Extrasolar object A/2017 U1 is now considered to be the first celestial object from interstellar space-in this case,from somewhere in the direction of the constellation Lyra-to have ever been observed transiting through our solar system.First reported by Rob Weryk of the University of Hawaii with the Pan-STARRS-1 telescope on Haleakala on 19 October 2017,it is beyond a reasonable doubt a major event in the history of astronomy.The original report was almost instantly confirmed by Marco Micheli of the European Space Agency on a telescope at the ESA's Optical Ground Station at Tenerife,Canary Islands.*
How do we know this?The object's speed was such,at 25.5 km/second,that it could not be in a closed elliptical orbit around the Sun,the way an object from our solar system would be.It is just too fast for that.Nor could it have been sling-shot by encountering a planet's gravity.It entered our solar system far above the ecliptic plane,near which all the planetary orbits are.
After its arrival,A/2017 U1 passed about 25 million km below Earth on 14 October.It has accelerated to a blistering 44 km per second as it makes for the constellation Pegasus.By 26 October,a refined set of orbital parameters had been calculated,confirming the interstellar origins of the object with a high degree of confidence.
We do not know exactly what type of object it is-perhaps something new to science.It doesn't conform to the current concept of a comet,as it has no tail or vapor trail from passing by the Sun.A/2017 U1 is thought to be about 400 m in diameter.*
According to Andy Kivkin,a planetary astronomer of the Johns Hopkins University Applied Physics Laboratory in Laurel,Maryland:
There seems to be no question in the community that this is really real.They think this is a legit,bona-fide insterstellar object.This is a visitor from another solar system,and we are here in a time and place to see it.Who knows where it's been before?Who knows where it's going after this?*
It is up to the International Astronomical Union to assign the object a permanent name.As of 3 November,it is expected to be beyond the range of all telescopes.
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