On Sunday morning, somewhere above the Utah desert, a parachute will open and a capsule containing about 250g of rubble will float to the ground. As it descends, four helicopters bearing scientists, engineers and military safety personnel will race across the arid landscape to recover the precious cargo.
Because this is not just any old dirt: these are 4.6bn-year-old chunks of space rock that could not only shed light on how planets formed but how life itself began.
“These are some of the oldest materials formed in our solar system,” says Ashley King of the Natural History Museum (NHM) in London. “Samples from asteroids [such as this] tell us what all those ingredients were for making a planet like the Earth and they also tell us what the recipe was – so how did those materials come together and start mixing together to end up with [habitable environments]?”
The final act of Nasa’s Osiris-Rex mission might seem like the opening sequence of an action movie, but it is the culmination of a seven-year journey in which a robotic spacecraft the size of a transit van was sent to study – and then plunder – the pile of rubble that comprises the asteroid Bennu.
The capsule containing this quarry is expected to be released from the spacecraft at 0642 EDT (1142 BST) on Sunday and enter Earth’s atmosphere four hours later, travelling at 27,650 miles per hour. As it plummets towards Earth its path will be tracked, with parachutes deployed to slow its descent to about 11mph at touchdown.
Once the team recover the capsule it will be loaded into a metal crate, wrapped and transported by helicopter to a temporary facility. On Monday it will be whisked to Nasa’s Johnson Space Center in Houston.
While scientists say there is little danger of the samples posing a risk to Earth, they stress avoiding contamination in the other direction is paramount. Filtered air will be allowed to flow into the capsule as it plummets to Earth to avoid leaks that could cause contamination, while the capsule will subsequently be hooked up to a flow of nitrogen.
One aim of the mission is to better understand how to predict and defend Earth against potential asteroid strikes, an endeavour King said would be aided by analysing the physical properties of the samples, such as their density and porosity.
Indeed Bennu is classed as a “potentially hazardous” asteroid, with Nasa suggesting that after the mid-2100s, and until at least 2300, it has a one in 1,750 chance of crashing into Earth.
Another significant area of research is the asteroid’s carbon-rich surface, which scientists are keen to study to explore whether such objects could have brought ingredients crucial to life – such as organic substances and water – to Earth.
King is part of a small team that will carry out the first investigations of the asteroid material in Houston on Wednesday.
“We have three days to try and very quickly characterise what minerals are in there [and] roughly what is its composition,” he says, adding that in particular the researchers are keen to see if water-containing minerals are present, as suggested by observations from the spacecraft.
Parts of the samples will subsequently be studied by myriad scientists working on the mission, with fragments also expected to be sent to Nasa’s partners from the Canadian and Japanese space agencies. The rest will be preserved for research by others, including future scientists.
Prof Sara Russell, also of the NHM and the deputy lead for mineralogy and petrology on the mission, will be studying the samples using techniques including scanning electron microscopy.
She says: “I’ll be looking for tiny grains in there that formed right at the beginning of the solar system. Before the planets formed, these grains were free-floating bits of dust, and can tell us what the environment was like then, and how long planet-building took.
“I’ll also be looking at how the minerals have changed over the history of the asteroid. That will tell us about how much water it contained as well as what temperatures it’s experienced.”
While space missions by Japan have previously recovered tiny samples of different asteroids, the Osiris-Rex capsule will contain the largest asteroid sample ever collected.
Such missions, says King, are crucial as they give scientists access to pristine material of a known provenance and context – unlike meteorites, which are often of unknown origin and contaminated by travelling through Earth’s atmosphere and landing on the ground.
Prof Neil Bowles of the University of Oxford, who will be heating up fragments of Bennu to explore the infrared radiation they emit, says one of the benefits of retrieving the samples is that scientists can compare the results of laboratory tests with remote observations made by the Osiris-Rex spacecraft.
That, he says, can help researchers calibrate the latter, allowing them to more accurately explore differences in composition across the surface of Bennu.
But Kerri Donaldson Hanna, a planetary geologist at the University of Central Florida who has been working with the Oxford team, says such “ground-truthing” could also help scientists interpret observations of other asteroids in the solar system that can only be studied by telescope or spacecraft. “That’s really the icing on the cake,” she says.
