SaU 169 is not only a unique meteorite because its chemistry is exceptionally KREEP-rich. Even though there are very small (milligram-sized) rock fragments in lunar soils collected during the Apollo program that are similar in chemistry, the meteorite SaU 169 is of a size which allowed, for the first time, to perform a complete petrographic investigation, chemical analysis and age dating on the same stone. The lucky constellation that two different regoliths were attached to the main lithology gave the opportunity to reconstruct its history and origin in detail. The stone offered also the possibility to date the Imbrium impact with high precision, using a method which is generally considered the most precise for rocks that old. This age is probably provides a new key date for lunar and even terrestrial stratigraphy. It is generally accepted that the Imbrium impact was the last of the large basin-forming impacts on the Moon and that its formation corresponds to the end (or better: strong decline) of the heavy meteorite bombardement in the inner solar system. It is also assumed that only after the cessation of large impacts the origin, spreading and evolution of life on Earth was possible.

SaU is a rock which demonstrates impressively how rocks can travel, like a ping-pong-ball, on a body or from one body to another.

It should also be stressed here that without the Apollo and Luna sampling programs and especially the huge advance in knowledge of the Moon acquired during investigations in the last 20 - 30 years (e.g., NASA's remonte sensing programs with the Clementine and Lunar Prospector missions) we would only be able to tell that SaU 169 is an exceptional lunar rock. Without the mission-based background information on the Moon we could never have linked ages and chemical data with lunar surface information. It will probably be a long go until a similar database is available for Mars which would allow to pinpoint characteristic rocks to specific source areas.

The main mass of SaU 169 is presently exhibited at the Natural History Museum in Bern, Switzerland, in the exhibition "Ping-Pong in Space", until end of September 2004.

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This research is supported by the Swiss National Science Foundation.