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Smaller than planets, but every bit as fascinating, there are over a million asteroids orbiting the sun and come in all shapes and sizes. Vesta, the largest, is around 530 kilometres in diameter, but others are just a few metres across. Somewhere in the middle is the asteroid named ‘Ryugu’.
Measuring around 900 kilometres in diameter and orbiting the sun in a position between Earth and Mars, Ryugu is of special interest, as it is classified as ‘carbonaceous’ (sometimes called ‘c-type’), which means that it is formed of carbon and other organic compounds and contains large quantities of water – putting it among the oldest types of heavenly bodies. Previous research suggests that c-type asteroids are relics of the early solar system and may hold clues about its birth and the origin of the life that inhabits it. So, it is Ryugu’s advanced age that makes it so important, and why The Japan Aerospace Exploration Agency (JAXA) sent the asteroid exploration spacecraft Hayabusa2 to retrieve samples of materials such as sand, rocks and gases from its surface.
Visiting the ‘Dragon Palace’
The name ‘Ryugu’ was given to the asteroid in 2015 by the Minor Planet Centre (the official body for observing and reporting on minor planets, including asteroids) and has a delightful origin. In a Japanese folktale, Ryūgū-jō (or ‘Dragon Palace’) is a magical underwater place, visited by a fisherman called Urashima Tarō, who travels there on the back of a turtle and returns with a mysterious box. However, at the time of Ryugu’s formal naming, the spacecraft Hayabusa2 (which means ‘Peregrine Falcon 2’ In Japanese) had already been in space for a year and the two eventually ‘met’ in 2018. Hayabusa2 surveyed the asteroid over a period of a year and a half, during which time it ejected two rovers and an observation lander onto the surface of the asteroid to collect data, as well as an ‘impactor’ to create an artificial crater on Ryugu, from which samples could be extracted.
To return the samples to JAXA for analysis, Hayabusa2 dropped a capsule from about 200 kilometres above Earth’s surface, which hit the ground in Woomera, in the Australian Outback on 6th December 2020. As well as delivering physical specimens, this historical moment was both the first time that gas samples had been retrieved from outer space and only the second largest sample ever recovered from an asteroid. The contents of the capsule subsequently went through four months of intense analysis. Part of this process was undertaken using a quadrupole mass spectrometer (QMS). Manufactured by Canon ANELVA Corporation, who are experts in the field of advanced vacuum technologies, it was installed on the testing device. Utilised by many government agencies and research facilities, a QMS is an instrument that can help identify and examine low-mass gases contained in gas test samples.
JAXA issued a press release stating that on the 14th of March “a black sand granular sample believed to be derived from the asteroid Ryugu was confirmed inside the sample container.” Since then, it reports that the commencement of spectroscopy and that initial observations of the sample have shown “characteristics of the hydrous and carbonate minerals that indicate the presence of water in the Ryugu parent body.” Observations will continue, but JAXA also plans to take the sample capsule ‘on tour’ in a travelling exhibition around Japan from August 2021, where viewers can see first-hand these miraculous remnants from the beginnings of our universe.