Don’t Worry About Bennu (Yet)

The near-Earth asteroid 101955 Bennu is greatest often called the curious, die-shaped world recently visited by NASA’s OSIRIS-REX spacecraft. But Bennu has one other declare to fame: It’s probably the most hazardous asteroids in our planet’s neighborhood.

The 500-meter-wide object follows an orbit that retains it near Earth, even crossing our planet’s path because it travels across the Sun. The two orbits are tilted a mere 6° from one another’s planes. This setup made Bennu a wonderful goal for a sample-return mission, but it surely additionally makes the asteroid a thorn in planetary protection specialists’ sides.

A diamond-shaped grey asteroid with ridges, holes, and craters in it, against a black background
This mosaic of asteroid 101955 Bennu was created utilizing knowledge from NASA’s OSIRIS-REX spacecraft, which visited the asteroid from late 2018 to mid-2021.
Credit: NASA GSFC / University of Arizona

Astronomers found Bennu in 1999 and since then have collected a whole lot of observations to find out the asteroid’s trajectory and the menace it poses. They can predict Bennu’s path intimately out to 2135, when it makes a detailed move by Earth. But that move may change every little thing. Depending on the precise location the asteroid traverses throughout its go to, Earth’s gravity may tug it such that on a future strategy, Bennu will hit us as a substitute of merely whizzing by.

These inimical factors are known as gravitational keyholes, and earlier than OSIRIS-REX, there have been 26 of them sitting like dynamical mines alongside Bennu’s 2135 path.

To assess simply how fearful we ought to be about Bennu, Davide Farnocchia (Jet Propulsion Laboratory) and colleagues used exact place and movement measurements gathered as a part of OSIRIS-REX’s go to to Bennu to refine the asteroid’s trajectory. They thought-about a variety of results on the item’s movement, from the gravitational nudges of greater than 300 different asteroids within the solar system to the small however persistent push created as Bennu’s sun-warmed floor reradiates its warmth into the chilly evening of space. This radiative thrust, known as the Yarkovsky impact, is so tiny that it’s equal to the load of three grapes pushing on the floor, Farnocchia mentioned throughout an August eleventh press convention.

Thanks to OSIRIS-REX’s knowledge, the scientists had been capable of rule out all however two of the keyholes, refining our data of Bennu’s trajectory by an element of 20. The new data places the asteroid’s total influence likelihood at lower than 0.06% between now and the year 2300 — which, to be clear, is a small uptick from the earlier estimate (which prolonged solely to 2200). The significance lies in what number of keyholes the staff eradicated and, thus, the doable variations of our long-term destiny.

The revised influence likelihood ties Bennu with 29075 (1950 DA), probably the most hazardous asteroid in the list from JPL’s Center for Near Earth Object Studies, because the staff notes of their upcoming Icarus paper. Bennu’s single highest likelihood of hitting Earth is available in September 2182 (0.03%). Astronomers begin worrying when the influence likelihood reaches 1%, mentioned planetary protection officer Lindley Johnson (NASA) throughout the press convention.

Extrapolating from the asteroids detected thus far, researchers suppose they’ve discovered practically 80% of objects of Bennu’s measurement, Johnson mentioned. NASA’s upcoming NEO Surveyor infrared space telescope goals to identify at the least two-thirds of every little thing right down to 140 meters, working towards Congress’s 2005 mandate to NASA to search out greater than 90% of all near-Earth objects bigger than this measurement.

Bennu’s 2037 shut strategy will current observers with one other alternative to review the asteroid — albeit not one so extended or intimate as OSIRIS-REX did. Astronomers will use radar measurements taken throughout the flyby to check these newest calculations and make any wanted refinements.

Watch a video abstract of this end result beneath.

Credit: NASA Goddard Space Flight Center


D. Farnocchia et al. “Ephemeris and hazard assessment for near-Earth asteroid (101955) Bennu based on OSIRIS-REx data.” Icarus. Posted on-line August 10, 2021.


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