The Hayabusa 2 was launched by the Japanese Space Agency. It studied the asteroid for over a year after it arrived. Hayabusa 2 sent four rovers to the asteroid. In December 2020, it flew past Earth and dropped off a sample.
The scientific results from that mission might be the most interesting one, as they might not be an asteroid. It could be a remnant of a comet.
The Hayabusa 2 mission showed that an asteroid is a rubble pile. It is a conglomeration of smaller rocks instead of being one large chunk of rock. It is shaped like a spinning top. This shape was forged by the asteroid's rapid rotation.
The authors say that a catastrophic collision between larger asteroids is a widely accepted formation scenario.
Astronomers assumed that the asteroid was the case since it was discovered in 1999. One thing stood out among the evidence that didn't fit with the asteroid definition, and that was the high concentration of organic matter.
If there is a rubble pile asteroid created from the collision of two smaller asteroids, why does it have so much concentrated organic matter?
That question is at the center of a new study published in The Astronomical Journal Letters.
According to the authors, rubble-pile asteroids could be former comets, as well as the remnant of a comet. Astronomers call these objects comets.
There are comets in the far reaches of the Solar System. Unlike asteroids, which are all rock, comets are icy and contain rock and volatiles. The volatiles are mostly water ice, but comets also contain frozen carbon dioxide, ammonia, methane, and carbon monoxide. Astronomers call them dirty snowballs and comets have an unbound atmosphere. They sublimate into space when they approach the Sun because of the warmth. Dust and volatile gases can be found in the atmosphere.
Some comets have lost their volatiles to space after passing close to the Sun. What is left is rock. They are sometimes called extinct comets.
Can the characteristics of a former comet be accounted for by Ryugu?
The comet's nucleus loses mass and shrinks, which increases its speed of rotation.
The high organic matter content can be explained by the extinct comet hypothesis. The organic molecule detected include CO, CO 2, methanol, carbonyl sulphide, formaldehyde, formic acid, methane, and cyanate. The organic materials would be deposited on the rocky debris.
The local concentration may account for the high organic content inferred from albedo.
The hypothesis was tested with simulations. They calculated how long it would take for Ryugu to become a rocky remnant. The increase in speed needed to shape the asteroid into what it is today was calculated.
The study says that the asteroid was once a comet and spent the rest of its life as a rubble pile.
The study focuses on asteroids with three characteristics: spinning top-shaped, rubble-pile composition and high concentration of organics. The results show that comet-asteroid transition objects, such as Ryugu, are indistinguishable from asteroids.
Hayabusa 2 returned its samples to Earth, and another mission will soon do the same. NASA's OSIRIS-REx will return its samples to Earth in 2023 after visiting the asteroid Bennu. The samples should be analyzed to see if they are asteroids or CATs.
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