As our closest neighbor in space, the moon has been the subject of popular legends, songs and poems since ancient times. And it also attracts scientists deeply.

    But even after centuries of research, many questions remain to be answered about the Earth's only satellite.

    Perhaps the Chang'e-4 lunar probe will be able to find out more of its secrets. On Dec 8, 2018 the probe lifted off from Xichang Satellite Launch Center in Sichuan province. It is the first probe to the far side of moon in human history.

    The Earth's gravity slows the moon's rotation, matching it to the speed of its orbit. Thus, the far side of the moon is always dark and has never been seen.

    It's this sense of the unknown that makes the far side of the moon such an interesting place for scientific and space exploration. Long exposed to solar winds, the far side may have the special soil and minerals in its upper mantle.

    For this reason, Chang'e-4 will study the effect of solar winds on the lunar surface and any minerals found beneath the probe. Chang'e-4 is also carrying flower seeds and potato and silkworm eggs to see whether life is possible on the moon. If it is, then the moon will become a more likely destination for space travel in the future.

    However, because of communication problems, exploring the dark side will not be easy. As the far side is blocked off from us, radio noise coming off Earth is also blocked. This is why China launched the relay satellite Queqiao in May, 2018, so that communication between Earth and the probe could go ahead.

    Power supply is also a challenge to the mission. Chang'e-4 gets energy from the sun through its solar panels. However, a lunar day has the length of 28 Earth days. It means that the probe will need to orbit the moon for over 20 days to be in a position to be able to land in moon daylight and so use its solar panels.

    According to Xinhua, theChang'e-4 lunarprobe landed on the far side of the moon on Jan 3, 2019 successfully, and everything goes well.

    The New York Times described the journey as "groundbreaking", and wrote that it would "give clues to the history and development of the moon".