Nasa probe hurtling back to Earth with crucial rocks from 'doomsday' Bennu asteroid that could wipe out entire cities

A NASA spacecraft has begun a 1.4billion-mile journey back to Earth after collecting rock samples from an ancient asteroid.

The trip home for the robotic prospector, Osiris-Rex, kicked off on Monday and will take two years.

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Osiris-Rex reached asteroid Bennu in 2018 and spent two years flying near and around it, before collecting rubble from the surface last October.

The huge space rock has previously been dubbed a "doomsday" asteroid due to the small chance that it will hit Earth in the next 200 years.

The University of Arizona's Dante Lauretta, Osiris-Rex's principal scientist, estimates the spacecraft holds between a half pound and one pound (200 grams and 400 grams) of mostly bite-size chunks.

Either way, it easily exceeds the target of at least two ounces (60 grams).

It will be the biggest cosmic haul for the US since the Apollo moon rocks.

While Nasa has returned comet dust and solar wind samples, this is the first time it's gone after pieces of an asteroid.

Japan has accomplished it twice, but in tiny amounts.

Scientists described Monday's departure from Bennu's neighborhood as bittersweet.

"I've been working on getting a sample back from an asteroid since my daughter was in diapers and now shes graduating from high school, so it's been a long journey," said Nasa project scientist Jason Dworkin.

Added Lauretta: "We have gotten used to being at Bennu and seeing new and exciting images and data coming back to us here on Earth."

Osiris-Rex was already nearly 200 miles (300 kilometers) from the solar-orbiting Bennu when it fired its main engines Monday afternoon for a fast, clean get-away.

Colorado-based flight controllers for spacecraft builder Lockheed Martin applauded when confirmation arrived of the spacecraft's departure: "We're bringing the samples home!"

Scientists hope to uncover some of the solar system's secrets from the samples vacuumed from Bennu's dark, rough, carbon-rich surface.

The asteroid is an estimated 1,600 feet (490 meters) wide and 4.5billion years old.

Bennu – considered a broken chunk from a bigger asteroid – is believed to hold the preserved building blocks of the solar system.

The returning pieces could shed light on how the planets formed and how life arose on Earth.

They also could improve Earth's odds against any incoming rocks. Bennu, for instance has a one-in-2,700 chance of impacting Earth in the late 22nd century, according to Nasa.

What’s the difference between an asteroid, meteor and comet?

  • Asteroid: An asteroid is a small rocky body that orbits the Sun. Most are found in the asteroid belt (between Mars and Jupiter) but they can be found anywhere (including in a path that can impact Earth)
  • Meteoroid: When two asteroids hit each other, the small chunks that break off are called meteoroids
  • Meteor: If a meteoroid enters the Earth's atmosphere, it begins to vapourise and then becomes a meteor. On Earth, it'll look like a streak of light in the sky, because the rock is burning up
  • Meteorite: If a meteoroid doesn't vapourise completely and survives the trip through Earth's atmosphere, it can land on the Earth. At that point, it becomes a meteorite
  • Comet: Like asteroids, a comet orbits the Sun. However rather than being made mostly of rock, a comet contains lots of ice and gas, which can result in amazing tails forming behind them (thanks to the ice and dust vapourising)

Although the asteroid is 178 million miles (287 million kilometers) away, Osiris-Rex will put another 1.4 billion miles (2.3 billion kilometers) on its odometer to catch up with Earth.

The SUV-size spacecraft will circle the sun twice before delivering its small sample capsule to Utah's desert floor on Sept. 24, 2023, to end the more than $800million mission.

It launched from Cape Canaveral in 2016.

The precious samples will be housed at a new lab under construction at Nasa's Johnson Space Center in Houston.

It's already home to hundreds of pounds of lunar material collected by the 12 Apollo moonwalkers from 1969 to 1972.

Scientists initially thought the spacecraft stored two pounds (one kilogram) of asteroid rubble, but more recently revised their estimate downward.

They won't know for certain how much is on board until the capsule is opened after touchdown.

"Every bit of sample is valuable," Dworkin said. "We have to be patient."

Nasa has lots more asteroid projects planned.

Set to launch in October, a spacecraft named Lucy will fly past swarms of asteroids out near Jupiter, while a spacecraft known as Dart will blast off in November in an attempt to redirect an asteroid as part of a planetary protection test.

Then in 2022, the Psyche spacecraft will take off for an odd, metallic asteroid bearing the same name.

None of these missions, however, involve sample return.

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In other space news, Nasa has released historic first audio recordings captured on the surface of Mars.

China and Russia have pledged to build a shared Moon base, marking the start of a new era in space cooperation between the two countries.

And, Mars will make a close approach to the Moon this week.

What are your thoughts on the Bennu mission? Let us know in the comments…

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