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Scientists just watched a newfound asteroid zoom by Earth. Then they saw its moon.

   By Meghan Bartels 13 February 2020

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   One of Earth's premier instruments for studying nearby asteroids is back to work after being rattled by earthquakes, and its first new observations show that a newly discovered space rock is actually two separate asteroids.

   The instrument is the planetary radar system at the Arecibo Observatory in Puerto Rico. The observatory was closed for most of January, after a series of earthquakes hit the island beginning on Dec. 28, 2019. The observatory reopened on Jan. 29. Meanwhile, on Jan. 27, scientists using a telescope on Mauna Loa in Hawaii spotted an asteroid that astronomers hadn't seen before. The team dubbed the newfound space rock 2020 BX12 based on a formula recognizing its discovery date.

   Because of the size of 2020 BX12 and the way its orbit approaches that of Earth, it is designated a potentially hazardous asteroid. However, the space rock has already come as close to Earth as it will during this pass (2.7 million miles or 4.3 million kilometers); astronomers have calculated the asteroid's close approaches with Earth for the next century, and all will be at a greater distance than this one was.

   Related: Photos: asteroids in deep space

   Radar images show the binary asteroid 2020 BX12, which scientists discovered this year.
   Radar images show the binary asteroid 2020 BX12, which scientists discovered this year. (Image credit: Arecibo Observatory/NASA/NSF)

   The asteroid's flyby wasn't a threat to life on Earth, but it was an opportunity for scientists who were hoping to learn more about space rocks. On Feb. 4 and 5, the radar station at Arecibo set its sights on 2020 BX12. Based on the observations, the scientists discovered that 2020 BX12 is a binary asteroid, with a smaller rock orbiting the larger rock. About 15% of larger asteroids turn out, on closer inspection, to be binary, according to NASA.

   The larger rock is likely at least 540 feet (165 meters) across, and the smaller one is about 230 feet (70 m) wide, according to the observations gathered by Arecibo. When the instrument observed the two space rocks on Feb. 5, they appeared to be separated by about 1,200 feet (360 m).

   Scientists couldn't gather enough data to be sure, but they suspect that the two rocks might complete an orbit of each other in 45 to 50 hours and that the smaller rock may be brighter than, and tidally locked with, its companion, meaning the same side always faces the larger object.

   Existential dread is a key motivator for asteroid discoveries, and planetary defense experts hope that, by surveying nearby space rocks, they will identify a threat with enough time for us to protect ourselves. But asteroids are also scientifically interesting, since they represent rubble from the formation of the solar system.
     *  See the dramatic increase in near-Earth asteroids NASA has discovered (video)
     *  NASA wants a new space telescope to protect us all from dangerous asteroids
     *  Huge asteroid Apophis flies by Earth on Friday the 13th in 2029. A lucky day for scientists

   Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

   Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.
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   4 Comments Comment from the forums 
     * rod 13 February 2020 15:15

     Admin said:
     One of Earth's premier instruments for studying nearby asteroids is back to work after being rattled by earthquakes. Its first new observations show that a newly discovered space rock is actually two.
     Scientists just watched a newfound asteroid zoom by Earth. Then they saw its moon. : Read more
       "However, the space rock has already come as close to Earth as it will during this pass (2.7 million miles or 4.3 million kilometers); astronomers have calculated the asteroid's close approaches with Earth for the next century, and all will be at a greater distance than this one was."
       4.3E+6 kilometers is 674 earth radii distance. The Moon's mean distance is near 60.3 earth radii distance. From my readings on binary asteroids, many do not hold together over 4.5 billion years according IAW the radiometric age of the solar system based upon meteorites. Binary asteroids suggest they are much younger in age, at least as binary asteroid orbits.
       Reply 
     * Flyingtiger1 13 February 2020 19:41

     Admin said:
     One of Earth's premier instruments for studying nearby asteroids is back to work after being rattled by earthquakes. Its first new observations show that a newly discovered space rock is actually two.
     Scientists just watched a newfound asteroid zoom by Earth. Then they saw its moon. : Read more
       At 58 LD it's barely in the neighborhood. Good to see that they now have the tracking data so there are no more "suprises".
       Reply 
     * ProfessorC 14 February 2020 14:52
       "Existential dread is a key motivator for asteroid discoveries, and planetary defense experts hope that, by surveying nearby space rocks, they will identify a threat with enough time for us to protect ourselves."
       Exactly (and I mean with all the engineering, celestial mechanics, kinetic energy dynamics, and other specifications) do we "protect ourselves"? At this time, to use some modern vernacular, we got nothin'. Ideas, proposals, silly movies, and everything else in our stop-that-big-rock inventory are meaningless and will remain as such for the next half-century at the very minimum. That means watching these beasts hurtle by is academic fun masquerading for funding purposes as some kind of early warning system, which it most certainly isn't, primarily because 1) we can't stop or redirect the incoming doom stones and 2) we don't see the city block-sized variety most likely to make a hit until they're almost on us or have just slid by: "Boy, that was a close call, heh-heh-heh," for the latter, and "Whelp, there's OUR extinction event in 18 hours" for the former.
       "Planetary defense experts," indeed.
       Reply 
     * Space_Manly 16 February 2020 20:17

     ProfessorC said:
     "Planetary defense experts," indeed.
       An effective defense relies on an effective offense, and an effective offense starts with targeting. There's no sense building any interception hardware until you know where to point it, which is what's being developed now.
       It won't take anywhere near half-a-century to be able to start taking shots at near (for practice), as well as actual threats, either. Orbital laser systems could be fielded within a few years based on the airborne high-energy systems already on the shelf that were developed to successfully destroy incoming ballistic missiles.
       The technology needs to be scaled up to make it possible to vaporize a spot on the surface of an asteroid/meteor/comet for a sustained period to create a jet that can then begin to divert the body away from a collision trajectory with Earth.
       "There is more in Heaven and Earth than are dreamt of in your philosophy, Horatio."
       Reply 
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