A probe is an unmanned flying object, which explores space. Different to a satellite, a probe does not circle the Earth but flies to other celestial bodies, which they circle, too, but are then called orbiters. Two of these probes have been on the way to the Moon since 10th September 2011, to take measurements with unprecedented accuracy. The GRAIL lunar probes have reached the orbit of the Moon as planned, at the turn of the year 2011/12 and are now currently at work, until they will shatter on the Moon’s surface. In the meantime, they will have transmitted lots of data back to Earth.
You actually have to envision this: there are two devices (in the size of a fridge) flying through space and we are sitting here on Earth to operate the remote control. Isn’t that fascinating? Humans are really doing some crazy things …
What are those probes actually doing? They are orbiting the Moon at a height of 30 mi (needing 113 minutes for one orbit), flying with a distance of approx 125 mi between them, and are measuring the Moon’s gravitational field. Conclusions can then be drawn about the consistency of the Moon’s surface and also the Moon’s interior and therefore many new findings can be obtained, among others about the origin of the Moon. The results will hereby be a thousandfold more accurate than any previous measurements. Especially about the reverse side of the Moon, many new things will be found out, thus new insights gained.
Incidentally, in a nationwide school contest in January 2012, names for both probes were searched amongst thousands of pupils, and the 4th grade of an elementary school won. The probe GRAIL-A is now called »Ebb«, the probe GRAIL-B is now »Flow«. A nice reference to the tides that are caused by the Moon.
By the way, the entire project costed a mere 496 million US Dollar – nothing to sneeze at ;-)