A pair of robotic twins that have been diligently mapping the moon this year went out with a bang Monday.

As scheduled, the Gravity Recovery and Interior Laboratory probes Ebb and Flow crashed into a mountain on the moon, ending a fruitful mission to study the surface and composition of the celestial body.

"The two probes were sent purposely into the moon because they no longer had enough altitude or fuel to continue science operations," NASA said.

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