MESSENGER went into safe mode before closest approach
I learned via Twitter this morning (from one of six master teachers who have been Tweeting to kids throughout the encounter) that MESSENGER went into safe mode just before closest approach -- I'm assuming at the time that that unexplained signal drop occurred. The teacher, Gene Gordon of New York, who Tweets as Porchdragon, reported that that means there was no science data gathered after closest approach, although approach imaging was unaffected. I'm sure we'll hear more about this later today, but here are some things to keep in mind
First, there's plenty of good news.
The most important purpose of this flyby was the last gravity assist that'll allow MESSENGER to enter orbit in 2011. MESSENGER did not need to use thrusters during the flyby -- it was all gravity. So, since we know the targeting was perfect before the encounter, MESSENGER should still be on its way to orbit. That's the number one most important thing.
For those of us who are fans of imaging, it was the approach imaging that included views of previously unseen territory, and that evidently got done. They just released a new pic (at the bottom of this post) from the wide-angle camera.
They are talking to the spacecraft now, which is always a good thing. They haven't said anything about the spacecraft health yet, but it is talking to Earth, and it's returned science data, which indicates that it's not in a critical state of health.
Of course there's bad news: There was unique science being performed after closest approach that just won't get done. The gravity data, the neutron spectrometer close approach sequence, and other things I don't know about -- the flyby was a uniquely close encounter with the equator that won't be repeated. But before people start moaning about science lost, let me just remind you that the only reason we know about what science was lost is because the science team was kind enough to share their plans with us before the flyby began. Some missions avoid this potential image problem simply by not telling people anything about what they plan to do, keeping expectations low. But you know what? If expectations are low, so is excitement and emotional involvement. So let me say right here: thanks to the MESSENGER team for telling us so much about what you were planning to do, even if the safe mode prevented it from getting done.
I'm sure we'll hear more. In the meantime, here's that new image. And one thing to look out for in any later images they release: I noticed yesterday while fiddling around with the Solar System Simulator that Venus should be sitting there, a brilliant light in the background, in most of the wide-angle camera image shots of Mercury taken as MESSENGER approached.
NASA / JHUAPL / CIW
Last wide-angle shot of Mercury before flyby 3
MESSENGER captured this image of Mercury on approach to its third flyby, at about 19:47 on September 29, 2009.