When the interstellar object 'Oumuamua swept past our solar system in 2017, it would raise an interesting mix of questions all around the globe, scientifically speaking. Never seen before in history, the interstellar visitor was the first confirmed visitor from another star system to enter the cosmic neighborhood of the Earth. Its strange elongated shape and behavior only made it a mystery, especially when it gave an unexpected kick after crossing Earth. This sudden change in speed threw the scientists into a whirl, raising more questions and controversies over what it was in reality. What could have caused this sudden acceleration?
A Mysterious Visitor from Afar
Named after the Hawaiian word for "scout" or "messenger," 'Oumuamua didn't look like, nor behave like any typical asteroid or comet. On first impression, astronomers assumed it was a comet, but unlike known comets, it did not sport the characteristic tail made of gas and dust as it approaches the Sun. Instead, it presented as a solid, elongated object bearing an unusual reddish hue-a color that hinted at exposure to cosmic rays over vast time and distance.
At first, scientists believed it would act like every other object known to exist in our solar system. Yet 'Oumuamua's strange orbit and lack of a discernible gas or dust trail confounded scientists. And just as it was passing out of visibility, it accelerated – but how?
What Could Explain 'Oumuamua's Acceleration?
The most common provided explanation for comet-like acceleration is due to outgassing, the process whereby a comet is giving off gas that serves as a form of thruster to speed it up. However, researchers did not see any gas coming out of 'Oumuamua. The failure of this object to clearly show visible outgassing led scientists to cast an eye around for something unusual.
Some suggested that outgassing may have stopped and already ceased to levels below detection. A cold layer of frozen hydrogen or nitrogen might have sublimated, propelling the object faintly. But this was purely speculative and not backed up by concrete observational evidence on outgassing by hydrogen. This riddle then led to alternative theories; some even stated that the acceleration of the object could be due to the strange shape and surface area of the object or unknown faint influences of solar radiation.
The Light Sail Hypothesis
But one of the more fascinating hypotheses to surface from the observations of 'Oumuamua was that perhaps it was an artificial object, maybe a "light sail" designed to accelerate with radiation from stars. That theory by Avi Loeb, an astrophysicist, and others set off lively debates. A light sail is a thin, lightweight material that could be pushed by light or solar radiation, like the way wind propels a sailboat. If 'Oumuamua indeed was such a structure, then it has to be very, very thin-– possibly even an alien probe or a technologically advanced chunk from another advanced civilization.
The critics said that this was speculation but certainly not impossible. Since 'Oumuamua is a slender, elongated shape, it was definitely not unfathomable. Without additional data, this hypothesis shall remain speculative and unproven.
Exotic Ice Hypothesis
In 2020, another theory was proposed, this time that 'Oumuamua might be composed of "exotic ices"-in particular, solid hydrogen. In this scenario, if 'Oumuamua were very rich in frozen hydrogen or nitrogen, such a thing would vaporize rapidly as it moved toward the Sun and provide enough thrust to explain its acceleration. However, solid hydrogen is an exceedingly rare material that requires a very specific set of conditions to form and survive interstellar travel. Were 'Oumuamua a hydrogen iceberg, it would likely have formed in the dense core of some remote molecular cloud and travelled a vast distance into our solar system.
The exotic ice hypothesis is plausible enough, but presently impossible to verify, as 'Oumuamua is now well beyond our view. In the absence of direct evidence for the release of hydrogen or nitrogen gas, this explanation remains hypothetical.
Can the acceleration be provided by solar radiation alone?
The other theory could be that 'Oumuamua's acceleration might have been caused by solar radiation pressure. Solar radiation acts like force on objects which have a large surface area compared to mass, such as thin, flat structures. If 'Oumuamua were a piece of space debris with an incredibly low density and with large surface areas, then solar radiation could have provided enough energy to push it to a little faster moving. Still, this cannot explain the elongated shape.
Case Remains Open
The acceleration of 'Oumuamua remains unsolved, but perhaps the biggest mystery of 'Oumuamua is that scientists are left with more questions than answers. Its nature as a hydrogen iceberg, as an alien probe, or that it was some other type of interstellar comet is only guesswork. While these exotic ice and solar radiation theories suggest plausible, not easily confirmable explanations for many of the concerns, with 'Oumuamua now long gone from the reach of our telescopes, a real understanding of 'Oumuamua's origins and nature may never be arrived at.
The Legacy of 'Oumuamua and its Future Prospects
The visit of 'Oumuamua brought to humanity's science a completely new field of study and called for rapid-response telescopes aptly utilized in the detection and tracking of interstellar objects. Its passage sparked off projects like the Vera C. Rubin Observatory, which will be aiming to better monitor the night sky. If another interstellar visitor enters the solar system, scientists will be fully prepared to study it closer because they have high-tech devices and understanding from the mysterious journey of 'Oumuamua.
Perhaps 'Oumuamua will be one of those greatest
unsolved mysteries in astronomy for eternity, an electrifying preview of the
wonders and discoveries that still await us across the vast expanse of
interstellar space.
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