NASA has selected the site for its asteroid sample collection mission from the four previously-proposed candidates after a year of study.
The spinning-top-shaped asteroid, ‘101955 Bennu’, is a 1,614 feet (492 m) wide near-Earth object with a cumulative 1-in-2,700 chance of hitting Earth from 2175–2199.
The chosen primary sample site — dubbed ‘Nightingale’ — is located in a young crater high up in the asteroid’s northern hemisphere.
The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer — or OSIRIS-Rex — craft has been analysing Bennu since December 2018.
If successful in its mission, OSIRIS-Rex will be the first US spacecraft to return samples of an asteroid to the Earth for analysis.
For NASA researchers, Bennu will act like a time-capsule from the birth of the solar system, containing information on its formation and evolution.
Its carbon-rich makeup will provide a window on the formation of the organic compounds that, on the Earth, ultimately enabled the origin of life.
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NASA has selected the so-called ‘Nightingale’ site, pictured, for its asteroid sample collection mission from the four previously-proposed candidates after a year of study
The chosen primary sample site — dubbed ‘Nightingale’ — is located in a young crater high up in the asteroid’s northern hemisphere, pictured here on Bennu with the backup site, Osprey
WHAT WILL THE OSIRIS-REX CRAFT BE DOING NEXT?
The rest of the probe’s mission has already been planned out:
Further reconnaissance flights:
First sample collection attempt:
Departure from Bennu:
Return to Earth
An artist’s impression of OSIRIS-REx in orbit around the asteroid 101955 Bennu
The OSIRIS-REx team have spent the last few months evaluating the potential of four candidate sampling sites on Bennu based on close-range data collected by the spacecraft.
Each of the four sites — which have been dubbed ‘Kingfisher’, ‘Nightingale’, ‘Osprey’ and ‘Sandpiper’ — had been initially put forward because they posed the fewest hazards to OSIRIS-REx’s safety while still affording great sampling potential.
The asteroid’s bird-based naming system stems from the name Bennu itself, which is taken from the ancient Egyptian bird deity that is linked with the sun, creation, and rebirth.
OSIRIS-REx will collect small (less than .8 inches / 2 cm in diameter) samples from Bennu by first slowly descending onto the asteroid’s surface.
A burst of nitrogen gas will then be used to blast the samples into a collection scoop at the end of the spacecraft’s robotic arm.
‘After thoroughly evaluating all four candidate sites, we made our final decision based on which site has the greatest amount of fine-grained material and how easily the spacecraft can access [such],’ said principal investigator Dante Lauretta.
‘Of the four candidates, site Nightingale best meets these criteria and, ultimately, best ensures mission success,’ he added.
The Nightingale site is located within a young crater on the north of Bennu that is around 460 feet (140 metres) wide.
Images taken of the crater show that its rocky surface material — the so-called ‘regolith’ — is dark in its colour, with its surface being relatively smooth.
The low northern temperatures and young age of the crater mean that the surface material at Nightingale is well-preserved and relatively freshly-exposed.
This would allow OSIRIS-REx to take a close-to ‘pristine’ sample of the asteroid, from which scientists will be able to reconstruct Bennu’s geological history.
The OSIRIS-REx team have spent the last few months evaluating the potential of four candidate sampling sites on Bennu based on close-range data collected by the spacecraft
Each of the four sites — which have been dubbed ‘Kingfisher’, ‘Nightingale’, ‘Osprey’ and ‘Sandpiper’ — had been initially put forward because they posed the fewest hazards to OSIRIS-REx’s safety while still affording great sampling potential
The Nightingale site, pictured, is located within a young crater on the north of Bennu that is around 460 feet (140 metres) wide. The low northern temperatures and young age of the crater mean that the surface material there is well-preserved and relatively freshly-exposed
Although Nightingale may have been determined to be the best option from the four proposed sample sites, inherent challenges will still be present.
For example, the original OSIRIS-REx mission plan had called for a sample site of around 164 feet (50 metres) in diameter.
While the crater surrounding Nightingale has a diameter nearly three times that size, the safe area where the spacecraft can make its brief contact with the asteroid surface is in contrast around ten times smaller than planned.
In fact, the touchdown site will only be around 52 feet (16 metres) in diameter — which will call for highly accurate and precise targeting of the surface.
To further complicate matters, a building-sized boulder is also located on the eastern ring of the crater surrounding Nightingale, providing a hazard for OSIRIS-REx to avoid as it retreats from the site after samples are collected.
OSIRIS-REx will collect small (less than .8 inches / 2 cm in diameter) samples from Bennu by first slowly descending onto the asteroid’s surface. A burst of nitrogen gas will then be used to blast the samples into a collection scoop at the end of the spacecraft’s robotic arm
‘Bennu has challenged OSIRIS-REx with extraordinarily rugged terrain,’ said OSIRIS-REx project manager Rich Burns of NASA’s Goddard Space Flight Center.
‘The team has adapted by employing a more accurate, though more complex, optical navigation technique to be able to get into these small areas.’
‘We’ll also arm OSIRIS-REx with the capability to recognise if it is on course to touch a hazard within or adjacent to the site and wave-off before that happens.’
The spacecraft has been designed to be able to perform multiple attempts to collect rock samples, but there is the risk that successive tries in one location may end up becoming unfeasible.
The hazard-avoiding so-called ‘wave off’ manoeuvre requires the activation of the probe’s thrusters — the exhaust from which has the potential to disturb the surface of the collection site in the low gravity.
Such could potential prevent the craft from collecting a sample there on a subsequent attempt.
Given this, the researchers have also selected Osprey as a backup sample-collection site, which the OSIRIS-REx spacecraft will visit in the event that it proves impossible to gather material from the Nightingale site.
The researchers have also selected Osprey as a backup sample-collection site, which the OSIRIS-REx spacecraft will visit in the event that Nightingale proves to be unviable
With the primary and backup sample collection sites selected, the mission team will move in January to have OSIRIS-REx perform further reconnaissance flights over both Nightingale and Osprey — with such continuing throughout the spring.
When these have been completed, the probe will begin rehearsing its first sample collection manoeuvre, with the actual attempt scheduled for August 2020.
Once its sampling is complete, OSIRIS-REx will be departing from Bennu the next year and is expected to return to the Earth in the September of 2023.
HOW WILL NASA’S OSIRIS-REX MISSION TO TAKE SAMPLES FROM AN ASTEROID WORK?
Osiris-Rex is the first US mission designed to return a piece of an asteroid to Earth.
Scientists say the ancient asteroid could hold clues to the origin of life.
It’s believed to have formed 4.5 billion years ago, a remnant of the solar system’s building blocks.
The spacecraft launched on September 8, 2016 at 19:05 EST aboard an Atlas V rocket.
After a careful survey of Bennu to characterise the asteroid and locate the most promising sample sites, Osiris-Rex will collect between 2 and 70 ounces (about 60 to 2,000 grams) of surface material with its robotic arm and return the sample to Earth via a detachable capsule in 2023.
To capture samples on the surface, the craft will hover over a specific area and ‘will be sent down at a very slow and gently’ 4 inches (10 cm) per second.
The spacecraft will also carry a laser altimeter, a suite of cameras provided by the University of Arizona, spectrometers and lidar, which is similar to radar, using light instead of radio waves to measure distance.