Chapter 2: The Tidal Disruption Hypothesis

In a paper published in Nature Astronomy, researchers Yun Zhang from the National Astronomical Observatories of the Chinese Academy of Sciences and Douglas Lin from UC Santa Cruz present a compelling hypothesis. They suggest that ‘Oumuamua originated from fragments of a planetesimal that ventured too close to its star, where it was torn apart by tidal forces.

Zhang states, “It is indeed a mysterious object, but certain indicators, such as its coloration and lack of radio emissions, suggest that ‘Oumuamua is a natural phenomenon.” Their model elucidates ‘Oumuamua's distinctive cigar shape and other peculiar features.

Lin emphasizes, “Our goal is to create a comprehensive scenario grounded in established physical principles to connect all the intriguing clues.” They argue that interstellar objects similar to ‘Oumuamua can emerge from significant tidal fragmentation during close encounters with their parent stars, subsequently being ejected into interstellar space.

Matthew Knight, an astronomer and co-leader of the ‘Oumuamua International Space Science Institute team, notes, “[This study] effectively clarifies a variety of unusual characteristics of ‘Oumuamua through a unified model.”

Section 2.1: Unusual Characteristics of ‘Oumuamua

Not only is ‘Oumuamua's shape remarkable, but its behavior also defies expectations. It exhibited acceleration not attributable to gravitational forces, tumbled irregularly every few hours, and maintained a relatively low velocity—uncommon for an object expelled from a distant star system.

Researchers initially anticipated ‘Oumuamua would resemble a comet, yet observations revealed it lacked many typical cometary features, closely aligning it with asteroids characterized by dry, rocky surfaces. Notably absent was the coma—an icy cloud that envelops comets, formed by sublimating materials as they approach a star. Its lack of a coma suggests minimal sublimation, allowing it to traverse the solar system largely undetected.

The absence of this feature raises questions about the mechanism that expelled ‘Oumuamua from its home star system. Icy objects typically found in the Oort cloud are rich in volatiles and evolve far from their stars, making them susceptible to gravitational interactions.

Section 2.2: Computer Simulations of Object Formation

The research team employed computer simulations to explore how objects akin to ‘Oumuamua might form under tidal influences. Their findings indicate that when a smaller body approaches a larger one, the resulting gravitational forces can lead to fragmentation.

The case of Comet Shoemaker-Levy 9, which was disintegrated by Jupiter's tidal forces, serves as a relevant example. This tidal disruption could explain how ‘Oumuamua exited its original system.

The team’s structural dynamics model suggests that close encounters with stars can create elongated fragments. Their thermal models reveal that fragments melting near a star would then recondense at greater distances, forming a cohesive crust that stabilizes the elongated shape.

Furthermore, the peculiar tumbling motion of ‘Oumuamua may relate to its lack of sublimation and a cometary coma. The researchers propose that non-gravitational motions could arise from the outgassing of residual water—an element preserved until ‘Oumuamua's close passage to the Sun.

Zhang explains, “Heat diffusion during the tidal disruption process consumes a significant amount of volatiles, which clarifies ‘Oumuamua's surface colors and the absence of a visible coma, while also shedding light on the inferred dryness of interstellar objects.”