Twin space probes, Ebb and Flow, are expected to crash into the moon next Monday, Dec. 17. The probes, which were developed and controlled by NASA, will hurl themselves into the surface of the moon intentionally, marking the end of their journey.
Since 2011, the twin probes have been orbiting the moon in order to create a detailed gravity map of the solar body. Nearly $500 million dollars later, the Grail project, which stands for Gravity Recovery and Interior Laboratory, has finished the map of the moon’s gravity field with an incredible amount of detail.
Ebb and Flow were launched in September 2011 and have been circling the moon for nearly a year after reaching its orbit on New Year’s Eve (Ebb) and New Year’s Day (Flow) of last year. The Grail mission was only supposed to last for 90 days from March until May, but the scientists involved in the project decided to extend Ebb and Flow’s trip in order to uncover additional data.
While orbiting the moon, Ebb and Flow have been circling the lunar surface in formation. They are able to detect small differences in the distance between them, which can be caused by mountains, craters, or subsurface mass concentrations. Researchers involved in the project then took the readings from the probes and created an incredibly detailed map of the moon’s gravitational field.
The gravity map, which was revealed at the meeting of the American Geophysical Union in San Francisco last week, showed some interesting results. One of the most shocking findings from the Grail project was the size of the moon’s crust. The probes found that the lunar crust is much thinner than was previously thought. This has led scientists to believe the moon and other rocky bodies in space, such as Earth and Mars, were impacted much more violently than they previously thought.
This major finding came from the data Ebb and Flow collected during the original Grail mission. Researchers expect to perfect the gravity map even more when data collected from the extended lunar stay is added. Following their initial missions, the probes flew much closer to the surface of the moon, moving from 34 miles (55 km) to just 14 miles (23 km). It is expected that the decrease in altitude from the surface will increase the accuracy of the map even further.
Since they were only expected to stay in orbit for 90 days, Ebb and Flow are now begging to run low on fuel, according to NASA officials who expected the fuel shortage to happen. The scientists behind the probes will program them to slam into the moon on Dec. 17, completing their mission for good.