- 3250 - ASTEROIDS - Bennu and what killed dinosaurs? Asteroid Bennu is one of the two most hazardous known asteroids in our Solar System. The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) spacecraft orbited Bennu for more than two years and gathered data that has allowed scientists to better understand the asteroid’s future orbit, trajectory and Earth-impact probability.
------------------ 3250 - ASTEROIDS - Bennu and what killed dinosaurs?
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- In the most precise calculations of an asteroid’s trajectory ever made, researchers determined Bennu’s total impact probability through the year 2300 is about 1 in 1,750 (or 0.057%).
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- The asteroid will make a close approach to Earth in 2135. Earth’s gravity will alter the asteroid’s path, and on September 24, 2182 as the date of a potential impact, with an impact probability of 1 in 2,700 (or about 0.037%). There is a 99.94% probability that Bennu is NOT on an impact trajectory.
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- Bennu was first discovered in 1999. Since its discovery, Bennu has been extensively tracked with 580 ground-based optical astrometric observations. The asteroid made three relatively close passes of Earth in 1999, 2005, and 2011, during which the Arecibo and Goldstone radar stations collected a wealth of data about Bennu’s motion.
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- OSIRIS-REx discovered particles being ejected from asteroid Bennu shortly after arriving at the asteroid. Its two-year reconnaissance and sample collection has provided crucial data about the 500-meter-wide asteroid.
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- Scientists expected Bennu’s surface to be smooth and sandy, but the first images from OSIRIS-REx revealed a rugged boulder-field, littered with large rocks and loose gravel.
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- The asteroid was expected to be geologically quiet, but just six days after arriving in orbit, the spacecraft observed the asteroid ejecting bits of rock, due to rocks on the asteroid cracking because of the day-night heat cycle.
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- Bennu even has pieces of “Vesta” on it. This spacecraft scooped up a sample of rock and dust from the asteroid’s surface in October of 2020, which it will deliver to Earth on September 24, 2023.
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- The researchers took into account all kinds of small influences, including the tiny gravitational pull of more than 300 other asteroids, and the drag caused by interplanetary dust. They even checked to see if OSIRIS-REx pushed the asteroid off course when the spacecraft briefly touched its rocky surface with its Touch-And-Go (TAG) sample collection maneuver. But that event had a negligible effect.
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- The researchers especially focused on a phenomenon called the “Yarkovsky effect“, where an object in space would, over long periods of time, be noticeably nudged in its orbit by the slight push created when it absorbs sunlight and then re-emits that energy as heat.
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- Over short timeframes, this thrust is minuscule, but over long periods, the effect on the asteroid’s position builds up and can play a significant role in changing an asteroid’s path.
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- The Yarkovsky effect will act on all asteroids of all sizes, and while it has been measured for a small fraction of the asteroid population from afar The effect on Bennu is equivalent to the weight of three grapes constantly acting on the asteroid, tiny, yes, but significant when determining Bennu’s future impact chances over the decades and centuries to come.
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- The spacecraft is now returning home, carrying a precious sample from this fascinating ancient object that will help us better understand not only the history of the solar system but also the role of sunlight in altering Bennu’s orbit since we will measure the asteroid’s thermal properties at unprecedented scales in laboratories on Earth when it arrives.
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- The Earth has experienced very many asteroids in the past. One of the most famous is the asteroid credited with the extinction of the dinosaurs 66,000,000 years ago. This asteroid is likely to have originated from the outer half of the solar system’s main asteroid belt.
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- Known as the “Chicxulub impactor“, this large asteroid has an estimated width of 6 miles and produced a crater in Mexico’s Yucatan peninsula that spans 90 miles .
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- After its sudden contact with Earth, the asteroid wiped out not only the dinosaurs, but around 75 percent of the planet’s animal species. It is widely accepted that this explosive force created was responsible for the mass extinction that ended the “Mesozoic era“.
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- Observations of 130,000 model asteroids, along with data and behavior seen in other known impactors, found that objects are 10 times more likely to reach Earth from the outer asteroid belt than previously thought.
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- Prior to crashing into Earth, the extinction-causing asteroid orbited the sun with others, in the main asteroid belt. This concentrated band lies between planets Mars and Jupiter, with its contents usually kept in place by the forces of gravity.
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- Researchers discovered that “escape hatches” could be created by thermal forces, which pull more distant asteroids out of orbit and in the direction of Earth.
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- The objects found in these outermost parts of the asteroid belt include many carbonaceous chondrite impactors. These are dark, porous and carbon-containing rocks which can also be found on Earth.
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- Geologists discovered that the Chicxulub asteroid had a similar composition to today’s carbonaceous chondrites. In the solar system, many objects surrounding Earth share similar composition to this impactor, however they are all much smaller, with widths around one mile.
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- By looking at wide timescales of the Chicxulub asteroid, the scientists could predict that a 6-mile asteroid is likely to come into contact with Earth once every 250 million years. Their model showed almost 50 percent of these significant impactors to be of the same carbonaceous chondrite composition.
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- Get ready for the next one.
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- August 17, 2021 ASTEROIDS - Bennu and what killed dinosaurs? 3201
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