As NASA prepares to return to the Moon by 2024 as part of its Artemis program, the agency is focusing its efforts on exploring the Moon’s polar regions. These are areas of the Moon which seem to have a lot of water mixed in with the regolith.
Some of these craters are permanently in shadow, and might still have large quantities of water, that’s accessible to human and robotic explorers. This is a critical resource, and the Moon might be just the place to help humanity as it pushes out to explore the rest of the Solar System.
But it might also be an illusion. We really won’t know until we look up close.
Before I talk about the south pole, let’s take a look at the landing sites chosen for the Apollo missions over 50 years ago.
In 1968, NASA announced the five landing sites for the Apollo missions. All of them were in roughly the same latitude across the lunar surface – a strip that extended just a couple of degrees above and below the Moon’s equator.
Their criteria? Regions 5 to 8 km across which were smooth, without dangerous mountains or craters, or steep slopes. All of the landing sites had to be within the region of a free-return trajectory back to Earth, and using the least amount of propellant possible. They wanted good illumination from the Sun during the entire mission, on the Moon’s near side.
The point here, is that they were looking for landing places that were safe and accessible. The fact that the astronauts did science, set up experiments on the surface of the Moon and brought hundreds of kilograms of lunar rocks and dust back to Earth was a wonderful bonus.
When Artemis goes to the Moon, it’s going to be more challenging, since they’re headed to the south pole. Here’s why.
In the inner Solar System, water is going to be one of the most valuable resources explorers can get their hands on. That’s because you can use it for so much. You can drink it, obviously. In fact, you’re made of 60% water. You can use water to grow plants for food.
You can separate water into hydrogen and oxygen and then use the oxygen to breathe. Combine them back together and you’ve got rocket fuel, exactly what the space shuttle used in its main tank. You can even use water itself as a propellant, with a space-based steam rocket.
Water is a fantastic shield against radiation. The surface of the Moon is exposed to charged particles from the solar wind as well as galactic cosmic radiation, but hide under a meter of water ice and it’s as safe as being on the surface of Earth.
The problem is that the Sun is constantly blasting radiation into space. Any water ice closer than the midpoint of the asteroid belt is sublimated away into space. This is known as the Solar System’s frost line. The Belters and Jovians have water to spare, but here in the inner Solar System, it’ll be a rare resource, the key to everything.
And water weighs a lot. Here in Canada, we use about 300 litres of water per person, per day. If you were willing to pay SpaceX $2,500/kilogram to launch it into space, you’d be looking at $1.75 million dollars for your daily water use.
But there are a few regions which might have protected water for billions of years: the permanently shadowed craters at the Moon’s south poles.
Almost every part of the Moon is constantly bathed in sunlight, or cloaked in darkness. During the lunar day, temperatures reach 120-degrees C (or 253 Fahrenheit), and then during the lunar night, temperatures drop down to -232 C (or -387 Fahrenheit). In other words, during the daytime, it’s definitely hot enough to sublimate away that ice.
But at the Moon’s south pole, sunlight strikes at a low angle. If you were standing on the Moon’s south pole, you’d see the Sun down on the horizon, casting long shadows across the lunar surface.
And there would be craters all around you where that sunlight never reaches the bottom, regions where there could be permanent ice deposits that have been there for billions of years.
In fact, back in 1998, NASA’s Lunar Prospector mission identified that there is significantly more hydrogen at the Moon’s south pole. More hydrogen means more water, clear evidence that these water deposits are there.
More evidence was gathered by NASA’s Lunar Reconnaissance Orbiter, which has been orbiting the Moon for years. It has spotted evidence of water on the Moon many times, most recently, it was able to map tiny amounts of water bound into the lunar regolith, more common at higher latitudes, and shifting around as the surface temperature heats up.
In 2009, NASA crashed the Lunar Crater Observation and Sensing Satellite, or LCROSS, into the Moon to search for water. The spacecraft went to the Moon with the Lunar Reconnaissance Orbiter and then detached on its way to the Moon.
On October 9, 2009, the mission’s upper stage Centaur engine crashed into Cabeus crater, about 100 km from the Moon’s south pole, blasting lunar material up into space. And then the Shepherding Spacecraft followed a few minutes later, sampling material from the first impact, and creating its own crater.
LCROSS showed that there’s hydrogen gas, ammonia and methane, as well as metals like sodium, mercury and silver.
The Moon’s south poles have vast resources for future explorers to use.
Or maybe not. According to new research from NASA, these deposits might actually be recent. Even though they’re permanently shadowed, there are still solar wind particles and micrometeorites striking the surface, which should be eroding the water ice.
Nearby micrometeorites kick up dust that can travel 30 km away from the impact site in the thin lunar gravity. These particles are heated by the Sun and then land in the ice and warm a tiny little bit, sublimating it away.
It could be that comet impacts have been constantly replenishing the water on the surface of the Moon, which means these deposits are just a few thousand years old.
How can we know if there’s enough water ice for astronauts to use?
The European Space Agency was planning to send a mission to the Moon’s south pole called Lunar Lander. It was supposed to have launched in later 2018, targeting the Moon’s south pole. Unfortunately, its funding dried up, and the mission was cancelled.
China’s Chang’e-4 Lander and Yutu-2 rover are at the Moon’s south pole right now, crawling around, exploring the region, and sampling the lunar regolith. They’ve been there since January 3, 2019, and can only operate during the lunar day, when there’s sunlight to keep their instruments working.
NASA’s Lunar Reconnaissance Orbiter has even photographed them as it orbits overhead.
I’m planning to do a whole video about India’s Chandrayaan-2, which just launched successfully on its way to the Moon. Over the next two months, the spacecraft will raise its orbit from Earth and transfer into a lunar orbit.
Then, it will attempt to make a soft landing on September 7, 2019, landing on a high plain between two craters, Manzinus C and Simpelius N at the Moon’s south pole.
The Vikram lander will deploy Pragyan, a six-wheeled robotic rover, to explore for as long as they can before they enter the lunar night, which they can’t survive.
Like I said, I’ll do a more in-depth video on this amazing mission in a couple of months, once it successfully lands.
In 2020, South Korea will be launching their first mission to the Moon, called the Korea Pathfinder Lunar Orbiter. This 550 kg spacecraft will be launched on a Falcon 9 rocket, and explore the Moon for at least a year. It will have several instruments on board to study the Moon: a terrain imager to map out landing sites and interesting terrain, a polarmetric camera to take photos of the lunar surface in various wavelengths, and a magnetometer, to map out the Moon’s magnetic field, especially its mysterious lunar swirls.
One instrument built by NASA is called ShadowCam. This is a camera similar to that carried by the Lunar Reconnaissance Orbiter, but with 800 times more sensitivity. It will study these permanently shadowed craters at the Moon’s poles.
The best strategy, of course, is to send robots or humans to dig into the regolith and figure out what’s there.
On July 1st, 2019, NASA announced that they had selected 12 new science and technology payloads that would be sent to the Moon, to help study its surface and help prepare for the arrival of astronauts as part of the Artemis program. All of these missions are expected to fly in the next couple of years as part of NASA’s Commercial Lunar Payload Services program. Some are just components, like new camera systems, and experiments. But a few are really interesting as it relates to exploration of the south pole.
The first is MoonRanger, a small rover which be built by Astrobiotic and Carnegie Mellon University. This 13-kilogram rover will test out autonomous exploration on the Moon, creating detailed 3D maps of the lunar surface around the south pole, including these shadowed craters. The rover will be able to travel and navigate on its own, without communicating with Earth.
PlanetVac is a citizen-funded technology being developed by the Planetary Society and Honeybee Robotics that will suck up lunar regolith from the surface of the Moon. Then it could be tested on site, or transferred back to Earth for scientists to study back home. This will allow NASA to sample a wide range of spots on the Moon to find out which ones have the highest concentration of water and other useful chemicals.
Next Generation Lunar Retroreflectors will provide an upgrade to the retroreflectors that were placed on the lunar surface back during the Apollo era, which scientists still use to measure how fast the Moon is drifting away from us. These new reflectors could tell us more about the Moon’s interior and answer questions about basic physics.
LISTER is a heat probe that’ll be drilled 2-3 meters into the lunar regolith to help measure temperature differences at different depths and tell us how geologically active the Moon is. Similar to the InSight mission at Mars.
The Sample Acquisition, Morphology Filtering and Probing of Lunar Regolith will use a spare robotic arm from the Mars Exploration Rover missions (you know, Spirit and Opportunity), to gather samples from the Moon.
Over the next decade, the Moon is going to get much busier. There are multiple missions planned by Russia, a collaboration between India and Japan, more missions from China, and a bunch of private landers. Of course, I’ll keep you updated as any of these are constructed.
Right now, we have a tantalizing hint that there are vast stores of water ice at the Moon’s south pole. Over the next few years, robots and then people will study this region very carefully, building up the evidence. If we’re lucky, the Moon will have everything we need to take a big step off Earth, and out into the Solar System.
Source: Universe Today, by Fraser Cain.