The first spacecraft to attempt a landing on the far side of the moon is due to blast off from a launch facility in China, a historic step in lunar exploration.
The Chinese space agency’s Chang’e 4 mission aims to drop a robotic lander and rover into the moon’s vast and unexplored South Pole-Aitken basin.
Named after the Chinese moon goddess, the Chang’e 4 spacecraft is expected to launch at about 6.30pm GMT on Friday from the Xichang satellite launch centre in Sichuan, south-west China. The basin it is bound for is more than 1,500 miles (2,400km) across and eight miles deep.
“Going to the far side of the moon is a major technological feather in the cap for China,” said Katherine Joy, a lunar scientist at the University of Manchester. “The Chinese lunar space programme is hugely ambitious.
“It’s going to a place that is really special for lunar science. The impact crater carved a huge hole in the lunar crust and possibly into the lunar mantle. It potentially unlocks rocks that we wouldn’t normally find on the surface of the moon.”
If the moon shot goes smoothly, the probe will swing into lunar orbit, descend on thrusters and then drop the final few metres to the barren surface in the first week of January. Once the dust has settled, the lander will deploy a ramp for the onboard rover to trundle down. In all, the mission will deliver more than a tonne of hardware to the moon’s surface.
Chinese officials have revealed few details about the probe’s precise landing site, but a study this May from researchers at the Planetary Science Institute at the China University of Geosciences described how Chang’e 4 would explore the Von Kármán crater found inside the enormous impact basin.
In targeting the side of the moon that constantly faces away from Earth, mission controllers must contend with the fact that they cannot communicate directly with the spacecraft. Instead, messages to and from Chang’e 4 will be relayed by the agency’s Queqiao satellite, which is in a “halo orbit” on the other side of the moon.
Chang’e 4 is the latest giant leap in China’s fast-moving and ambitious lunar programme. The first two Chang’e missions in 2007 and 2010 sent probes into orbit around the moon. They were followed by Chang’e 3, a lander and rover that touched down on the Mare Imbrium lava plain on the moon’s near side. For the third phase of the programme, the Chang’e 5 and 6 missions will attempt to collect lunar samples and return them to Earth. Chang’e 5 is due to launch in December next year.
Instruments onboard the lander and rover will allow them to study the local lunar geology, probe the moon’s interior, and analyse the solar wind – the stream of high-energy particles that come flooding out of the sun. One onboard experiment will test how well plants grow in the feeble lunar gravity.
“By landing on the far side for the first time, the Chang’e 4 lander and rover will help us understand so much more about the moon’s formation and history. But just as importantly, it gives us practice operating a mission from the far side of the moon, and relaying data back to Earth via a satellite circling the far side,” said Tamela Maciel, from the UK National Space Centre in Leicester.
The moon always shows the same face to Earth because it is close enough to become locked in position by the planet’s gravitational field. One of the enduring mysteries of the moon is why the near side has a different chemical makeup to the far side. By landing on the far side and examining its geology, scientists may get some hints as to how this came about.
The Chinese mission reflects a broader resurgence of interest in the moon by national space agencies. The US, European, Russian, Japanese and Canadian agencies have set their sights on a “lunar gateway”, a habitable station that will orbit the moon and provide a stopping-off point for astronauts working on the lunar surface.
Beyond the science of understanding how the moon came to be, scientists see other benefits in working on the surface. The moon makes an excellent observation post for the Earth and sun. And on the far side of the moon, the electromagnetic noise from terrestrial broadcasts are almost entirely blocked out, making it a prime spot from which to perform radio astronomy.
“Astronomers have long dreamed of a radio telescope array built on the far side of the moon, said Maciel. “Since the far side of the moon never faces the Earth, it’s shielded from all of our radio noise, and a radio telescope here would be like escaping from city light pollution and seeing the night sky from the top of a mountain.
“With a radio telescope on the far side of the moon, we would be able to explore the furthest and oldest objects in the universe like never before. But first we have to practice operating a mission from the far side first, and that’s what Chang’e 4 will help us do.”