NASA's GRAIL Spacecraft in Science Collection Phase

An artist's depiction of the twin spacecraft that comprise NASA's Gravity Recovery And Interior Laboratory (GRAIL) mission. During the GRAIL mission's science phase, spacecraft (Ebb and Flow) transmit radio signals precisely defining the distance between them as they orbit the Moon in formation. As the two fly over areas of greater and lesser gravity caused by both visible features, such as mountains and craters, and masses hidden beneath the lunar surface, the distance between the two spacecraft will change slightly. Mission scientists use this information to create a high-resolution map of the Moon's gravitational field. The data will allow scientists to understand what goes on below the lunar surface. This information will increase knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today.

Illustration credit: NASA/JPL-Caltech/MIT

Note: See also PIA13965: GRAIL Spacecraft Over the Moon.

Poinsot Crater

This image of the lunar surface was taken by NASA's MoonKAM system onboard the Ebb spacecraft on March 15, 2012. The 42.3-mile-wide (68-kilometer-wide) crater in the middle of the image (with the smaller crater inside) is Poinsot. Crater Poinsot, named for the French mathematician Louis Poinsot, is located on the northern part of the moon's far side.

MoonKAM (Moon Knowledge Acquired by Middle school students), is led by Sally Ride, America's first woman in space, and her team at Sally Ride Science, in collaboration with undergraduate students at the University of California in San Diego. Over 2,700 schools in 52 countries have signed up to participate in MoonKAM.

Photo credit: NASA/Caltech-JPL/MIT/SRS

Note: For more information, see NASA GRAIL Returns First Student-Selected Moon Images.

The Earth from the Moon

This image of the far side of the lunar surface, with Earth in the background, was taken by NASA's MoonKAM system onboard the Ebb spacecraft as part of the first image set taken from lunar orbit from March 15-18, 2012. A little more than half-way up and on the left side of the image is the crater De Forest. Due to its proximity to the southern pole, De Forest receives sunlight at an oblique angle when it is on the illuminated half of the Moon.

MoonKAM (Moon Knowledge Acquired by Middle school students), is led by Sally Ride, America's first woman in space, and her team at Sally Ride Science, in collaboration with undergraduate students at the University of California in San Diego. Over 2,700 schools in 52 countries have signed up to participate in MoonKAM.

Photo credit: NASA/Caltech-JPL/MIT/SRS

Note: For more information, see NASA GRAIL Returns First Student-Selected Moon Images.

Copernicus Crater in Ultraviolet Light

LROC Wide Angle Camera (WAC) visible to ultraviolet portrait of Copernicus Crater, image 458 kilometers (284 miles) wide.

Understanding how scientists determine the relative age of geologic units on the Moon is straightforward, most of the time. One simply follows the law of superposition; what is on top is younger, what is below is older. In some cases, superposition relations are not clear, so scientists then compare crater densities. That is the number of impact craters on a common size of ground. Since impacts occur randomly both in time and on the Moon's surface, any piece of ground has an equal chance of being hit. Over time, the number craters in a given area increases. Simply stated, the older an area the more craters you will find.

Photo credit: NASA/GSFC/Arizona State University

Note: For more information, see Absolute Time.

Tour of the Moon

"Tour of the Moon" takes viewers to several interesting locations on the moon. Tour stops included in this breathtaking journey across the moon's surface are: Orientale Basin, Shackleton crater, South Pole-Aitken Basin, Tycho crater, Aristarchus Plateau, Mare Serenitatis, Compton-Belkovich volcano, Jackson crater and Tsiolkovsky crater.

Video credit: NASA; text credit: NASA.

Evolution of the Moon

"Evolution of the Moon" explains why the moon did not always look like it does now. The moon likely started as a giant ball of magma formed from the remains of a collision by a Mars-sized object with the Earth about four and a half billion years ago. After the magma cooled, the moon's crust formed. Then between 4.5 and 4.3 billion years ago, a giant object hit near the moon's South Pole, forming the South Pole-Aitken Basin, one of the two largest proven impact basins in the solar system. This marked the beginning of collisions that would cause large scale changes to the moon's surface, such as the formation of large basins.

Because the moon had not entirely cooled on the inside, magma began to seep through cracks caused by impacts. Around one billion years ago, it's thought that volcanic activity ended on the near side of the moon as the last of the large impacts made their mark on the surface. The moon continued to be battered by smaller impacts. Some of the best-known impacts from this period include the Tycho, Copernicus, and Aristarchus craters. So, while the moon today may seem to be an unchanging world, its appearance is the result of billions of years of violent activity.

Video credit: NASA