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GRAIL
GRAIL Mission to Earth's Moon

Goals: GRAIL flew twin spacecraft -- named Ebb and Flow -- in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The goal was to reveal differences in density of the Moon's crust and mantle and will help answer fundamental questions about the Moon's internal structure, thermal evolution and history of collisions with asteroids.

Accomplishments: The twin GRAIL probes orbiting Earth's moon generated the highest resolution gravity field map of any celestial body. The gravity field map revealed an abundance of features never before seen in detail, such as tectonic structures, volcanic landforms, basin rings, crater central peaks and numerous simple, bowl-shaped craters. Data also show the moon's gravity field is unlike that of any terrestrial planet in our solar system. The map will provide a better understanding of how Earth and other rocky planets in the solar system formed and evolved.

At the end of an extended mission, Ebb and Flow were sent purposely into the lunar surface because their low orbit and low fuel levels preclude further scientific operations. They impacted at mountain near Goldschmidt crater on the lunar near side.


GRAIL: Studying the Moon from Crust to Core
Key Dates
10 Sep 2011:  Launch
31 Dec 2011:  GRAIL A Orbit Insertion
1 Jan 2012:  GRAIL B Orbit Insertion
17 Dec 2012:  GRAIL-A Lunar Impact (22:28:41 UTC)
17 Dec 2012:  GRAIL-B Lunar Impact (22:29:01 UTC)
Status: Science Analysis Phase
Fast Facts
GRAIL Facts GRAIL is the lunar counterpart of the successful GRACE mission (right), twin satellites launched in 2002 to make detailed measurements of Earth's gravity field.

GRAIL is part of NASA's Discovery Program of lower-cost, highly focused planetary science investigations.

Studying the Moon is key to understanding how terrestrial planets evolved because it is the most accessible body that preserves a surface record spanning most of our solar system's history.

The GRAIL orbiters -- Ebb and Flow -- were named by Nina DiMauro's fourth graders at Emily Dickinson Elementary School in Bozeman, Mont.
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Last Updated: 6 Mar 2013