Winston
Lorenzo von Matterhorn
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Bumpy Road Ahead For NASA’s Osiris-REX
Asteroid Bennu is turning out to be a hazardous place for the NASA spacecraft to sample: It has uneven, rugged terrain and occasionally even hurls rocks into space
https://www.skyandtelescope.com/astronomy-news/bumpy-road-ahead-for-nasa-osiris-rex/
Even before the spacecraft lands, it has already learned a great deal about the asteroid’s characteristics and history.
Bennu is slightly wider than the Empire State Building is tall, and researchers describe its shape as that of a spinning top; though, as Dave Dickinson puts it, it also bears an uncanny resemblance to a 10-sided die typical of table games. The asteroid’s shape is also strikingly similar to that of 162173 Ryugu, the target of Japanese Aerospace Exploration Agency’s Hayabusa 2.
Based on Osiris-REX’s images of the asteroid’s surface, Barnouin (Johns Hopkins University Applied Physics Laboratory) and colleagues have determined that Bennu is a so-called rubble pile, with a porous, sponge-like interior. However, its shape — especially the presence of a series of ridges that run from pole to pole — also indicates an internal stiffness that helps hold the asteroid together, at least for now.
Currently, Bennu rotates with a period of 4.3 hours, but its period is shortening by about a second every 100 years. This is due to the something called the YORP effect (Yarkovsky-O'Keefe-Radzievskii-Paddack), where the asteroid gradually spins up as sunlight heats its surface unevenly. Mission scientists think that this YORP effect is driving changes in Bennu’s surface. Despite its estimated 100 million to 1 billion years old surface, Bennu doesn’t always show its age — it has large, ancient-looking craters but few small ones, hinting that its surface is slowly evolving.
Researchers had classified Bennu as a primitive carbonaceous chondrite, many of which have water and carbon-based compounds on their surfaces. Osiris-REX has now taken spectra of the asteroid’s surface, revealing hydrated minerals as well as evidence of hydroxyls, molecules that contain hydrogen and oxygen atoms bonded together. Researchers think that these molecules are part of water-bearing clay materials, which point to a past interaction with water, most likely before Bennu broke off from a much larger parent asteroid.
Osiris-REX has also witnessed the asteroid spew rocks and dust into space at irregular intervals. “I would say [these events are] one of the biggest surprises of my science career,” said Lauretta on March 19th at the Lunar and Planetary Science Conference. The team still isn’t sure what’s causing these ejections. One idea is that, now that the asteroid is at perihelion — the closest it gets to the Sun in its orbit — the increased heating of its surface might play a role.
Bennu: An Ancient but Active Rubble Pile
The Mysterious Exploding Asteroid
A NASA spacecraft reached a space rock and found it orbited by tiny moons—a phenomenon that “has never been seen before in any solar-system object.”
https://www.theatlantic.com/science/archive/2019/03/nasa-bennu-osiris-rex-asteroid/585256/
Billions of years ago, something—perhaps the vibrations of an exploding star—jostled a cloud of cosmic gas and dust suspended in space. The cloud collapsed on itself and flattened into a spinning disk. The center grew heavy and ignited, forming our sun. The stuff that remained ricocheted, collided, and congealed. The biggest clumps of space stuff smoothed into spheres—the planets and moons. The smallest, the asteroids and comets, stayed as they were, like crumbs left over from an elaborate feast.
And right now one of those crumbs is exploding.
An asteroid named Bennu has been caught spewing particles into space—hundreds of gravel-size bits, hurtling from the surface at high speed.
The tiny explosions were spotted by a NASA spacecraft named OSIRIS-REx. The probe settled into an orbit around the asteroid in late December and noticed the first ejection within days. Over the next two months, OSIRIS-REx observed nearly a dozen of these events. And more are still being detected.
“It’s one of the biggest surprises of my scientific career,” says Dante Lauretta, the lead investigator of the mission.
Asteroid Bennu is turning out to be a hazardous place for the NASA spacecraft to sample: It has uneven, rugged terrain and occasionally even hurls rocks into space
https://www.skyandtelescope.com/astronomy-news/bumpy-road-ahead-for-nasa-osiris-rex/
Even before the spacecraft lands, it has already learned a great deal about the asteroid’s characteristics and history.
Bennu is slightly wider than the Empire State Building is tall, and researchers describe its shape as that of a spinning top; though, as Dave Dickinson puts it, it also bears an uncanny resemblance to a 10-sided die typical of table games. The asteroid’s shape is also strikingly similar to that of 162173 Ryugu, the target of Japanese Aerospace Exploration Agency’s Hayabusa 2.
Based on Osiris-REX’s images of the asteroid’s surface, Barnouin (Johns Hopkins University Applied Physics Laboratory) and colleagues have determined that Bennu is a so-called rubble pile, with a porous, sponge-like interior. However, its shape — especially the presence of a series of ridges that run from pole to pole — also indicates an internal stiffness that helps hold the asteroid together, at least for now.
Currently, Bennu rotates with a period of 4.3 hours, but its period is shortening by about a second every 100 years. This is due to the something called the YORP effect (Yarkovsky-O'Keefe-Radzievskii-Paddack), where the asteroid gradually spins up as sunlight heats its surface unevenly. Mission scientists think that this YORP effect is driving changes in Bennu’s surface. Despite its estimated 100 million to 1 billion years old surface, Bennu doesn’t always show its age — it has large, ancient-looking craters but few small ones, hinting that its surface is slowly evolving.
Researchers had classified Bennu as a primitive carbonaceous chondrite, many of which have water and carbon-based compounds on their surfaces. Osiris-REX has now taken spectra of the asteroid’s surface, revealing hydrated minerals as well as evidence of hydroxyls, molecules that contain hydrogen and oxygen atoms bonded together. Researchers think that these molecules are part of water-bearing clay materials, which point to a past interaction with water, most likely before Bennu broke off from a much larger parent asteroid.
Osiris-REX has also witnessed the asteroid spew rocks and dust into space at irregular intervals. “I would say [these events are] one of the biggest surprises of my science career,” said Lauretta on March 19th at the Lunar and Planetary Science Conference. The team still isn’t sure what’s causing these ejections. One idea is that, now that the asteroid is at perihelion — the closest it gets to the Sun in its orbit — the increased heating of its surface might play a role.
Bennu: An Ancient but Active Rubble Pile
The Mysterious Exploding Asteroid
A NASA spacecraft reached a space rock and found it orbited by tiny moons—a phenomenon that “has never been seen before in any solar-system object.”
https://www.theatlantic.com/science/archive/2019/03/nasa-bennu-osiris-rex-asteroid/585256/
Billions of years ago, something—perhaps the vibrations of an exploding star—jostled a cloud of cosmic gas and dust suspended in space. The cloud collapsed on itself and flattened into a spinning disk. The center grew heavy and ignited, forming our sun. The stuff that remained ricocheted, collided, and congealed. The biggest clumps of space stuff smoothed into spheres—the planets and moons. The smallest, the asteroids and comets, stayed as they were, like crumbs left over from an elaborate feast.
And right now one of those crumbs is exploding.
An asteroid named Bennu has been caught spewing particles into space—hundreds of gravel-size bits, hurtling from the surface at high speed.
The tiny explosions were spotted by a NASA spacecraft named OSIRIS-REx. The probe settled into an orbit around the asteroid in late December and noticed the first ejection within days. Over the next two months, OSIRIS-REx observed nearly a dozen of these events. And more are still being detected.
“It’s one of the biggest surprises of my scientific career,” says Dante Lauretta, the lead investigator of the mission.
