The Apollo Program was a monumental moment in human history – landing the first human beings on the surface of the Moon. However, the Apollo missions contributed more than putting humans on the Moon, it also produced a lot of new scientific data and discoveries which expanded our knowledge of both the Moon itself and our Solar System. 

Here are ten of our top Apollo discoveries:

1. The Moon is not a primordial object; it is an evolved rocky body with an internal structure similar to that of Earth and the other terrestrial planets. 

What does this mean? Before Apollo, the state of the Moon was a subject of almost unlimited speculation. We now know that the Moon is made of rocky material that has been melted, erupted through volcanoes, and crushed by meteor impacts. The Moon possesses a crust about 25 miles thick, a mantle that is about 849 miles thick, and a core about 205 miles thick. The core is made up of a solid inner core about 150 miles thick and a fluid outer core about 56 miles thick. Some rocks preserve a remnant magnetic field, although no active magnetic field exists today.

2. The Moon is ancient and still preserves its early history (the first billion years). 

The extensive record of impact craters on the Moon, when calibrated using absolute ages of lunar rock samples, provides a key for unravelling time scales for the geologic evolution of Mercury, Venus, and Mars based on their individual crater records. Remote sensing of other planets, or the interpretation of geologic features via images and other data, is based in part on lessons learned from the Moon. Before Apollo, for example, the origin of lunar impact craters was not fully understood and the origin of similar craters on Earth was highly debated.

3. The oldest Moon rocks are older than the oldest Earth rocks.  

The oldest Moon rock returned to Earth is an anorthosite found by the Apollo 16 astronauts. It is estimated to be about 4.46 billion years old.  It is an anorthosite, the rock that makes up the light-colored lunar highlands. The oldest rocks found on Earth are about 4.28 billion years old. Ancient rocks are rare on Earth because active geologic forces, including plate tectonics and erosion, recycle and remove the oldest surfaces.

4. The Moon and Earth are genetically related and formed from a common source of materials. 

The distinctively similar compositions of Moon rocks and Earth rocks (particularly the oxygen isotopic compositions) clearly show formation from a common source of debris from a collision between Earth and a Mars-sized body nicknamed Theia. Relative to Earth, however, the Moon is highly depleted in iron and in volatile elements.

5. The Moon is lifeless; it contains no living organisms, fossils, or native organic compounds. 

Extensive testing revealed no evidence for life, past or present, among the lunar samples. Even non-biological organic compounds are amazingly absent; traces can be attributed to contamination by meteorites.

6. All Moon rocks originated through high-temperature processes with little or no involvement with water. They can be grouped in three rock types: basalts, anorthosites, and breccias. 

Basalts are dark lava rocks that fill mare basins on the Moon; they resemble lavas that comprise the oceanic crust of Earth but are much older.  

Anorthosites are light rocks that form the ancient highlands; they generally resemble the silicate rich rocks of Earth’s continents.  

Breccias are composite rocks formed from other rock types that have been broken into fragments, mixed together, and compacted to form a solid rock mass by heat and pressure from impact events. The Moon has no rocks like sandstones, shales, or limestones which form in bodies of water on Earth.

7. Early in its history, the Moon was melted to great depth to form a "magma ocean." The lunar highlands are the ancient, low-density rocks that floated to the surface of the magma ocean. 

The lunar highlands were formed about 4.1-4.4 billion years ago by an early flotation crust in a magma ocean that covered the Moon to a depth of tens of kilometers or more. Innumerable impacts through geologic time shaped the ancient crust.

8. The lunar magma ocean was followed by a series of huge asteroid impacts that created basins which were later filled by lava flows. 

The large, dark lowlands such as Mare Imbrium are gigantic impact basins, formed early in lunar history, that were later filled by basalt lava flows from about 3.2-4.0 billion years ago with some flows as recent as 1.2 billion years old. Flood volcanism buried the floors of the lowland basins under thick sequences of lava flows. Some pyroclastic eruptions produced deposits of orange and emerald-green glass beads.

9. The thickness of the Moon’s crust is asymmetrical — its crust is thicker on the far side, while most basalt-filled basins, and the mass concentrations some form, occur on the near side. 

It is not well understood why the crust of the Moon is thicker on the farside (by 6 or 12 miles) than the nearside. On the nearside, the accumulation of thick sequences of dense mare basalt in the large impact basins resulted in mass concentrations called mascons.  Relative to its geometric center, the Moon's center of mass is displaced toward Earth by several kilometers. 

10. The surface of the Moon is covered by dust and rock fragments that form the lunar soil or regolith. The lunar regolith contains abundant hydrogen implanted by the Sun.   

The regolith was produced by innumerable impacts through geologic time. Hydrogen trapped in the silicate dust derived from pulverized rock and mineral grains in the regolith can react with oxygen to make water molecules. In the very cold permanently shadowed craters at the lunar poles, water molecules might have accumulated into water ice deposits.