The asteroid is considered to be a potentially hazardous one because it can come so close to Earth. There is no immediate risk of an impact.
The Japanese space mission Hayabusa2 rendezvoused with Ryugu to learn more about the rock, which is 900 meters wide and has two cones attached to it. A rubble pile is a collection of smaller rocks held together by gravity. It takes just 7.6 hours to spin once. It's dark, like a chunk of charcoal, and the rocks seem to have a high carbon content.
The idea is that it used to be more solid, then it was hit by a large object that was strong enough to shatter it into pieces, but not strong enough to completely destroy it. All that debris was reaccumulated by the asteroid. As it spun, the force of the wind caused pieces to fall down to the equator, creating a ridge and making the sack of rocks it is today.
That explains why it has an odd shape. The carbon content is still odd. We think meteorites come from asteroids after they break off pieces and fall to Earth. The amount of carbon in the meteorites is lower than in the Ryugu meteorite. Why?
New research by a team of scientists suggests that it isn't an asteroid per se. It is a dead comet.
There are similarities between comets and asteroids. Some asteroids are metallic and some are rocky. Most comets are ices with some rock. There isn't a real dividing line between the two. A comet is an object that shows activity when it gets close to the Sun, warming up so that the ice turns directly into a gas.
The asteroid 3200 Phaethon is known to release material when it gets within 21 million kilometers of the Sun. Comets have a lot of ice in them. They will eventually lose all that ice and become dead comets if they are on a short path around the Sun.
asteroids formed closer to the Sun, so they don't have as much ice as comets, which formed far out. There is more organic material in the outer solar system. On average, comets are more carbon-rich than asteroids.
The scientists modeled the behavior of a comet's nucleus, assuming it was a mix of ice and rock, and let it warm to a temperature of 73 degrees. The comet leaves the vacuum of space ice when it is at a low temperature. It leaves rocky bits behind. When the ice goes away, the rocks fill in the space in the matrix.
They found that a comet can lose all its ice in 50,000 years. A pile of rubble, smaller than the original comet nucleus, is rich in carbon. The nucleus spins faster as the rocks settle. An ice skater's spin will increase as they draw their arms in the ice. This accounts for the rapid spin that Ryugu has.
It is an interesting idea. We know that comets can die, and what they leave behind could be similar to Ryugu. We know of a lot of near-Earth objects, but the percentage of them that could be dead comets is unknown.
After leaving the asteroid, Hayabusa2 retrieved 5 grams of small bits that were dropped to Earth in December 2020 as it flew by our home planet. Or something. Whatever. The point is that the samples are being studied. If the lab tests show that the rocks are from an asteroid or a comet, it will tell us more about the environment near Earth.
These small bodies were formed when the solar system was young and evolved over time due to impacts and close encounters with planets. The early days of our solar system are told by learning more about them. They are time capsule.
Sometimes those objects hit us. In the future, he could. The more we know about their structure, the better. The scientific exploration and defense of our planet go hand in hand. Either works for me, but both together? Sounds like a good idea to me.
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