AFTER a journey of three-and-a-half years, Japan鈥檚 Hayabusa 2 spacecraft is sidling up to its destination, a small asteroid called Ryugu. Its mission: to bring some space dust back to Earth.
The approach is tricky, says Elizabeth Tasker of the Japan Aerospace Exploration Agency. Ryugu is a relatively small asteroid, less than a kilometre across, so it is hard to pin down its exact location at any one time. 鈥淎 tiny mistake can mean you miss the target entirely,鈥� she says. 鈥淭he distances are equivalent to trying to hit a 6-centimetre target in Brazil from Japan.鈥�
Because of that, Hayabusa 2 is zigzagging towards Ryugu instead of heading straight for it. That allows the probe to repeatedly measure the asteroid鈥檚 position with respect to background stars.
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Assuming everything goes to plan, in August, Hayabusa 2 will descend to just 1 kilometre above Ryugu to measure its gravity. The spacecraft will later drop off one big lander and three smaller ones on the surface to study the asteroid鈥檚 composition, geology and temperature.
Hayabusa 2 will make numerous observations from orbit. And, after deploying the landers, it will itself touch down on Ryugu three times to collect samples in 2018 and 2019.
鈥淭he distances are equivalent to trying to hit a 6-centimetre target in Brazil from Japan鈥�
It will also collect samples by shooting a bullet at the surface and then collecting the dust thrown up afterwards.
To collect deeper samples, the spacecraft will use an even more violent procedure. It is carrying a 2.5-kilogram projectile loaded with high explosives that will blast into Ryugu at 2 kilometres per second. Hayabusa 2 will then collect fresh dust, previously unexposed to space, by descending to the resulting crater.
鈥淯sing an impactor and observing the explosion as it strikes the asteroid is going to tell us a lot 鈥� way more than we currently know 鈥� about the internal structure of these objects,鈥� says Daniella DellaGiustina at the University of Arizona. 鈥淚t鈥檚 a little bit cowboy, but it鈥檚 really cool.鈥�
The spacecraft will start heading home at the end of 2019. Ryugu鈥檚 close orbit makes sample return particularly easy: it swings from just within Earth鈥檚 orbit to just beyond Mars鈥檚 orbit .
The dust samples will be only the second lot retrieved from an asteroid. But the first Hayabusa mission, which returned in 2010, managed to grab only a few micrograms. NASA also has a sampling mission, OSIRIS-REx, which is due to arrive at asteroid Bennu in August. These efforts are the first baby steps in what could eventually become a full-blown asteroid-mining industry.
Hayabusa 2鈥檚 first detailed pictures of Ryugu (above) showed an angular rock with a ridge circling its equator 鈥� an unusual shape that may make it harder to land. There is a large boulder or cliff about 150 metres across sitting at the top of the image, as well as other apparent clusters of rocks settled on Ryugu鈥檚 surface. It is riddled with small depressions that might be craters from collisions with other space rocks.
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鈥淐omets and asteroids are the dinosaur bones of the solar system. They were here first,鈥� says Carey Lisse at Johns Hopkins University in Maryland. Asteroids splintered off larger rocks that were the building blocks of planets in the early solar system. Studying asteroids like Ryugu can tell us what those building blocks were made of, which may help us determine how certain materials 鈥� such as water, and the first ingredients for life 鈥� came to be on Earth and other planets.
鈥淭his means that we are analysing a snapshot of our own past,鈥� says Tasker. 鈥淚f we find water and organics that are similar to those on Earth, it will be evidence that space rocks like Ryugu are how we all began.鈥�
This article appeared in print under the headline 鈥淭ime to catch a space rock鈥�
