GRAIL completes primary mission

The next phase will see the probes orbit just 23 km above the lunar surface



The GRAIL probes have been flying in formation above the lunar surface

It was determined long ago that the Moon is not made from cheese, but despite studying its surface for thousands of years little was known about how it came to be. Now, after completing its primary mission ahead of time, NASA’s Gravity Recovery and Interior Laboratory (GRAIL) has gathered an unprecedented amount of data about not only the structure of Earth’s satellite, but also how it evolved.

For 89 days GRAIL’s two probes, Ebb and Flow, have been orbiting the Moon in tandem, gathering data that scientists have used to create a high-resolution map of our satellite's gravitational field.

Throughout the mission, NASA monitored the exact distance between the probes. Any fluctuations signaled a change in the Moon’s gravity field, indicating a crater, mountain or mass below the Lunar surface.

Both probes have been powered of until 30 August, after which they will continue with the next phase of their mission, taking an even closer look at the Moon's gravity field. For this, the GRAIL team will halve the height at which the probes orbit to a mere 23 kilometres above the surface.

Scientists hope that, over time, data from GRAIL will increase our knowledge of how Earth and its rocky neighbors in the inner Solar System developed into the diverse worlds we see today.

For a more in depth analysis of the GRAIL mission, read our feature Inside the Moon from the September 2011 issue of Sky at Night Magazine.

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