After two years hurtling through space, NASA's probe has reached one of the oldest asteroids in our solar system. It could bring back clues to the origins of planet Earth — and perhaps save it from collision.
101955 Bennu is an asteroid the size of the Empire State Building and it could be heading straight for us.
"If it really comes close to the Earth and we have to remove it before it hits our planet, we need to know as much about it as possible," Dr. Harald Michaelis of the DLR Institute for Planetary Research in Berlin, who was on the team preparing the OSIRIS-Rex mission, told DW. "This can help us predict how to remove such a body away from its original orbit."
They are curious as to what it's made of, and the mission's primary goal is to collect samples from the asteroid's surface.
"Everything was mixed up during the formation of our planet, but these bodies [asteroids] are building blocks of our Earth and other planets," Michaelis explains. "We would like to know what these 'raw materials' are in order to understand the whole process of planet formation and planet development."
Scientists think Bennu stands out from millions of other minor planets in its composition: It's one of the most primitive asteroids, largely made up of carbon, and has not changed significantly over the last 4 billion years, they believe.
The stuff of myth and legend
Both Bennu and OSIRIS take their names from ancient Egyptian mythology.
Reaching the asteroid was relatively easy. But getting up close and collecting the sample is a real challenge, Michaelis says: "The most critical phase is to go down: You have to move very slowly, otherwise the spacecraft hits the surface and gets damaged."
The probe is equipped with a robotic arm that will make contact with the surface of the asteroid for approximately five seconds.
The plan is for it shoot liquid nitrogen into the rock, breaking it up and collecting it in a container. It will have three attempts. This part of the mission is scheduled for July 2020, before OSIRIS-REx heads home.
If everything goes to plan, it should arrive back on planet Earth in September 2023, carrying extraterrestrial material that will help scientists understand more about the origins of our solar system.
Named for the king of the underworld and god of the afterlife, the mission could even reach back into our own distant past to reveal something about the very beginnings of life.
European early warning system
About 10,000 asteroids loom close to Earth. They could be dangerous. The European Space Agency (ESA) is building an early warning system in Frascati, Italy. Data from telescopes like this one on Tenerife will be collated there.
If you're wondering how important early warning systems are, think of the meteorite that struck Earth near Chelyabinsk in Russia on 15 February 2013. The blast was estimated to have been as strong as between 100 and 1000 kilotons of TNT explosives. Almost 1500 people were injured.
A big splash
Before it had burned up in the Earth's atmosphere, the meteorite is estimated to have had a diameter of 20 meters. All that was left was a piece weighing only about a kilogram. But it still managed to smash a six meter wide hole in the ice.
Bigger and badder
But an asteroid named "2012 DA14" was much more dangerous. It weighed 130,000 tons. On the same day as the Chelyabinsk strike, 2012 DA14 flew passed our planet at a distance of just 27,000 kilometers. That is closer than some satellites.
Whizz by Earth
A number of other asteroids and comets are expected to come close to Earth this year. Scientists are keeping a close eye on them because even the smallest rocks can be dangerous.
Comets and shooting stars
Comets consist of a cloud of gas and a huge tail of gas, stones and particles of dust. When the tiny grains of dust from a comet scrape the Earth's atmosphere, they can get as hot as 3,000 degrees Celsius. They start to glow and become a shooting star.
The most famous meteor shower
The Perseids are a prolific meteor shower, associated with the comet Swift-Tuttle. Every summer, the meteor shower crosses the Earth's orbit. The Perseids are named after the constellation they are closest to when they can be seen. It is derived from Perseus, a character from Greek mythology.
When meteoroids don't burn up
Meteors dust burns up in our atmosphere. Most meteorites (meteoroids that survive falling through the atmosphere) are harmless and are often no bigger than a stone. But large meteorites can cause a lot of damage. One of the largest meteorite craters is the Barringer Crater in Arizona. It has a diameter of 1,000 meters and is 50,000 years old.
End of an era
About 65 million years ago, a giant meteorite slammed into the Yucatan Peninsula (simulated in the image to the right). It led to the creation of the Chicxulub Crater, which is more than 180 kilometers in diameter. Experts believe the impact wiped out the dinosaurs. More recent evidence suggests that debris from a collision between two asteroids 160 million years ago led to the event.
Burnt rocks from outer space
Meteorites look like burnt rocks. Their crust is formed when the meteorite melts upon entering the Earth's atmosphere. Other planets are also struck by meteorites. NASA's Opportunity Rover discovered the first extraterrestrial meteorites on Mars in 2005.
Dust and gas
It's not just the dust from comets that reaches Earth - but the comets do, too. Experts believe comets to be bits leftover from the creation of planets. They may also hold secrets about the beginnings of our solar system.
Large chunks of rock
Almost all of meteorites found on Earth have come from asteroids - that is 99.8 percent of the more than 30,000. And just like comets, asteroids are created when a planet is being formed. They have no permanent atmosphere and hardly any gravity.
And after all that...
... the chance of a large asteroid hitting Earth in the next 100 years is (said to be) quite small.