It’s the Thelma and Louise of space exploration. Lunar probes Ebb and Flow will going out in a blaze of glory this afternoon, hurling themselves at a mountain range on the Moon’s surface.
Also like Thelma and Louise, the two probes’ journey has been short-lived. The GRAIL mission in which they were enlisted started in September of last year. Since then, Ebb and Flow have been orbiting the Moon one after the other, gathering information on its gravitational fields. The probes have become very well acquainted with the Moon’s surface, dipping as low as six miles above its surface.
The idea was to have Ebb and Flow work as a team to map the gravitational field. When the two probes would pass over higher altitudes like mountain ranges, the higher gravity would pull on Ebb, creating a larger distance between the two probes. Likewise, when they flew over craters or valleys, the pull would shorten the distance.
While this created a very complete topographic map of the Moon, it also led to new discoveries. By measuring density below the Moon’s surface, Ebb and Flow found that there are subterranean cracks hundreds of miles long, which formed when the still partially-molten Moon was forming. Asteroid collisions are likely responsible for the cracks’ being underground.
But all good things must come to an end. Their work done, Ebb and Flow’s fuel deposits are dwindling. Rather than have them possibly crash into the preserved moon landing site, NASA is programming the two to collide with the lunar mountain range between 4:28 and 4:29 p.m. CT, most likely vaporizing at as they approach at 3,760 m.p.h.
But Ebb and Flow are lucky. Most probes that have finished their missions are dispatched into other planets or moons alone. At least the GRAIL probes are going down together.