asteroid off course.

  Finally, one of the simplest ways to move an asteroid is to send up a big can of paint and color the whole thing white. No, really, it’s not a joke! Sunlight reflecting off the white paint would push on the asteroid gently, turning the asteroid into a solar sail and altering its course.

  SPACE PLACES

  In a desert of Arizona, in the southwestern United States, there is a very large hole in the ground called Meteor Crater. The big circular hole, shaped like a deep salad bowl, is more than a kilometer across and was gouged out by a meteorite the size of a house that crashed to Earth fifty thousand years ago. Since the area is a desert, there has been very little rainfall to wash the crater away, so it is almost perfectly preserved. This is one of the few places on Earth where you can see how much damage an object falling from space can do to the ground.

  Now imagine the destruction sixty-six million years ago, when the object that hit the Earth was the size of a mountain. You can see what the dinosaurs were up against!

  The most important part of moving an asteroid off its collision course with the Earth is to reach it when it’s really far away. From a great distance, the Earth is a much smaller target, so it doesn’t take much of a push to make the asteroid miss us, the same way that even a small change from a pitcher’s arm can mean the difference between a strike and a ball in baseball. But as the asteroid gets closer, it has to move a much greater distance to get out of the way. That takes a lot more energy. If it’s too close, though, there’s nothing we can do. Earth will have another bad day.

  Asteroid impacts are a natural hazard that we could prevent with enough advance notice. That means that, for what may be the first time in our planet’s history, we can prevent an asteroid apocalypse. Too bad the dinosaurs didn’t have that option.

  YOU TRY IT! Collision Course

  The Earth has been hit by large objects from space more than once, which means it could happen again in the future. Fortunately, we have telescopes looking out for any that may be heading our way. Here’s how you can see why it is important to get to them early and nudge them off course.

  WHAT YOU NEED

  A globe of the Earth, or a large ball

  A handful of small pebbles or marbles

  WHAT TO DO

  Stand beside the globe or ball and try to hit it by throwing a pebble.

  Take five steps away from the ball and try to hit it with another pebble.

  Take another five steps back and try again. Continue stepping back until it is almost impossible to hit the ball.

  It’s easy to hit the ball when you are close because it’s a big target. But as you get farther away, the ball looks smaller and is more difficult to hit. From really far away, your aim only needs to be off by a tiny bit and you will miss.

  If we can send spacecraft out to meet an asteroid when it is far away from the Earth, it would only take a small push to change its course enough to ensure it passes by our planet without hitting us. If we wait too long, or don’t see an asteroid until it is closer, though, it would have to be moved much more to steer it out of the way; otherwise the Earth would be an easy target. And if it’s too close, there will probably be nothing we can do except get ready for impact and hope we don’t go the way of the dinosaurs.

  25 Do Other Planets Have Weather?

  Almost all the planets in our solar system have weather. The only one that doesn’t is Mercury, because, like the moon, it doesn’t have any air or atmosphere. After all, that’s what weather is: moving air. But not all planets have the same type of air that we have here on Earth, so weather on other worlds can be quite different.

  We live on a very active planet. Our air is always moving. It swirls around the globe, stirring up the oceans. It blows water, snow, and sand around with such incredible force that it can wipe out just about anything we can build. Tornadoes rip houses apart; hurricanes do incredible damage to entire cities. All that damage is done by air, the stuff you’re breathing right now.

  Venus, the second planet from the sun, has much more air than the Earth, with clouds so thick we can’t even see through them. Mars, planet number four, has much less air, but it has very strong winds that produce enormous dust storms that occasionally cover the whole planet. Then there are the gas giant planets—Jupiter, Saturn, Uranus, and Neptune—which are nothing but weather. These huge gas worlds, much farther from the sun than Earth, swirl constantly in endless storms. There is no land, only clouds, and they’re always moving—the weather is always bad. Clouds on Jupiter are thousands of kilometers tall and come in different colors—white, blue, and red. That’s because they’re made of different chemicals, including ammonia and hydrogen sulfide, which smells like rotten eggs.

  To give you an idea of just how bad the weather can be on another planet, the Great Red Spot on Jupiter is a storm that has been raging nonstop for as long as we’ve had telescopes to observe it, which is almost four hundred years. This storm was spotted by Galileo when he pointed the first telescope on Jupiter in 1610. The storm is so big it could swallow the entire Earth with room to spare. It makes our hurricanes look tame.

  The Earth is heated by the sun, and the sun shines most powerfully on the middle of our planet. As the Earth goes around the sun every year, the North Pole always faces up and the South Pole always points down. That means the sun shines mostly on the equator, and so the middle of the Earth gets more heat than the top and bottom of the planet. This warm air around the equator tries to move toward the cold regions, and as it pushes outward, the cold air at the top and bottom tries to come toward the equator to replace it. And if that isn’t enough, this air is moving around a globe that spins on its axis every day, which really mixes things up!

  The same principle of heat works on other planets, except those worlds are either closer to or farther away from the sun than we are, and the gases that make up the air are different. Take Venus, for example. The weather on Venus is pretty gloomy. It’s very hot and totally covered in clouds. There’s not much sunlight down on the ground because so little gets down through the clouds. The clouds themselves are made of sulfuric acid, which would burn your skin when it rains. If it rains at all.

  You can’t breathe the air on Venus because it’s made of carbon dioxide, which is a greenhouse gas that traps heat. The average temperature on Venus is more than 450 degrees Celsius. That is as
hot as a pizza oven. And it doesn’t matter if it is day or night, summer or winter—the temperature never changes. It’s a nasty, nasty place. You don’t want to go there for a summer vacation.

  What happens when we go farther away from the sun, though? The next planet out from Earth is Mars, which doesn’t have very much air, but it does have weather. Mars’s atmosphere is made of carbon dioxide just like Venus’s, but on Mars, that atmosphere is very, very thin. It would be like being on the top of two Mount Everests—very little air to breathe and exceedingly cold.

  Even though it’s so cold on Mars, the planet still has four seasons. A summer day on Mars may get to zero degrees Celsius at the equator. The planet has ice caps at the North and South Poles and winds blowing on the surface. White clouds fill valleys in the early morning, and in the afternoon, when the sun heats the surface, the winds start playing with the dust on the ground. One of the robot rovers that landed on Mars in early 2004 captured images of dust devils—little tornadoes dancing across the desert. All that dust blowing around makes the sky on Mars orange instead of blue.

  So these three planets—Venus, Earth, and Mars—are all quite different. One is too hot to have much weather, the other is too cold to have extreme storms, and one is just right. Aren’t you glad we live here?

  Things get even weirder the farther out in our solar system you go. Uranus is tilted on its side (for what reason, nobody knows)—so for a quarter of the year, its North Pole is aimed at the sun, then for another quarter, its South Pole is aimed at it. And between those times, the sun shines on the equator.

  Sound a bit confusing? Hold a pencil in front of your face with the point up. The point represents the North Pole of a planet; the eraser at the bottom is the South Pole. Most of the planets in our solar system have their North Poles pointed in the same general direction we call north. The Earth’s pole is tilted a little, but still more or less upright.

  Now turn the pencil sideways to the right, so the point faces a wall. That is the way Uranus is positioned, lying on its side. If your head is the sun, the North and South Poles of Uranus always face the same way in space as it goes around in its orbit. Move the pencil to the left side of your head, and the pencil’s point, or North Pole, will be aimed right at you. Move it around to the right side of your head, and the end with the eraser, the South Pole, will be pointed at you.

  This makes for extreme seasons on Uranus, where the top of the planet is heated by the sun for half of its year and the bottom for the other half. And a year on Uranus is eighty-four Earth years long!

  Some of the weirdest weather isn’t found on planets, though—it’s on their moons. Titan, a moon orbiting Saturn, is one of the weirdest worlds of weather anyone has ever seen. It’s one of the largest moons in the solar system, and it has a cloudy atmosphere. A robotic probe called Huygens landed on Titan in 2005. It passed through brown clouds, was blown by winds, and touched down on a surface that looked wet. It rains on Titan, but it’s nothing like the rain we get on Earth.

  Titan is extremely cold, hundreds of degrees below zero. When it’s that cold, water is frozen solid. In fact, the ground on Titan is made of ice that’s as hard as rock. Titan’s surface is covered with river valleys and what look like shorelines and beaches. There are very large lakes, too—one of them is as large as Lake Superior in Canada. The lakes are filled with rain, but it’s not made of water. Because on Titan, it rains liquid methane, the same stuff we use in gas appliances in some homes.

  Pluto is also an ice world with a very thin methane atmosphere. In fact, Pluto is so far from the sun that occasionally its thin methane atmosphere completely freezes, forming snow that falls to the ground. But the snow isn’t frozen water. It’s frozen air.

  Imagine the wonders you would see, if only you could brave the bad weather on other planets. You’ll need some special gear and a spacecraft, but what a ride!

  YOU TRY IT! Weather in a Glass

  Find out how different layers form in the atmosphere and how they interact with one another to make weather.

  WHAT YOU NEED

  A large glass jar

  A small glass that fits inside the bigger one

  Food coloring

  Tongs

  Warm and cold water

  WHAT TO DO

  Fill the large glass jar three-quarters full of cold water.

  Pour hot water into the second, smaller glass, filling it right to the top.

  Add some food coloring to the hot water.

  Using the tongs, carefully lift the small glass without spilling any of the water and gently lower it into the larger glass. Make sure the small glass of hot water completely sinks under the cold water.

  Watch what happens to the hot water.

  You have just made a storm in a glass.

  You should see that the warm water rises out of the small glass and floats to the top of the larger one. It doesn’t mix with the cold water at all. That’s because warm water is lighter than cold, so it floats. Air does the same thing. When warm air runs into cold air, it is pushed up by the cold air flowing under it, just like you see in the glass jar. When the warm air rises, it cools, and moisture in the air condenses into drops. The drops grow until they are too heavy to stay in the air, and the result is rain. This is the basic principle behind weather and storms, both here on Earth and across the galaxy.

  26 What Are Gravitational Waves?

  There are water waves that make water move, sound waves that move the air, earthquake waves that shake the Earth, and, well, gravitational waves make space move.

  We know that gravity works by curving space. Large objects bend space inward to form a well, like a bowling ball pressing down on a mattress, and they draw other, smaller objects close by either falling down into the well or orbiting around the larger object. That’s pretty amazing by itself, but consider this: if space can bend like that, then it means that space can also vibrate like a drum.

  How do you vibrate space, you ask? With black holes!

  Black holes have a lot of gravity, which means their gravity wells—the area close to the black hole where gravity gets stronger and stronger the closer you get—are really, really deep. Imagine two black holes that approach each other. As they get close, they will fall into each other’s gravity well, forming a single, deeper one. The black holes will spin around each other like two figure skaters, twirling faster and faster until they finally join together. That spinning actually vibrates the space around them, sending waves of space itself out across the universe, like ripples in a pond.

  Think of it like the surface of a drum. When you beat a drum with a stick, the surface of the drum bounces up and down, vibrating the air above it. As the air vibrates, sound waves travel away from the drum. Those sound waves are technically called compression waves, because the drum squeezes and releases the air, making little pulses of pressure. When those pulses hit your eardrums, they are pushed in and out at the same beat, and we hear the waves as sound.

  Gravitational waves are also compression waves, but instead of compressing air, they squeeze space itself. Gravitational waves actually pass through us all the time. Fortunately, they’re very small, so we don’t feel them. But if a bigger one passed through you from head to toe, you would get a little taller, then a little shorter as the wave went by. And if it came from the side, you might get a little fatter and then skinnier. It’s similar to the way that water waves make you bounce up and down while swimming.

  It turns out that gravitational waves vibrate at about the same frequency as sound waves. Lucky for us, because if we can hear gravitational waves, it means we can hear the sound of space itself!

  To listen to the sounds of space, we use an extremely sensitive instrument. And it doesn’t look anything like an ear.

  The Laser Interferometer Gravitational-Wave Observatory (LIGO) is made of two arms, each four kilometers long, that are arranged in an L shape. Inside each arm is a laser beam that shoots down the length of the hallway and reflects off
a mirror at the end, allowing the technicians to measure the exact length of each arm.

  When the beams bounce back to the base of the arms, they are combined together in a light detector. Lasers are made of light waves, and so long as the lasers don’t move, all of the light waves line up with one another when they pass through the instrument.

  ON THE DRAWING BOARD

  Some scientists believe it may be possible to design a new type of spaceship that doesn’t actually fly through space, but instead warps space around the ship using gravitational waves. It’s the theory behind the fictional warp drive that enables the crew of the starship Enterprise in Star Trek to hop around the galaxy with ease. The idea is that a ship could squeeze the space in front it so that the distance to its destination is shorter. At the same time, it would make the space behind the ship larger, so that it was farther away from where it started. That way, the ship isn’t actually moving—it’s the space around the ship that’s changing.

  A ship powered by a warp drive wouldn’t even need seat belts, because the people inside wouldn’t feel as though they were moving. A warp drive is, as the name suggests, warping gravity, and gravity acts on all objects at the same time. So, when space is distorted around a starship, the ship, the people, and all the objects in it—every atom—are pulled at once, making sure there’s no kick-in-the-pants jolt from acceleration. It’s a long way from today’s astronauts, who are pushed back into their seats with a force that makes them feel three times their own weight as the rocket blasts into space.