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One of the truly stimulating things about writing this column is that periodically I need to revisit an earlier effort. It happened last week with the Collatz Conjecture; it’s happening again this week with ‘Oumuamua.

‘Oumuamua (broadly, Hawaiian for “scout") was an object that, in 2017, shot through our solar system. That in itself wasn’t so unusual: asteroids rush about, comets from Halley’s to Kohoutek zoom through, these things happen. But astronomers were fascinated by ‘Oumuamua for a few special reasons.

To start with, we first noticed the object only when it was already speeding out of the solar system, already at a distance of some 30 million km from us. This meant that it was only visible for a short while, and astronomers had to scramble to observe it before it vanished. That alone created something of an ‘Oumuamua buzz.

But more important, this was one strange object. Take its shape. Its brightness varied so much and so rapidly that astronomers concluded it had to have a peculiar shape. Why so? Imagine looking at a football that’s spinning as it flies through the air. However near or far it is, however much it spins, it will still look round. But now imagine a boomerang, flipping over and over as it flies. Clearly, its apparent size and shape will vary. If both were made of material that reflected the Sun’s light, the ball’s brightness would seem more or less constant; the boomerang’s, though, would go up and down with its flips. Something like that happened with ‘Oumuamua—its brightness varied over a period of about eight hours by a factor of 10, and that variation suggested it was cigar- or pancake-shaped.

Now most asteroids are generally round, though there are odd-shaped ones out there too. Toutatis for example, which in 2004 passed only about a million km from us, was roughly like a dumbbell. But a cigar or a pancake? And at a few hundred metres long but only a tenth of that much wide—some 35 metres—‘Oumuamua may have been a gigantic cigar, but a tiny celestial object indeed. And yet, the amount of light it reflected was several times greater than other asteroids and comets: why was it so shiny?

Then there was the way it moved. Comets zoom through our solar system, but they have distinctive tails made of dust and ice. This object had none. Yet it had shot past the Sun at a speed—about 90km per second—that in fact far exceeds a typical comet’s speed. What had propelled it to that velocity? Also, while comets follow a distinctive elliptical path, ‘Oumuamua’s path was nearly a straight line. What did that mean?

In any case, most astronomers concluded in 2017 that, even with its odd shape and high speed and gleaming surface, ‘Oumuamua was just another rock. Alan Fitzsimmons of Queen’s University in Belfast put it this way: “This is a natural object ... pretty much a space cucumber."

And there ‘Oumuamua’s story might have ended.

Except that some astronomers were sceptical of this conclusion. Prominent among them is Abraham Loeb of Harvard University. In articles, scientific papers and now a new book (Extraterrestrial: The First Sign of Intelligent Life Beyond Earth), he suggests that ‘Oumuamua was really ... a spaceship dispatched by an alien civilization.

Yes: an extraterrestrial intelligence.

All its observed peculiarities contributed to that impression for Loeb. But there was a particular “eyebrow-raising bit of data" that was even more peculiar, he noted. A comet’s path through our solar system is governed in large part by how the Sun’s gravity acts on the comet. This is why we can trace its path and precisely predict when it will next approach the Sun and be visible from the Earth (Halley’s Comet? July 2061). But ‘Oumuamua’s path, as I mentioned briefly above, was quite different. While the Sun’s gravity had an effect on ‘Oumuamua, it does not fully explain its motion.

So what does?

There’s a Rashomon-like quality to how astronomers have answered that question. No doubt you’ve heard it said that when presented with different explanations for a mysterious phenomenon, Occam’s Razor applies: the simplest explanation is most likely the correct one. With ‘Oumuamua, faced with deciding whether it was a strange rock or a spacecraft built by aliens, most astronomers chose to believe in the rock. That’s because, to them, the simplest explanation was a rock. No need to spell out who built the spacecraft, how it is fuelled, who’s travelling in it and more. This also helps explain why the whole Search for Extraterrestrial Intelligence (SETI) effort has always had its fair share of sceptics. Just grasping the idea of another intelligence altogether seems difficult, almost like a flight of fancy, a leap of faith.

But to Loeb, Occam’s Razor applied in precisely the opposite way: the simplest explanation for ‘Oumuamua, Loeb believed, was that it had been crafted and dispatched by an alien civilization that’s somewhere out there. Will we ever know for sure which of these is right?

Well, that may depend on what we mean by “for sure". We can no longer examine ‘Oumuamua itself, that’s for sure. (Or at least not from where we sit today, but hold that thought). What’s left is the evidence. Or, in this case, attitudes to the evidence, how we interpret the evidence. Consider what Loeb made of just one aspect of it all, the unexpected way it reacted to the Sun’s gravity. Specifically, how it accelerated to its remarkable velocity as it receded from us.

Loeb thinks that happened “due to radiation pressure from the Sun." In effect, he suggests ‘Oumuamua is like a sail, a thin sheet spread wide to catch, in our corner of the universe at any rate, “solar wind" from our Sun. That’s the photons of light that stream from the Sun. A sufficiently light object could be propelled by such a stream. Out in space, it would be enough to push ‘Oumuamua, if it is actually such a “lightsail", to far higher speeds than any engine could—the kind of speed that ‘Oumuamua exhibited anyway.

Understand that this is not something out of science fiction. The Breakthrough Starshot programme—which Loeb advises, incidentally—has already sent prototypes of such crafts into space, even using an Indian rocket (see my column “Tiny SpaceChips to take us to stars", 5 August 2017, bit.ly/3lNTnjT). Sails are not natural creations; on and around the Earth, the only ones you’ll find are human-made. So, if we humans are contemplating and now building sails to catch solar winds, why shouldn’t another civilization have done the same?

It’s true that Loeb’s ideas have been greeted with scepticism and even scorn. But after all, that’s the way science must progress. In any case, Loeb remains undeterred. In an article in Scientific American, he writes that ‘Oumuamua’s very strangeness has “the potential to usher in a dramatic new era in space science".

In that vein, he spells out a fascinating challenge for us humans. Even if ‘Oumuamua has vanished into the darkness, it will take “thousands of years to leave the solar system entirely". This gives us time and a unique opportunity: “Getting a closer look [at ‘Oumuamua] through a flyby remains a possibility if we were to develop new technologies for faster space travel within a decade or two."

Carl Sagan once said: “Extraordinary claims require extraordinary evidence". Take that a little further and think of this: What can we learn from an extraordinary mission to catch up to ‘Oumuamua?

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. His Twitter handle is @DeathEndsFun

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