Cosmic cigar

Why scientists still can't solve the curious case of 'Oumuamua

Mystery around the cigar-shaped alien visitor endures.

ESO/K. Meech et al.

On September 9, 2017, a rocky, elongated body visited our solar system from beyond the realms of the Sun — the first-ever recorded interstellar object to cruise through our part of the galaxy.

'Oumuamua was like nothing astronomers have observed before, not quite a comet nor an asteroid. They could not agree on where it came from or what it was made of.

They still can't.

European Southern Observatory / M. Kornmesser

'Oumuamua was originally classified as a comet.

That proved to be wrong: Further research showed it lacks the telltale coma, or envelope surrounding a comet’s core, and tail of gas and dust.

It also has a dry surface more akin to that of rocky asteroids.


It also couldn't be an asteroid given its acceleration as it sped by the Sun.

'Oumuamua slingshotted past the Sun at a speed of 196,000 miles per hour — which is too fast to be explained by the pull of the Sun's gravity alone.


‘Oumuamua is also highly elongated, stretching across 900 feet in its longest dimension.

Astronomers believe that it roamed space for hundreds of millions of years before its chance encounter with our Solar System.


So, what is its origin story?

According to NASA, the object seems to have come from the direction of Vega, one of the stars that make up the constellation Lyra.

But its trajectory shows it would have been at Vega around 300,000 years ago — and that star was in a different location back then.

Yun Zhang

Meanwhile, another study suggests that 'Oumuamua was once part of a planet that got too close to its host star.

Like Icarus flying too near to the Sun, the planet was destroyed in its close encounter, violently shredded by the star's gravity into long, thin, rocky pieces.

Another study suggests 'Oumuamua is made up of hydrogen ice that was expelled from a massive molecular cloud.

It's simply a giant block of hydrogen ice that was spawned in the icy core of a massive molecular cloud — according to that study team.

Most recently, a study published on August 17 contradicted the earlier one, claiming 'Oumuamua is not made up of hydrogen ice after all.


Instead, it suggests that if it were made up of hydrogen ice, 'Oumuamua would not have survived the journey through interstellar space.

This is because heat from collisions would have evaporated the object in space.

Gemini Observatory/NSF/AURA

Although 'Oumuamua was the first interstellar object discovered, a second one was shortly spotted afterward.

In August 2019, Comet Borisov was found orbiting the Sun. Astronomers believe there are many more of these objects out there.

The more of these interstellar objects we observe, the better understanding we will have of their origin story and how they found their way to us.

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