2 moons or­bit gi­ant as­ter­oid that buzzed Earth

Weekend Mirror - - CHILDREN’S CORNER -

The

huge as­ter­oid that cruised past Earth last week in a record-break­ing flyby has two moons, radar im­ages re­veal.

On Sept. 1, the 2.8-milewide (4.5 kilo­me­ters) nearEarth as­ter­oid 3122 Florence zoomed within 4.4 mil­lion miles ( 7 mil­lion km) of our planet — a mere 18 times the dis­tance from Earth to the moon. No other space rock that big has come so close since NASA be­gan track­ing as­ter­oids in earnest, agency of­fi­cials have said.

The flyby there­fore pre­sented a rare sci­en­tific op­por­tu­nity, and as­tronomers around the world trained a num­ber of in­stru­ments on Florence as it ap­proached. One such fa­cil­ity was NASA’s Gold­stone Deep Space Com­mu­ni­ca­tions Com­plex in Cal­i­for­nia, which cap­tured some dra­matic and in­for­ma­tive views.

For ex­am­ple, im­agery ob­tained by the 230-foot (70 m) dish at Gold­stone con- firmed Florence’s size and its 2.4-hour ro­ta­tion pe­riod, val­ues that sci­en­tists had al­ready fig­ured out thanks to pre­vi­ous ob­ser­va­tions. And Gold­stone re­vealed that the as­ter­oid is roughly spher­i­cal, with an equa­to­rial ridge and at least one big crater, NASA re­searchers said.

Florence’s shape was a mys­tery be­fore last week’s flyby. Also un­known was whether the space rock had any moons, but Gold­stone’s im­agery re­vealed two.

“The sizes of the two moons are not yet well­known, but they are prob­a­bly be­tween 100-300 me­ters ( 300- 1,000 feet) across,” re­searchers Lance Ben­ner, Shan­tanu Naidu, Marina Bro­zovic and Paul Cho­das, of the Cen­ter for NEO (Near-Earth Ob­ject) Stud­ies at NASA’s Jet Propul­sion Lab­o­ra­tory in Pasadena, Cal­i­for­nia, wrote in a Sept. 1 up­date.

“The times re­quired for

Radar im­age of as­ter­oid Florence and one of its moons (small bright smudge above the main space rock) ob­tained on Sep. 1, 2017 us­ing the 70-m an­tenna at NASA’s Gold­stone Deep Space Com­mu­ni­ca­tions com­plex

each moon to re­volve around Florence are also not yet known pre­cisely, but ap­pear to be roughly 8 hours for the in­ner moon and 22 to 27 hours for the outer moon,” the re­searchers added. “The in­ner moon of the Florence sys­tem has the short­est or­bital pe­riod of any of the moons of the 60 near-Earth as­ter­oids known to have moons. In the Gold­stone radar im­ages, which have a res­o­lu­tion of 75 m [250 feet], the moons are only a few pix­els in ex­tent and do not re­veal any de­tail.”

Florence is just the third “triple as­ter­oid” known out of more than 16,400 rocks that have been dis­cov­ered and tracked in near-Earth space. The last time two moons were spot­ted around one as­ter­oid was in 2009, Ben­ner and his col­leagues wrote.

The sci­en­tists stitched some of the Gold­stone im­ages to­gether, cre­at­ing a movie that shows Florence com­plet­ing more than two ro­ta­tions, with the two moons seen mov­ing around the huge space rock.

Ad­di­tional radar views may re­veal yet more de­tail; re­searchers aim to keep study­ing Florence us­ing Gold­stone and the Arecibo Ob­ser­va­tory in Puerto Rico through Sept. 8, the NASA re­searchers said. But Hur­ri­cane Irma ap­par­ently thwarted part of this plan; Arecibo has ceased op­er­a­tions and will not re­sume them un­til the storm has moved on, ob­ser­va­tory rep­re­sen­ta­tives an­nounced Tues­day (Sept. 5).

There was never any risk that Florence would hit Earth dur­ing Friday’s flyby, and the as­ter­oid doesn’t pose a threat to the planet for the fore­see­able fu­ture, NASA of­fi­cials have stressed.

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