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It was our first known interstellar visitor when it was detected in front of the Sun last October. Nicknamed "Oumuamua" – Hawaiian for messenger – it was quickly determined that he was not part of this solar system.
His trajectory had been traced. And the track on which he stood could not have been an orbit around our Sun. So, this must come from deep space.
Follow-up observations after the Pan-STAARS-1 telescope in Hawaii announced that its discovery had revealed that the object was strange.
It was lying down. It was about a kilometer long. It was a strange reddish color. And he seemed to have properties that belong to both comets and asteroids.
Of course, some have assumed that it could be an extraterrestrial spacecraft. SETI (Search for Extraterrestrial Intelligence) was interested enough to spin one of his electronic ears in his direction.
He did not find anything. No observable omission was observed in the interstellar tumbling visitor.
And as Oumuamua moved so fast that he was already whipped into the confines of our solar system, the interest faded.
We did not have much more to do to verify it.
Now, a new study by two astronomers from the Harvard Smithsonian Astrophysics Center postulated that it could, after all, have been an extraterrestrial object.
A light sail.
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The study entitled "Solar Radiation Pressure Could Explain" Oumuamua's Particular Acceleration "was presented by Shmuel Bialy and Professor Abraham Loeb.
Professor Loeb is a member of the Breakthrough Starshot Committee, a project announced by the late astrophysicist Stephen Hawking and funded by Russian billionaire Yuri Milner, which aims to accelerate our quest for extraterrestrial intelligence.
Any consideration of the unusual nature of Oumuamua must include "the possibility that it is a sail of artificial origin," he writes.
ALIEN OBJECT
Oumuamua has been found to have a high density. Normally, this would indicate that it is an object made of rock and metal.
It seemed to be supported as he flew over the sun. No comet-like gas cloud formed like a tail in the solar wind.
But a spectral analysis – in which light is broken down into its components to identify the chemicals that influence its colors – indicated that it was much more icy than expected.
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But the big eyebrow was Oumuamua's speed.
After spending the sun, he really accelerated. It should, according to all accounts, have slowed down …
Unless it's a comet, releasing gas from the hottest face near the sun. This could give him the necessary boost to increase his speed.
So where was this comet-like tail?
It has not been found yet.
Harvard astronomers also point out that such "degassing" would have quickly changed the nature of Oumuamua's rotation.
This too was not observed.
With these anomalies, Bialy and Loeb suggest that there is only one viable alternative: it is a lightweight mechanical sail, designed to use starlight to propel it into space.
"The first artificial relic has been discovered in the past year, when Pan StarRS 'sky study identified the first interstellar object in the solar system," Oumuamua, "writes Professor Loeb.
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This is a concept similar to the Breakthrough concept that Starshot is currently working on.
He wants to send "stars" – tiny solar sail sensors – to Proxima B.
"We explain Oumuamua's" excess of acceleration away from the Sun, resulting in the force that sunlight exerts on its surface, "they write. "In order for this force to explain the measured excess of acceleration, the object must be extremely thin, in the order of a fraction of a millimeter in thickness but of several tens of meters. This makes the object lightweight for its surface and allows it to act like a light sail. Its origin could be natural (in the disks of interstellar or proto-planetary medium) or artificial (like probe sent for a reconnaissance mission in the internal region of the solar system). "
RETROENERGY OUMUAMUA
Harvard astronomers have attempted to calculate the likely shape, size and mass of such an interstellar sail sail.
He would have to survive the intense cold and extreme radiation of far-off space. It should also be structurally rigid enough to cope with the constraints of its rotation.
Their calculations indicate that this could be achieved with an incredibly thin metal sheet – just a fraction of a millimeter – of thickness.
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"For a thin sheet, this requires a width of 0.3-0.9 mm," says the study. "We find that, although extremely thin, such an object would survive an interstellar journey over galactic distances of about 5 kpc, resisting collisions with gases and dust grains as well as stresses due to to rotation and tidal forces. "
Professor Loeb explained that similar lighthouse sails have already been designed and built here, such as the Japanese IKAROS and his own Starshot initiative.
Why would such an alien ship be here?
Bialy and Loeb assume that it could be dirt – a jet solar sail floating in the interstellar winds. That would explain the lack of transmissions, they say.
"This opportunity forms a potential basis for a new frontier of space archeology, namely the study of remnants of past civilizations in space," Loeb recently wrote in American scientist.
"Finding evidence of space debris of artificial origin would provide an affirmative answer to the secular question" Are we alone? "This would have a dramatic impact on our culture and add a new cosmic perspective to the meaning of human activity."
Similarly, said Loeb, Oumuamua could be a space probe.
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"The alternative is to imagine that" Oumuamua was on a reconnaissance mission, "he told Universe Today. He said that the path of things was simply too convenient.
It rose to less than 0.25 AU (Astronomical Units, the distance from the Earth to the Sun) of the Sun that avoided the worst of its solar radiation. He then crossed at only 0.15 AU from the Earth.
The two astronomers admit that we know too little about Oumuamua to guess the nature. But, at the very least, to have the characteristics observed, it must be an entirely new type of material or object.
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