Earth is one of eight planets in our solar system. These huge space objects whirl around the sun in oval-shaped paths. They’re not alone. Millions of smaller space rocks called asteroids orbit the sun too.

Asteroids come in many shapes and sizes. Some are round. Others are shaped like dog bones, ears, or mushrooms. The smallest are 3 feet (1 meter) wide. The largest is wider than the state of Arizona!

For decades, scientists have used strong telescopes to observe asteroids from Earth. They search space for asteroids that could impact our planet.

Small space rocks head toward Earth all the time. The smallest ones burn up in Earth’s atmosphere before they hit the ground. When a very large asteroid impacts Earth, it can lead to disaster.

Sixty-six million years ago, an asteroid more than 6 miles (10 kilometers) wide smashed into the planet. It struck Earth off the coast of what is now Mexico. Scientists think the impact caused earthquakes, massive waves, and wildfires. Dust and ash blocked the sun. As a result, many animals became extinct, including the dinosaurs.

So should we worry about another giant asteroid hitting Earth today? Definitely not, Chabot says. Scientists have studied the large asteroids in our solar system. They have found no asteroids more than 0.6 miles (1 kilometers) wide will hit our planet in the next 100 years.

But there are thousands of medium-sized asteroids that scientists haven’t found yet. “If an asteroid a few hundred meters wide were to strike Earth, it could wipe out an area the size of a city,” says Chabot. “It could mean incredible devastation.”

Earth is one of eight planets in our solar system. These huge objects move around the sun. They follow paths shaped like ovals. They’re not alone. There are millions of asteroids. They orbit the sun too.

Asteroids come in many shapes and sizes. Some are round. Others are shaped like dog bones, ears, or mushrooms. The smallest are 3 feet (1 meter) wide. The largest is wider than the state of Arizona!

Scientists have been looking for asteroids for decades. They use strong telescopes to spot them. They identify ones that could hit our planet.

Small space rocks head toward Earth all the time. The smallest ones never hit the ground. They burn up in Earth’s atmosphere. But a very large asteroid could strike Earth. That could lead to disaster.

That happened 66 million years ago. An asteroid smashed into our planet. The space rock was more than 6 miles (10 kilometers) wide. It struck Earth off the coast of what is now Mexico. Scientists think the impact caused earthquakes, massive waves, and wildfires. Dust and ash blocked the sun. Many animals died out as a result. That includes the dinosaurs.

Should we be worried? Could another giant asteroid hit Earth today? Definitely not, Chabot says. Scientists have studied large asteroids in our solar system. They’re ones more than 0.6 miles (1 kilometers) wide. None will hit our planet in the next 100 years.

But there are thousands of medium-sized asteroids in our solar system. Scientists haven’t spotted all of them yet. “If an asteroid a few hundred meters wide were to strike Earth, it could wipe out an area the size of a city,” says Chabot. “It could mean incredible devastation.”

If a dangerous asteroid is headed toward Earth, scientists want to be ready. That’s where DART comes in. In 2015, Chabot and hundreds of scientists from around the world got together. Their mission was to figure out how to defend our planet from Earth-bound space rocks.

Scientists have come up with many possible solutions. They could blow up an asteroid with explosives. Or they could use a spacecraft to drag the asteroid in a new direction. But for each of these ideas, engineers would need to create new technology.

Scientists want to be ready. They want to prepare in case a dangerous asteroid is heading toward Earth. That’s where DART comes in. Hundreds of scientists from all over got together in 2015. They had a mission. It was to defend our planet from space rocks.

Scientists have come up with many ways to do this. They could blow up an asteroid. Or a spacecraft could drag it in a new direction. But engineers would need to create new technology for these ideas to work.

The DART team had a simpler plan. They would crash a spacecraft into an asteroid. They hoped that, like a marble colliding with another rolling marble, the nudge could change the asteroid’s path. And that new path would send it soaring away from Earth.

Would the plan work on a dangerous asteroid? To find out, the team needed to test it on an asteroid that was not a threat. They soon found the perfect space rock for the task: a football field-sized asteroid called Dimorphos (dye-MOR-fuhs). It moves around a larger asteroid, named Didymos (DID-ee-mohs). The pair travel together around the sun near Earth and Mars.

The DART team had a simpler plan. They’d crash a spacecraft into an asteroid. That would give it a push. They hoped it would change the asteroid’s path. And it would go soaring away from Earth. Picture two rolling marbles colliding. The crash would send them shooting off in different directions.

Would the plan work? The team needed to test it to find out. They’d target an asteroid that wasn’t a threat. They soon found the perfect space rock for the task. It was called Dimorphos (dye-MOR-fuhs). It was about the size of a football field. It moves around a larger asteroid. It’s named Didymos (DID-ee-mohs). The pair travel together around the sun near Earth and Mars.

One reason Dimorphos was a good asteroid for the test is that its movements were easy to see from Earth. Scientists could use telescopes to watch its shadow moving across Didymos. If that path changed after the spacecraft hit it, that would mean the test was a success!

Scientists knew Dimorphos was not a threat to Earth. They had calculated that even after the test, there was no chance it could hit our planet.

It took the DART team five years to prepare the mission. On November 24, 2021, a rocket carrying the DART spacecraft took off from California. Once in space, two enormous solar panels unfolded. They would give DART power. Its journey to Dimorphos had begun!

Dimorphos was easy to track from Earth. Scientists used telescopes. They watched the rock’s shadow moving across Didymos. They’d easily be able to see if its path changed after the spacecraft hit it. That would mean the test was a success!

Scientists knew Dimorphos wasn’t a danger to Earth. They could knock the asteroid off course. There’d still be no chance it could hit our planet.

It took the DART team five years to get the mission ready. A rocket took off from California. It launched on November 24, 2021. It carried the DART spacecraft. The spacecraft reached space. Then two huge solar panels unfolded. They would give DART power. Its trip to the asteroids had begun!

Finally, 10 months later, the day of the test arrived. The DART team called it “impact day.” Scientists and engineers were about to see if their planning, building, and testing would pay off. And it wasn’t just the DART mission team watching. Video from DART was broadcast on the internet to the whole world!

The DART team had not seen Dimorphos up close, so no one knew what it would look like. “We know asteroids can have weird shapes,” says Chabot. If the rock was not round, that might make it hard to crash the DART spacecraft into it as planned.

The spacecraft closed in on Dimorphos. The team watched and waited. For the test to work, a computer program had to guide the spacecraft to hit Dimorphos. The room grew quiet as the asteroid’s round shape and bumpy surface came into view. DART moved closer and closer and closer...

The day of the test arrived 10 months later. The DART team called it “impact day.” The group was about to see if their planning, building, and testing would pay off. And it wasn’t just the DART mission team watching. Video from DART played on the internet. The whole world would see!

The DART team had not seen Dimorphos up close. So no one knew what it would look like. “We know asteroids can have weird shapes,” says Chabot. A strange shape might make it hard to crash the DART spacecraft.

The spacecraft closed in on the asteroid. The team watched and waited. A computer guided the spacecraft on a crash course. The room grew quiet. The asteroid’s round shape came into view. It had a bumpy surface. DART moved closer and closer and closer...

Then all of a sudden, CRASH! The room erupted in cheers. “It was a really powerful moment,” Chabot says. The spacecraft had hit its target. But would it move the asteroid?

In the months after the impact, scientists observed Dimorphos closely. Its orbit around Didymos was smaller and took less time to complete. The test had worked!

Then all of a sudden, CRASH! The room erupted in cheers. “It was a really powerful moment,” Chabot says. The spacecraft had hit its target. But would it move the asteroid?

Scientists watched the asteroid for months after the impact. Its orbit around its neighboring asteroid was smaller. It took less time to complete. The test had worked!

The DART mission proved that humans could change the path of an asteroid. But scientists’ work defending Earth from objects in space is far from over.

NASA is now working on a new space telescope, called the Near-Earth Object (NEO) Surveyor. It will spot asteroids up to 30 million miles (48 million kilometers) from Earth. Medium-sized asteroids at that distance are too far away for telescopes on Earth to spot. And they are too close for most space telescopes to detect. The telescope is set to be launched in 2028.

“We’ve taken this first step to protect our planet from objects that might hit it,” says Chabot. “There’s a lot more work to do!”

The DART mission proved that humans could change the path of an asteroid. But scientists’ work defending Earth from objects in space is far from over.

NASA is now working on a new space telescope, called the Near-Earth Object (NEO) Surveyor. It will spot asteroids up to 30 million miles (48 million kilometers) from Earth. Medium-sized asteroids at that distance are too far away for telescopes on Earth to spot. And they are too close for most space telescopes to detect. The telescope is set to be launched in 2028.

“We’ve taken this first step to protect our planet from objects that might hit it,” says Chabot. “There’s a lot more work to do!”