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2017-10-26. Astronomers Spot First-Ever Space Rock from Another Star.

posted Nov 2, 2017, 3:51 PM by Alan Gould   [ updated Nov 9, 2017, 7:07 PM ]
By Lee Billings, Scientific American. For GSS A Changing Cosmos chapter 7. Excerpt: For the first time ever, an asteroid or comet from another star has been caught hurtling through our solar system, astronomers announced late Thursday. Provisionally designated A/2017 U1, the object appears to be less than a half-kilometer in diameter and is traveling at just over 40 kilometers per second—faster than humanity’s speediest outbound space probes. Because this is the first object of its type to be found, there are as yet no official rules for naming it, and its discoverers have balked at suggesting anything besides “Interstellar.” Whatever one might call it, though, it is presently racing away from the sun and has sparked a stampede of astronomers rushing to observe it before it fades entirely from view in the darkness of interstellar space. “All we can say right now is this was something that was tossed out of another star system,” says Karen Meech, an astronomer at the University of Hawaii. Meech is helping coordinate a global observation campaign, which presently includes nights on large telescopes in Chile and Hawaii, as well as five orbits of the Hubble Space Telescope. “Everyone is trying to get time to look at this thing on big telescopes right now, urgently, within the next few days,” she explains. ...Based on these analyses, A/2017 U1 came from the direction of the constellation Lyra, swooping in from high above the ecliptic plane in which the sun’s planets orbit at a breathtaking 25 kilometers per second. According to calculations by Micheli, that trajectory placed it 25 times farther out than Pluto in the year 1837, and it crossed the orbit of Neptune in November of 2012 on its sunward plunge. Pulled by our star’s gravity, on Sept. 9 A/2017 U1 approached within 40 million kilometers of the sun—well within the orbit of Mercury—before being flung back up and out of the ecliptic plane in the direction of the constellation Pegasus at nearly 44 kilometers per second. On Oct 14 it passed less than 25 million kilometers from Earth—about 60 times the Earth-moon distance. Astronomers could not see it, then, however, because its trajectory took it too close to the sun as seen from our planet's skies.... https://www.scientificamerican.com/article/astronomers-spot-first-ever-space-rock-from-another-star/
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