Astronomy Cast Ep. 478: Apollo 8 with Paul Hildebrandt

On Christmas Day, 1968 Frank Borman, James Lovell and William Anders became the first human being to see the far side of the Moon. Their mission, of course, was Apollo 8, the first time human beings had ever left Earth orbit and seen the far side of the Moon. Today we talk all about Apollo 8, with special guest Paul Hildebrandt, director of a new documentary about the mission.

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Astronomy Cast Ep. 477: State of Exploration: Once and Future Moon

It’s been decades since humans set foot on the Moon. Well, it’s time to go back, in theory. Of course, we’ve heard this all before. What are the plans afoot to send humans back to the Moon this time. What hardware will we use, and what other strategies are in the works to make this happen?

We usually record Astronomy Cast every Friday at 3:00 pm EST / 12:00 pm PST / 20:00 PM UTC. You can watch us live on AstronomyCast.com, or the AstronomyCast YouTube page.

Visit the Astronomy Cast Page to subscribe to the audio podcast!

If you would like to support Astronomy Cast, please visit our page at Patreon here – https://www.patreon.com/astronomycast. We greatly appreciate your support!

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

Upcoming Chinese Lander Will Carry Insects and Plants to the Surface of the Moon

It would be no exaggeration to say that we live in an age of renewed space exploration. In particular, the Moon has become the focal point of increasing attention in recent years. In addition to President Trump’s recent directive to NASA to return to the Moon, many other space agencies and private aerospace companies are planning their own missions to the lunar surface.

A good example is the Chinese Lunar Exploration Program (CLEP), otherwise known as the Chang’e Program. Named in honor of the ancient Chinese lunar goddess, this program has sent two orbiters and one lander to the Moon already. And later this year, the Chang’e 4 mission will begin departing for the far side of the Moon, where it will study the local geology and test the effects of lunar gravity on insects and plants.

The mission will consist of a relay orbiter being launched aboard a Long March 5 rocket in June of 2018. This relay will assume orbit around the Earth-Moon L2 Lagrange Point, followed by the launch of the lander and rover about six months later. In addition to an advanced suite of instruments for studying the lunar surface, the lander will also be carrying an aluminum alloy container filled with seeds and insects.

The Chinese Yutu rover, part of the Chang’e 3 mission, on the Moon. Credit: CNSA

As Zhang Yuanxun – chief designer of the container – told the Chongqing Morning Post (according to China Daily):

“The container will send potatoes, arabidopsis seeds and silkworm eggs to the surface of the Moon. The eggs will hatch into silkworms, which can produce carbon dioxide, while the potatoes and seeds emit oxygen through photosynthesis. Together, they can establish a simple ecosystem on the Moon.”

The mission will also be the first time that a mission is sent to an unexplored region on the far side of the Moon. This region is none other than the South Pole-Aitken Basin, a vast impact region in the southern hemisphere. Measuring roughly 2,500 km (1,600 mi) in diameter and 13 kilometers (8.1 mi) deep, it is the single-largest impact basin on the Moon and one of the largest in the Solar System.

This basin is also source of great interest to scientists, and not just because of its size. In recent years, it has been discovered that the region also contains vast amounts of water ice. These are thought to be the results of impacts by meteors and asteroids which left water ice that survived because of how the region is permanently shadowed. Without direct sunlight, water ice in these craters has not been subject to sublimation and chemical dissociation.

Since the 1960s, several missions have explored this region from orbit, including the Apollo 15, 16 and 17 missions, the Lunar Reconnaissance Orbiter (LRO) and India’s Chandrayaan-1 orbiter. This last mission (which was mounted in 2008) also involved sending the Moon Impact Probe to the surface to trigger the release of material, which was then analyzed by the orbiter.

Elevation data of the Moon, highlighting the low-lying regions of the South Pole-Aitken Basin. Credit: NASA/GSFC/University of Arizona

The mission confirmed the presence of water ice in the Aitken Crater, a discovery which was confirmed about a year later by NASA’s LRO. Thanks to this discovery, there have been several in the space exploration community who have stated that the South Pole-Aitken Basin would be the ideal location for a lunar base. In this respect, the Chang’e 4 mission is investigating the very possibility of humans living and working on the Moon.

Aside from telling us more about the local terrain, it will also assess whether or not terrestrial organisms can grow and thrive in lunar gravity – which is about 16% that of Earths (or 0.1654 g). Previous studies conducted aboard the ISS have shown that long-term exposure to microgravity can have considerable health effects, but little is known about the long-term effects of lower gravity.

The European Space Agency has also been vocal about the possibility of building an International Lunar Village in the southern polar region by the 2030s. Intrinsic to this is the proposed Lunar Polar Sample Return mission, a joint effort between the ESA and Roscosmos that will involve sending a robotic probe to the Moon’s South Pole-Aitken Basin by 2020 to retrieve samples of ice.

In the past, NASA has also discussed ideas for building a lunar base in the southern polar region. Back in 2014, NASA scientists met with Harvard geneticist George Church, Peter Diamandis (creator of the X Prize Foundation) and other parties to discuss low-cost options. According to the papers that resulted from the meeting, this base would exist at one of the poles and would be modeled on the U.S. Antarctic Station at the South Pole.

Artist’s concept of a possible “International Lunar Village” on the Moon, assembled using inflated domes and 3D printing. Credits: ESA/Foster + Partners

If all goes well for the Chang’e 4 mission, China intends to follow it up with more robotic missions, and an attempted crewed mission in about 15 years. There has also been talk about including a radio telescope as part of the mission. This RF instrument would be deployed to the far side of the Moon where it would be undistributed by radio signals coming from Earth (which is a common headache when it comes to radio astronomy).

And depending on what the mission can tell us about the South Pole-Aitken Basin (i.e. whether the water ice is plentiful and the radiation tolerable), it is possible that space agencies will be sending more missions there in the coming years. Some of them might even be carrying robots and building materials!

Further Reading: Sputnik News, Planetary Society

There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities

Every year since 1970, astronomers, geologists, geophysicists, and a host of other specialists have come together to participate in the Lunar and Planetary Science Conference (LPCS). Jointly sponsored by the Lunar and Planetary Institute (LPI) and NASA’s Johnson Space Center (JSC), this annual event is a chance for scientists from all around the world to share and present the latest planetary research concerning Earth’s only moon.

This year, one of the biggest attention-grabbers was the findings presented on Tuesday, March 17th by a team of students from Purdue University. Led by a graduate student from the university’s Department of Earth, Atmospheric and Planetary Sciences, the study they shared indicates that there may be stable lava tubes on the moon, ones large enough to house entire cities.

In addition to being a target for future geological and geophysical studies, the existence of these tubes could also be a boon for future human space exploration. Basically, they argued, such large, stable underground tunnels could provide a home for human settlements, shielding them from harmful cosmic radiation and extremes in temperature.

The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed (NASA/JAXA)
The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed. Credit: NASA/JAXA

Lava tubes are natural conduits formed by flowing lava that is moving beneath the surface as a result of a volcanic eruption. As the lava moves, the outer edges of it cools, forming a hardened, channel-like crust which is left behind once the lava flow stops. For some time, Lunar scientists have been speculating as to whether or not lava flows happen on the Moon, as evidenced by the presence of sinuous rilles on the surface.

Sinuous rilles are narrow depressions in the lunar surface that resemble channels, and have a curved paths that meanders across the landscape like a river valley. It is currently believed that these rilles are the remains of collapsed lava tubes or extinct lava flows, which is backed up by the fact they usually begin at the site of an extinct volcano.

Those that have been observed on the Moon in the past range in size of up to 10 kilometers in width and hundreds of kilometers in length. At that size, the existence of a stable tube – i.e. one which had not collapsed to form a sinuous rille – would be large enough to accommodate a major city.

For the sake of their study, the Purdue team explored whether lava tubes of the same scale could exist underground. What they found was that the stability of a lava tube depended on a number of variables- including width, roof thickness and the stress state of the cooled lava. he researchers also modeled lava tubes with walls created by lava placed in one thick layer and with lava placed in many thin layers.

The city of Philadelphia is shown inside a theoretical lunar lava tube. A Purdue University team of researchers explored whether lava tubes more than 1 kilometer wide could remain structurally stable on the moon. (Purdue University/courtesy of David Blair)
The inside of a theoretical lunar lava tube, with the city of Philadelphia shown for scale. Credit: Purdue University/David Blair

David Blair, a graduate student in Purdue’s Department of Earth, Atmospheric and Planetary Sciences, led the study that examined whether empty lava tubes more than 1 kilometer wide could remain structurally stable on the moon.

Our work is somewhat unique in that we’ve combined the talents of people from various Departments at Purdue,” Blair told Universe Today via email. “With guidance from Prof. Bobet (a civil engineering professor) we’ve been able to incorporate a modern understanding of rock mechanics into our computer models of lava tubes to see how they might actually fail and break under lunar gravity.”

For the sake of their research, the team constructed a number of models of lava tubes of different sizes and with different roof thicknesses to test for stability. This consisted of them checking each model to see if it predicted failure anywhere in the lava tube’s roof.

“What we found was surprising,” Blair continued, “in that much larger lava tubes are theoretically possible than what was previously thought. Even with a roof only a few meters thick, lava tubes a kilometer wide may be able to stay standing. The reason why, though, is a little less surprising. The last work we could find on the subject is from the Apollo era, and used a much simpler approximation of lava tube shape – a flat beam for a roof.

 Mons Rümker rise on the Oceanus Procellarum was taken from the Apollo 15 while in lunar orbit.
Mons Rümker, an extinct volcanic formation on the Moon’s surface, as imaged by the Apollo 15 spacecraft while in orbit. Credit: NASA

The study he refers to, “On the origin of lunar sinuous rilles“, was published in 1969 in the journal Modern Geology. In it, professors Greeley, Oberbeck and Quaide advanced the argument that sinuous rilles formation was tied to the collapse of lava flow tubes, and that stable ones might still exist. Calculating for a flat-beam roof, their work found a maximum lava tube size of just under 400 m.

“Our models use a geometry more similar to what’s seen in lava tubes on Earth,” Blair said, “a sort of half-elliptical shape with an arched roof. The fact that an arched roof lets a larger lava tube stay standing makes sense: humans have known since antiquity that arched roofs allow tunnels or bridges to stay standing with wider spans.”

The Purdue study also builds on previous studies conducted by JAXA and NASA where images of “skylights” on the Moon – i.e. holes in the lunar surface – confirmed the presence of caverns at least a few tens of meters across. The data from NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) – which showed big variations in the thickness of the Moon’s crust  is still being interpreted, but could also be an indication of large subsurface recesses.

As a result, Blair is confident that their work opens up new and feasible explanations for many different types of observations that have been made before. Previously, it was unfathomable that large, stable caverns could exist on the Moon. But thanks to his team’s theoretical study, it is now known that under the proper conditions, it is least possible.

The thickness of the moon's crust as calculated by NASA's GRAIL mission. The near side is on the left-hand side of the picture, and the far side on the right. Credit: NASA/JPL-Caltech/S. Miljkovic
NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) mission calculated the thickness of the moon’s crust. Credit: NASA/JPL-Caltech/S. Miljkovic

Another exciting aspect that this work is the implications it offers for future exploration and even colonization on the Moon. Already, the issue of protection against radiation is a big one. Given that the Moon has no atmosphere, colonists and agricultural operations will have no natural shielding from cosmic rays.

“Geologically stable lava tubes would absolutely be a boon to human space exploration,” Blair commented. “A cavern like that could be a really ideal place for building a lunar base, and generally for supporting a sustained human presence on the Moon. By going below the surface even a few meters, you suddenly mitigate a lot of the problems with trying to inhabit the lunar surface.”

Basically, in addition to protecting against radiation, a subsurface base would sidestep the problems of micrometeorites and the extreme changes in temperature that are common on the lunar surface. What’s more, stable, subsurface lava tubes could also make the task of pressurizing a base for human habitation easier.

“People have studied and talked about all of these things before,” Blair added, “but our work shows that those kinds of opportunities could potentially exist – now we just have to find them. Humans have been living in caves since the beginning, and it might make sense on the Moon, too!”

In addition to Melosh, Blair and Bobet, team members include Loic Chappaz and Rohan Sood, graduate students in the School of Aeronautics and Astronautics; Kathleen Howell, Purdue’s Hsu Lo Professor of Aeronautical and Astronautical Engineering; Andy M. Freed, an associate professor of earth, atmospheric and planetary sciences; and Colleen Milbury, a postdoctoral research associate in the Department of Earth, Atmospheric and Planetary Sciences.

Further Reading: Purdue News