Ryugu Samples Reveal Asteroid Likely Originated From Solar System’s Outermost Reaches
© NASA . ISAS, JAXA
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A new analysis of samples returned from the asteroid Ryugu by a Japanese space probe may have uncovered the bizarre object’s birthplace.
By using a scanning electron microscope and secondary ion mass spectrometer to examine a sample taken from Ryugu’s surface by the Hayabusa2 probe, scientists at Hokkaido University in Japan believe they’ve found the telltale signs that Ryugu formed in the outer reaches of the solar system, rather than anywhere near Earth, where it presently orbits the Sun.
The scientists found high levels of oxygen-16, a stable isotope of oxygen that’s formed late in the life of stars, when they’ve run out of hydrogen and have begun fusing together progressively heavier elements. Objects from the outer solar system have more of this isotope than inner system objects, since solar radiation tends to split up heavier oxygen isotopes.
In addition, the scientists found that Ryugu’s chemical composition looks a lot like 81P/Wild, a comet from the tail of which NASA’s Stardust spacecraft captured particle samples in a 2004 mission. Comets, which also form at the edges of the solar system, tend to be made more of ice than of rock, as asteroids are. Carbonate minerals and amino acids also point to Ryugu forming in very low temperatures, since it has retained much of its water.
This computer graphics image provided by the Japan Aerospace Exploration Agency (JAXA) shows an asteroid and asteroid explorer Hayabusa2.
© AP Photo / JAXA handout
However, the scientists also found some crystals more typically associated with inner solar system objects, such as olivine, spinel, and perovskite, in small numbers. This, they concluded, meant that Ryugu had also been struck by inner solar system objects at some point.
The scientists’ report was published last week in Science Advances.
The capsule of dust from Ryugu that was captured by the Hayabusa2 probe arrived back on Earth just over two years ago, when the capsule touched down in Australia. The spacecraft observed Ryugu and performed a number of tests on it, including landing on its surface twice and firing a small projectile into it.
The bizarre object, which orbits close enough to Earth to be of concern, is some 3,000 feet across and has a very low visibility. While it is considered an asteroid, Ryugu is actually a rubble pile held together by its own gravity, and mostly hollow in the center.
