TOKYO -- The moon is back in the telescopes of the world's scientists as major powers -- notably China and the U.S. -- as well as some highflying companies, push their space programs to new frontiers.
In the next chapter of this great space adventure, the moon has a key role to play, both as a potential base for further exploration and as a treasure chest of key resources -- most importantly, water.
"When it comes to developing resources in space, water comes first," said Hideaki Miyamoto, a professor and expert on space resources at the University of Tokyo.
But why search for water on the moon when there is so much on Earth?
It all has to do with rocket fuel.
Currently, the main components of rocket fuel are liquid hydrogen and liquid oxygen. A rocket is propelled by the gas ejected when liquid hydrogen and liquid oxygen are mixed and burned in a combustion chamber.
Through a process of electrolysis, both hydrogen and oxygen can be produced from water, meaning water can be the basis of rocket fuel.
For space travel beyond the moon, it would be quite inefficient to bring rocket fuel from the Earth.
But that would not be necessary if water could be collected and turned into fuel on the moon. The implications for space programs would be dramatic.
And such programs are taking wing around the globe.
In 2017, U.S. President Donald Trump unveiled plans to send humans back to the moon for the first time in over four decades. China, meanwhile, is pushing ahead with its own lunar exploration program.
Private space companies such as Jeff Bezos' Blue Origin and Japanese startup ispace are developing their own moon programs.
A key part of these programs is exploring the possibility of developing the moon's resources so it can be used as a steppingstone to travel to Mars and the planets beyond.
China's progress in this area has been especially impressive. In 2013, it became the third country to land a probe on the moon after the U.S. and the former Soviet Union. It has successfully explored parts of the moon's surface using a roving vehicle.
And in May, China launched a telecommunications satellite in preparation for landing a probe on the moon's dark side. Such a satellite is needed as direct communication is impossible between the dark side and the Earth.
India also has plans to land its first probe on the moon in 2018. Japan, however, has made little progress in moon exploration since its lunar orbiting satellite, Kaguya, ended operations in 2009.
The U.S. has said it plans to carry out a manned mission to Mars in the 2030s. The private U.S. company SpaceX aims for such a mission in 2024.
At an international workshop on space law and developing the moon's resources at the University of Tokyo in March, U.S. National Space Council executive secretary Scott Pace said sending humans back to the moon would be an international undertaking involving many countries.
To carry out manned Mars exploration while keeping costs down, the U.S. appears to want to develop the moon's resources -- especially water -- through international cooperation.
By analyzing data collected by space probes, scientists have concluded there likely is a certain amount of water on the moon.
A sophisticated 2010 analysis of moon rocks brought back by the Apollo space program of the 1960s and '70s showed that the rocks did contain traces of water.
Expectations for finding water are especially high for the moon's north and south poles, where ice may be trapped in extremely low-temperature areas, such as the shadows of crater walls, where no sunlight penetrates.
In 2009, the U.S. National Aeronautics and Space Administration, or NASA, sent a probe into a crater near the moon's south pole to analyze light reflected by material thrown out in the crash. Based on the experiment, NASA said there was a strong likelihood of considerable water on the moon.
But such aerial explorations are not enough to accurately confirm how much water there is, or where it is located. For that, probes must be landed.