By now, you have probably heard of Oumuamua (Hawaiian for “scout”), the interstellar object hurtling out of our solar system past the orbit of Jupiter.
Oumuamua “is a lightsail, floating in interstellar space as . . . debris from an advanced technological equipment,” Harvard astrophysicist Avi Loeb wrote with his colleague Shmuel Bialy in Astrophysical Journal Letters last November. Yep, you read that right. They say that Oumuamua is, in a word, a piece of an alien spacecraft.
Uh, just a second. A lightsail? I remember lightsails from my boyhood reading in science fiction. But the scientific theory behind it goes back a long way.
Johannes Kepler, the great seventeenth-century astronomer, first helped us understand why comet tails always point away from the sun, no matter what direction the comet is actually traveling. A “solar wind” pushes the debris from the comet away from Sol, our star.
James Clerk Maxwell, the brilliant Scottish scientist of the nineteenth century most famous for his theory uniting electricity and magnetism, showed that light actually has momentum and thus exercises a tiny push on whatever it encounters.
And Jules Verne may be the first author to speculate on technology that could harness that light for propulsion. Later authors took the cue and suggested, among other possibilities, a gigantic sail driving a ship through space.
So why does the head of one of the world’s most distinguished astronomical departments think this object, which he guesses is about a millimetre thick but vastly extended, is a lightsail rather than, say, just some unusually shaped rock ejected from a distant star?
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