#astronomy Don’t Fear About Bennu (But) – Sky & Telescope

August 16, 2021 - Comment

The near-Earth asteroid 101955 Bennu is finest often known as the curious, die-shaped world lately visited by NASA’s OSIRIS-REX spacecraft. However Bennu has one other declare to fame: It’s one of the crucial 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


The near-Earth asteroid 101955 Bennu is finest often known as the curious, die-shaped world lately visited by NASA’s OSIRIS-REX spacecraft. However Bennu has one other declare to fame: It’s one of the crucial 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 Solar. The 2 orbits are tilted a mere 6° from one another’s planes. This setup made Bennu a superb 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 backgroundThis 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 score: NASA GSFC / College of Arizona

Astronomers found Bennu in 1999 and since then have collected a whole bunch of observations to find out the asteroid’s trajectory and the menace it poses. They’ll predict Bennu’s path intimately out to 2135, when it makes an in depth move by Earth. However that move might change all the things. Relying on the precise location the asteroid traverses throughout its go to, Earth’s gravity might tug it such that on a future strategy, Bennu will hit us as an alternative of merely whizzing by.

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

To evaluate simply how fearful we needs 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 of a variety of results on the article’s movement, from the gravitational nudges of greater than 300 different asteroids within the photo voltaic system to the small however persistent push created as Bennu’s sun-warmed floor reradiates its warmth into the chilly evening of house. This radiative thrust, referred to 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 11th press convention.

Because of OSIRIS-REX’s knowledge, the scientists have been capable of rule out all however two of the keyholes, refining our information of Bennu’s trajectory by an element of 20. The brand new data places the asteroid’s total affect likelihood at lower than zero.06% between now and the yr 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 workforce eradicated and, thus, the doable variations of our long-term destiny.

The revised affect likelihood ties Bennu with 29075 (1950 DA), essentially the most hazardous asteroid within the record from JPL’s Middle for Close to Earth Object Research, because the workforce notes of their upcoming Icarus paper. Bennu’s single highest likelihood of hitting Earth is available in September 2182 (zero.03%). Astronomers begin worrying when the affect likelihood reaches 1%, mentioned planetary protection officer Lindley Johnson (NASA) throughout the press convention.

Extrapolating from the asteroids detected thus far, researchers assume they’ve discovered practically 80% of objects of Bennu’s measurement, Johnson mentioned. NASA’s upcoming NEO Surveyor infrared house telescope goals to identify not less than two-thirds of all the things 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 consequence under.

Credit score: NASA Goddard House Flight Middle

Reference:

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

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