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This Harvard professor claims an alien spaceship visited us in 2017

A highly unusual object was spotted traveling through the solar system in 2017. Given a Hawaiian name, ʻOumuamua, it was small and elongated – a few hundred meters by a few tens of meters, traveling at a speed fast enough to escape the Sun’s gravity and move into interstellar space.

I was at a meeting when the discovery of ʻOumuamua was announced, and a friend immediately said to me, “So how long before somebody claims it’s a spaceship?” It seems that whenever astronomers discover anything unusual, somebody claims it must be aliens.

Nearly all scientists believe that ʻOumuamua probably originates from outside the solar system. It is an asteroid- or comet-like object that has left another star and traveled through interstellar space – we saw it as it zipped by us. But not everyone agrees. Avi Loeb, a Harvard professor of astronomy, suggested in a recent book that it is indeed an alien spaceship. But how feasible is this? And how come most scientists disagree with the claim?

Researchers estimate that the Milky Way should contain around 100 million billion comets and asteroids ejected from other planetary systemsand that one of these should pass through our solar system every year or so. So it makes sense that ‘Oumuamua could be one of these. We spotted another last year – “Borisov” – which suggests they are as common as we predict.

What made ʻOumuamua particularly interesting was that it didn’t follow the orbit you would expect – its trajectory shows it has some extra “non-gravitational force” acting on it. This is not too unusual. The pressure of solar radiation or gas or particles driven out as an object warms up close to the Sun can give extra force, and we see this with comets all the time.

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Experts on comets and the solar system have explored various explanations for this. Given this was a small, dark object passing us very quickly before disappearing, the images we were able to get weren’t wonderful, and so it is difficult to be sure.