The third and final flyby of the probe MESSENGER about the planet Mercury before it returns and enters orbit of the innermost planet happened a few days ago. As expected, the probe was able to image a bit more of the planet never before seen and also took some measurements of Mercury’s exosphere to determine more about the complex atmospheric dynamics of the planet. However, before the probe made it close enough to the planet to take some images of areas identified as interesting in the two previous flybys, the probe entered safe mode and suspended operations. Fortunately, the probe left on course for its return and orbital insertion. The flight engineers noted that they still had to learn how to fly the thing, referring to the difficulties in running a spacecraft at such a great distance, so close to the Sun for such a long time.
Users of twitter listening to reports of the flyby coming through MESSENGER’s twitter account shared in the exultations of the first indications of data, such as these pictures, and then the confusion at the sudden lack of signal, later explained. Some erroneously said at the time that MESSENGER had simply gone behind the planet and blocked its antenna, but as the probe hadn’t actually reached the planet, that was soon dismissed. It now appears that the on board computer shut down the instruments as the batteries ran low while the probe was in Mercury’s shadow and so unable to charge up through solar power.