In the end, asteroid Ryugu might actually be a comet. Credit: ESA

Massive Space Rock Visited by Spacecraft Turns Out to be Extinct Ancient Comet from the Early Solar System

It turned out that the parent body of Ryugu in the distant past was a comet that exhausted its volatile reserves in ten thousand years.

Asteroid Ryugu: Research, Properties, Theories

The research of the near-Earth asteroid (162173) Ryugu was carried out by the Hayabusa-2 interplanetary station, which also received and delivered to Earth two samples of its soil and landed three descent modules on the asteroid.

The properties of Ryugu determined by the mission, such as its top-shaped shape, rapid rotation, high organic content, and high porosity, as well as the presence of large boulders on its surface, led to a widely accepted hypothesis in scientific circles.

Close-up image of the rocks and soil on asteroid Ryugu. Credit: MASCOT/DLR/JAXA
Close-up image of the rocks and soil on asteroid Ryugu. Credit: MASCOT/DLR/JAXA

According to the theory, this body, related to the “rubble pile” type, could be formed due to a powerful collision of two large asteroids and the subsequent slow process of accumulation of fragments under the influence of gravity into a single body. However, the reaccumulation scenario cannot fully explain the abundance of organic matter.

An alternative scenario for the formation of Ryugu is that we have a degenerate comet that has exhausted its volatile reserves. The sublimation of ice generates a strong spin-up of the comet’s nucleus, due to which it can acquire the shape of a top, and organic substances formed in the interstellar medium could be included in the ice composition of the comet’s nucleus during its formation.

Is asteroid Ryugu the remnant of a comet?

A group of planetary scientists led by Hitoshi Miura of Nagoya University set out to test the Ryugu comet origin scenario through numerical simulations.

The scientists looked at the comet’s homogeneous, spherically symmetrical, highly porous nucleus, composed of micron-sized water ice particles and centimeter-sized stone fragments.

As water ice sublimates from the outer layer of the nucleus, the remaining rock debris accumulates on its surface to form a dusty mantle and the comet’s nucleus contracts.

A model for the transformation of a comet's nucleus into a porous asteroid due to the sublimation of water ice. Credit: Hitoshi Miura et al. / The Astrophysical Journal Letters, 2022
A model for the transformation of a comet’s nucleus into a porous asteroid due to the sublimation of water ice. Credit: Hitoshi Miura et al. / The Astrophysical Journal Letters, 2022

Scientists presented their scenario of the origin and evolution of Ryugu. The cometary nucleus, which was the parent body of the asteroid, formed outside the orbit of Jupiter and contained water ice, and silicate dust in its composition.

Subsequently, it fell into the main asteroid belt due to interaction with the terrestrial planets, after which it moved to the inner asteroid belt due to the drift caused by the Yarkovsky effect.

Due to heating from the Sun, the comet’s nucleus turned into a “heap of rubble” and was active during the first 10 thousand years of its existence.

This scenario is consistent with the dynamic evolution of modern comets in the solar system. In addition, it is possible that this theory is applicable to the asteroid Bennu.

It is expected that a comprehensive analysis of the collected Ryugu and Bennu samples in laboratories will prove or disprove the connection between porous asteroids and comets.


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Sources:

Miura, H., Nakamura, E., & Kunihiro, T. (2022, January 31). The Asteroid 162173 Ryugu: a Cometary Origin. The Astrophysical Journal Letters.
Phys.org. (2022, March 22). Could the asteroid Ryugu be a remnant of an extinct comet?
ScienceDaily. (2022, March 22). Could the asteroid Ryugu be a remnant of an extinct comet? scientists now answer.
Tonkin, S. (2022, March 22). Asteroid Ryugu could be a remnant of an extinct comet. Daily Mail Online.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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