A series of diagrams illustrating the formation of Mercury's polar ice deposits.

(A) A high-latitude impact crater illuminated by the angled rays of the Sun creates a region of very warm temperatures on the illuminated rim, lower temperatures on the illuminated floor of the crater, and extremely cold temperatures in regions of permanent shadow.

(B) A comet or water-rich asteroid that also contains organic compounds impacts Mercury.

(C) The water and organic compounds are spread over a wide geographic region, and a small fraction of both compounds migrate to the poles where they can become cold-trapped as ices.

(D) Over time, the water ice in the warmer regions vaporizes, leaving behind the more stable organic impurities at the surface.

(E) The ice retreats further to a stable long-term configuration. In the coldest areas, water ice remains on the surface. In the warmer areas, the ice is covered by an ice-free surface layer that is rich in organic impurities that have been darkened by exposure to Mercury's space environment.

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. Visit the Why Mercury? section of this website to learn more about the key science questions that the MESSENGER mission is addressing. During the one-year primary mission, MDIS acquired 88,746 images and extensive other data sets. MESSENGER is now in a year-long extended mission, during which plans call for the acquisition of more than 80,000 additional images to support MESSENGER's science goals.

For information regarding the use of images, see the MESSENGER image use policy.