# Liquids/Liquid objects/Moon

The true shape of the Moon is "slightly flattened, with a bulge on one side."
The shape of the Moon is like "a lemon with an equatorial bulge. If you can imagine a water balloon flattening out as you spin it.”
The "moon barely spins, yet it appears to have the sort of equatorial bulge caused by rotation. And why would a giant ball of cooled liquid be anything but spherical?"
“There’s no plate tectonics like on the earth. Why is it so deformed?”
"Its squashed appearance is probably a result of the gravitational process called tidal heating or acceleration, which stretched the moon’s crust as it was being formed. The equatorial bulge probably dates to a later period, when the moon was still spinning but was slowing down and moving away from earth, freezing a tidal surge in place."
“There is an expected ratio you get for each of those two tidal processes. We found the exact ratios you would expect for each process.”

## Water on the Moon

Water does occur on the Moon usually as ice.

## Protons

The Apollo Lunar Surface Experiments Packages (ALSEP) determined that more than 95% of the particles in the solar wind are electrons and protons, in approximately equal numbers.
"Because the Solar Wind Spectrometer made continuous measurements, it was possible to measure how the Earth's magnetic field affects arriving solar wind particles. For about two-thirds of each orbit, the Moon is outside of the Earth's magnetic field. At these times, a typical proton density was 10 to 20 per cubic centimeter, with most protons having velocities between 400 and 650 kilometers per second. For about five days of each month, the Moon is inside the Earth's geomagnetic tail, and typically no solar wind particles were detectable. For the remainder of each lunar orbit, the Moon is in a transitional region known as the magnetosheath, where the Earth's magnetic field affects the solar wind but does not completely exclude it. In this region, the particle flux is reduced, with typical proton velocities of 250 to 450 kilometers per second. During the lunar night, the spectrometer was shielded from the solar wind by the Moon and no solar wind particles were measured."
In February 2009, the ESA SARA LENA instrument aboard India's Chandrayaan-1 detected hydrogen ENAs sputtered from the lunar surface by solar wind protons. Predictions had been that all impacting protons would be absorbed by the lunar regolith but for an as yet unknown reason, 20% of them are bounced back as low energy hydrogen ENAs. It is hypothesized that the absorbed protons may produce water and hydroxyls in interactions with the regolith.

## Infrareds

Four radiometers [aboard Luna 13 ] recorded infrared radiation from the [Moon's] surface indicating a noon temperature of 117 ±3 °C.
"An infrared camera image from the moon is taken with the Lunar Crater Observation and Sensing Satellite (LCROSS) mid-infrared camera. LCROSS has nine science instruments that collect different types of data which are complementary to each other. These instruments provide for a robust collection of data about the composition of the lunar regolith." On the 9th of October, 2009, the Diviner team announced detection of a hot spot on the moon at the location of the LCROSS impact.
Frank Washington Very's most important work was in measuring the temperature of the surface of the Moon using a bolometer. Samuel Pierpont Langley published in 1890 a widely read paper on the Moon observations, but for unknown reasons omitted Very's name from the list of authors. In 1891, Very published his own paper about the "Distribution of the Moon's Heat," which also included measurements taken during a lunar eclipse.
"NASA's Moon Mineralogy Mapper, an instrument on the Indian Space Research Organization's Chandrayaan-1 mission, took [the image at right] of Earth's moon. It is a three-colour composite of reflected near-infrared radiation from the sun, and illustrates the extent to which different materials are mapped across the side of the moon that faces Earth. Small amounts of water were detected on the surface of the moon at various locations. This image illustrates their distribution at high latitudes toward the poles. Blue shows the signature of water, green shows the brightness of the surface as measured by reflected infra-red radiation from the sun and red shows a mineral called pyroxene."
"Blue shows the signature of water, green shows the brightness of the surface as measured by reflected infrared radiation from the sun and red shows an iron-bearing mineral called pyroxene."
"Small amounts of water were detected on the surface of the moon at various locations. This image illustrates their distribution at high latitudes toward the poles."
"These images show a very young lunar crater on the side of the moon that faces away from Earth, as viewed by NASA's Moon Mineralogy Mapper [M$^3$] on the Indian Space Research Organization's Chandrayaan-1 spacecraft. On the left is an image showing brightness at shorter infrared wavelengths. On the right, the distribution of water-rich minerals (light blue) is shown around a small crater. Both water- and hydroxyl-rich materials were found to be associated with material ejected from the crater."
"The mid-infrared image of the Moon [at left] was taken during a 1996 lunar eclipse by the SPIRIT-III instrument aboard the orbiting Midcourse Space Experiment satellite. At these wavelengths, MSX was able to characterize the thermal (heat) distribution of the lunar surface during the eclipse. The brightest regions are the warmest, and the darkest areas are the coolest. The well-known crater Tycho is the bright object to the south of center. Numerous other craters are also seen as bright spots, indicating that their temperature is higher than in the surrounding dark mare. The Moon is geologically inactive for the most part, and any temperature differences are a result primarily of variations in solar heating (rather than volcanoes, for example). The Moon lacks an atmosphere to moderate temperatures, which can vary from 130 degrees Celsius (265 degrees Fahrenheit) in the sun to -110 degrees Celcius (-170 degrees Fahrenheit) in the shade."
M$^3$ found a rock dominated by Mg-spinel with no detectable pyroxene or olivine present (<5%) occurring along the western inner ring of Moscoviense Basin (as one of several discrete areas). The occurrence of this spinel does not easily fit with current lunar-crustal evolution models.

## Radars

The Moon is comparatively close and was detected by radar, soon after the invention of the technique, in 1946. Measurements included surface roughness and later mapping of shadowed regions near the poles.
"Clementine orbited the Moon in 1994 for 71 days, mapping the Moon globally in 11 wavelengths and measuring its topography by laser ranging. [... The] bistatic radar experiment (so-called because the spacecraft transmitted while we listened to the echoes on Earth) found evidence in the dark areas near the south pole of the Moon for material with high circular polarization ratio [CPR]".
"Meanwhile, astronomers on Earth began publishing results questioning the Clementine and Lunar Prospector [1998-2000] results. With the giant Arecibo radiotelescope, radar images were taken from the Earth. They found radar reflections with high CPR lying in both permanent darkness and in sunlit areas. Ice is not stable in sunlight, so they postulated that all high CPR is caused by surface roughness; if any ice is at the lunar poles, it must be in a finely disseminated form, invisible to radar mapping."
The experiment from Clemintine "was bistatic, i.e., the transmitter and receiver were in different places. Bistatic radar has the advantage of observing reflections through the phase angle, the angle between transmitted and received radio rays [...]. This phase dependence is important. It’s similar to the effect one gets from looking at a bicycle reflector at just the right angle: at certain angles, the internal planes in the transparent plastic align and a very bright reflection is seen. Similarly, in both radio and visible wavelengths on the Moon, we see an “opposition surge”, an apparent increase in brightness looking directly down from the sun (zero phase). Clementine orbited the Moon such that we could observe its phase dependence [...] and we specifically looked for this “opposition surge”, called the Coherent Backscatter Opposition Effect (CBOE). CBOE is particularly valuable to identify ice on planetary surfaces."
"Clementine transmitted right circular polarized (RCP) radio and we listened on Earth in both right- and left-circular polarized (LCP) channels. The ratio of power received in these two channels is called the circular polarization ratio (CPR). The dry, equatorial Moon has CPR less than one, but the icy satellites of Jupiter all have CPR greater than one. We know these objects have surfaces of water ice; in this case, the ice acts as a radio-transparent media in which waves penetrate the ice, are scattered and reflected multiple times, and returned such that some of the waves are received in the same polarization sense as they are sent—they have CPR greater than unity"
"The problem with CPR alone is that we can also get high values from very rough surfaces, such as a rough, blocky lava flow, which has angles that form many small corner reflectors. In this case, a radio wave could hit a rock face (changing RCP into LCP) and then bounce over to another rock face (changing the LCP back into RCP) and hence to the receiver [...]. This “double-bounce” effect also creates high CPR in that “same sense” reflections could mimic the enhanced CPR one gets from ice targets."
At lower right is an image using the Goldstone DSS-14 antenna as a transmitter and the DSS-13 as a receiver, a form of radar interferometry. The cross for the south pole in the Arecibo image is in the Shackleton crater of the Goldstone image.

## Astroglaciology

The discoveries of water ice on the Moon, Mars and Europa add an extraterrestrial component to the field, as in "astroglaciology".

## Craters

Lunar craters "are pits or depressions in the surface of the Moon, produced by great impacts of gigantic meteoroids which mostly took place billions of years ago. They range in size from huge walled plains more than a hundred miles across to microscopic pits. The smallest craters which can be glimpsed through ordinary binoculars are about twenty miles across. These craters are most common in the light-colored Lunar highlands. They are named after historical figures, mostly scientists."
"During its flight, the Galileo spacecraft returned images of the Moon. The Galileo spacecraft took these images on December 7, 1992 on its way to explore the Jupiter system in 1995-97. The distinct bright ray crater at the bottom of the image is the Tycho impact basin. The dark areas are lava rock filled impact basins: Oceanus Procellarum (on the left), Mare Imbrium (center left), Mare Serenitatis and Mare Tranquillitatis (center), and Mare Crisium (near the right edge). This picture contains images through the Violet, 756 nm, 968 nm filters. The color is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision."
The dark irregular mare lava plains are prominent in the fully illuminated disk. A single bright star of ejecta, with rays stretching a third of the way across the disk, emblazons the lower centre: this is the crater Tycho on the Near side of the Moon. But, on the far side, the full disk is nearly featureless, a uniform grey surface with almost no dark mare. There are many bright overlapping dots of impact craters. And, an almost complete lack of dark maria.
The topography of the Moon has been measured with laser altimetry [using the sodium D2 line in the yellow] and stereo image analysis. The most visible topographic feature is the giant far side South Pole – Aitken basin, some 2,240 km in diameter, the largest crater on the Moon and the largest known crater in the Solar System. At 13 km deep, its floor is the lowest elevation on the Moon. The highest elevations are found just to its north-east, and it has been suggested that this area might have been thickened by the oblique formation impact of South Pole – Aitken. Other large impact basins, such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale, also possess regionally low elevations and elevated rims. The lunar far side is on average about 1.9 km higher than the near side.
"These images show a very young lunar crater on the side of the moon that faces away from Earth, as viewed by NASA's Moon Mineralogy Mapper [M$^3$] on the Indian Space Research Organization's Chandrayaan-1 spacecraft. On the left is an image showing brightness at shorter infrared wavelengths. On the right, the distribution of water-rich minerals (light blue) is shown around a small crater. Both water- and hydroxyl-rich materials were found to be associated with material ejected from the crater."
"Unusual minerals in impact craters on the moon may not have originated on the moon, but may be from asteroids that created the craters"
"Future studies of the moon's composition will have to show that exposed surface rocks really come from the moon and were not delivered by impacts, especially for unusual or exotic minerals ... "We cannot infer the deep composition of the moon from rocks in the centers of large craters without more care than has been used to date".
"[C]omputer models [have been used] to simulate the formation of lunar craters by asteroid impacts and ... [in] some impacts much of the asteroid's material is not vaporized but is instead deposited in the center of the impact craters."

## Lava on the Moon

Lava appears to be far more common as basalt than water is as ice.

## Greens

"During its mission, the Galileo spacecraft returned a number of images of Earth's only natural satellite. Galileo surveyed the moon on Dec. 7, 1992, on its way to explore the Jupiter system in 1995-1997."
"This color mosaic was assembled from 18 images taken by Galileo's imaging system through a green filter. On the upperleft is the dark, lava-filled Mare Imbrium, Mare Serenitatis (middle left), Mare Tranquillitatis (lower left), and Mare Crisium, the dark circular feature toward the bottom of the mosaic. Also visible in this view are the dark lava plains of the Marginis and Smythii Basins at the lower right. The Humboldtianum Basin, a 400-mile impact structure partly filled with dark volcanic deposits, is seen at the center of the image."

## Hypotheses

* The Moon did not originate in orbit around the Earth.