Apollo 12 Lunar Samples
Lunar Sample Overview
When viewed through a telescope, the Apollo 12 landing site has fewer craters and a slightly redder color than the Apollo 11 landing site. It was thought that these characteristics indicated that the rocks at the Apollo 12 landing site were both younger and different in chemical composition than the rocks at the Apollo 11 landing site. Apollo 12 returned 34 kilograms of samples, including 45 rocks, samples of lunar "soil," and several core tubes that included material from as much as 40 centimeters below the lunar surface. This material both confirmed the pre-mission expectations and also posed some new questions.
The Apollo 11 rocks were a mixture of basalts and breccias. In contrast, the Apollo 12 rocks were almost all basalts, with only two breccias in the returned samples. Basalts are dark-colored rocks solidified from molten lava. They are a common type of volcanic rock on Earth and are found in places such as Hawai'i. The basalts at the Apollo 12 site formed 3.1 to 3.3 billion years ago, roughly 500 million years later than the Apollo 11 basalts. Basalt consists primarily of the minerals pyroxene and plagioclase. At the Apollo 12 landing site, several different varieties of basalt were identified from the presence of other minerals such as olivine or ilmenite. Overall, there is much less of the element titanium in the Apollo 12 samples than in the Apollo 11 samples, which explains the more reddish color of this region. The differences in age and chemical composition between the Apollo 11 and Apollo 12 samples demonstrate that mare volcanism did not occur as a single, Moon-wide melting event. The Apollo 12 basalts formed from material that melted at depths of at least 150 to 250 kilometers below the surface and then ascended to the surface prior to solidifying.
A ray of material ejected from the crater Copernicus crosses the Apollo 12 landing site. Studies of some Apollo 12 soil samples suggest that the Copernicus impact occurred about 800 million years ago, but this estimated age is not certain.
The most unusual type of rock found at the Apollo 12 landing site is known as KREEP. This is an acronym for rocks that are rich in the elements potassium (denoted as K by chemists), rare earth elements (REE), and phosphorus (P). Only one sample of KREEP was returned by Apollo 12, but many additional samples were collected on Apollo 14 and Apollo 15. KREEP is believed to have formed early in the history of the Moon during the solidification of the Moon's molten stage, known as the magma ocean.