On Thursday, a NASA spacecraft will launch on a seven-year round-trip journey to an asteroid with one simple mission: scoop up pieces of the space rock and bring them back to Earth. It’s the space agency’s OSIRIS-REx mission, and if it’s successful, the spacecraft will collect the largest sample ever from a near-Earth asteroid. And those asteroid pieces could tell us a great deal about how the Solar System came to be and possibly how life got started on our planet.

Asteroids are thought to be tiny snapshots of the early Solar System

Asteroids are thought to be tiny snapshots of the early Solar System. Researchers believe these objects have remained relatively untouched for billions of years, so tapping into one could tell us what the original chemical makeup of the Solar System looked like. There’s also speculation that asteroids may contain the so-called building blocks for life — water, organic molecules, and amino acids. Analyzing an asteroid could then tell us if these space rocks are responsible for bringing life’s precursors to Earth.

"This really is what drives our program," Dante Lauretta, principal investigator of the OSIRIS-REx mission, said in a NASA pre-launch briefing. "We’re going to [an asteroid] because it’s a time capsule from the earliest stages of Solar System formation."

It will be some time before we have some answers, though. OSIRIS-REx won’t get a sample from an asteroid for another four years, and the spacecraft won’t return to Earth until 2023. But when the spacecraft does come back, scientists will have a tiny piece of our galactic neighborhood from 4.5 billion years ago.

The target

OSIRIS-REx’s target is Bennu, a near-Earth asteroid that occasionally enters our planet’s neighborhood. Every six years, Bennu’s and Earth’s orbits match up, and the asteroid swings within about 200,000 miles of our planet. Bennu caused a bit of a stir a few years ago when astronomers thought there was a decent chance it might smash into Earth in the next century. More recent projections, however, show the chances are actually slim, but that doesn’t mean it won’t happen.

A 3D model of what Bennu looks like. (NASA)

However concerning, Bennu has many characteristics that make it alluring for scientists. For one, Bennu is in the right location. NASA wanted an asteroid on an Earth-like orbit that’s somewhat close to our planet. Bennu’s size also makes it ideal for getting a good sample. Asteroids that are smaller than about 650 feet across (or 200 meters) tend to spin pretty fast, and this can cause any loose material to fly off their surfaces. With a diameter of about 1,600 feet (492 meters), Bennu is large enough so that its spin is under control and probably isn’t flinging rocks everywhere.

But most of all, Bennu is made up of the right stuff: carbon. Astronomers believe that carbon-rich asteroids are the most primitive and have remained relatively unchanged since the beginning of the Solar System — unlike most of the planets and moons, which have undergone a lot of change and geological activity since they first formed 4.5 billion years ago. That means whatever chemicals are on Bennu were probably around when the Solar System was in its infancy.

Researchers believe that life’s building blocks may have been brought to Earth by asteroids

And that could provide clues about the origins of life here on Earth. Researchers believe that life’s building blocks may have been brought to Earth by asteroids slamming into the planet’s surface. That’s because many of the meteorites that have fallen to our planet contain organic molecules and water. But it’s hard to be absolutely certain about the chemical makeup of meteorites once they reach our surface, since they usually mingle with chemicals on Earth. "A lot of our analyses are confused by the fact that meteorites are very quickly contaminated," Lauretta said at a press briefing.

That’s why NASA is so interested in studying a relatively untouched asteroid sample in the clean laboratories here on Earth. If OSIRIS-REx finds these ingredients on Bennu, it may help strengthen the idea that the components needed for Earth’s life rode in on an asteroid billions years ago.

Round trip to Bennu

OSIRIS-REx is hitching a ride to Bennu on an Atlas V rocket — the premiere vehicle of the United Launch Alliance. The rocket is scheduled to take off on Thursday at 7:05PM ET, helping to put OSIRIS-REx in an orbit around the Sun. So far, weather looks good for the launch, but the mission team has the option to launch once a day for the next month if necessary.

Once OSIRIS-REx is in space, it’ll be a bit of a waiting game

Once OSIRIS-REx is in space, it’ll be a bit of a waiting game. The spacecraft will cruise around the Sun for a year and then pass by Earth again to get a little boost from the planet’s gravity. This flyby will help change the spacecraft’s plane of orbit, putting it on the same plane as Bennu. Once OSIRIS-REx reaches the asteroid by August 2018, it won’t pick up its samples right away. It will spend a year surveying the space rock to find the best place to scoop some material. "We’ll make the decision based on which site is safe for the spacecraft, which site has abundant material to sample, and if we’re lucky enough ... which one is scientifically most interesting," Ed Beshore, deputy principal investigator of the OSIRIS-REx, tells The Verge.

An artistic rendering of the OSIRIS-REx spacecraft over Bennu. (NASA)

While NASA decides on a spot, OSIRIS-REx will be working on a secondary, important goal: understanding how the Sun affects Bennu’s orbit. When an asteroid travels through space, it’s constantly bombarded by the Sun’s photons — tiny particles of light and electromagnetic radiation. These photons are often absorbed by the asteroid, causing it to heat up. The asteroid eventually reradiates that heat out into space, a process that creates a small amount of thrust and slightly throws the space rock off its orbit. It’s a phenomenon known as the Yarkovsky effect, and it’s made predicting the long-term orbits of asteroids difficult for astronomers.

When OSIRIS-REx is at Bennu, it will be studying the orbit of the asteroid very closely

So when OSIRIS-REx is at Bennu, it will be studying the orbit of the asteroid very closely, allowing researchers to see the Yarkovsky effect in action. "It’s kind of a long-term investigation of very slowly watching how much solar radiation the asteroid receives and how it perturbs the orbit of the asteroid over that time," says Beshore. That could help astronomers better predict the orbits of asteroids — especially those with the potential for crashing into our planet.

How the OSIRIS-REx collection head will quickly grab a sample from Bennu. (NASA)

Then in July 2020, it’ll be time to grab a sample from Bennu — and it will only take five seconds. Rather than land on the asteroid, OSIRIS-REx will slowly approach Bennu and tap its surface — a maneuver NASA calls TAG, for Touch-And-Go. The spacecraft will extend a tiny robotic arm with a specialized collection head at the end. Right as the arm touches the asteroid’s surface, a bottle of nitrogen gas will fire, causing any loose material to shoot up into the collection head. The OSIRIS-REx mission team hopes to grab at least 0.13 pounds (60 grams) of material this way. If successful, that will be the largest sample of space material to return to Earth since the Apollo era. (Just in case the first attempt fails, NASA can do up to three TAG attempts.)

The spacecraft has to leave Bennu around March 2021 to make it back to Earth by September 2023. Once it returns, the spacecraft’s sample container will detach from the rest of OSIRIS-REx and land gently in the Utah desert thanks to a parachute. Then begins the process of scrutinizing Bennu’s leftovers, to see what they can tell us about the Solar System’s formation and the origins of life. "There’s nothing more most geochemists would like than to be able to know exactly what the chemical constitution of the early Solar System was like," says Beshore.