Exploring the Possibility of Ryugu as an Extinct Comet
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Chapter 1: Understanding Rubble Pile Asteroids
Recent studies have piqued scientific interest due to the significant levels of organic materials found on the asteroid Ryugu. Researchers are now considering the intriguing hypothesis that rubble pile asteroids like Ryugu might actually be extinct comets.
The image above shows the complete disc of asteroid 162173 Ryugu as observed by the Hayabusa2 spacecraft on June 26, 2018, taken from a distance of 20 kilometers (12 miles). This photograph was obtained using the spacecraft’s Optical Navigation Camera — Telescopic (ONC-T). CREDIT: JAXA, ONC team: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.
Rubble pile asteroids have a complex nature, which has led to both fascination and frustration in scientific communities, particularly at CosmoQuest, where we focus on cataloging the numerous rocks on Bennu. Our analysis played a critical role in helping the [OSIRIS-REx] team determine the optimal site for sample collection from Bennu. Although it was intended to be a gentle touch, later assessments revealed it was more akin to a forceful impact. Nonetheless, that precious sample is en route back to Earth.
In parallel, Japan's Hayabusa2 mission successfully collected a sample from the asteroid Ryugu in 2020, generating excitement within the scientific community. This sample has since been distributed for analysis, yielding several preliminary findings. Notably, data collected remotely prior to the sample retrieval revealed that Ryugu possesses an unusually high concentration of organic matter.
A quick clarification: 'organic content' refers to materials rich in carbon, not necessarily indicative of extraterrestrial life—at least, we are skeptical on that front.
Section 1.1: Composition and Formation
The intriguing composition of Ryugu raises questions. Rubble pile asteroids, such as Ryugu and Bennu, can be likened to spinning tops, made up of loosely aggregated rocks. Their structure made sampling a relatively straightforward task due to their loose composition. However, the significant organic content, yet to be confirmed through sample analysis, challenges previous theories regarding their formation.
Subsection 1.1.1: New Insights from Recent Research
A recent study published in The Astrophysical Journal Letters proposes that rubble pile asteroids might actually represent extinct comets. The research led by Hitoshi Miura involved simulations that calculated the duration it takes for a comet's icy components to sublimate, subsequently enhancing its rotation speed—similar to what is observed with Ryugu. The findings imply that Ryugu may have been an active comet for tens of thousands of years before transitioning to its current position in the inner asteroid belt.
As it moved closer to the Sun, higher temperatures caused any remaining volatiles to sublimate, leaving behind a loosely bound spinning mass of rocks.
Dr. Miura elaborates that the process of ice sublimation results in the comet's nucleus losing mass, leading to an increase in its rotational speed. This rapid rotation could explain the spinning-top shape observed in these bodies. Furthermore, the icy elements found in comets are believed to contain organic matter formed in the interstellar medium, which would eventually be deposited onto the rocky remnants as the ice sublimates.
Section 1.2: Implications of the Findings
In essence, rubble pile asteroids like Ryugu could be categorized as comet-asteroid transition objects (CATs). This classification suggests that the small bodies in our solar system exist on a continuum rather than being strictly defined as one or the other. Dr. Miura points out that due to the similarities shared by comets and asteroids, CATs could offer valuable insights into the solar system’s evolution.
We now await further results from the ongoing analysis of the physical samples to confirm or refute this hypothesis. Stay tuned for updates as new findings emerge.
Chapter 2: Asteroid Ryugu in the Spotlight
The first video titled "Asteroid Ryugu May Actually Be an Extinct Comet, Here's What This Means" delves into the implications of Ryugu's organic material and its potential cometary origins.
The second video titled "Ryugu asteroid sample arrives at the Museum | Natural History Museum" showcases the arrival of the Ryugu samples and their significance in planetary science.
More Information
- Nagoya City University press release
- “The Asteroid 162173 Ryugu: a Cometary Origin,” Hitoshi Miura, Eizo Nakamura, and Tak Kunihiro, 2022 January 31, The Astrophysical Journal Letters
This article was produced for the Daily Space podcast/YouTube series. For more updates from Dr. Pamela Gay and Erik Madaus, visit DailySpace.org.