NASA’s latest Moon mission will end on Monday — not with a whimper, but a splat.
Two splats, actually.
Ebb and Flow, two space probes the size of washing machines that have been orbiting the Moon and measuring its gravity field, will perform an orchestrated death plunge on Monday, crashing into the body’s dark side.
The exercise will not be for the advance of science, but rather something of a garbage-disposal operation, to make sure that the probes — which are running out of fuel — do not come to rest in a historically significant place, like on Neil Armstrong’s footprints.
The Moon has been affronted this way many times before, especially during the space race of the 1960s, but NASA is now trying to dispose of its litter more carefully.
This time, the first impact will come 40 seconds past 5:38 p.m. Eastern Standard Time on Dec. 17 when Ebb slams into a mountain near the Moon’s north pole at 3,760 miles per hour. The second, from Ebb’s twin, Flow, will come 20 seconds later.
Unfortunately, since the action will happen on the dark side of the Moon, there will be nothing for earthlings to see.
“We’re not expecting a flash that is visible from Earth,” Maria T. Zuber, the mission’s primary investigator, said Thursday during a telephone news conference.
That is all by design as NASA wraps up its Gravity Recovery and Interior Laboratory mission, or Grail, for short.
To map the gravity, the two spacecraft are in an orbit passing over the Moon’s north and south poles. They pass over all parts of the lunar surface as the Moon rotates below.
If the probes’ fuel ran out and their orbits decayed, they could crash anywhere on the Moon, including a slim chance — eight in one million — that one of them could obliterate those famous footprints or another historic site.
With the spacecraft guided into a mountain, the chances are zero.
Even in their demise, however, Ebb and Flow may be able to aid the cause of science. Another of NASA’s spacecraft, the Lunar Reconnaissance Orbiter, will pass over the crash sites, and scientists hope that they will be able to tell something about the mountain — which is a remnant of a crater rim — from the gouges created by Ebb and Flow.
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