Everything We Could Learn From China's Daring Moon Landing
The South Pole-Aitken basin, on the far side of the Moon, is almost seven times deeper than the Grand Canyon, and six times as wide. On Thursday, China’s Chang’e 4 mission landed a spacecraft in it.
The first successful landing on the far side of the lunar surface represents a huge technical accomplishment for China’s young space program. With the lander unable to communicate directly with Earth for the final phases of its approach, it relied on image recognition and lasers to find a flat area to touch down on.
But what happens next, and what will we actually learn from the mission? Both the Chang’e 4 lander, and the Yutu-2 rover that it carried are packed with scientific equipment that could shed light on how our solar system was formed, and even pave the way for eventual human settlements on the Moon.
“They’ve landed in one of the largest basins on the Moon. It cuts very deeply into the surface, and we think it probably penetrates down into the Moon’s mantle,” says Matthew Genge, a lecturer in earth and planetary science at Imperial College London. “Learning about how planets separate into these distinct layers during their formation is really important, because it controls how a planet behaves for the rest of its lifetime.”
To aid in this mission, the lander is equipped with a panoramic camera, and a ground penetrating radar that can yield information about the composition of the first ten metres or so of the lunar surface.
Detailed observations of the crater could help astronomers pin down the date of one of the most important events in the history of the solar system. Between 700 million and a billion years after the universe was formed, something sent a huge number of objects streaking through the solar system in an event known as the Late Heavy Bombardment.
These space rocks smashed into the moon – the far side of which is much more cratered and scarred than the face that we see from Earth. The timing also seems to coincide with the period when life first appeared on our planet. “The late bombardment is fascinating because it may well have delivered a lot of the organics to Earth,” says Genge.
On the near side of the Moon, much of the evidence from the shape of craters and ejected material around them has been obscured by outflows of lava that oozed out after impact, leaving the dark, smooth areas that make up the “seas” of the lunar surface.
This has happened much less on the far side of the moon, which always faces away from us – scientists aren’t quite sure why, but think it might have something to do with the pull of the Earth’s gravity. As a result, craters still exist in their original form, and can be examined for clues about the history of the solar system.
However, there’s a limited amount of data that the rover and lander can actually collect on this mission, according to David Rothery, a professor of planetary geosciences at the Open University. “The Yutu-2 lander hasn’t got a large and sophisticated suite of instruments on board,” he says. “The Curiosity Rover on Mars is far better equipped.” Rothery says this mission is more about China proving and testing its capabilities ahead of further planned missions – including Chang’e 5, launching in December 2019, which will collect and return samples from the near side of the Moon.
Although the rocks can’t be precisely dated with the tools available on this mission, it will help constrain the time periods that the craters were formed. Some have argued that the Late Heavy Bombardment didn’t actually happen, and what looks like a brief barrage is actually the result of lots of craters being created on top of each other. If that’s the case, says Susanne Pfalzner of the Max Planck Institute for Radio Astronomy in Germany, then we might need to rethink our model of how the solar system was formed.
The South Pole-Aitken crater could also be vital in future efforts to establish a permanent human presence on our nearest neighbour. “This basin is one of the major reservoirs of water ice on the moon,” says Genge. “But we don’t know how much, how deeply it’s buried and we don’t know what form it’s in.” Finding resources such as water would cut the cost and difficulty of a hypothetical moon base or gateway station in lunar orbit.
One of the mission’s more surprising bits cargo is a sealed ‘biosphere’ that contains tomato and potato seeds, and silkworm eggs. This capsule will stay on the lander, where the temperature and atmosphere will be kept at Earth-like levels. This experiment will determine whether an ecosystem will develop in a sealed, low-gravity environment. This could be relevant when it comes to building habitats for humans on the surface of the Moon, although Genge says it is a bit of a PR stunt.
A lot of the science being done on this mission is actually looking outwards, rather than at the Moon itself. Ever since Apollo, the far side of the Moon has been suggested as a promising site for a radio telescope, which in theory could peer into the farthest reaches of the universe without interference and noise from Earth, says Andrew Coates, a Professor of Physics at UCL’s Mullard Space Science Laboratory.
The Queqiao relay satellite, which is in a halo orbit around the moon to bounce signals from the lander and rover back to Earth, is doing some radio telescope work, which will help assess “the electromagnetic quietness” on that side of the lunar surface.
Going to the far side of the moon also provides a unique vantage for studying the solar weather, says Coates – including solar winds from our own sun, and cosmic rays from further afield. The lander has a neutron dosimeter for measuring radiation, while the rover carries spectrometers that can be used to detect trace gases, and an atom analyser to investigate how the solar wind interacts with the lunar surface. “A far side solar wind detector might see some interactions that one based on the near side won’t see,” says Rothery.
There is, however, one more challenge for the mission to overcome if it’s going to be truly scientifically valuable, as Coates points out. In a few weeks, the Chang’e 4 rover and lander will be plunged into the lunar night, where temperatures will plunge to almost two hundred degrees below freezing. Coates’ team are working on the camera system for the Mars ExoRover, which will be launched towards the Red Planet in 2020 – it stores heat from the sun during the Martian day, and then releases it at night. But the lunar night lasts two weeks. “You lose the power from the sun that is used for charging the battery to run the heaters,” he says. “It will be interesting to see how well it survives.”
That echoes the mission as a whole, which is notable more for its technical achievements than its scientific scope. “It’s a very important step, and something no one had ever attempted before, but the science they’re doing there is not all that special,” says Rothery. “Their main purpose is to get down there and prove their capabilities so they can do something else.”
Although there is important science going on, the real legacy of the Chang’e 4 mission will be the work that it enables in future - if all goes well with the Chang’e program, China is expected to send a manned mission to the moon between 2025 and 2030. Genge says: “It’s very clear that China is thinking about the future of human exploration.”