Tag: Moon

The Far (not Dark) Side of the Moon

On October 4th 1959, exactly two years after the launch of Sputnik, the Soviet Union launched Luna 3 to solve one of astronomy’s enduring mysteries.  You’ve probably never heard of it as it has since been overshadowed by the race to land a man on the Moon the following decade.  However, this four-foot probe gave humanity its first glimpse at the far side of the Moon.  And while it helped solve the mystery how the other side of the Moon looks, it opened up new questions to answer on the nature of the Moon.

Before we get into all that, it’s important to clarify one misconception regarding the Moon.  The far side, famous Pink Floyd album notwithstanding, is not the dark side of the Moon.  The far side is dark during a full Moon while the familiar near side is facing the Sun.  It is not dark during a new Moon when the near side is facing away from the Sun and the far side is facing towards the Sun.  That is after all, how images of the far side are obtained-when it is bathed in sunlight.

First image taken of the far side of the Moon. Credit: Luna 3-1, Russian Space Agency

When we look upon the Moon, the near side is divided into two types of regions.  The highlands are the bright regions and are quite old (4.5 billion years old) and heavily cratered.  The mare are darker, younger, and less cratered.  These regions formed some 3-3.5 billion years ago when large impact events occurred on the Moon, causing magma to flood the impact basin then solidifying into darker, basaltic plains.

The first images from Luna 3 were quite noisy but had enough resolution to determine the far side was mostly highlands.  As you might imagine, the Soviet Academy of Science gave the far side features Soviet orientated names.  The one major mare region was called Mare Moscoviense and the lava filled crater was dubbed Tsiolkovsky after the Russian rocket pioneer.

Tsiolkovsky Crater is 185 km (115 miles) wide and features a central peak 3200 m (10,500 ft) high.  This is a few hundred feet lower than San Jacinto Mountain in California.  As the crater has a smooth mare floor, it would make for a good landing spot and was a proposed, but eventually rejected, landing site for Apollo 17.  The central peak was formed by the rebound effect of the original impact.  You can see such a rebound effect if you drop an object into a glass of milk.  In the case of the crater, the uplifted rebound material solidified creating the central peak.

Tsiolkovsky Crater imaged by Apollo 17. Credit: NASA

The crater is named for Konstantin Tsiolkovsky, who in the early 1900’s, developed many of the theoretical underpinnings of modern rocketry.  He independently derived the ideal rocket equation relating a rocket’s change in velocity to the change in mass and thrust.  In 1929, he published his theory of multi-staged rockets.  His work was key to the Soviet Union’s initial burst into space.

Mare regions account for only 1% of the far side surface area as opposed to a third of the near side.  Both sides have had an equal amount of impacts during its history but the far side did not experience the upwelling of magma after these events.  The interior of the Moon is not symmetric.  The core of the Moon is closer to Earth and the near side.  As a result, the near side has a thinner crust than the far side.  It is thought this extra crust made it more difficult for magma to flood the surface on the far side after the impact events.

Interior of the Moon. Credit: NEEP
Interior of the Moon. Credit: NEEP

Only 27 humans in history have seen the far side personally.  Those would be the astronauts from the Apollo program that orbited and/or landed on the Moon.  All the Apollo missions landed on the near side although there was the proposal to land Apollo 17 on the far side.  No doubt, this would have provided rich scientific returns, but would have necessitated the cost of a lunar orbiting communications satellite.  As the Apollo program was winding down, this was deemed too expensive.  The Apollo program did provide some high-resolution images of the far side as seen below.

Far side of Moon taken by Apollo 16. Credit: NASA
Far side of Moon taken by Apollo 16. Credit: NASA

After the Apollo program, there was a lull in lunar exploration.  A sense of been there, done that, pervaded the public mindset.  However, the lunar surface is four times the size of the United States.  The six Apollo landings covered a very small area and none of it was on the far side.  Exploration of the Moon would not resume until the 1990’s.  This modern phase would make some key discoveries on the far side, especially in the Polar Regions.

The presence of a large impact basin on the far side near the South Pole was suspected during the early 1960’s.  It was not until the Clementine mission in 1994 that the true extent of the basin was discovered.  The South Pole-Aitken Basin stretches some 2,500 km (1,600 miles-about the same from New York City to Cheyenne, WY)) from the South Pole to the Aitken crater.  The basin is five miles deep (five times deeper than the Grand Canyon) and is the second largest impact basin in the Solar System.  Only Hellas Basin on Mars is larger.

The basin is thought to have been created by a 170 km wide asteroid striking the lunar surface at 10 km/s.  To put this in perspective, the asteroid responsible for the dinosaur extinction was about 10 km wide.  From a scientific perspective, this basin is of interest as such an impact would uncover the deeper parts of the Moon’s crust.  Another aspect of interest is some parts of the basin are permanently shadowed.

South Pole and Aitken Basin (darker region) imaged by the Lunar Reconnaissance Orbiter. Credit: NASA/GSFC/Arizona State University

The Earth’s axis is titled 23 degrees from the orbital plane.  What this means at the poles is that the Sun at its highest point during the Summer Solstice is 23 degrees above the horizon.  The Moon’s axis is only tilted 1.5 degrees.  Thus at the lunar poles, the highest the Sun rises above the horizon is 1.5 degrees.  This is about how high the Sun is fifteen minutes after sunrise in the mid-latitudes on Earth.  As a result, a basin as deep as the Aitkin will have cratered sections that never see the light of day.  As the Moon has no atmosphere to distribute heat from daylight areas to dark regions, any water that collects in the basin will not evaporate.  And indeed, ice and water has been discovered in the basin near the pole.

Topography of the Aitkin Basin (lower right) relative to rest of the Moon. Credit: Brian Fessler and Paul Spudis, LPI

How does water get to the Moon?  The main suspect is the solar wind which transports hydrogen nuclei to the lunar surface.  Unlike Earth, the Moon does not have a magnetic field to deflect the solar wind away from the surface.  The hydrogen interacts with oxygen in the lunar soil to form water.  We typically think of oxygen as an atmospheric gas rather than something in rocks.  However, 47% of the Earth’s crust is oxygen in mass and 94% in volume.  Oxygen and silicon form chemical bonds quite easily and make up silicate oxides such as silicon dioxide (SiO2) and ferrous oxide (FeO) or iron as it is more commonly known.  The same is true of lunar soil and this provides oxygen to combine with hydrogen from the solar wind resulting in water.

Typically, water cannot exist on the lunar surface.  Any water would sublimate (transform directly from ice to water vapor) due to the lack of atmospheric pressure.  However, in areas without sunlight to start this process, water can exist on the surface.  Now, we’re not talking about lakes or seas here, the average amount of water comes out to one liter per ton of lunar soil.  The total amount of water on the surface is estimated as several hundred million metric tons.  And that is enough to extract and make human settlement on the Moon possible.  One possible site for a base would be Shackleton Crater at the South Pole in the Aitken Basin.  This site has the benefit of both sunlit and shadowed regions in close proximity of each other.

Blue indicates presence of hydrogen and most likely, water. Credit: NASA

Any talk of settlement on the Moon needs to include cost.  Currently, it costs about $10,000 to lift an ounce of payload from Earth.  Although companies such as SpaceX endeavor to bring that cost down with reusable rockets, it will still be quite expensive at this point for humans to migrate into space.  Utilizing resources on the Moon would be key for any permanent settlement.  Before we talk about space colonies, we need to take baby steps first.  This could include a rover and/or sample return mission to the far side followed up by human landings.  At that point in time, an assessment of the potential for a permanent presence on the Moon, whether it is on the near side, far side, or at the poles can be made.

Still, the far side is distinct enough compared to the near side that it definitely deserves a look into.  And while the idea of a human settlement on the far side seems pretty speculative today, consider this, sixty years ago no one had seen the far side.  In 2012, the GRAIL mission MoonKAM, a video instrument devoted to K-12 outreach, took the first video of the far side.  Whose to say what the next fifty years will bring?

* Image atop post is a look of the far side of the Moon with the Earth in the background from the DSCOVR satellite.  Credit:  NASA

Where Apollo Landed on the Moon

During the Apollo era, I remember gazing at the Moon to find the areas where astronauts were exploring at the time.  Even with the most powerful telescopes, we are unable to detect the flags and equipment left behind, but it still is an interesting challenge to pick out these spots and not a bad way to learn about the Moon as well.  Recently, the Lunar Reconnaissance Orbiter has been able to image these landing spots and made some discoveries that point to some other interesting potential landing regions should we return.

Apollo landing sites. Credit: Soerfm/Wiki Commons

The Moon is divided into two types of terrain, the highlands which are the bright regions and the maria which are the darker areas.  The highlands are very old, about 4-4.5 billion years and thus, heavily cratered.  This makes the highlands geologically rich but challenging to land on.  The maria are younger and thus easier to make a landing attempt as the terrain is smoother.  The maria were formed 3-3.5 billion years ago when large impacts flooded basins with lava eventually to solidify into the dark, iron rich basaltic surfaces we see today.  Maria is derived from the Latin word for seas which ancient astronomers thought these dark areas were.  Of course, there are no large bodies water to be found in the maria.  Like the first Apollo landings, a return to the Moon will likely begin in the maria and expand outward into more challenging landing zones.

Apollo 11

Neil Armstrong and Buzz Aldrin spent 21.5 hours on the lunar surface on the Sea of Tranquility.  Just before the famous Christmas Eve reading of Genesis by the Apollo 8 crew, William Anders noted the Sea of Tranquility was selected as a future landing site in order to preclude dodging mountains.  While there were not any mountains to dodge, there were several large boulders causing Neil Armstrong to take manual control of the lunar module, eventually finding a safe landing spot with 25 seconds of fuel to spare.  Apollo 11 returned 22 kg (48 lbs) of samples back to Earth.  As would be expected from landing in a mare region, the rocks were mostly basalt created from lava when the region formed.  There were also breccias which are smaller fragmented rocks fused together over time.

Apollo 11 landing site from 15 miles above the lunar surface. The foot trail to the crater right center is 50 m (164 ft) and was furthest Armstrong and Aldrin ventured from the lunar module. Credit: NASA.

Apollo 12

Launched during a rainstorm, the crew of Apollo 12 had to experience the adventure of getting hit by lightning before reaching orbit and proceeding to the Moon.  Like Apollo 11, this mission landed in a mare region.  The Ocean of Storms (or Oceanus Procellarum in Latin) was the landing site of Surveyor 3 in 1967.  NASA wanted to aim for a precise landing near Surveyor 3 and examine samples in this region which appeared younger than the Sea of Tranquility.  Astronauts Pete Conrad and Alan Bean made two excursions on the lunar surface reaching half a mile away from the lunar module.  The samples were mostly basalt and, as expected, were 500 million years younger than the Sea of Tranquility establishing a range for lunar volcanic activity.  The crew also visited the Surveyor 3 and retrieved its television camera which is currently on display at the Smithsonian Air & Space Museum.

Pete Conrad checks out Surveyor 3 with lunar module 600 feet away in the background. Credit: NASA.

Apollo 14

After the Apollo 13 landing was aborted due to an explosion in a service module oxygen tank, its intended landing site in the Fra Mauro formation was slated for the Apollo 14 mission.  This was the first landing to occur in the lunar highlands.  This region contains rocks ejected by the formation of the Imbrium basin and it was hoped to capture samples that originated deep under the lunar surface.  The plan was also to capture samples from the nearby Cone Crater but the rugged terrain prevented the astronauts from reaching the rim.  Alan Shepard and Edgar Mitchell collected almost 42 kg (92 lbs) of rock samples most of which were breccia formed by rocks fragmented by the impact event.  The crew did collect some basalts which clocked in at 4-4.3 billion years old, significantly older than the earlier basalts collected.  Apollo 14 also had perhaps the most humorous event of the program with Alan Shepard’s attempt to play golf on the Moon.

Apollo 15

Hadley Rille from space with circle denoting Apollo 15 landing site. Credit: NASA

Apollo 15 began the J-series missions for the program.  These missions were more ambitious with longer duration stays and with the lunar rover, the ability to travel longer distances from the lunar module.  Apollo 15 was the first landing to stray away from the equatorial region.  David Scott and James Irwin spent some 18 hours exploring the lunar surface and traveled 28 km (17 miles-compared to 2 miles on foot for Apollo 14) on the rover.  A major target was the Hadley Rille.  Rilles are sinuous features on the Moon thought to be ancient lava tubes whose ceilings have since collapsed.  Indeed, the rocks returned from this region were basaltic in nature.  By the time Apollo 15 landed on the Moon, the final three missions (Apollo 18-20) were cancelled due to budget cuts, meaning there were only two trips to the Moon left for the program.

The 300 meter (1,000 feet) deep Hadley Rille from the lunar surface. Credit: NASA.

Apollo 16

This mission was specifically designed to bring back samples from the highlands.  Landing in the Descartes formation, Apollo 16 would return 96 kg (211 lbs) of Moon rocks that would fundamentally alter our understanding of the highlands.  Previously thought to be of volcanic nature, the sample contained very few basalt rocks.  Instead, the samples were breccia in nature.  Rocks on the Moon are fragmented when impacts occur.  These fragmented rocks are then fused together to form breccia rocks by the heat caused by subsequent impacts.  The age of the highland are 4.5 billion years old.  This dates back to the origin of the Moon as it cooled from a molten to a solid state.

Charlie Duke takes a sample of permanently shadowed soil next to the large boulder named, appropriately enough, Shadow Rock. Credit: NASA

Apollo 17

As this was the final Apollo mission, a sense of urgency was placed on obtaining a high scientific yield.  At one point, a landing on the far side was considered but rejected as it would require the additional cost of a communication satellite.  The far side is often confused as the dark side of the Moon.  However, during the new Moon phase the far side is facing the Sun and experiences daylight.  The far side differs from the near side as it is mostly highlands and has very little maria regions as can be seen below.

Credit: NASA/Goddard/Arizona State University

The site selected was Taurus-Littrow Valley, a very geologically diverse region that required a precision landing.  For this mission, Harrison Schmitt was moved up from the cancelled Apollo 18 mission to become the first astronaut-scientist.  Three days after the only night launch of the Apollo program, America made its final Moon landing.  Three excursions extending 25 km (15 miles) brought back a haul of 111 kg (245 lbs) of samples including highland rocks ranging from 4.2-4.5 billion years old, basaltic rocks from the valley floor indicating volcanic activity about 3.7 billion years ago, and ejecta from the Tycho crater that was 100 million years old.  By lunar standards, the Tycho crater is a relatively young feature even though dinosaurs were walking on Earth when created.

Apollo 17 lunar rover at the edge of Shorty Crater. Near the rim there is orange soil that is titanium rich pyroclastic glass originated from 10 meters below the surface but was ejected during the impact event. Credit: NASA.

Lunar Interlude

The scientific phase of the Apollo program, which was to be 18-20, was cancelled by President Nixon as the economy began to experience its first bout of both high inflation and unemployment that would plagued the economy during the 1970’s.  Two of the unused Saturn V’s are on display at the Kennedy and Johnson Space Centers.  NASA began to develop the space shuttle and its planetary exploration program.  The public lost interest in lunar exploration as there was a sense of been there, done that.  However, the lunar surface covers an area 38 million square km (14.6 million square miles), about four times the surface area of the United States.  As NASA began to recommence unmanned lunar exploration in the 1990’s, the Moon began to offer some surprises.

Lunar exploration was started again in 1994 with the Clementine mission that globally mapped the Moon, in particular, the 15 km (9 mile) deep South Pole-Aitken Basin.  This was followed by the Lunar Prospector in 1998.  The Moon had been thought to be completely water free but the Lunar Prospector detected the presence of 300 million tons of water mixed in the soil at both polar regions.  How could water exist on the Moon?  The Moon’s axis is only tilted 1.5 degrees.  This means the Sun in these regions can only reach 1.5 degrees above the horizon, roughly the same as the Sun about ten minutes after sunrise in the mid-latitudes on Earth.  Hence, large craters remain in permanent shadow so that any water there will not evaporate into space.

Blue indicates regions on Moon where water may exist. Credit: NASA.

However, the Lunar Reconnaissance Orbiter (LRO), launched in 2009, discovered the presence of hydrogen beyond shadowed areas of the Moon.  The water could have been delivered to the Moon very early in its history via comets.  It is also thought the solar wind, which carries hydrogen, could interact with oxygen embedded in silicates on the surface to form water.  To be sure, we’re not talking lakes or even underground springs here.  The water amounts to about 45 parts per million, but given the cost to lift material from Earth into space (about $10,000 per ounce), any long-term settlement on the Moon will require the use of raw material situated there.  This gives some promise that the Moon could be used as a base to colonize space.

Above – LRO’s high-resolution tour of the Moon

NASA is currently developing the Orion crew module along with the heavy lift Space Launch System which will make an unmanned test run past the Moon in 2018.  The ultimate goal of this program is to land humans on Mars although a lunar program to test mission systems beforehand is not out of the question.  Going to the Moon is only a three-day hop compared to seven months for Mars.  Using the Moon as a testbed could make sense before making the leap to Mars.  It is often argued that unmanned missions are less expensive, and less hazardous than crewed spaceflight.  However, humanity is hardwired to explore and expand its presence.  That is how we expanded beyond our origins on the African continent across the oceans to all corners of the Earth.  Hopefully, in the near future, children will once again gaze at the Moon and ponder the about the people exploring our nearest celestial neighbor.

Vollmond, High Tides and Lunacy

When teaching astronomy to non-science majors, I try to make connections with the student’s field of study or personal interests.  Sometimes this is not difficult.  For example, I can discuss NASA budgets and cost estimating with business majors.  For art majors, the deep red sunsets that followed the Krakatoa eruption of 1883 found their way into many paintings of the era.  The most notable example of this was The Scream painted by Edvar Munch in 1893.

The Scream by Edvard Munch. National Gallery, Olso, Norway. Aerosols injected into the atmosphere by powerful volcanic eruptions can cause very deep red skies at sunset.

A while back, I talked with someone whose career was in the performing arts, specifically dance.  I was stumped at the time to think of a possible tie in between astronomy and dance.  The closest analogy I could come up with was the classic case of a figure skater demonstrating the concept of angular momentum during a spin such as below.

Angular momentum is conserved, that is, it is not created or destroyed (it can be converted to heat via friction).  Angular momentum (L) is defined as:

L = mrv

m = mass, r = radius, v = velocity

As angular momentum is conserved, the value L is constant.  In the case of the figure skater in the video, she reduces r by drawing in her arms and legs closer to herself.  As the skater’s radius decreases, velocity must increase.  Hence, the rate of spin increases as radius decreases.  You can try this at home even if you do not  know how to skate.  Just find a swivel chair and have a friend spin you around with your arms extended, then draw in your arms close to your body.  You’ll feel your spin velocity accelerate.  Not as much as the skater, but enough to notice.

The conservation of angular momentum has several applications in astronomy, in particular, pulsars.  Pulsars are the remnants of stars that went supernova.  As the outer layers of the star are dispersed in the aftermath of a supernova, its inner core compresses forming the pulsar.  In a pulsar, the gravitational force is so great that electrons merge with protons to form neutrons.  Consequently, pulsars are a sub-class of what are known as neutron stars.  As the radius of a pulsar is reduced, its spin rate greatly accelerates.

We can measure the spin rates of pulsars as they emit radio waves in the same fashion a lighthouse emits a light beam.  The most famous pulsar is located in the Crab Nebula, which is a remnant of a supernova observed by Chinese astronomers in 1054.  This pulsar spins at a rate of 30 times per second.  To put that in perspective, the skater in the video above is spinning 5 times per second.

The pulsar in the Crab Nebula emits high energy x-rays. Red is lowest energy and blue highest energy x-rays. Credit: NASA/CXC/SAO

Is there any sort of analogy in the world of dance?  Ballet dancers use the same method as figure skaters to increase their spin.  However, as there is more friction from a wood floor than there is from ice, the effect is not as pronounced.  Looking around I found a different approach when it came to this and found a connection, albeit allegorical, to the dance performance Vollmond.

Translated from German, Vollmond means Full Moon.  Choreographed by Pina Bausch, the performance centers on two themes addressed in my class.  One is scientific, how the full Moon increases tides, the other not so scientific, how a full Moon affects human behavior.

During a full (and new) Moon, the difference between high and low tides are at their greatest.  During these two phases, the Earth, Moon, and Sun are aligned with each other.  At this time, the effect of the Sun and Moon’s gravity is greatest on the oceans as can be seen below.

Full Moon Tides
Credit: Wikipedia

The gravity from the Sun amplifies the lunar tides.  During a full Moon, high and low tides occur twice a day.  Tides during the full and new phases are referred to as spring tides.  This has nothing to do with the season of Spring.  In a way, it is during this time when the tides spring to life.  When the Moon and Sun are at a right angle relative to Earth, the Sun’s gravity partially offsets the Moon’s gravity and modulates the tides so low and high tidal differences are not as great as the spring tide.  These are referred to as neap tides.  Local conditions can also amplify the tides.  The most dramatic example of this is the Bay of Fundy where high and low tide can differ by 56 feet.

Spring tides at the Bay of Fundy Credit: Samuel Wantman/Wiki Commons.

So, if you live by the ocean, you’ll associate high tides with a full (and new) Moon.  How about the Great Lakes?  Not so much.  The lakes greatest tide is only 5 cm, not enough to be noticed with the naked eye.  The earth you stand on also feels the tidal pull from the Moon.  Like the lakes, it is not noticeable at 25 cm.  As the landmarks rise up and down with the ground, your eye cannot detect ground tides.  We can say, quite confidentially, that the full Moon affects tidal motions.  Can we say the same regarding human behavior?

The words lunar and lunatic have their roots in the Latin word luna.  In ancient Rome, Luna was the goddess of the Moon.  Lunatic means to be moon struck.  We are all familiar with the phrase, “It must be a full Moon.”  Meaning that the full Moon provides an explanation for an increase in bizarre/criminal behavior.  Does the empirical evidence support this?  The short answer is no.  Studies have indicated no change in criminal behavior during a full Moon, or even a scientific model to explain why that would happen.  This highlights the key difference between science and mythology.

Statue of the Roman Goddess Luna. Credit: Wiki Commons

Whenever a student writes the phrase, “I believe” in a science paper, I advise them to take pause and ask yourself why do you believe that?  Science is not about beliefs, but about investigation of the nature and causes of phenomena we observe around us.  If you want to assert something as being true in science, you need a model to explain why it happens, empirical evidence it actually does happen, and independent verification of the original results.  Sometimes you might have a model you think is reasonable, but the empirical evidence does not back it up.  One such case is in economics, where demand and supply curves indicate a minimum wage set above the market rate creates unemployment.  The evidence does not support that meaning a newer, more sophisticated model is required to explain what is happening.

The purpose of this exercise was to find ways to connect a student’s personal interest to a scientific topic.  If that can be accomplished, the chances of building the student’s interest and motivation in the class increases.  In this case, we can use two situations to discern between what passes for science and what does not.  For the teacher, it provides the opportunity to explore areas that were previously unknown.  I would have never learned of the Vollmond dance performance without attempting to match my specialty with the student’s.  It’s a good experience to reach out of your comfort zone to find common ground with your students.  Often, in the classroom, who is the teacher and who is the learner can be a fluid situation.  You have to permit yourself enter your current student’s world of interests.  I have found that as a teacher, that prevents my lessons from going stale over the years.

*Image on top of post is the full Moon, or Vollmond in German.  Credit:  Katsiaryna Naliuka/Wiki Commons.