Asteroid No.1 with a bullet

OSATURDAY, MARCH 16, 2019 themercury.com.au SUBSCRIPTIONS 1300 696 397 VER my rather long time of being passionate about all things to do with astronomy and space exploration, there have been many wonderful achievements, but there are some that stand out as being especially impressive.

Of course, landing people on the moon would have to be included. Others, such as a soft landing on Saturn’s moon Titan, the more recent fly-bys of Pluto and the object known as Ultima Thule, and the amazing long “lifetime’’ of the Opportunity Mars rover are also in the list.

Adding to it now is the collection of a sample from the surface of the asteroid called Ryugu, achieved by Japan’s Hayabusa 2 spacecraft.

The mission has had great successes so far, arriving at the asteroid several months ago and deploying three landers, which returned the first-ever photographs from the surface of an asteroid.

On February 22 (Tasmanian time), the main Hayabusa 2 craft landed briefly on the surface of the one-kilometre-diameter asteroid and fired a shot into the surface, using a bullet made of tantalum. This was to dislodge material that could then be collected by the spacecraft, and it seems that it worked very well.

Earlier, however, mission

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planners had quite a surprise when it was found that Ryugu’s surface is covered with centimetre-sized “gravel’’ rather than a dusty coating, and there was some concern that the bullet may not dislodge material in the way they had hoped. They therefore had to perform an experiment on Earth, firing the same kind of bullet into similar material to that on the asteroid. Fortunately, they observed that it did indeed do the job as intended.

JAXA, the Japanese Space Agency, which is responsible for the mission, recently posted a wonderful image sequence showing the effect of the bullet on the surface of Ryugu.

One of my favourite images from the mission so far, however, is a picture that Hayabusa 2 took as it “lifted off’’ again from the asteroid, showing the highly

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recognisable shadow of the spacecraft that was cast onto the surface.

A colleague in Japan has told me that the mission has schoolchildren very excited, cheering at the news. JAXA has also created a rather cute cartoon character, representing the intrepid spacecraft.

So, why go to all of this trouble?

Asteroids are fascinating objects that offer insights into the history of the solar system. Being able to obtain samples of their material and study them in the laboratory can reveal even more information about their composition than obtaining information radioed back from a spacecraft, despite that being very important in itself.

Another important reason for studying asteroids is that from time to time, they do collide with the Earth. The typical period between kilometre-sized impacts is about half a million years. That may seem very infrequent, but the more that is known about them, the more likely we are to be able to plan the best way of preventing a collision.

Another much-discussed advantage of studying asteroids is the possibility of asteroid mining and making use of their raw materials.

Of course, it is very difficult and expensive to bring this material back to Earth, so the optimal use of it would be for construction projects in space. A similar type of situation would arise for permanently crewed bases on the surface of the moon: using water from the moon itself, rather than transporting it from Earth, would be far more sensible.

There are two more sample-gathering ventures planned. One of them is to deliver a copper impactor to the surface of the asteroid in order to produce a new crater. Gathering material from the bottom of this crater would be important in understanding the interior of the asteroid.

The problem is that it is now known that a sample from the surface has already been gathered, a valuable cargo indeed. Should the spacecraft be put at risk with such a manoeuvre? This must surely be something very much on the minds of all at JAXA.

Assuming all goes well, a container of the precious material will be brought back to Earth and come down over Australia in December next year. Martin George is manager of the Launceston Planetarium (QVMAG).