Asteroid Ryugu Definitely Comes From The Outer Solar System

Asteroid Ryugu Definitely Comes From The Outer Solar System

Scientists around the world are excited about the findings of the 5.4 gram rock sample from the asteroid known as “Ryugu”. This is absolutely no ordinary dirt.

The dirt was brought back from the asteroid on the Hayabusa2 spacecraft and landed in the sands of South Australia nearly two years ago. It has given researchers unprecedented insight into the history of our solar system.

The space dust sample is the culmination of a six-year, 5 billion kilometer journey and has now been analyzed by an international team of more than 200 researchers. They used ultra-bright X-ray beams, finding tiny “inclusions” of water containing carbon dioxide inside the rock.

Researchers say this is further evidence that Ryugu’s parent body formed in the outer solar system, just 2 million years after the solar system began to form.

“There is sufficient evidence that Ryugu began in the outer solar system,” says Esen Alp, a physicist at Argonne National Laboratory.

“Asteroids found in the far reaches of the solar system would have different characteristics than those found closer to the Sun.”

“For planetary scientists, this is first-degree information directly from the solar system, and therefore invaluable.”

At its closest orbit, Ryugu is only a quarter of Earth’s distance from the Moon, which could suggest the asteroid formed in the inner solar system.

However, this research, and a study from earlier this year that supports this finding, seems to suggest otherwise.

The team explains that the grains that make up the asteroid are much finer than you would expect if it had formed at the higher temperatures found closer to the sun.


Read more: Ryugu asteroid samples delivered directly to South Australia contain extremely rare space dirt


Earlier this year, researchers determined that the structure was incredibly similar to a rare type of outer solar system asteroid called CI chondrites.

“We have received other samples from other planetary bodies before, but never the most primitive material from the solar system,” Curtin University astrogeologist Professor Gretchen Benedix explained at the time.

“On earth we have 70,000 meteorites (as far as we know) – of these only nine are classified as CI.”

These asteroids are thought to form in the outer asteroid belt, more than four times the distance from Earth. This is because ‘4 AU’ is beyond the ‘snow line’ where the temperature is so low that all the water will automatically freeze, but it’s also cold enough for volatile components like CO2 to condense in these grains of ice.

These asteroids are also more abundant in evidence of organic molecules and water in these small inclusions. Think of inclusions as the holes inside a sponge, rather than actual “drops” of water.

“Take the hydrogen and helium out of the sun and you get a CI chondrite,” said Phil Bland, director of Curtin University’s Space Science and Technology Center.

“Because most of the mass in the solar system is in the sun, if you want to choose a composition for average solar system elements, it’s CI chondrite. That’s what it was all about.

Using the finely tuned spectroscopy capabilities of a machine called the Advanced Photon Source, the new team was able to measure the amount of oxidation the samples had undergone. This was particularly interesting since the fragments themselves had never been exposed to oxygen – they were delivered in vacuum-sealed containers, undamaged after their journey through space.

The team also discovered something that sets the Ryugu fragments apart from other CI chondrites – a large amount of an iron sulfide called pyrrhotite. This result also helps scientists limit the temperature and location of Ryugu’s parent asteroid at the time of its formation.

“Our results and those of other teams show that these asteroid samples are different from meteorites, in particular because the meteorites have passed through the entry of the fiery atmosphere, weathering and in particular oxidation on Earth”, said Argonne National Laboratory physicist Michael Hu.

“It’s exciting because it’s a completely different type of sample from way out in the solar system.”

The research has been published in Science.



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