Key events
The significance of Bennu explained
Nicola Davis
Discovered in 1999, it is a ‘rubble-pile asteroid’ which means it is a large jumble of space rocks compressed together by gravity. These rocks are thought to have broken off from a larger body, and are about 4.6 bn years old – meaning that they formed around the same time as the solar system.
Crucially, the asteroid is known to be rich in carbon-based substances and water-containing clay minerals – suggesting that liquid water was once present on the larger body from which Bennu formed.
That, researchers say, means the samples that are currently hurtling towards Earth could help scientists to understand the ingredients that went into making planets including our own, and how those materials came together to create environments suitable for life.
But there are other reasons for studying Bennu. Among them, researchers want to better understand how to predict and defend Earth against potential asteroid strikes – and Bennu is poses a risk for a future hit.
Classed as “potentially hazardous” Bennu orbits our sun every 1.2 years, coming close to Earth every six years. But while Nasa has said there is no chance of it hitting Earth through the mid 2100s, after that point – and until at least 2300 – it has a one in 1,750 chance of crashing into our planet.
Nicola Davis
As we await the arrival of the capsule containing chunks of space rock from asteroid Bennu, it is worth looking back at how we got to this point and the incredible achievement of the scientists involved.
The name of the mission in full is quite a mouthful: origins, spectral interpretation, resource identification, security-regolith explorer. But in brief, it might be better described as a space-based smash and grab.
The target, Bennu, is essential a pile of rubble that is loosely held together by gravity. It is about as wide as the Empire State Building is tall and is on an orbit around the Earth, passing close to our planet every six years or so.
The Osiris-Rex spacecraft, which is about the size of a transit van, blasted off towards Bennu in September 2016, reaching the asteroid two year later, in December of 2018. Once in orbit – flying just a mile above the asteroid, scooping the record for the closest orbit of a planetary body by a spacecraft – it began mapping Bennu, allowing scientists to select the best site for recovery of the samples.The destination, it was decided, would be the asteroid’s Nightingale Crater.
Sample capsule expected to land at 10:55am ET near Salt Lake City
The sample capsule carrying rocks and dust from Bennu is expected to land near Salt Lake City at 10:55am ET today.
According to Nasa, once the Osiris-Rex spacecraft reaches within 63,000 miles of Earth’s surface on Sunday, or about one-third the distance from Earth to the moon, it will release the sample capsule. The time of the release will be at 6:42am ET.
The capsule, traveling at 27,650 miles per hour, is expected to enter Earth’s atmosphere at around 10:42am ET off the northern California coast at an altitude of about 83 miles above the surface.
The capsule is then set to land 13 minutes later at 10:55am ET in an area on the defense department’s Utah Test and Training Range near Salt Lake City.
Mission team members are set to retrieve the sample as soon as it lands “to ensure the sample is not contaminated by exposure to Earth’s environment,” said Nasa.
They will then fly it via helicopter to a temporary clean room to prepare it to be transported to Nasa’s Johnson Space Center in Houston on Monday.
Good morning US readers and good afternoon UK readers,
A high-anticipated asteroid sample from Nasa’s seven-year Osiris-Rex mission is set to enter Earth’s atmosphere today.
Earlier this morning, at 6:42 ET/11:42 BST, the Osiris-Rex spacecraft released a capsule containing samples of rubble and dust it collected from the near-Earth asteroid Bennu.
That capsule is now hurtling towards Earth at around 27,650 miles per hour.
About 20 minutes after releasing the capsule, the spacecraft itself turned tail and has blasted away from Earth to begin a new mission to explore another asteroid, known as Apophis, which it will take around six years to reach.
For now, we wait with baited breath for the Bennu samples to reach Earth, with touchdown expected around 10:55 a.m ET/15:55 BST.
The sample from Bennu “acts as a time capsule from the earliest days of our solar system and will help us answer big questions about the origins of life and the nature of asteroids,” said Nasa.
Stay tuned as we bring you the latest updates on this historic return.
