Tomorrow morning, an asteroid-bound mission will launch towards a shadowy space rock, Bennu. There, it will scoop up a bit of dirt and deliver it back to us, all without ever attempting a landing. It's not just any dirt, though. Bound up in these grains could be the answer to how life first emerged here on Earth. Image: NASA
Researchers have long theorised that comets or asteroids could have been responsible for delivering the first specks of organic materials or perhaps water that got things brewing on our planet. We have even found organic materials and chemically-bound water in meteorites that may have come from carbonaceous asteroids like Bennu.
The problem is that these meteorites have spent so long on Earth that there's no way of knowing whether organic compounds inside them came from asteroids, Earth itself or somewhere else along their journey. This will be the first time that we ever have the opportunity to check that profile directly from the asteroid.
"The reason we go to an asteroid like Bennu is we believe it's a pristine remnant of the very early solar system," Ed Beshore, the project's deputy principal investigator, told Gizmodo. "It's important because we want to answer questions about the rise of life on Earth."
It will take two years until OSIRIS-REx even arrives at Bennu, and another two years before the sample is taken. The samples will get back to Earth in 2023.
Still, there are several things that the mission can teach us even before we bring a little piece of the asteroid back. For one, it could help us better predict which asteroids are going to come close to us, and how close they will get.
Bennu belongs to a category of close-by asteroids called Near Earth Asteroids (NEAs). In fact, this proximity was one of the reasons it was chosen for the mission. But, as we've seen lately, the orbit of those NEAs — even when they buzz right next to us — can be hard to predict. This is due primarily to something called the Yarkovsky effect, which happens when asteroids are heated by the sun.
"Asteroids get hot," explained Beshore, "like how asphalt streets get hot on the Earth. They rotate like the Earth does and that re-radiated heat acts like a tiny rocket thruster which can actually move the asteroid around."
Since 1999, NASA has seen Bennu shift its trajectory over 160km from this effect. By studying Bennu's movements up-close, researchers hope to get a better idea of just how — and how much — the Yarkovsky effect is moving asteroids around.
The real prize from Bennu, though, are the four tablespoons of asteroid dirt that will be scooped up by the spacecraft at the mission's conclusion and packed into its return capsule. How it will accomplish this collection is one of the trickiest aspects of the mission.
Before any sample-taking is even attempted, scientists will first make a painstakingly complete map of the entire asteroid, a process that could take up to two years. From that first map, they will identify a dozen or so potential sampling sites, then create even more refined maps to choose the spot most likely for success.
"By the end, we'll be able to see an object the size of a penny on Bennu," said Daniella DellaGiustina, the mission's lead image processing scientist. Once they have selected a spot, though, things get even more harrowing.
While the craft buzzes the asteroid, a 3m-long "pogo arm" comes forth — like a boxing glove on a spring — to grab the sample. It's not just a simple scoop, though. The arm uses puffs of nitrogen gas to swirl some dirt from the asteroid up into a storage compartment in a matter of seconds. If the sample collection isn't successful the first time, engineers have made plans to do a couple of loop-backs, but as soon as the compartment has a full sample, the craft will immediately depart back to Earth.
"It's a safe, slow, smooth high-five to collect that sample and bring it back to Earth" explained Christina Richey, the mission's deputy program scientist. The entire collection will take just five seconds, she noted, but in those few seconds and approximately 60 grams of dirt, scientists are hoping to find answers to some of their oldest questions about life on Earth.
"We're fairly confident that there's going to be some of these organic compounds but until we get it back down to earth we won't know for sure," Richey said.
Getting the samples back to Earth also presents a significant challenge. The spacecraft will take the dirt most of the way back, but it's not equipped for a landing. Instead, it will eject the capsule four hours above Earth at a speed of 43,450km/h. A parachute will help it descend safely in Utah and, after seven years, researchers will finally be able to get their hands on those bits of dirt from an asteroid.
"This is really an opportunity to bring back a piece of the very early solar system," Beshore said. "These samples can be analysed for decades, just like the moon samples returned over 40 years ago are still being analysed using tools we didn't even know would exist, and of course the same will happen on the samples from Bennu."
The launch takes place Friday morning from Florida's Cape Canaveral station, aboard one of the United Launch Alliance's Atlas V rockets. It's the 13th major NASA mission to use that rocket.
There was some concern that last week's fire from a SpaceX rocket — which also took place at the Cape Canaveral station, but from a different launch pad — might delay the launch. But after a full assessment, NASA said there was no damage to facilities for this launch or any elevated risk from the blazing Falcon 9 rocket.
OSIRIS-REx is expected to leave on-schedule in a two-hour launch window starting at 9:05AM AEST. From then, it will be a wait of seven years before we start to get answers about what's really up on Bennu — and, perhaps, even how life on our planet really got started.