Just before 5:30 p.m. EST, NASA will crash two spacecrafts into a mountain on the moon.
The GRAIL spacecrafts, called Ebb and Flow, were launched last September and entered the moon's orbit at the beginning of the year.
Their purpose was to measure changes in the moon's gravitational field in order to locate structures like mountains, impact craters, and volcanic landforms.
Earlier this month, at the American Geophysical Union meeting in San Francisco, researchers unveiled the highest resolution map of the moon's gravity field created from data collected by the probes. The map will make it easier to land on the moon in the future.
Now it's time to say goodbye. The washing-machine-size spacecrafts are running low on fuel and they've fulfilled their science duties.
The probes will smash into the lunar surface at 3,760 mph near a crater named Goldschmidt. There won't be any pictures of the crash landing because the region will be in a shadow at the time, though NASA will stream live commentary of the event from the Jet Propulsion Laboratory in California beginning at 5 p.m. EST.
Watch live below:
This animation shows the final flight path for Ebb and Flow:
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