Next stop Earth: Hayabusa2 bids farewell to asteroid Ryugu

Japanese craft’s mission is the first to gather material from under an an asteroid’s surface.

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Navigation Image from the Ryugu asteroid departure.

The asteroid Ryugu, pictured by the departing Hayabusa2 spacecraft.Credit: JAXA, Chiba Institute of Technology & collaborators

The Hayabusa2 spacecraft is heading home after performing a series of risky and unprecedented manoeuvres on its six-year mission to asteroid Ryugu.

The Japan Aerospace Exploration Agency’s (JAXA’s) probe gently fired its thrusters at 10:05 a.m. Japan Standard Time on 13 November, moving away from the asteroid at a speed of less than 10 centimetres per second. From 10 December, the probe will start to use its ion engines to propel its journey back to Earth, where it is due to arrive at the end of 2020. A re-entry capsule will deliver its samples to the surface.

Hayabusa2 launched in late 2014, and arrived at Ryugu in June 2018. It is the first mission to release landers onto the surface of an asteroid; the first to collect a sample from a 'dark' asteroid’s surface; and, after bombarding the surface to create a crater, the first to collect a sample of an asteroid’s subsurface material.

Just one kilometre wide and shaped like a spinning top, Ryugu is an unusually dark body, probably the result of having a high concentration of carbon.

Hayabusa2 found the asteroid to have a surprisingly low density, suggesting that it is an assembly of small rocks loosely held together by gravity, and with a surface strewn by more boulders per unit surface area than any asteroid explored so far. Initial studies based on the probe’s data suggest that Ryugu formed from the debris of an impact between two larger Solar System bodies.

doi: 10.1038/d41586-019-03514-3

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