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Douglas MacDougal

Remember 'Omuamua?

Updated: May 25, 2020

On the occasion of our second interstellar visitor to our solar system, 2I/Borisov, I was reminded of a talk I gave a year ago to a mixed student and faculty audience in the physics department at Portland State University. It was a non-technical (though mildly mathematical) presentation on1I/2017 U1 'Oumuamua, our first outside-solar system guest. Let's recall its journey for a moment; it will help put Borisov in perspective.


Artist's concept of interstellar object1I/2017 U1 ('Oumuamua) as it passed through the solar system after its discovery in October 2017. According to NASA, the aspect ratio of up to 10:1 is unlike that of any object seen in our own solar system. Image Credit: European Southern Observatory / M. Kornmesser


I began my talk with these facts about 'Oumuamua: It appeared in in the sky on October 2017, discovered last October by the Pan-STARRS telescope on Haleakala in Maui. It was moving fast – very fast. Two of NASA’s space telescopes (Hubble and Spitzer) tracked it at 38.3 kilometers per second relative to the Sun. It also varied greatly in brightness, was reddish, had no dust around it, and had no tail. Its speed suggested a hyperbolic path; its magnitude variations hinted at a highly elongated shape; its reddish color resembled some outer solar system objects; and its inertness told that it was not a comet. According to NASA, it likely had been “wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our star system.” I have attched a powerpoint of a part of my talk below. It gets into a little bit of physics, energy in orbits and some basic equations. The most interesting math nuggets are at the end of the show.




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