Farewell, MESSENGER

There is one less robot exploring the solar system today. MESSENGER, which has orbited Mercury for four years, finally ran out of fuel and crashed into the planet at 17:26 UT on Thursday, April 30, 2015. The impact happened out of sight of Earth, with MESSENGER occulted by Mercury; we knew it was gone when it failed to reestablish contact with the Deep Space Network a few minutes later.

MESSENGER was just a robot, an inanimate object; but its human operators and fans were full of emotion yesterday as we stood vigil over its final moments. I watched, as I do, on Twitter. Some people responded to the emotional moment with jokes:

Others were sad.

Mary Kerrigan, noting that MESSENGER was crashing near the Mercury crater named for Shakespeare, looked for inspiration from the Bard.

Many, many people just watched, no doubt feeling lots of different things.

MESSENGER was doing science to the very end....

...and even doing science that would never be returned to Earth.

And then it was over. The Deep Space Network antenna at Goldstone listened for MESSENGER to re-emerge from behind Mercury, and it didn't.

But it wasn't completely over. The Deep Space Network station at Canberra kept listening for MESSENGER, just in case. The tracking pass had been scheduled before the final date of MESSENGER's demise was known, and they kept the scheduled pass because of their usual thoroughness.

At first, I found myself at a loss for what to say or think. I had a momentary feeling that the whole mission had never happened. If a spacecraft crashes on a distant planet and there's no human there to hear it, does it make a sound? I had imagined it there at Mercury for so long, and then it didn't exist anymore; I had the disconcerting feeling that I'd imagined it right out of existence. But Sarah Hörst brought me back to Earth with this crucial point:

Indeed, there are lots of space robot people who still have work to do with all the data that MESSENGER returned, down to the last moment.

Shortly after issuing the press release summarizing the spacecraft's death, the MESSENGER mission -- which will continue on Earth, at least, for at least a year or so, as they archive data -- gave us MESSENGER's final image.

And of course there will be another Mercury mission that will allow us puny humans to take the science further, building on what MESSENGER sent us, and Mariner 10 before it.

Farewell, MESSENGER. You did good.