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Planetary scientists can usually tell a great deal about a world’s history by looking at its surface. This is particularly true of the Moon. Of course, we’re all familiar with the so-called “near side”—it’s what we see from here on Earth. It has large plains called “maria” (Latin for “oceans”). These are wide, dark-colored old lava flows that flooded the surface between 1 and 3 billion years ago. There are also many craters, which were “excavated” by objects plowing into the surface. In fact, the entire Moon is pockmarked with craters from that period.

The lunar Near side, as seen by NASA's Lunar Reconnaissance Orbiter in 2010. The large dark areas are the Mare, created by extensive volcanic flows. Impact craters surround the maria and imply a lot of bombardment early in the Moon's history. Courtesy NASA. — The lunar Near side, as seen by NASA’s Lunar Reconnaissance Orbiter in 2010. The large dark areas are called “maria”, created by extensive volcanic flows. Impact craters surround the mare and imply a lot of bombardment early in the Moon’s history. Courtesy NASA.

The lunar far side (the one that always faces away from us), looks much different. There are no maria, but we can see a LOT more craters over there. It’s almost like each side of the Moon has its own history. The Moon is tidally locked to Earth (meaning the far side always faces outward from Earth). So, we had no idea how different they were until the Space Age allowed orbiters to study the entire lunar surface.

The lunar Far side shows much more impact cratering and very few basins. The darkened area in the lower middle is the Aikin-South Pole basin. Image made by the Lunar Reconnaissance Orbiter between 2009-2011. Courtesy NASA. — The lunar Far side shows much more impact cratering and very few maria and basins. The darkened area in the lower middle is the Aikin-South Pole basin. Image made by the Lunar Reconnaissance Orbiter between 2009-2011. Courtesy NASA.

Explaining the Moon’s Two Sides

Most of the Moon’s craters formed during an event called the “Late Heavy Bombardment”. That happened some 3.8 billion years ago, although objects do still collide with the Moon today.

Still, there are some mysteries about the Moon that need solving. One of them involves a strange mix of chemical elements known as KREEP, and what their existence on the lunar near side tells us about its history.

Could KREEP be related to the difference between the two sides of the Moon? That’s a question that planetary scientists have been working to answer for many years. The visual evidence tells them that something happened. But, to get a true understanding of the event that caused the Moon to look so different, they looked for reasons that might explain the “two-sided dichotomy”.

A Heck of an Ancient Impact

Lately, scientists have pursued an idea that may tell the tale. It all starts with a feature near the lunar south pole called the “South Pole-Aitkin” (SPA) basin. It’s an impact basin that measures about 2500 kilometers across and over eight kilometers deep. It probably formed about four billion years ago. The most likely explanation is that a slow-moving object plowed into the Moon. The force of that impact melted a lot of rock and launched a plume of heat through the Moon.

An LRO image map of the Aitken-South Pole region on the Moon. Courtesy NASA. — An LRO image map of the Aitken-South Pole region. C ourtesy NASA.

As it traveled through the Moon, the plume would have carried such elements as thorium (which produces heat), rare earth metals, phosphorus, and other metals. That “splash” of heat would have spurred volcanic activity on the near side, creating the maria. In fact, there’s evidence for this idea in the chemical composition in a near side region called Oceanus Procellarum. It has a high concentration of these materials, often referred to as KREEP (K for potassium, REE is for rare earth elements, P is for potassium).

KREEP Tells the Tale

For a long time, scientists wondered how Procellarum could be rich with KREEP materials when the rest of the Moon isn’t. The impact that created the South Pole-Aitkin region would have been the trigger. In addition, the far side didn’t get “resurfaced” by volcanism since all the heat went to the near side. That could explain why the far side appears so much more cratered—its impacts weren’t obliterated by volcanic flows.

A computer model of heat convection in the Moon during and after an impact that sent a plume of heat and heat-producing elements through the lunar interior. Courtesy Brown University.

This hypothesis about the South Pole-Aitkin impact and its effect on the near side of the Moon is the latest attempt to tell the tale of the Moon’s two faces. It has been the subject of intense computer modeling by scientists at Brown University, Purdue, the Lunar and Planetary Science Laboratory, Stanford University, and NASA-JPL. You can read more about their work at this site.

At first glance, the connection between Mars and space lettuce might seem to be a wee bit tenuous. After all, the Red Planet seems to be this shining beacon in people’s minds as THE place to go next in space. Certainly, it was the impetus for Elon Musk’s leap to fame as a builder of reusable rockets. He’s mentioned more than a few times that he wondered why we aren’t already at Mars and decided that he’d be the one to get us there. So, what does food have to do with it?

Future Mars exploration will require healthy humans who can learn to survive alien conditions. It may be a few years before we fly above the surface in Mars planes, but we’re learning how to cope with the challenges now.

NASA, ESA, Roscosmos, India’s ISRO, and others are also aiming at Mars, and developing ways for astronauts to travel to and from other worlds (and survive nicely while doing so), so it’s not exactly a new thought.

Going to Mars (and beyond) is a standard staple of science fiction. In story after story, people blithely travel to Mars, build colonies, cities, and civilizations. In some tales, they even find indigenous life forms. So, Elon’s—and everyone else’s dream—isn’t so farfetched, in our imaginations. And, neither will be the problems we need to solve so that humans can go safely to and from other worlds of the solar system. For as much as we already know, there are a lot of other lessons we’ll be learning as we go, including bringing our habitat and food (and space lettuce) with us.

Danger, Danger

Reality, however, has a different take on things. The advent of space travel taught a visceral lesson about moving beyond Earth: it’s dangerous. We evolved to live and propagate on Earth. Going elsewhere means that we have to take our environment with us. Hence the pressurized space stations, spacecraft, suits, and other needs. And, as astronauts have learned with their own bodies, living and working in space presents hidden dangers to their health. Bones soften. Eyes change. Organs change. Even the space traveler’s mental condition is subject to change. Lengthy missions in space will challenge even the hardiest among us. And, we’ve never had the experience of living for long periods on other worlds.

Gardening (and Space Lettuce) May Hold the Key

As much as possible, anyone who lives and works in space needs to take precautions to preserve their health. Future astronauts may well adapt to space through a combo of diet and exercise, much as those of us here on Earth try to preserve our health here in the gravity well. This works especially well for our bones. They evolved to be constantly balanced between the processes of growth and resorption. They can repair themselves when injured and grow as our bodies grow. However, take our bones into space, and things aren’t the same. Living in a low- or microgravity environment causes bones to lose mass in the process of resorption. This is why you see images of astronauts exercising like mad while on orbit. If they don’t, their bones soften.

Astronauts exercise daily, while in space as well as when they’re on Earth. It helps maintain health — and strong bones. Courtesy NASA.

Now, on short missions, this poses a problem that gets solved when the astronaut returns to Earth. But, what happens if the astronaut is leaving Earth, going on a lengthy trip to Mars, and then spending time on the Red Planet? Yes, they can exercise like crazy, but the changes are going to be very hard to reverse if and when they return to Earth. There has to be another solution, like growing some kind of food that will help maintain bones and other body systems.

Salad in Space

It turns out biologists and doctors have been researching other ways to “fix” the problem. One of them turns out to be something edible: space lettuce. This is a form of lettuce that its developer calls “transgenic”. It was developed by Kevin Yates, a graduate student at the University of California Davis department of chemical engineering. He’s created this lettuce that utilizes a fusion protein that combines a parathyroid hormone with a human antibody protein. Parathyroid hormones can be used to treat bone loss here on Earth. So, this new space lettuce would not only be a source of a drug they could use to ward off bone loss while in transit and on Mars, but it would give them a fresh, renewable source of food along the way.

Researchers at UC Davis are developing transgenic lettuce, such as this romaine lettuce, containing a treatment that astronauts could grow and consume during the voyage. Courtesy Kevin Yates, UC Davis.

Long space flights like a trip to Mars are always going to pose challenges since the missions will need to bring along stocks of consumables such as medicines. Astronauts have been growing food on space stations for years, so space gardening technology is fairly robust. Being able to grow them along the way is a step forward to a renewable source of consumables in space.

The Spacewriter's Ramblings

KREEP on the Moon