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FAQ - Moon

1. Any new developments on studies of the Moon?

Yes, water ice has been detected in permanently shadowed craters on the Moon.

2. Since the Moon is similar in composition to Earth’s mantle, is there a mechanism which would accrete precious minerals into mineable concentrations?

Ores can be concentrated by hydrothermal processes (unlikely), magmatic processes (possible), and really big impacts (very likely). So, for some precious minerals, there may be mechanisms for concentrating minerals on the Moon. When NASA impacted a spacecraft last year in search of water near one of the lunar poles, they discovered traces of some precious metals, but too low to be of any use.

3. Where are the 880 pounds [probably closer to 840 pounds] of lunar rocks?

Most of the lunar rocks are stored at Johnson Space Center in Houston. It is illegal for a private individual to own a lunar rock. However, one rock from Apollo 17 was cut up into many small pieces, put on plaques and given to heads of 135 countries and 50 states. Some lunar rocks have been used by scientists around the world for research purposes and sets of lunar rocks have been encased in lucite disks and distributed to museums (e.g. Flandrau Science Center in Tucson, AZ), which can be used by teachers. In addition, there are other lunar rocks on Earth—meteorites. These are included in PSI's meteorite kits. Fewer than 50 kilograms of lunar meteorites have been found on Earth, mostly in Northwest Africa and the Antarctic.

4. Is there magma currently inside the Moon?

There could be, but scientists don’t know for sure. The Moon’s interior has probably cooled somewhat.

5. How fast does the Moon rotate on its axis?

The Moon rotates once on its axis in 27.321582 days (27 d 7 h 43.1 min), which is also the same time it takes to revolve around the Earth. However, the time from full moon to full moon (the phase cycle) is 29.530588 days (29 d 12 h 44.0 min).

6. What are the temperatures on the surface and in the interior of the Moon?

At the equator, the minimum temperature is about -173°C and the maximum is about 125°C. Near the poles, the minimum temperature is about 50 degrees colder! It is believed that the core of the Moon may be as hot as 1600°C (2900°F), hot enough to melt the lunar rocks, so the interior of the Moon may be molten.

7. What contributes to the heat of the Moon?

Some of it may be from tidal heating, but the majority of it is probably from the decay of radioactive material. Its unlikely that there is any heat left over from when the Moon formed, when it was molten. The is no agreement as to why more mare is on the near side of the Moon compared to its far side, but measurements seem to indicate that there is radioactive material in the rocks on the near side. One other theory is that there was a big impact on the far side of the Moon that sent a shock wave through the Moon and melted the rocks on the opposite side. Again, there is no agreement on this among scientists.

8. What percentage of the Moon’s mass came from impacts?

Generally speaking, all of it! The Moon was formed by a giant impact on the Earth. The ejecta from the impact formed a ring of material around the Earth, and then came together to form the Moon. At the same time, the Earth was formed from protoplanetary objects (comets and asteroids) in our solar system. However, we do not have a clue how much material was involved or whether the Moon gained or lost mass. The Late Heavy Bombardment created the big basins on the Moon. Assuming that the impact rate has been relatively constant since the end of the Late Heavy Bombardment (only a guess), then we can come up with an estimate. The total mass being added to the Moon now is estimated to be about 1,000 kilograms a day (with large uncertainty), 365 days a year over 3.5 billion years gives you 1.3x1015 kilograms. The Moon’s mass is 7.3x1022 kg, so the total mass of the Moon is 50 million times larger than the total mass added in the last 3.5 billion years! This ignores mass lost due to the impacts which is probably small. This adds up to a layer a little more than one centimeter thick over the entire surface, but would be well mixed in with the original surface materials.

9. What happens to the surface of the Moon when it is heated by the Sun?

Essentially, it "weathers." The warming and cooling cycle breaks up the surface material. There hasn't been any detailed study of this other than data recorded from small moonquakes.

10. What happens chemically to the surface of the Moon due to heating by the Sun?

There are several things going on. The Moon has a very thin atmosphere. Its total mass is about 1x1015 atmospheres, 4 kg, and is made up of neon, helium, hydrogen, argon, sodium, potassium, and some other gases. Some of these elements are due to radioactive decay of materials within the Moon and some are due to the interaction of the surface with micrometeorites and solar radiation (ultraviolet radiation and solar wind), which knock atoms off of the surface material (sputtering). However, the solar wind works the other way by implanting helium into the surface (a potential source of energy for future lunar exploration). It is the sputtering that ultimately "weathers" the bright lunar rays over time and makes them disappear.

11. What possibility is there to place a habitable "biosphere" on the Moon?

There is nothing to prevent us from living on the Moon. Many books have been written on this subject. Because of space hazards (meteorites, solar radiation, etc.) one would want to live underground (covered by a lunar rille or something like that). The biggest problems would be food, water, and fuel. What could you grow in the lunar soil? Where would you get water? What can provide power, etc.?

12. How was the depth of the crust, mantle, and core of the Moon determined?

From a variety of methods, we have a fairly good idea what the interior of the Earth looks like. Thus, we can model what we think the interior of other objects should look like. For the terrestrial planets, it is believed that as they formed, the heavier elements such as iron, sank to the core. Therefore, "rocky" planets should have a light crust, a moderately dense mantle, and a highly dense iron core. As for the Moon, we do not know how much iron it "took away" from the Earth by impact and we do not know whether or not it has an iron core (left image below). But, it should have a light crust (we see this as the highlands), a rocky mantle (we see this as lava that filled the maria), and a “core” made of more dense, partially molten rocky and maybe some iron. Why partially molten? This is heat left over from the formation of the Moon. How do we know that there is a mantle and a core? Data from seismographs of Apollo 12, 14, 15, and 16 (1969-1977) detected “moonquakes” from deep within the interior of the Moon that are consistent with this model.

13. How much activity is there currently in the Moon’s interior?

What we know about any activity within the Moon comes from the seismographs from Apollo 12, 14, 15, and 16 (1969-1977). They detected over 12,500 "moonquakes": 1) 3,000 deep moonquakes (700 to 1,000 km below the surface); 2) 1,700 meteorite impacts; 3) 28 shallow moonquakes (20 to 30 km below the surface); and 4) other small quakes. The deep quakes are directly related to the interaction of the Moon with the Earth and the suntides. The timing of the quakes themselves shows that most of them were the result of tidal stresses, but that a few of them may have been due to the tidal effects triggering weak areas within the Moon (the core-mantle boundary). The impacts were due to objects ranging in size from 1 kg up to over 1,000 kg. The shallow quakes were as strong as magnitude 5.5 and are thought to be related to landslides in the interior of craters. The majority of the quakes are weak and seem to be related to thermal stress near the surface as the Moon warms up and cools off as it is heated and cooled by the daylight to non-daylight cycle. When there are large shallow quakes, the Moon actually rings like a bell. On Earth, earthquakes dampen out in a minute or two (thanks to the surface composition of the Earth). For the Moon, these quakes can last for 10 minutes or more because the rock is drier and does not dampen the shaking as much.

14. How much activity was there in the past?

There is no evidence for any activity in over 3 billion years, since the formation of the maria.

15. Are tunnels on the Moon formed by trapped gas?

What we see on the surface of the Moon are rilles, such as Hadley Rille. Hadley is a collapsed lava tube, which looks just like collapsed lava tubes on Earth, and was formed when the lava filled the mare basins. Hadley was visited by Apollo 15, so astronauts have actually explored the area around it. Because there are collapsed tubes, it is thought that there should also be tubes that are not collapsed. These would be great places to build habitats!

16. Why are the poles the only points to have water [ice]?

The Moon has day and night, and while low temperatures can be as low as -110°C = -170°F, the high can get up to 130°C = 265°F during the day. In order to have the ice cold enough to survive, it must be in areas that are always cold, so always in shadows. The only place for this is near the poles in the interiors of craters. Also, the water must be in the form of water ice, not liquid. The Moon is essentially in a vacuum (no atmosphere) and so the only stable form of water is ice. On Earth, "dry ice" converts directly from solid to a gas. On the Moon, with no atmosphere, water ice acts the same way. Liquid water is not stable, it would just boil away.

17. How soon may the United States send astronauts back to the Moon? Is any country looking at sending people to the Moon?

The US has now cancelled its plan to send astronauts back to the Moon. The program (rocket) had problems and it was not clear that these were easily fixed. Right now, the only country that is thinking of sending humans back to the Moon are the Chinese, but there aren't any firm dates for this (well after 2015 and probably after 2020).

18. If there was to be a Moon colony, how would the colony obtain the necessary oxygen and water to survive?

Finding water (ice) on the Moon is probably not a long-term solution. There have been several lunar spacecraft missions that have reported very small quantities of water at other locations on the Moon, but these have not been confirmed and are probably too small to be useful. Therefore, what is presently considered to be the best way to get water is as follows. The lunar rocks are silicates, like on Earth, so contain oxygen. One can extract the oxygen from the rocks and combine it with liquid hydrogen brought from Earth. This makes water. Also, fuel cells (like the ones used in electric cars) combine oxygen and hydrogen to make electricity. So, one can produce energy with water as a byproduct!

19. Are there any moves being made towards a research station on the Moon?

Right now, no. The US has cut back on its manned space program while the Chinese are talking about sending humans to the Moon. The world's nations are a long way from sending people to the Moon to establish a permanent base that would be able to support itself (or at least with minimal support from Earth). At the present time, it is estimated that it will cost about $50,000 a pound to get anything to the Moon. That translates to about $400,000 a gallon for water, a very expensive cup of tea or coffee!

20. How does the maria fill up the craters?

In some cases, like Sinus Iridium, the mare (lava) flowed into the crater through gaps or low spots along the rim.

21. On a map/picture, how can you tell the difference between certain features like ridges/troughs/lava flows/rilles?

This question can be taken in two different ways. First, is something a high spot or a low spot (dome vs. crater)? By knowing the direction of the Sun, one can tell by looking at the shading/shadows what is high and what is low. Second, we can compare pictures, say of the Moon or Mars, with what we see on Earth. While this is not perfect, it is not a bad start for determining what a feature is: ripples down-slope from a volcano, a lava flow; a gully-like feature on the slope of a volcano that looks like it was made by a thick fluid, a lava channel or rille; a channel that looks like it was made by something more fluid than lava, a dry river stream; etc.

22. What are the other theories for the formation of the Moon?

ConstraintFormation Model
 FissionCaptureCo-AccretionTidal DissapationGiant Impact
Moon is bignoyes??????yes
Moon was closeryesyes???yesyes
Lack of ironyesnonoyesyes
Moon-Earth mantleyesnoyesnoyes
Volatiles depleted?????????yesyes

23. Would the Earth be different if something had not flung off the material that made the Moon, if that is in fact what happened?

There are two ways to look at this. First, the mass of the Moon is only 1/81 that of the Earth and the impactor was probably only about 1/10 the mass of the Earth. So, this would make very little difference to what we have now. The other way to look at it is from the point of how the Moon has affected the Earth. Recall that the tilt of Mars may have changed significantly over time. The same could have been true for Earth, but Earth is thought to act as a stabilizing effect and help keep the tilt about the same. Another thing that might have been more important is life on Earth. It is thought that life on Earth may have started in tidal pools. Without a Moon, the evolution of life on Earth may have been different.

24. Does the nearside of the Moon look different if viewed from the northern part of Greenland vs. the southern tip of Chile?

The Moon is 30 Earth diameters away, so the part of the Moon one sees from the north is not very different from what one sees from the far south. However, there is one big difference. In the northern hemisphere, we look toward the south to see the Moon. In the southern hemisphere, we look toward the north to see the Moon—it would look upside down!

25. Why does the Moon appear round?

The Moon is actually not perfectly round, but the difference between its pole-to-pole diameter and its equatorial diameter is only about 0.1%. This is far too small to be noticeable by the human eye.

26. How was it determined that the impact of Earth to creation of the Moon occurred in a month?

We can only give a general answer to this question: computer modeling. You model an impact (using an impactor size, velocity, and impact angle) and then model the material ejected from the impact. Much of the ejecta either falls back to Earth or goes into orbit around the Earth. You can then model what happens to the material as it orbits the Earth and you find that most of it very quickly lumps together to form the Moon. Think of as a snowball rolling down a hill, getting bigger in size as it goes.

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