China probes far side of moon
The Chang’e-4 lunar lander should touch down next month
CHINA is aiming to go where no one has gone before: the far side of the moon. A rocket carrying the Chang’e-4 lunar lander blasted off last Saturday from Xichang Satellite Launch Centre in southern China.
Exactly when it will set down at its destination has not yet been announced – possibly early next month – but Chang’e-4 will provide the first close-up look at a part of the moon that is eternally out of view from Earth.
What is Chang’e-4?
It includes two main parts: the lander weighing about 1 000kg and a 136kg rover. By comparison, Nasa’s Opportunity rover on Mars weighs about 180kg pounds, and the Curiosity rover there is much bigger, at 900kg.
The spacecraft is largely a clone of Chang’e-3, which landed on the moon in 2013. Indeed, Chang’e-4 was built as the backup in case the first attempt failed. With the success – the first soft landing of any spacecraft on the moon since 1976 – the Chinese outfitted Chang’e-4 with a different set of instruments and decided to send it to a different location.
Where is Chang’e-4 going? The rover will land in the180kmwide Von Kármán crater. It is on the far side of the moon, which is always facing away from Earth. (The moon is what planetary scientists call “tidally locked” to the rotation of the Earth. That is, its period of rotation – its day – is the same as the time it takes to make one orbit around Earth.)
The crater is within an area known as the South Pole-aitken basin, a gigantic, 2 500km-wide crater at the bottom of the moon, which has a mineralogy distinct from other locations. That may reflect materials from the inside of the moon that were brought up by the impact that created the basin.
The far side is also considerably more mountainous than the near side for reasons not yet understood.
What will Chang’e-4 study?
Instruments on the rover and the lander include cameras, ground-penetrating radar and spectrometers to help identify the composition of rocks and dirt in the area. And China’s space agency has collaborated with other countries. One instrument was developed at Kiel University in Germany; another was provided by the Swedish Institute of Space Physics.
The instruments will probe the structure of the rocks beneath the spacecraft and study the effects of the solar wind striking the lunar surface.
Chang’e-4 will also test the ability of making radio astronomy observations from the far side of the moon, without the effects of noise and interference from Earth.
According to the Xinhua news agency, Chang’e-4 is also carrying an intriguing biology experiment to see if plant seeds will germinate and silkworm eggs will hatch in the moon’s low gravity.
How will the spacecraft communicate with Earth?
Because the moon blocks radio signals from our planet, the Chinese launched a satellite, Queqiao, in May. It’s circling high over the far side of the moon and will relay messages between Earth and the Chang’e-4 lander.
China’s space agency has not announced a landing date, though some expect that will be the first week of next month, when the sun will be shining over the far side of the moon, an important consideration because Chang’e-4 is solar-powered.
Zhang Xiaoping, an associate professor from the Space Science Institute/of Macau University of Science and Technology, said that the spacecraft would arrive in three to five days and then orbit the moon for several days while preparing for the landing.
And if you thought the far side of the moon was dark: it’s not dark all of the time.