16 December 2019

Naming the Comets

Time-lapse of Comet 2I Borisov

An artist’s impression of `Oumuamua as a dark red highly-elongated metallic or rocky object,
about 400 meters long, and unlike anything normally found in the Solar System.

On December 8 this year, a newly discovered comet looped around our Sun after a journey of more than 100 million years from the birth of some very distant star. It makes its closest pass to Earth today and then heads out of our solar system again. By the middle of 2020, the comet will streak past Jupiter's distance of 500 million miles on its way back into interstellar space where it will drift for untold millions of years before skirting close to another star system.

It's only the second interstellat object to visit us, so it's a big deal. But it has the very boring name of "Comet 2I Borisov." It was discovered by Gennady Borisov, a Crimean astronomer, and, of course, he wanted his piece of history.

A much more interesting name goes to the first interstellar object to visit our solar system. That was ʻOumuamua.

The International Astronomical Union assigns designations for astronomical objects and they originally classified it as Comet C/2017 U1. Then it was reclassified as the equally boring asteroid A/2017 U1. The renaming was because it had no "coma" - the nebulous envelope around the nucleus of a comet formed when the comet passes close to the Sun and warms so that it gets a "fuzzy" appearance when viewed in telescopes and distinguishes it from stars. The word coma comes from the Greek "kome" (κόμη), which means "hair" and is the origin of the word comet itself.

Once this comet was identified as coming from outside the Solar System, a new designation was created: I, for Interstellar object. ʻOumuamua, as the first object so identified, was designated 1I but is also referred to as 1I; 1I/2017 U1; 1I/ʻOumuamua; or 1I/2017 U1 (ʻOumuamua). I'm only interested in ʻOumuamua.

What caught my attention first was that first character which is a Hawaiian ʻokina, and not an apostrophe. It is pronounced as a glottal stop.  The name comes directly from the Hawaiian word ʻoumuamua, meaning "scout," because the object has come from so far away to check us out. The name was chosen by the Pan-STARRS team in consultation with Kaʻiu Kimura and Larry Kimura of the University of Hawai‘i at Hilo. It was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory, Hawaii.

That is a much better name than 1I. But I would have been quite happy if they had gone with another suggested name: Rama. That is the name given to an alien spacecraft discovered under similar circumstances in the 1973 science fiction novel Rendezvous with Rama by Arthur C. Clarke. It's a novel I really enjoyed reading. That object was seen as an alien craft that was on a scouting expedition checking out the rest of the universe.

 ʻOumuamua is tumbling, rather than smoothly rotating, and is moving so fast relative to the Sun that there is no chance it originated in the Solar System and it cannot be captured into a solar orbit. It will leave our Solar System and resume traveling through interstellar after roughly 20,000 years of travel in the Solar System.

ʻOumuamua's planetary system of origin and the amount of time it has spent traveling amongst the stars are unknown. I love that mystery.

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