Asteroid exploration

SOME years ago I had the pleasure of visiting ISAS, the Japanese Institute of Space and Astronautical Science.

It was one of three organisations that had, only two years earlier, merged to form JAXA, the Japanese Aerospace Exploration Agency.

Now, JAXA has achieved what I regard as its greatest success to date: having two tiny craft touch down on the surface of an asteroid called Ryugu as part of the mission called Hayabusa 2.

Japan has had some fine space-related successes, although for many people around the world they tend to have been eclipsed by the spectacular results of NASA, which has obtained close-up images of so many objects in the solar system and studied them in great detail.

Interestingly, NASA was not so much in the limelight in 1986, when two Japanese craft — Sakigake and Suisei — and others from the European Space Agency and the Soviet Union flew much closer to Comet Halley than NASA’s International Cometary Explorer mission, which flew through the tail from a great distance. An impressive model of the rocket that launched Sakigake is on display at ISAS.

However, back to the Hayabusa story.

Hayabusa 2’s predecessor, Hayabusa, visited the asteroid called Itokawa in 2005. My time at ISAS was just before the craft’s arrival at its target, and there was much excitement among Japanese space scientists at the time.

Its little lander, called Minerva, failed to reach the surface, and was lost.

However, the mission succeeded in returning a small sample of surface material from Itokawa to Earth. A special capsule containing the material reached the Earth’s surface in the outback of South Australia in June 2010, and the capsule was found to contain about 1500 particles of matter confirmed to be from Itokawa.

This time around, there has been a wonderful success so far with not just one, but two landers. Called Rover-1A and 1B, they were sent down to the surface just over a week ago and carried instrumentation to analyse the surface of the asteroid and send back pictures.

The will move to different parts of the surface by “hopping” from one point to another. There are two other landers, one called MASCOT which will reach the surface on Wednesday, and the other called ROVER-2, which is expected to be deployed next year.

As with the original Hayabusa, Hayabusa 2 has the goal of returning samples of the asteroid’s material to Earth. It will use two methods of doing this, firstly by dropping down close to the surface and collecting material in a horn. Later it will collect samples from underneath the surface by sending an impactor to the surface to disturb the material, then flying through it, collecting the samples. If all goes well, a capsule containing the material will arrive back here in December 2020, once again landing in South Australia.

As I have written before, studying asteroids like this helps us to understand more about the history of our solar system. However, in particular, it enables us to match our Earth-based observations with those made (and samples returned by) such spacecraft. This will allow even observations made years or decades ago to have more meaning for us.

An interesting difficulty in studying these relatively small bodies — Ryugu is only about a kilometre in diameter — is its low gravity. In particular, an important figure is the object’s escape velocity. This is the speed at which a spacecraft, or any object for that matter, would need to move away in order to leave the object forever and not return due to its gravitational pull.

For the Earth, the escape velocity is just over 11km a second. However, for Ryugu, it is only about 38cm a second. If you were there and even gently threw a ball upward, it would never come back. This makes landing, and hopping about over the surface, quite a challenge.

I’m sure that there will be a lot more news from Hayabusa 2 and its lander as the weeks and months go by. Martin George is manager of the Launceston Planetarium (QVMAG).