Close encounter: OSIRIS-REx meets Bennu asteroid

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.

Every six years, Bennu hurtles closer to the Earth than our own moon. And it could come closer still. Scientists fear it a possible collision with our planet some time in the 22nd century.

Which is why the OSIRIS-Rex space mission is trying to getting a better grasp of the risk and how it might be averted.

Nasa | Asteroid Bennu

OSIRIS-REx took this picture of Bennu from around 300 kilometers away in late October

"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."

Read more: Protecting Earth from an asteroid strike — what can we do?

One option would be to hit the asteroid with a missile, nudging it into just enough of a change to its orbit around the sun to avoid our planet.

Collecting clues to the past

We don't yet know if Bennu poses a threat to Earth. But that's not the only reason scientists want to study the asteroid.

OSIRIS-REx Origins Spectral Interpretation Resource Identification Security - Regolith Explorer NASA

The spacecraft is equipped with five instruments, including spectrometers and a laser altimeter to investigate the asteroid.

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."

Read more: 7 facts about NASA's 7-year OSIRIS-REx mission to the asteroid Bennu and back

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.

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NASA's InSight spacecraft touches down on Mars

A third-grade student from North Carolina in the United States won a "Name That Asteroid!" competition with the name Bennu, an Egyptian mythological bird and symbol of rebirth.

The spacecraft's moniker is an acronym of its main goals: Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer.

Grab and go

Scientists have long been interested in the composition of asteroids.

The first space probes were orbiting missions. Then in 2010, the Japanese probe Hayabusa brought home the first samples from the near-Earth asteroid Itokawa.

This time, scientists are aiming for a bigger sample of between 60 grams and 2 kilograms – far larger than previously possible.

Having journeyed through space for the last two years, OSIRIS-Rex will now orbit Bennu for about a year, snapping pictures and taking measurements.

It will also look for a suitable landing spot to collect the samples.

Read more: French-German space probe MASCOT lands on Ryugu asteroid

A delicate operation

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."

OSIRIS-REx Origins Spectral Interpretation Resource Identification Security - Regolith Explorer NASA

OSIRIS-REx will blast the asteroid with liquid nitrogen to break off samples

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.

Passing blast

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.