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Japan's Hayabusa2 starts descent to collect asteroid samples

This supplied computer graphic shows an image of the Japan Aerospace Exploration Agency's asteroid explorer Hayabusa 2 landing on the Ryugu asteroid. (Photo courtesy of JAXA) (Kyodo)

TOKYO (Kyodo) -- Japan's Hayabusa2 space probe started Wednesday its descent to a distant asteroid, part of a mission aimed at discovering insights into the origin of life and the evolution of the solar system, the Japan Aerospace Exploration Agency said.

The probe's first-of-a-kind objective is to collect subsurface samples of the Ryugu asteroid, which is now 250 million kilometers from Earth. It is Hayabusa2's second landing on Ryugu, having touched down in February to collect samples from the rocky surface.

The samples targeted this time are debris from an artificial crater which Hayabusa2 created in April by firing a projectile at the asteroid's surface.

The debris is believed to contain organic substances and water, with remnants of the primitive solar system. Should it succeed in getting the subsurface samples, the probe's mission will be almost complete.

Asteroids like Ryugu are often likened to a fossil, as they are thought to have preserved traces of the time when the solar system was born. But Ryugu's surface has weathered due to the impact of solar winds, making it necessary to dig deep to collect the material.

Hayabusa2 began its descent at around 11 a.m. Japan time, from its usual stationary position of 20 km above the asteroid surface, at a speed of 40 centimeters per second.

Once it reaches 5 km above the surface Wednesday night, it will slow down and descend at a speed of 10 cm per second.

It takes 14 minutes to transmit information between Earth and the space probe, raising the possibility the control room will be too late to intervene if a problem arises. Hayabusa2 will navigate on its own, before and after the landing.

Launched in December 2014 from the Tanegashima Space Center in southwestern Japan, the probe arrived at the point 20 km above the asteroid in June last year, after traveling 3.2 billion km on an elliptical orbit around the sun for more than three years.

It is due to return to Earth at the end of 2020.

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