“We have never modeled the trajectory of an asteroid with this precision before,” explains Davide Farnocchia of NASA, the first author of a new study that recalculated the orbits of the asteroid Bennu with the data obtained from the Osiris-Rex spacecraft. the next two centuries. Until 2135 we can rest assured; after that, he has some small chance of going through the wrong gravity gate
On September 24, 2023, an abundant handful of carbonaceous regolith is expected to arrive on earth that the NASA Osiris-Rex spacecraft collected in October 2020 directly from the surface of the asteroid Bennu . Also on September 24, but many years later, precisely in 2182, the Earth risks being delivered home to the entire mass of the asteroid from half a kilometer in diameter. Let’s see why.
The asteroid (101955) Bennu , discovered in 1999 and repeatedly observed with optical telescopes and radar, is a Near-Earth Object potentially at risk of intersecting its orbit with Earth’s. Indeed, in the Palermo scale – used by astronomers to assess the risk of impact – it is one of the two objects with the highest overall probability of causing damage to the Earth .
A new study , published in the journal Icarus , has now considerably refined the predictions on a possible encounter between Bennu and our planet, based on the information gathered by the Osiris-Rex mission in the more than two years in which he visited Bennu. Osiris-Rex has closely investigated the size, shape and composition of the asteroid, studying its rotation and orbital trajectory in much more detail than any Earth-based telescope could. This has now made it possible to more accurately estimate its path over the next couple of centuries .
The new study determined an overall probability of impact by the year 2300 of 1 in 1750 (or 0.057 percent), while – as mentioned – September 24, 2182 would be the single most significant date in terms of potential, with a probability of impact of 1 in 2700 (or about 0.037 percent).
“The Osiris-Rex data give us much more precise information, we can test the limits of our models and calculate Bennu’s future trajectory with a very high degree of certainty up to 2135”, comments the first author of the study Davide Farnocchia , of the Center for Near Earth Object Studies ( Cneos ) by NASA. “We have never modeled the trajectory of an asteroid with this precision before.”
In 2135, the asteroid Bennu will get very close to Earth. While not posing any risk at that time , it is essential for scientists to be able to understand as accurately as possible how Earth’s gravity will alter the asteroid’s path around the Sun. In particular, if the space body will travel some specific , passing trajectories . through certain points called ” holes of gravity lock ” ( gravitational keyhole ), which would put it on a collision course with Earth during future orbit.
To calculate exactly where Bennu will be during his close passage of 2135 and whether or not he can pass through a gravitational keyhole , Farnocchia and his team evaluated various types of forces that, however small, can affect the path of the asteroid while orbiting the Sun.
Among these forces, the heat of the Sun itself plays a crucial role thanks to a phenomenon called the Yarkovsky effect , which, with the rotation of the body between “day” and “night”, causes the energy absorbed by the Sun to be dispersed into space, generating a small amount of thrust on the asteroid. With the forthcoming availability of a sample of the Bennu surface, the thermal properties of the asteroid can be determined even more accurately .
“The Yarkovsky effect acts on asteroids of all sizes and, although it was measured for a small fraction of the asteroid population from afar, Osiris-Rex gave us the first opportunity to measure it in detail as Bennu traveled around the Sun”, explains Steve Chesley of Jpl Nasa, one of the authors of the new study. “The effect on Bennu is equivalent to the weight of three grapes constantly acting on the asteroid: tiny, yes, but significant when determining the future possibilities of Bennu impact in the decades and centuries to come.”
The research team also considered many other perturbing forces , including the gravity of the Sun, planets, their moons and more than 300 other asteroids, resistance caused by interplanetary dust, solar wind pressure, and ejection events from particles from Bennu himself.
The researchers also evaluated the force exerted by Osiris-Rex during the performance of its Touch-And-Go sample collection event on October 20, 2020, to see if it could slightly alter Bennu’s orbit. Theoretical estimates were confirmed, according to which the small touch of the sampler would have a negligible effect .
To know more:
- Read on Icarus the article ” Ephemeris and hazard assessment for near-Earth asteroid (101955) Bennu based on OSIRIS-REx data “, by Davide Farnocchia, Steven R. Chesley, Yu Takahashi, Benjamin Rozitis, David Vokrouhlický, Brian P. Rush , Nickolaos Mastrodemos, Brian M. Kennedy, Ryan S. Park, Julie Bellerose, Daniel P. Lubey, Dianna Velez, Alex B. Davis, Joshua P. Emery, Jason M. Leonard, Jeroen Geeraert, Peter G. Antreasian and Dante S Lauretta
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Featured image: The asteroid Bennu in a mosaic of images taken by the Nasa Osiris-Rex probe. Credits: NASA / Goddard / University of Arizona
Provided by INAF