The Japanese spacecraft Hayabusa 2 has successfully pulled off a second touchdown on the surface of the distant asteroid Ryugu. The risky maneuver saw the probe dive down to collect material that had been exposed during the creation of an artificial crater on April 5, when the probe smashed a copper weight into the surface of the ancient Solar System body.
Simply catching up with and entering the orbit of an asteroid whipping around the Sun at 29.8 km/s (18.6 miles per second) is an incredible feat. However, this was not enough for the Japan Aerospace Exploration Agency (JAXA), which wanted to go one massive step further – to swoop down to touch the asteroid and gather samples from the primordial body to return to Earth for analysis.
The agency had previously managed to secure a sample from an asteroid during the original Hayabusa mission, and hoped to repeat their success with the more advanced Hayabusa 2 spacecraft.
These well-preserved, ancient samples could help scientists unlock some of the secrets surrounding the formation of the solar system. It may also shed light on the origin of the water that forms Earth's oceans, as well as the organic matter necessary for the emergence of life.
After the first dive, the solitary probe created a large artificial crater by accelerating a copper weight into Ryugu's surface on April 5. The impact exposed a mass of fresh material from the asteroid's interior.
With the bombing operation a success, JAXA had to consider whether it would be worth putting the probe in harm's way once more to collect a sample from the newly-exposed interior. These rendezvous are high risk, high reward propositions. Just because the spacecraft had successfully pulled off one dive did not mean that it would survive another. Furthermore, due to the distance between the mission handlers and the probe, there would be no way to correct an issue with the descent in real time, should one occur.
On one hand, if the spacecraft could successfully capture subsurface material from around the crater, then the scientific merit would be well worth the risk. Sampling from a second site would also give a better overall view regarding the composition of the asteroid than simply analyzing material taken from a single region, which may not be representative of the larger body.
On the other, the team risked smashing the probe against the surface of the asteroid, in the process losing the precious samples that the robotic explorer had already retrieved from the wandering giant.
In the end, JAXA decided that the potential benefits outweighed the risks, and the second dive was declared a go.
The team selected a touchdown point roughly 20 m (65.6 ft) to the north of the artificial crater. This area is surrounded by large boulders and rock piles that could pose a threat to Hayabusa 2. However, it was judged that if the spacecraft were to successfully touch down in the 3.5 m (11.4 ft) radius target area, that the risk would be lower than that of the first dive.
At 10:59 am JST on July 10, Hayabusa 2 began its descent to the surface from an altitude of 20 km (12.4 mi). The probe then descended to an altitude of just 30 m (98.4 ft), where it hovered for a brief period before making its final plunge to the barren surface.
Between 10:18 – 10:20 JST on July 11, the probe touched down and fired a weight into the surface of Ryugu at point blank range, kicking up material to be collected by the sampler horn. Immediately after, the probe began to rise away from the asteroid. Telemetry from Hayabusa 2 soon after revealed that the spacecraft was healthy, and that the entire maneuver had been performed as scheduled.
The high-risk mission has been declared a success by JAXA, and the daredevil probe is currently in the process of returning to its safe orbit around Ryugu.
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