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Mean­ing: “A mes­sen­ger that reaches out from the dis­tant past” (in Hawai­ian).

Ap­pear­ance: Dark, red­dish, about 400 me­tres long by 40 me­tres wide, so roughly the size and shape of a sky­scraper.

Age: Maybe a few hun­dred mil­lion years?

You don’t know, do you? No. But ‘Ou­mua­mua is gen­er­ally mys­te­ri­ous. It was spot­ted last Oc­to­ber whizzing past the sun, too fast to have orig­i­nated in our so­lar sys­tem. It was de­clared the first in­ter­stel­lar ob­ject ever dis­cov­ered, be­fore dis­ap­pear­ing from view in Jan­uary.

Cool. It was long and thin, un­like any as­teroid or comet seen be­fore. And its sur­face was car­bon-based, not ice or rock. And – get this – af­ter pass­ing the sun, it sud­denly sped up. So now some sci­en­tists are spec­u­lat­ing …

Aliens! Per­haps. In a new pa­per in the Astro­phys­i­cal Jour­nal Let­ters, the Har­vard pro­fes­sors Sh­muel Bialy and Abra­ham Loeb dis­cuss a range of the­o­ries to ex­plain ‘Ou­mua­mua’s strange be­hav­iour. I don’t want a range of the­o­ries. I want aliens. Set­tle down. Ini­tially, the ac­cel­er­a­tion was put down to out­gassing.

(Snig­ger.) When comets pass close to stars, they re­lease gas that can speed them up. No gas was de­tected from ‘Ou­mua­mua, but it might have been re­leased quite gen­tly.

Silent but vi­o­lent. In­deed. How­ever, Bialy and Loeb say it could also have been pushed by the sun­light strik­ing it, like a de­lib­er­ately de­signed so­lar sail.

That’s right. De­signed by aliens. Of course, it was scanned last year for ra­dio sig­nals, and wasn’t send­ing any. They prob­a­bly use sub­space trans­mis­sion, like on Star Trek. ‘Ou­mua­mua was also tum­bling wildly around. How else would you gen­er­ate ar­ti­fi­cial grav­ity? Nor is it clear why aliens would send a probe that would take mil­lions of years to reach us.

They’re aliens. They live to probe. “One pos­si­bil­ity,” the au­thors sug­gested, “is that ‘Ou­mua­mua is a light sail, float­ing in in­ter­stel­lar space as de­bris from an ad­vanced tech­no­log­i­cal equip­ment.”

So it’s a piece of bro­ken space­ship? Well … we can’t prove it’s not. Although it is much more likely to be an as­teroid, or a comet cov­ered with an ir­ra­di­ated crust. The alien the­ory re­ally doesn’t have much ev­i­dence.

Boo, ev­i­dence! I want fun lies. Of course, if it’s an as­teroid it might be a splin­ter of an­other planet de­stroyed by an ex­plod­ing star. All right. I sup­pose that’s quite fun, too. Un­less there were aliens on the planet. Do say: “Typ­i­cal! You fi­nally find an alien probe and the damn thing’s bro­ken.” Don’t say: “We come in pieces.”

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