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Explore the World 9
Amazing Animals 1
What If? Lab 71
How Things Work 18

What If? Lab What if Earth were the only planet? Imagine a solar system with just the Sun, Earth and our Moon. The bright 'wandering stars' would vanish from our night sky, the paths of asteroids and comets would change, and scientists would lose the other worlds that teach us how planets work. Explore what Earth would miss.
What If? Lab What if we built a space elevator? Rockets burn huge amounts of fuel to reach space. A space elevator would be a cable stretching from the equator about 35,786 kilometers up to a special orbit, with robot climbers riding up and down. NASA studies say it might cut the cost of reaching orbit hugely, but it needs a material far stronger than anything we can make in long lengths today. Explore the cable, the materials and the ride.
What If? Lab What if you tried to swing in space? A swing is a pendulum: gravity pulls the seat back down to the middle every time it rises. In our model, a swing with 2-meter ropes takes about 2.9 seconds to go there and back on Earth. Switch gravity off and the seat simply stays where you let it go.
What If? Lab What if you lived on a space station? On the International Space Station, astronauts and everything around them float. That sounds fun, but without the steady pull of gravity to work against, bones and muscles get weaker. That's why astronauts exercise for about two hours every day. Imagine moving in, and find out how they stay strong.
What If? Lab What if planets were not round? Big worlds are round because gravity pulls everything toward the center from all sides. Small asteroids don't have enough gravity to do that, so most stay lumpy. Imagine a cube-shaped planet, meet the lumpy asteroids, and compare worlds to see how big something must be before gravity rounds it off.
What If? Lab What if telescopes found planets around every star? Astronomers have confirmed thousands of planets around other stars, called exoplanets: 6,451 in NASA's Exoplanet Archive in October 2026. Most were found by watching a star dim slightly as a planet passed in front. Imagine planets around every star, meet some worlds a bit like Earth, and see how a tiny dip in starlight reveals a planet.
What If? Lab What if Pluto were still called a planet? Pluto was called our ninth planet for 76 years. Then astronomers found many similar icy worlds beyond Neptune, and in 2006 the International Astronomical Union wrote a definition of 'planet' that made Pluto a dwarf planet. What if Pluto had kept its old title? Explore how a planet is defined, the other dwarf planets, and why science sometimes changes its words.
What If? Lab What if there were a planet between Mars and Jupiter? Between Mars and Jupiter lies the asteroid belt: millions of rocky leftovers that never built a planet. NASA explains that young Jupiter's gravity stopped them. Explore the belt, Jupiter's tug, the dwarf planet Ceres, and what kind of planet could have formed there.
What If? Lab What if a spacecraft traveled faster? A rocket's top speed depends on how fast its hot exhaust gas shoots out and on how much of the rocket is fuel. In our model, switching from a kerosene engine to a faster hydrogen engine lets the same rocket gain nearly half as much speed again.
What If? Lab What if gravity disappeared? Gravity is the pull that makes a dropped ball fall and keeps your feet on the ground. Switch it off in our model and watch what a ball does instead, then find out why astronauts float.
What If? Lab What if you found a meteorite? Meteorites are pieces of space rock that survived a fiery trip through Earth's air. Most come from asteroids, a few from the Moon or Mars, and many are older than any rock ever found on Earth. Imagine finding one: learn the clues scientists look for, what is inside, and why the right first step is to tell a grown-up and ask a museum or university.
What If? Lab What if the Sun had no sunspots? Sunspots are darker, cooler patches on the Sun made by strong magnetic fields, and their numbers rise and fall about every 11 years. Imagine a Sun with none: what would happen to its light, to solar storms and to the auroras they bring? Once, for about 70 years, the real Sun came close.
What If? Lab What if people built homes on Mars? Mars has air you cannot breathe, temperatures far below freezing and no magnetic shield like Earth's. A home there would need sealed rooms, a way to make oxygen and water, and gardens for fresh food. NASA is already testing pieces of the puzzle, from an oxygen maker on Mars to a 3D-printed practice habitat in Texas.
What If? Lab What if auroras could be seen everywhere? Auroras glow when tiny particles from the Sun crash into the air high above Earth. Earth's magnetic field steers them toward the poles, so that is where auroras shine most. Imagine lights over the whole planet, find out what makes the colors, and see how people keep satellites safe in big solar storms.
What If? Lab What if sound couldn’t travel through air? Sound is a push passed from particle to particle. In air it travels about 343 meters every second. Take the air away, as in empty space, and there is nothing to pass the push along, so a clap makes no sound at all. Water and steel still carry it, and much faster.
What If? Lab What if Earth were much bigger? Astronomers have found many planets bigger than Earth, called super-Earths. A simple calculation shows that an Earth twice as wide, made of the same rock, would pull twice as hard. Such a world might hold on to more air and might not grow such tall mountains.
What If? Lab What if you could stand on Saturn? You could not really stand on Saturn: it is a ball of gas and liquid with no solid surface. But imagine floating at its cloud tops. Saturn has 95 times Earth's mass, yet in our model you would weigh only about 14 percent more than at home, because Saturn is so wide that its cloud tops are very far from its center.
What If? Lab What if our Sun were a different color? A star's color tells you how hot it is: red stars are the coolest and blue stars the hottest. Our Sun is actually white, though it looks yellow through our air. NASA scientists have even worked out that plants on planets around other stars might not be green.
What If? Lab What if Earth had two suns? More than half of the stars in the sky have a partner star. Astronomers have even found planets that go around two stars at once. Imagine Earth with two suns: you might see two shadows and two sunsets. Explore what scientists have really found.
What If? Lab What if Earth were covered in ice? White ice bounces sunlight back to space, so an icy planet soaks up less of the Sun's warmth. In our energy-balance model, making Earth reflect 60 percent of its sunlight instead of 30 percent drops its average temperature from about 15 °C to about −23 °C.
What If? Lab What if the whole Earth were covered by ocean? Water soaks up a lot of heat before it gets hot, and gives it back slowly. Turn a patch of damp ground into ocean in our model and watch the gap between day and night temperatures shrink, then see how the sea already keeps coastal towns mild.
What If? Lab What if you could ride a comet? A comet's center is a dusty ball of ice a few kilometers across, racing around the Sun. In 2014, the European Space Agency's Philae lander touched down on comet 67P, and because the comet's gravity is so weak, it bounced! Imagine riding a comet, then see what a real spacecraft found.
What If? Lab What if a comet passed close to Earth? Comets are icy leftovers from when our solar system formed. Near the Sun, they warm up and grow a glowing cloud and long tails. Dust they leave behind gives us meteor showers. Astronomers have predicted comets' returns for centuries: Halley's Comet is due back in 2061.
What If? Lab What if the Moon had air? The Moon has almost no air, so its sky is always black and it has no weather. Scientists have found that the Moon once had an atmosphere, billions of years ago, but it was lost to space or became part of the ground. Explore what air would change, and why small worlds lose theirs.
What If? Lab What if the Moon had no craters? The Moon is covered with craters made by space rocks crashing into it. With no wind, rain or flowing water, the Moon keeps its craters for billions of years, while Earth wipes most of its craters away. Imagine a smooth Moon, and discover how scientists count craters to tell how old a surface is.
What If? Lab What if an asteroid struck the Moon? The Moon's craters are a record of space rocks landing over billions of years, and small ones still land there every day. Scientists watch for tiny flashes of light on the Moon and later find the brand-new craters. Explore what happens when a rock hits the Moon, and why the Moon keeps going around Earth as always.
What If? Lab What if the universe stopped expanding? Since the 1920s, astronomers have known that distant galaxies are moving apart as space stretches. In 1998 they found the stretching is speeding up, driven by something nobody understands, called dark energy. What if the expansion stopped? Our galaxy wouldn't notice, but the universe's long future would change, and scientists are still working out where it is heading.
What If? Lab What if paper were waterproof? Paper is a mat of tiny plant fibers that water loves to cling to. Water creeps into the spaces between them and loosens the bonds that hold them together, so wet paper goes soft. Coatings can keep water out. Imagine paper that was always waterproof and follow what might change.
What If? Lab What if you visited an icy moon? Jupiter's moon Europa and Saturn's moon Enceladus are covered in ice, but scientists think salty oceans lie underneath. The squeezing pull of their giant planets keeps the insides warm. Imagine walking on the ice, peeking at the ocean below and joining the search for places where life could exist.
What If? Lab What if the stars were much closer? Every star is a sun, but even the nearest one is more than four light-years away, so stars look like faint points. Bring them closer and they would shine much more brightly. In real crowded star clusters, the sky would be full of bright stars, but stars that close may make it hard for planets to form.
What If? Lab What if Earth had rings? Saturn's rings are made of billions of chunks of ice and rock, all circling the planet. Earth has no rings today, but scientists have found clues that it may once have had one. Explore what rings are, where they come from, and what a ring might do to our sky.
What If? Lab What if Saturn’s rings vanished? Saturn's rings are billions of icy chunks, and some of that ice is slowly raining down onto the planet. NASA scientists estimate the rings could be gone in less than 300 million years. Explore what the rings are, how they fade, how they already seem to vanish from Earth's view, and what Saturn would be like without them.
What If? Lab What if the water cycle changed? Warm air can hold more water vapor, about 7 percent more for each degree. In our model of the whole planet's water cycle, a world 2 °C warmer evaporates about 14 percent more water each year if rain kept up with that rule, or about 4 percent more at 2 percent per degree, a rate within the range climate models find.
What If? Lab What if Earth had no magnetic field? Deep inside Earth, swirling melted iron makes a magnetic field all around our planet. It turns compass needles, helps sea turtles find their way and shields our air from the solar wind. Imagine it gone, compare Earth with Mars, and find out why scientists are calm about Earth's changing field.
What If? Lab What if Earth were farther from the Sun? Sunlight spreads out as it travels, so a planet farther from the Sun gets less of it. Move Earth out to where Mars orbits in our model, keep everything else the same, and its average temperature drops from about 15 °C to about −40 °C.
What If? Lab What if there were more greenhouse gases? Adding greenhouse gases makes it harder for Earth's heat to escape, so the planet warms until it balances again. In our model a small change in how freely heat escapes warms Earth by about 2.6 °C, and the oceans make the warming take years.
What If? Lab What if you could see Earth from the Moon? From the Moon, Earth hangs in a pitch-black sky, glowing with blue oceans and white clouds. Like the Moon, it goes through phases: when we see a crescent Moon, Earth looks nearly full from the Moon. Discover Apollo 8's famous Earthrise, Earth's phases and the photos astronauts took of our blue planet.
What If? Lab What if Earth had no Moon? The Moon's pull stretches Earth's oceans and gives us most of our tides. Take the Moon away in our tide model and see what is left: the Sun still makes tides, but they are less than half as big as the Moon's.
What If? Lab What if you lived on Mars? You would be made of exactly the same amount of stuff on Mars, but Mars pulls on you less than Earth does. In our model, a bathroom scale there would show only a little over a third of your Earth reading, and your jumps would go more than twice as high.
What If? Lab What if Earth had two moons? Our Moon goes round Earth in a neat, repeating loop. Add a second moon in our orbit model and watch what changes: the two moons tug on each other as well as on Earth, so their paths start to wobble.
What If? Lab What if the Moon turned red? During a total lunar eclipse, Earth moves exactly between the Sun and the Moon, and Earth's shadow covers the full Moon. The Moon does not go black. NASA explains that sunlight passing through Earth's air loses its blue light and bends toward the Moon, so the Moon glows red or orange, lit by all of Earth's sunrises and sunsets at once.
What If? Lab What if the Sun disappeared? The Sun cannot vanish, and it will keep shining for billions of years. But imagining it gone answers a real question: what keeps Earth going round? Switch off the Sun's pull in our model and Earth stops curving and travels on in a straight line.
What If? Lab What if a plane flew on Mars? A wing makes lift by pushing air down, so the thickness of the air matters a lot. In our model, a small plane at 60 meters per second makes about one and a half times its weight in lift on Earth. In Mars's thin air, the same plane makes only about 2 percent of what it needs.
What If? Lab What if Earth rotated faster? One spin of Earth gives us one day and one night. Spin Earth twice as fast in our model and the days and nights each shrink to about six hours, with less time for the ground to warm up or cool down.
What If? Lab What if Earth rotated slower? Slow Earth's spin to one turn a week in our model and a single afternoon lasts days. The ground has time to bake in the long sunshine and to chill in the long dark, so the gap between the hottest and coldest times grows far bigger.
What If? Lab What if Earth’s tilt changed? Earth's axis leans 23.4 degrees, and that lean is what gives us seasons. Straighten Earth up in our sunlight model and the Sun climbs to the same height every noon, every day lasts 12 hours, and summer and winter disappear.
What If? Lab What if the Moon were closer? The Moon's tides depend very strongly on distance. Bring the Moon to half its distance in our model and its stretching of the oceans becomes 2 × 2 × 2 = 8 times stronger, while each trip around Earth takes only about ten days.
What If? Lab What if the Sun were heavier? The Sun's gravity bends Earth's path into a yearly loop. Make the Sun twice as heavy in our model and its pull gets stronger, so Earth must race around faster to stay on the same circle. The year shrinks from about 365 days to about 258.
What If? Lab What if a day lasted 48 hours? Earth spins once about every 24 hours, and almost every living thing has a body clock tuned to that day. Imagine a day twice as long: long, bright days and long, dark nights. What would happen to your sleep, to plants and to animals?
What If? Lab What if Mars had oceans again? Mars is a cold, dusty desert today, but rovers have found dry riverbeds, deltas and an ancient lake. Its air is now so thin that liquid water can't last on the surface. Imagine a blue Mars, find out what it would need, and see a possible clue to past life that NASA's Perseverance rover has found.
What If? Lab What if Venus had Earth's air? Venus is about the same size as Earth, but its surface is hot enough to melt lead. Its thick carbon dioxide air traps heat in a runaway greenhouse effect, so Venus is even hotter than Mercury. Imagine swapping in Earth's air, and explore what a NASA climate model says about a cooler, cloudier Venus long ago.
What If? Lab What if Earth stopped rotating? You might think a world that does not spin would have no day and night. But Earth also travels around the Sun. Stop the spin in our model and the Sun still crosses the sky, just once a year: six months of daylight, then six months of night.
What If? Lab What if you jumped on the Moon? The Moon's gravity is only about one sixth as strong as Earth's. In our model, a jump that lifts a child about 29 centimeters on Earth carries them about 1.8 meters on the Moon, and they stay in the air for about 3 seconds instead of half a second.
What If? Lab What if Earth had weaker gravity? When you throw a ball, gravity curves its path back down to the ground. Halve gravity in our model and the same throw climbs twice as high, stays up twice as long and lands twice as far away.
What If? Lab What if there were no satellites? Thousands of satellites quietly circle Earth every day. They watch the weather, help phones find where you are with GPS and carry TV signals and phone calls. Imagine a world without them, and discover how people found their way and forecast the weather before the first satellite launched in 1957.
What If? Lab What if a rocket carried less fuel? Most of a rocket is fuel. In our model, a rocket that is 85 percent fuel gains about 5.7 kilometers per second. Cut the fuel to half the rocket and it gains only about 2.1, less than half as much speed. Find out why rockets need so much fuel, and why they drop parts on the way up.
What If? Lab What if you used a parachute on Mars? A parachute works by pushing against air. Mars pulls more gently than Earth, but its air is extremely thin. In our model, a 10-kilogram box under a parachute lands at about 8 meters per second on Earth but about 18 on Mars, barely slower than with no parachute at all.
What If? Lab What if our galaxy met another galaxy? The Andromeda galaxy is heading toward our Milky Way. Astronomers once expected a head-on meeting in about 4 billion years. A 2025 study called it a 50-50 chance in the next 10 billion years; a 2026 study says about 90 percent. Nobody is certain yet. If they meet, stars are so far apart that they would almost never bump, but the galaxies could blend into one new shape.
What If? Lab What if a solar eclipse lasted all day? During a total solar eclipse, the Moon's shadow races across Earth at more than 2,400 kilometers per hour, so the Sun stays fully covered for only a few minutes in any one place. In April 2024, the longest was 4 minutes and 28 seconds. Find out why eclipses are so short, how animals react to the sudden dusk, and imagine one that never ended.
What If? Lab What if Earth slowed down in its orbit? A slower Earth does not just go round the same circle more slowly. In our model, starting Earth at 70 percent of its speed makes it fall inward on an oval that swoops closer to the Sun than Mercury's average distance, racing at over 64 kilometers per second at its closest, before swinging back out. Its year shrinks to about 197 days.