In 2017, the discovery of the interstellar object ‘Oumuamua piqued the interest of astronomy enthusiasts. Being the first object ever seen from another solar system, its tube-like shape and small size left many bewildered. Moreover, it was observed to have accelerated at one point in its orbit, a phenomenon that is regular with comets, but ‘Oumuamua did not have the typical gassy tail associated with them, leading some to believe it could be an alien spacecraft.
On March 22, a new hypothesis was published in the journal Nature which provides an alternative reasoning behind the unusual trajectory of ‘Oumuamua. According to astronomers Jennifer Bergner and Darryl Seligman, the massive object, measuring half a mile in length, is a comet that underwent a chemical transformation during its journey through interstellar space. As opposed to the previous notion that water was responsible for the additional thrust, ‘Oumuamua apparently expelled hydrogen that was barely noticeable.
The lead author of the new paper and astrochemist at the University of California, Berkeley, Bergner, expresses enthusiasm about the explanation for ‘Oumuamua’s peculiar actions not requiring any unconventional physics. Kaitlin Rasmussen, author of the forthcoming book, Life in Seven Numbers: The Drake Equation Revealed, hopes that this revelation will dispel any bizarre notions of ‘Oumuamua being a foreign investigation.
Chunks of ice and debris from planet formation, comets wait at the fringes of our solar system. These wandering celestial bodies embark on elongated journeys, occasionally swooping in towards the sun. As they approach, the sun’s radiant beams melt the ice and dust of the comet, creating the distinct hazy coma and trails visible to us.
It is possible that ‘Oumuamua was initially a comet, brimming with water ice, similar to those found in other star systems. However, due to the tumultuous conditions of a developing solar system, it was propelled into the vast expanse of space. Experts Bergner and Seligman suggest that during its interstellar journey, ‘Oumuamua was pelted with powerful cosmic rays. These energetic particles caused water molecules to disintegrate, producing molecular hydrogen (H2) that became trapped within the ice’s crystalline framework.
After its encounter with the sun, ‘Oumuamua underwent a transformation where the heat altered the arrangement of its ice crystals, freeing the molecular hydrogen to act as a propulsion system, akin to a rocket booster. According to David Jewitt, an astronomer from UCLA, this theory is more feasible than the alternatives that propose carbon monoxide, which wasn’t detected, nitrogen ice, which is scarce, or even the spaceship notion.
In 2017, ‘Oumuamua briefly grazed within 15 million miles of Earth before disappearing beyond the limits of our strongest telescopes, now drifting on the periphery of Pluto. In lieu of firsthand observations, Bergner and Seligman propose examining the behavior of comets similar in size to ‘Oumuamua within our own solar system, but these diminutive comets have yet to be detected. The astronomical community anticipates that the forthcoming generation of telescopes, such as the newly launched James Webb Space Telescope by NASA, will be the first to locate these elusive objects.
In the years ahead, astronomers anticipate uncovering a plethora of interstellar entities, following the detection of the second such object, which was identified as comet 2I/Borisov, in 2019. Darryl Seligman, an astronomer from Cornell who co-wrote the study published in Nature, asserts that at any point in time, there is around one comparable object situated within the inner solar system. Upon the commencement of operations at the NEO Surveyor and Rubin Observatory, even more of these objects are expected to be uncovered.
The study of interstellar objects presents an opportunity to peer into alternate solar systems and potentially observe the fundamental components of distant planets. According to Bergner, the value of any interstellar object lies in the insight it provides into the mechanisms at work outside our own celestial home.